Investigating New Service System Solutions for High...

Investigating New Service System Solutions

for High Altitude Balloons

Feasibility Study and Design Challenges

Joakim Peterson

Space Engineering, masters level

2016

Luleå University of Technology

Department of Computer Science, Electrical and Space Engineering

Investigating new Service System Solutions for

High Altitude Balloons∗Feasibility study and design challenges

Joakim Peterson

08/11/2016

∗Examiner Dr. Anita Enmark from LTU. Supervisor Kent Andersson from SSC

Abstract

The high altitude balloon operations at Esrange Space Center have been goingon since 1972, and about 550 launches have been performed. Their presentservice system for the high altitude balloons is about 18 years old. To be ableto meet the requests from their customers, SSC have started the developmentof a new service system. A service system contains all features and technologyrequired to perform a high altitude balloon mission. This system is separatedfrom the payload. Important design aspects for the new service system havebeen investigated to be able to leave recommendations to SSC. These are fre-quency for the radio communication, modulation scheme for the communicationlink, prevention of corona discharge, and available computer systems to be usedas on-board computers. These design aspects have been evaluated according tothe requirements for the development project. Theory, articles, available stan-dards and analyzes have been read and evaluated to reach a conclusion aboutthese subjects. It was found that the best frequency bands are the 400MHz-band, downlink, and the 450MHz-band, uplink. The operation in these bandswill be unmodified for many years, and the link suffers little loss. The 2.3GHzband is interesting from a international perspective, and it is suggested that SSCwork to get a band dedicated to aeronautical services in this band. The bestmodulations scheme for the service system is GMSK, as it has very good spec-tral efficiency. The corona discharge can only be prevented indirect by SSC, asthe phenomena occurs within or between components, aspects which SSC can’tcontrol. Standardized methods for tests and specifications lists was suggestedto minimize the risk of a discharge. The best computer system is an in-housedesigned service system that have been used on sounding rockets. It fits thepresent requirements the best. It suggested that the Beaglebone Black shouldbe implemented in basic systems, providing processing and storage via simpleserial communication, as it is a very cost efficient solution.

Investigating new Service System Solutions for High Altitude Balloons

Contents

1 List of abbreviations iv

2 Introduction 12.1 Outline of report . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Research Questions . . . . . . . . . . . . . . . . . . . . . . . . . . 22.4 High Altitude Ballooning . . . . . . . . . . . . . . . . . . . . . . 2

2.4.1 The Balloon system . . . . . . . . . . . . . . . . . . . . . 32.4.2 Operating the balloon . . . . . . . . . . . . . . . . . . . . 42.4.3 The environment . . . . . . . . . . . . . . . . . . . . . . . 4

2.5 Service system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.6 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Theory 83.1 Present Service systems . . . . . . . . . . . . . . . . . . . . . . . 8

3.1.1 EBASS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1.2 NOSYCA . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2.1 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 Corona discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.4 On-board computers . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.4.1 Development boards . . . . . . . . . . . . . . . . . . . . . 203.4.2 Industry single-board computers . . . . . . . . . . . . . . 213.4.3 DAQ systems . . . . . . . . . . . . . . . . . . . . . . . . . 223.4.4 Custom design - DHS . . . . . . . . . . . . . . . . . . . . 23

4 Results 254.1 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.3 Corona discharge prevention . . . . . . . . . . . . . . . . . . . . . 30

4.3.1 Measures against corona discharge . . . . . . . . . . . . . 324.4 on-board computers . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.4.1 Development boards - Beaglebone Black . . . . . . . . . . 334.4.2 Single-board computers - SBCT43 . . . . . . . . . . . . . 384.4.3 DAQ system UEIPAC . . . . . . . . . . . . . . . . . . . . 434.4.4 Custom Designed Control System - DHS boards . . . . . 47

4.5 Concept service system . . . . . . . . . . . . . . . . . . . . . . . . 51

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5 Analysis 555.1 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565.3 Corona discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.4 Service System and On-board computer . . . . . . . . . . . . . . 59

6 Conclusion 63

7 Future Work 64

A Specification table 66

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1 List of abbreviations

ADC Analog-to-digital converter

AGT Argos GPS and ATC transponder

AM Amplitude modulation

ATC Air traffic controller

ASK Amplitude shift keying

BER Bit error rate

BLOS Beyond line of sight

BPSK/NRZ Binary phase shift keying non-return-to-zero

CAN Controller area network

CCSDS Consultative Committee for Space Data Systems

CNES Centre National d’Etudes Spatiales

COTS Commercial of the shelf

CPU Central processing unit

DAC Digital-to-analog converter

DAQ Data acquisition

DC Direct current

DHS Data Handling System

DLR Deutsches Zentrum fur Luft- und Raumfahrt

EBASS Esrange Balloon Service System

EEPROM Electrically erasable programmable read-only memory

ELINK Ethernet up & downlink system

FM Frequency modulation

FPGA Field-programmable gate array

FQPSK Filtered QPSK

FSK Frequency shift keying

FSPL Free-space path loss

GMSK Gaussian minimum shift keying

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GPIO General purpose input output

GPS Global positioning system

GPU Graphic processing unit

HDMI High-definition multimedia interface

I2C Inter-integrated circuit

IO Input output

ITU International Telecommunications Unit

JPL Jet Propulsion Laboratory

LOS Line of sight

MFB Multi function board

MIL-STD Military standard

MSK Minimum shift keying

NaN Not a number

NASA National Aeronautics and Space Administration

NCU Nacelle Charge Utile

NEV Nacelle EnVeloppe

NFAE Nacelle Feu A Eclat

NOSYCA New Operational System for the Control Of Aerostats

NSO Nacelle de Servitude Operationnelle

OQPSK Orthogonal QPSK

PCB Printed circuit board

PCDU Power control and distribution Unit

PhD Doctor in philosophy

PM Phase modulation

PoGo+ Polarized gamma-ray observer

PSK Phase shift keying

PTS Post- & Telestyrelsen

PWM Pulse width modulation

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QPSK Quadrature phase shift keying

RAM Random access memory

RF Radio frequency

S/s Sample/second

SBC Single-board computer

SD Secure digital

SDR Software-defined radio

SOM System-on-module

SPI Serial peripheral interface

SSC Swedish space corporation

TMTC Telemetry telecommand

UART Universal asynchronous receiver/transmitter

UAV Unmanned aerial vehicle

UEI United Electronic Industries

UEIPAC United Electronic Industries Programmable Automation Controller

ULV Unmanned land vehicle

UN United Nations

USB Universal serial bus

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2 Introduction

A service system of a high altitude balloon consists of all on-board equipmentand functions which are necessary to perform a high altitude balloon flight. Itinvolves all practical functions to perform a flight, but also all necessary safetyequipment required for all aeronautical vehicles. The service system is not tobe mistaken with the payload. They may be connected physically, but arecompletely separate functions of the balloon system. It could be explained as;the service system makes it possible to fly, but the payload is the reason to doso.

The structure of this Master’s thesis report is aimed to cover most of the workdone during this project. As a few different design challenges with designinga new service system for high altitude balloons have been investigated, thishave made its mark on the work flow and result of the project. The purposeof this report is to act as an aid when taking the first decisions in developinga service system, especially for high altitude balloons, but also for other flying(semi)autonomous vehicles.

2.1 Outline of report

The outline of the report is structured to follow work flow of the project. Section2, Introduction, presents the different possible design challenges and gives a briefintroduction to high altitude ballooning at Esrange’s facilities. It also describeswhat a service system is and its purposes. In section 3, Theoretical Background,the different fields of the design challenges, communication and environmentaleffects, are covered. A brief description of two present service system beingused in the field of high altitude ballooning today, and four different typesof on-board computers are presented. Section 4, Results, shows the resultsobtained from studying each design challenge. The available frequencies, theperformance of modulation schemes, and the prevention of corona discharge.The four on-board computers are examined and a concept service system, madedirectly according to the requirements, is presented. In section 5, Analysis, theresults are compared with each other end evaluated. In section 6, Conclusion,the outcome of the project and suggestions to SSC are presented. Section 7,Future work, the next step of developing the service system is explained

2.2 Background

This work have been done as the final project in the studies of becoming Civilin-genjor(a Master) in Aerospace Engineering at Lulea University of Technology.This thesis has been done at SSC’s facilities at Esrange outside Kiruna. Super-visor have been Kent Andersson, systems engineer. This thesis got my interestas a new platform was to be studied. During our education satellites and rocketshave been covered, but high altitude balloons felt new and challenging. The abil-ity to do this thesis at a future possible employer and to see the space businesswas also a part of the reason to do this thesis.

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The service system used at Esrange today are so old that components haveto be obtained from legacy storage to repair it. It has done its share for thecompany, but with almost 20 years experience, it is soon time to retire. Thenew service system is a part of the new investment at Esrange, to become thespace capitol in Europe, with several different services to offer. The new highaltitude balloon service system is just one piece to the puzzle in modernize theoperations going on at Esrange.

This thesis is done in the early phases of the development project. Functionalrequirements have been written, but are not finished yet. To be able to knowhow to approach different design aspects, my task have been to investigate theseand give recommendations to SSC.

2.3 Research Questions

The challenges with developing a service system are many, and to be able todeliver a professional, state-of-the-art system these challenges need to be stud-ied. The old service system was developed during the late 90’s, and is lackingsignificant documentation, which have lead to the decision from SSC to developa new service system, instead of upgrading their present system. Four topicshave been covered during this work which are presented bellow.

• Investigate available communication frequencies, available the upcoming10 years, for the service system and give recommendations.

• Investigate available modulation methods, and give recommendations.

• Investigate the corona discharge phenomena and give recommendationshow this shall be addressed.

• Investigate the feasibility of four different types of computers for the ser-vice system, and give recommendations

These four topics was picked by the supervisor as something SSC wanted toknow before they continue with the development of the new service system.

2.4 High Altitude Ballooning

SSC have been launching high altitude balloons, stratospheric balloons, at Es-range since 1972. So far 550 launches have been done from this site. Some ofthese are small equipage with student payloads consisting of nothing more thana camera and some sensors, others are 1000000 m3 balloons with telescopes aspayload flying across the Atlantic ocean. This summer SSC launched a Swedishmission, PoGo+, flying to Canada. The payload was a telescope to observe thenight sky.

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2.4.1 The Balloon system

In figure 1 the complete balloon system as it launched from Esrange is presented.This may not be the set up for every flight as some functions can be discardeddue to mission specifications. Each feature in the picture is explained bellow.

Figure 1: The balloon system as launched from Esrange.

The VALVE in the figure is a vent to be able to let out gas of the bal-loon. The BALLOON is what makes the balloon lift, and is filled with helium.The CUTTER separates the balloon from the rest of the system for descend.PARACHUTE provides a steady descend speed. EBASS contains all electron-ics of the service system. The BALLAST MACHINE is used to loose weightfrom the vehicle. The pipe hanging out is used to not drop the ballast mass onthe systems bellow. The STROBE LIGHT is a light source required on aero-nautical vehicles for visual detection. FLIGHT TRAIN AGT contains required

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safety equipment. The RADAR REFLECTOR is used for tracking the balloonwith radar. The PAYLOAD GONDOLA contains the payload for the balloonmission.

The valve, cutter, EBASS, ballast machine and radar reflector are equipmentthat contribute to the functions of the service system. The strobe light and flighttrain AGT are equipment required for all aeronautical vehicles. The payloadgondola’s purpose is only to carry the payload [34] [49].

2.4.2 Operating the balloon

Upon launch the balloon is partially filled with helium, to allow the gas toexpand. The size of the balloon and the amount of gas filled is decided accordingto the expected altitude. The whole mission is operated by the pilot located atthe ground station. The pilot can steer the balloon by making it catch differentwind layers with different wind directions. This is done by either releasinghelium or ballast, making the balloon sink or rise.

The balloon ascends until it bursts, or reaches its float altitude, where itsaltitude is stable. The balloon is stable at its float level until it bursts or thedescend phase is started. For descend the valve is opened and the balloon ispunctured, to ensure all gas is released. The balloon is separated from therest of the system as it could fold over the parachute. This would deform theparachute, as the balloon can weigh up to two tons, and lead to a free-fall. GPSis used to track the balloon system after landing, and an helicopter is used toretrieve all equipment[1].

2.4.3 The environment

A high altitude balloon reaches an altitude of 30 to 40 km. This is within thepart of the atmosphere called the Stratosphere [51]. The atmospheric pressuredecreases with altitude. Numbers are presented in figure 2. The temperature ofthe surrounding air is dependent on the season and time of day. It changes withaltitude according to the profile shown in figure 3. The temperature affects thevolume of the gas inside the balloon, and an eventual altitude change have tobe compensated by the pilot. Wind layers, with different directions, could belocated a few hundred meters apart.

During winter and summer, the winds above 30 km goes around the NorthPole. Counterclockwise and clockwise respectively [7]. It is possible to catchthese winds from the location of Esrange and perform circumpolar flights. Theperiod between the two stable seasons is called the turn around period. Thechange in direction of these winds enable flights that stay within the northregion of Scandinavia. During this period it is harder to estimate the missiontrajectory of the balloon.

1After conversations with relevant engineers at SSC

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Figure 2: This is how the air pressure decreases with altitude. (data from [38])

Figure 3: Temperature profile of the atmosphere, obtained during summer [18].

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2.5 Service system

A service system for high altitude balloons is used to ensure a safe flight. Allfunctions and equipment are used so the launching entity can ensure the safetyof the people involved, and the inhabitants and the environment of the overflownarea. It shall not be confused with the payload. The two may be connected,but a balloon cannot fly without a service system, whilst is can fly withoutpayload. The service system in use at Esrange is called EBASS, and consist ofthe following equipment:

• A complete communication system, radio, antenna.

• Sensors for various measurements, pressure, speed, temperature, load.

• Ballast machine and valve operating functions.

• Balloon burst detection.

• Flight termination equipment.

• GPS and ATC.

• On-board computer.

• Life supporting system, insulation, heaters.

Redundancy of equipment and fail-safe solutions are two ways to ensure thereliability of the service system. Two service system which are used today arethe EBASS and the NOSYCA(NOSYCA). These are presented in more detailin section 3.1.

2.6 Requirements

The functional and project requirements have been written, but no completedocument has been made. The adequate requirements presented in [20], [3],and [35] have been summarized for this project bellow:

1. 10 units of the new balloon service system shall be obtained. With thepossibility to order new systems or spare parts for a period of 10 years. [35]

2. The system shall be able to perform any task that the present EBASScan do today. Control and monitor valve and ballast, collect and trans-mit telemetry, respond to commands, store high resolution data, measurepressure, temperature, and wind speed, detect balloon burst, and performflight termination. [3]

3. It shall be lightweight and allow for flexible mounting and handling, whilestill be able to withstand the environmental effects of a high altitudeballoon flight. [3]

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4. It shall be simple enough for non-specialists to work with, and only oneoperator shall be needed at the time during operation. [35]

5. The design shall be modular, with a common interface, and units shall beable to be placed in different configurations and easy to exchange. [3]

6. The design shall allow for easy integration and design of new units to thesystem. [3]

7. The system shall have redundancy and encryption to ensure reliability. [20]

8. No single-point-of-failure, and the system shall be adoptable to other or-ganizations and agencies safety requirements. [35]

9. Power distribution shall be external. [35]

10. The production and manufacturing of the system shall be outsourced asmuch as possible, to keep the regular operation of the division going. [35]

11. The service system shall be separated from customer systems on-board.[20]

12. The configuration time for the system shall be no longer than 3 days, andthe reconfiguration time no longer than 1 day. As long as no physicaldamage has occurred during the last flight, thus new environmental testshave to be performed again. [20]

13. It shall be designed with synergy to other, and future possible, platformswithin the company, such as sounding rockets, CubeSats and drones. [20]

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3 Theory

This section includes a brief presentation of two service system that are usedtoday. The applicable communication theory, frequency and modulation, ispresented. A description of the corona discharge phenomena, and four differentcomputer systems to be used as on-board computers.

3.1 Present Service systems

Two service systems that are used for high altitude ballooning today are theEBASS and the NOSYCA. EBASS is used by SSC, flown from Esrange, andNOSYCA is used by the French space organization CNES.

3.1.1 EBASS

EBASS was co-developed by SSC and DLR about 17 years ago. SSC providedthe requirements, and DLR produced the hardware and the software. EBASS isdesigned as one compact system, to be simple and have low power consumption.Its reliability is implemented trough simplicity. EBASS is only intended forballoon control.

EBASS consists of one gondola, shown in figure 4. Located in the top of thisbox are all electronics of the service system. Transceiver, GPS, MFB, interfaceboard, and batteries. The antenna and load cell are also located inside the box.A steal structure connects the attachments in the bottom and at the top of thebox. This is load carrying. The load cell measures the load upon this structure,to detect a balloon burst. Connections for equipment outside is located in thetop or bottom. The box is made out of insulating styrofoam.

The MFB is the on-board computer of EBASS, block schematic shown infigure 5. It is custom designed for this system. Functionalities of the MFBare 32 ADC channels with 16 bit resolution, 14 bit DAC, serial interface, micro-controller, flash memory and RAM. The integrated modem is bypassed to anexternal modem. The micro-controller is programmed bare metal.

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Figure 4: Photo of the exterior of the EBASS [34].

Date: 11/15/02 Time : 03:02:02 PM

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Figure 5: Block scheme of the MFB on-board computer [48]

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3.1.2 NOSYCA

The NOSYCA service system was developed by CNES and ELTA. It was takeninto operation 2 years ago. It is designed to be reliable. This is done throughredundancy. Two different on-board computers is located in the NSO gon-dola [30]. Micro-controllers are used as interfaces towards the operating units.These are controlled by a management micro-controller [32]. Three valves areimplemented [50]. A custom software was developed to cope with the complex-ity of the system [30]. The NOSYCA is intended for both balloon and payloadcontrol, and data download. An interface system is used for the payload opera-tors to only access their equipment. Payload communication is performed overthe NOSYCA link [32].

The NOSYCA system is shown in figure 6. It consists of three gondolas,named in the figure. NEV, NSO(NSO), NFAE. The NCU, is the payload gon-dola, which is separated from the service system. The NEV gondola containstransponder, strobe light, GPS via Iridium, and an Argos system. The NSOgondola; on-board computers, transceiver, GPS and Iridium modem. And theNFAE gondola; strobe light and an ATC [30]. The NCU gondola is connectedto the NSO via Wi-Fi or Ethernet.

Figure 6: Illustration of the NOSYCA service system [30].

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3.2 Communications

The communication between the balloon and the ground station is usually sup-ported on two different links. One used during line of sight, LOS, and onebeyond line of sight, BLOS. BLOS communication is used when the ground sta-tion is incapable of communicating with the balloon. This could be caused byobstacles, a mountain or forest, or the distance to the balloon. Often a satellitenetwork, such as Iridium, is used to relay the messages to and from the bal-loon. LOS communication is performed via a traditional communication link.The performance of the link depends on many parameters, of which two are thecarrier frequency and the modulation scheme used.

3.2.1 Frequency

An important measure for wireless communication is how much power is re-ceived by the receiving antenna. This is one of the fundamental calculations incommunication theory, called the Frii’s equation [4].

For electromagnetic waves the decrease in intensity due to the distance ithas traveled is expressed by the inverse-square law

PD =PT

4πD2[W/m2] (1)

where PD is the power flux at the distance D[m], and PT [W ] is the trans-mitted power by an omnidirectional antenna. An omnidirectional antenna isa theoretical device which radiates the same power in all directions. In com-munication links, the power is transmitted by an non perfect(not completelyomnidirectional) or a directional antenna, the gain of that antenna can increasethe power transmitted. Equation 1 is written

PD =PT

4πD2GT [W/m2] (2)

where GT is the gain of the transmitting antenna expressed as a ratio. Thegain is presented as the ratio to a omnidirectional antenna feed with the sameamount of power. So a directional antenna with the gain 10, is radiating 10 timesthe power(in that specific direction) than an omnidirectional antenna would do.The amount of power received by the receiving antenna is determined by theantenna aperture, also called the effective area of the antenna Aeff . This isa measure of how good the antenna picks up the electromagnetic waves. Theeffective area is expressed as the actual area of the antenna times its efficiency,Aeff = A ·η. The antenna efficiency η is a product of many factors such as spill-over loss, surface degradation, impedance mismatch etc. The received power,PR can the be expressed as

PR =PT

4πD2GTAeff [W ]. (3)

The effective area can also be written as a function of the gain of the receivingantenna, Aeff = GR4πc2/f2, where GR is the antenna gain, f is the frequency

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of the signal, and c is the speed of light. Exchange for Aeff and equation 3gives

PR =PT

4πD2GTGR

4πc2

f2=PTGTGRc

2

(4πRf)2 [W ]. (4)

which is the Frii’s equation. The power received by an antenna.The amount of power lost during transmission is given by the ratio

PTPR

=PTGT

PTGTGRc2

(4πRf)2

. (5)

To eliminate the hardware influence in equation 5, the gain of the receivingantenna is set to 1, GR = 1. After simplification equation 5 looks like

PTPR

=

(4πRf

c2

)2

= FSPL (6)

which is called the Free-space path loss, FSPL [23]. This equation is animportant tool in communication to know how much power is required to achievea good communication link. The Free-space path loss over 500 km with respectto frequency is plotted in the upper part of figure 7. As can be seen the valuesare rather big, so for convenience it is converted to dB, shown in the lower partof figure 7.

Figure 7: The Free-space path loss over 500 km with respect to frequency, ex-pressed in a non-logarithmic scale and as dB.

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3.2.2 Modulation

The modulation of a signal, determines how the message is added to the carrier.There are three ways to modulate a signal, amplitude, frequency and phasemodulation.

• Amplitude modulation: the amplitude of the signal is varied, frequencyand phase are unaltered.

• Frequency modulation: the frequency of the signal is varied, amplitudeand phase are unaltered.

• Phase modulation: the phase of the signal is varied, amplitude and fre-quency are unaltered.

These three methods can be used in combination to perform more advancedmodulation schemes. A RF signal is often modeled using a bandpass signal,represented by

v(t) = Re{g(t)ejωct

}= Re {g(t) [cos(ωct) + jsin(ωct)]} (7)

where Re(...) takes the real part of (...) and ωc is the angular frequency.g(t) is called the complex envelope of v(t). g(t) can be described in polarform, by R(t) and Θ(t), where R(t) represents amplitude modulation, and Θ(t)represents phase modulation. For modulation the information is given by m(t),the modulating signal, which is modulated onto s(t). The modulated signal isgiven by

s(t) = Re{g(t)ejωct} = Re{g[m(t)]ejωct}. (8)

For amplitude modulation the complex envelope is given by

g(t) = Ac[1 +m(t)] (9)

where Ac is the carrier amplitude. By using equation 9 in 8, the real part ofthe complex envelope is

s(t) = Ac[1 +m(t)]cos(ωct) (10)

where m(t) is assumed to be m · cos(ωmt). The expression in equation 10can be expanded to

s(t) = Ac · cos(ωc) +Acm · cos(ωmt)cos(ωct). (11)

Equation 11 is plotted in figure 8 with the values Ac = 2, ωc = 2000 · 2π,m = 1, and ωm = 200 · 2π.

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Figure 8: Amplitude modulation, showing both the modulating signal(top), thecarrier(middle) and the modulated signal(bottom).

Frequency and phase modulation are two special cases of angle-modulation.The complex envelope is

g(t) = AcejΘ(t) (12)

where Θ(t) is a linear function of the modulating signal, m(t). g(t) is anon-linear function of m(t). The modulated signal is

s(t) = Re{g(t)ejωct} = Re{AcejΘ(t)ejωct} = Accos[ωct+ θ(t)]. (13)

The phase, in phase modulation is proportional to m(t)

θ(t) = Dpm(t) (14)

where Dp[radians/volt] is the phase deviation constant of the phase mod-ulator. For frequency modulation, the phase is proportional to the integral ofm(t)

Θ(t) = Df

∫ t

−∞m(σ)dσ (15)

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where Df [radians/volt/second] is the frequency deviation constant.

m(t) is assumed to be Amcos(ωmt). For phase modulation, by using thisassumption in equation 14, this gives

Θ(t) = DpAmcos(ωmt) = βpcos(ωmt) (16)

where βp is called the phase modulation index. For frequency modulationthe same assumption is done for m(t) and used in equation 15

θ(t) = Θ(t) = Df

∫ t

−∞Amcos(ωmσ)dσ = AmDf

1

ωmsin(ωmt) = βfsin(ωmt)

(17)where βf is the frequency modulation index. For frequency modulation

equation 13 becomes ( [36])

s(t) = Re{g(t)ejωct} = Accos[βfsin(ωmt) + ωct]

= Accos[ωct+

∫ t

−∞

DfAmωm

cos(ωmt)].(18)

Equation 18 is shown in the bottom of figure 9. Included are also the modu-lating signal(top) and the instant frequency of the carrier(middle). An exampleof phase modulation is shown in figure 10, with the modulation signal(top), thephase (middle), and the modulated signal(bottom). The values used for bothfigures are over exaggerated to better see the effect of the modulation.

Figure 9: Frequency modulation, showing both the modulating signal(top), theinstant frequency of the carrier(middle) and the modulated signal(bottom).

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Figure 10: Phase modulation, showing the modulating signal(top), the instantphase(middle), and the modulated signal(bottom)

The examples shown above are for analog communication. For digital com-munication the modulating signal is represented by a sequence of bits. The bitsare represented as symbols on the transmitted signal. Symbols are the termused in digital communication for each individual information carrying part ofthe modulated signal. In phase modulation the positive and negative phasesare interpreted as two different symbols. The symbols represent different bits.For a binary system, with two different modulation levels(positive and negativephase), the symbol rate is equal to the bit rate. One symbol represents one bit.In a multilevel system, with four different phases, each symbol can representtwo bits. A bit sequence of two bits can be ordered in four different configu-rations. Each symbol represent one possible bit configuration. Example shownin figure 11. In this case the bit rate is twice the symbol rate. Systems with8 symbols(levels), bit rate three times the symbol rate, and 16 symbols(levels),bit rate is four times the symbol rate, are used to increase the data transfer of acommunication link. The number of symbols N is express as N = 2n, where n isthe number of bits per transmitted symbol. Amplitude-shift keying, frequency-shift keying, and phase-shift keying are the digital equivalents to amplitude,frequency, and phase modulation.

Page 16


Figure 11: Mapping example of quadrature phase shift keying.

An ASK receiver detects the different amplitudes of the received signal.Phase locked loop receivers can be used. Linear amplifiers are required whenusing ASK/AM. Linear amplifiers are less efficient than non-linear amplifiers[36].

An FSK receiver detects the different frequencies of the signal. A phaselocked loop can be used. It can be either coherent or non-coherent. A coherentreceiver uses a replica of the signal as comparison with the received signal [36].Non-linear amplifiers can be used with FSK/FM.

A PSK receiver detect the different phases of the signal. It can be eithercoherent or non-coherent. To use a phase locked loop, the phase shift has to beless than 180°. Non-linear amplifiers can be used with PSK.

Important measures for a radio communication link are the Spectral Effi-ciency

η =R

B[bits/s/Hz] (19)

and the Power spectral density [W/Hz] [36].

Page 17


3.3 Corona discharge

Corona discharge is a phenomena that was discovered long before it was identi-fied as problem to airplanes or high altitude balloons. Sailors have told storiesabout how the masts of their ships could glow in the night as a storm was ap-proaching. They called this St. Elmo’s fire [21], but was the earliest observationsof the corona discharge phenomena.

Corona discharge is a phenomena that occurs due to the ionization of a fluidsurrounding a conductor. It can be seen as a glow around the conductor, butthe corona phenomena has already appeared before the glow is visible. Thevisible light is caused by the ionized atoms sending out photons as they returnto their natural state. a corona discharge can occur within a capacitor, witha gas as dielectric between the two conducting plates, or at an antenna. Thecorona is often described with the help of two electrodes spaced a apart by air,as a typical conductor. Sharp corners or edges will lower the initiation voltagerequired. This is due to the electric field concentrating around a sharp edge.This can be studied further in [21].

Corona is not a complete breakdown between two electrodes, as arcing is.In [37] Dheena Moongilan describes the difference between corona and arcingas follows; ”The corona event is typically a high voltage and lower currentevent. While arcing typically is a higher initial high voltage event followedby a lower voltage and higher current event”. This means that the initiationvoltage for corona is lower than for arcing, and in terms of damage, less severe.If corona arises, and the voltage keeps increasing it will soon transform intoa complete breakdown between the electrodes and arcing will occur. Someeffects from a corona discharge can be power loss, thermal breakdown, andradio interference [37]. Corona discharge depends in first hand on pressuretimes distance, as was described by F. Pashchen back in 1889. He published apaper about how the breakdown voltage for two electrodes separated by a gas isdependent on the pressure of the gas and the distance between the electrodes.This was later to be called Pashchen’s law. What can be seen from figure12 is that the strength of the electric field required for corona discharge isinverse dependent on the pressure times the gap. However, after a certain pointthe dependency is reversed and the breakdown voltage increases with lowerpressure and shorter gap. The lowest voltage required is called the Paschenminimum and is about 350 volts for air, found at 0.2Torr · inch. This is equalto 677.164Pa ·mm [15]. This number corresponds to an altitude of about 3 km,for a gap distance of 0.01 mm, ranging to an altitude of about 29 km for distancesup to 0.5 mm.

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Figure 12: Paschen’s curve, breakdown voltage in volts vs pressure times gapdistance in Torr and inches. [15]

Corona discharge can either be positive, ions, or negative, electrons, depend-ing on the electric field applied. The weight difference between the two particlesaffects their respective drift velocities, with the electron being faster as it islighter. Due to this difference the positive corona has been shown to occur atan higher threshold voltage. The difference can also bee seen on the glow, aspositive corona is blueish-white, and the negative is reddish [37].

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3.4 On-board computers

The heart of the service system is its on-board computer. It controls and pro-cesses everything that happens on the balloon. It provides communication in-terfaces, connectors, converters, networks, etc. The on-board computer is acrucial part of the development of on-board system, as it must comply to manyrequirements, as well as sets requirements. For the service system four differentcomputer systems have been investigated,

- Development boards

- Industry single-board computers

- DAQ system

- Custom designed units

These four computer systems all have micro-processors. Their purposes dif-fers a lot between them all. The term computer system is used, as some of thesesystem includes other features than just processing.

The DAQ system and the custom design units have been a part of thisstudy as they are accessible at Esrange. Development boards and single-boardcomputers are of interest as they are COTS products.

3.4.1 Development boards

A development board is a complete single-board computer made for hobbyistsand project development. (A single-board computer is a computer build on onePCB.) It contains all the necessary features to make it as a general computer.Each brand have their own niche and functions.

A development board is made to enable easy access to programming andcomputer solutions. It allows the user to focus on the project, rather thancomplicated setups. Many development boards have pin-connectors that canbe used to attach extensions shields to increase the possibility of the computer.These shields are standardized to each brand, often compatible on all models.Some manufacturers have adopted the connector layout from other brands, toallow the use of that computers available shields. Many boards are completelyopen source, others partially. They are small, less than 10x10 cm2, and havelow power consumption.

Common features for a development board are Ethernet, Wi-Fi, USB, se-rial communication, GPIO, ADC, and PWM. These are often available throughpin-connectors, to safe space on the computers. Extension capes can be used toutilize these functions with standard connectors.

These features have made the development boards very popular and bigcommunities have risen, tied to the specific board they use. Within these com-munities projects and ideas are shared. The communities are the support sourcefor these computers, through mailing lists, chats and forums.

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Development boards can be used in various application. Weather it is tocontrol a Segway, fly a drone or provide dynamic back lightning to a tv-screen,the development board can be used. ARDUSAT was the first satellite in whichan Arduino(a development board) was used as an on-board computer [1]. Ahow-to guide to use a Raspberry Pi for amateur high altitude ballooning is pre-sented by Dave Akerman [2].

The development boards chosen for this study are the Raspberry Pi, theBeaglebone Black, and the Intel Galileo Gen 2. The results of this is presentedin section 4.4.

3.4.2 Industry single-board computers

An industry single-board computer built on one PCB, made for industry pur-poses.

An industry classed SBC is made to withstand the reliability demanded bythe industry. Its functionality can be assured trough classifications within tem-perature, shock, vibration, etc. Space classified computers dedicated for cubesatsystems are available. Industry SBCs support various different communicationprotocols and standard connectors, to fit many purposes.

Single-board computers can be designed in two ways. Either as one boardwith all components on it, or as a System-on-Module, SOM, put into a carrierboard. A SOM is a computer without any standard connectors. It contains allfeatures, protocols and technology of a computer. To access these, the SOM haveto be connected to a unit providing these connectors and physical interfaces. ASOM may provide SD-cad functions, but the SD-card socket have to be providedby, for example a carrier board.

A design solution for SBCs which have been more common is to combinethe micro-processor with an FPGA. This is done to enable the benefits of hard-ware programming, while still having the software processing capabilities withthe micro processor. The FPGA allow for efficient signal processing and logiccomputing.

Common features for industry classed single board computers are Ethernet,Wi-Fi, serial communication, bus communication, digital outputs, etc.

Industry SBCs can be used where reliability is crucial. NASA have usedthese types of computers for at least two applications. A computer with bothmicro-processor and FPGA was used in [59] as interface between the main on-board computer and the experiment. And in [33] a regular computer is used asmiddle layer unit to provide standard connectors.

Five computers have been studied, the Zynq-7020, the GOMSPACE NanoMindA712D, the SBC-T43, the SBC-FX6, and SBC-T335. The result is shown insection 4.4.

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3.4.3 DAQ systems

A DAQ system is a system whose main purpose is data acquisition. Theseare used when high demands, of sample rate and resolution, are put on theperformance of the data acquisition. It could be research facilities [53], or foradvance technical operations such as rocket launches [52]. DAQ systems can actas interface between sensors and the computer, while relying on the computerfor control, or be equipped with a micro-processor for internal control and be astand-alone unit.

The system Esrange is interested in is the UEIPAC [26]. They posses a lesserversion, without micro-processor, which can be upgraded with control and pro-cessing capabilities. The UEIPAC is a system where a processing unit is locatedin a chassi, in which I/O boards are inserted to provide interfaces towards theuser applications. These interfaces could be ADC, for measurements, DAC, forcontrol, or serial for communications. Without the I/O boards the UEIPACis just an empty chassi with a processor. The UEIPAC is made to be simpleto handle, exchange boards, and configure software, while still deliver top classperformance. It is designed to work as a stand-alone unit. Specifications of theCube chassi is presented in table 1.

Table 1: The specification of the UEIPAC without taking the I/O boards intoaccount [26] (Not for all chassis).

Processor 32 bit 400 MHz FreescaleUser application memory 64 MBSD card Up to 32 GBEthernet 10/100(/1000) RJ-45 connectorUSB (2.0)Serial port RS-232, 9-pin D connectorPower consumption 3.5 W, 9-36 V

There are three types of chassis available, two made to be put in racks.These can fit up to twelve boards, depending on the chassi. The external inter-face towards the boards are D-sub connectors of various size, 37-D is common.The UEIPAC contains 128 MB of application data storage, of which 64MB isavailable for the user. The other 64 MB are pre-loaded with the necessary soft-ware to run the boards, and make them available for the user application.

The I/O boards contain an EEPROM with configuration data which theprocessor uses to identify the board as it has been connected. UEI provide over60 different board models, each with their own function and specifications. TheI/O boards are independent of each other. Specifications for some I/O boardsare presented in table 2.

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Table 2: Specifications for some I/O boards available for the UEIPAC [27].

ADC 8 differential channels, 18 bit resolution, 1 kS/s, ±10 VADC thermocouple 12 channels, 24 bit resolution, 100 S/s,DAC 8 channels, 16 bit resolution, ±10 V ±5 mADigital IO 48 channels, TTL-levelsPWM 8 counters/timers, 32 bit resolutionPower conversion ±24 V, 18-40 V DC-in, 40 W

Except for the features in table 2, serial communication, gps, cellular net-work, and MIL-STD-1553 are available. The physical appearance of the boardscan differ between the chassis, but the functional properties are the same.

The results for the UEIPAC system is presented in section 4.4.

3.4.4 Custom design - DHS

The custom designed system in this study refers to the DHS project by SSC. Theuniversal data handling system is an initiative within SSC to produce a servicesystem that would suit all launching operations within the company. This coverssounding rockets and high altitude balloons as for now. These modules aredesigned by SSC but the manufacturing is outsourced. This project started in2013, and 2015 was its first flight of the system, on a sounding rocket.

The DHS system is designed to be independent of the platform it is usedon. It consist of same sized modules, with different purposes. These modulesare independent of each other, and can be configured in any way. The designshall also invite partners of SSC to develop their own boards compatible to thesystem. Figure 13 shows the architecture of the DHS service system.

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Figure 13: The architecture of the DHS [22].

All DHS boards have identical processors, a PIC32, and the same commu-nication interfaces, Ethernet and CAN. They have also got a synchronizationline and galvanic isolated serial I/O. All boards carry an EEPROM with con-figuration data, and are of the same size, 195x110x22 mm3. The connectors arelocated on the same two sides of each board.

The two main modules of the system are the PCDU board and the TMTCboard, PCDU B and TMTC CCSDS in figure 13. These are crucial for thesystem to run, and to be able to communicate with. The PCDU board is con-trolling the power on-board the platform, i.e to the other modules. It alsoreceives telecomands and transmits telemetry. The TMTC board has two FP-GAs that works as the modem for the radio signals. It also provides an umbilicalconnection while the system is handled on ground.

The results for the DHS system is presented in section 4.4.

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4 Results

These are the results from the investigation of the subjects covered in section3. Last is a concept service system presented. This is made directly after therequirements in section 2.6.

4.1 Frequency

The frequencies used by the Science Service division at Esrange today are

• 402.2 MHz

• 449.95 MHz

• The 2.3 GHz-band

• The 2.4 GHz-band

402.2 MHz and 449.95 MHz are downlink, respectively uplink for the EBASS.This is a permanent license. 2.3 GHz are uplink and downlink for the soundingrockets. This is not a permanent license. Temporary licenses have to be appliedfor before each launch. 2.4 GHz are used for uplink and downlink for the ELINKsystem. This is a permanent license.

Figure 14: The frequency allocation for Sweden for the 400 MHz band. [39].

The decision making authority when in comes to frequency allocation andspectrum of use in Sweden is the Post- och Telestyrelsen, PTS. They plan thefrequency spectrum, and make sure this plan is followed.

From studying the frequency plan of Sweden [39] and the Targeting re-port [40] from PTS, it was found that four frequencies were available for radiocommunication with a high altitude balloon. These were the 400 MHz-band,450 MH-band, 2.3 GHz-band, and 2.4 GHz-band. For a communication linkto be allowed on a certain frequency is must be of the service for which the

Page 25


bandwidth is allocated. And conform with the already existing communica-tion links within that service. Figure 14 shows an extract from the Swedishfrequency plan. Both Ballongburna radiosonder(balloon carried radiosondes)and Landmobil radio(ground based mobile radio) falls under the mobile radioservice. But nevertheless a balloon communication link could not be used on406.1 MHz-410 MHz, as it is not ground based.

• 400.15-404 MHz

Present services allocated within this band are Earth research via satellite,meteorology via satellite(space→earth), meteorological tools, mobile radio viasatellite(space→earth), space research(space→earth), spacecraft control (space→earth), permanent radio, mobile radio except aviation radio [39]. There areno planned changes to this band from PTS [40].

• 449.95 MHz.

The present services allocated within this band are permanent radio, mobileradio except aviation radio, radiolocation [39]. There are no planned changesfor this or adjacent bands according to PTS [40].

• 2.3 GHz.

The present services allocated in this band are permanent radio, mobile radio,amateur radio, radiolocation [39]. This band stretches to 2.4GHz, and tempo-rary permissions for amateur, mobile video link, sounding rockets and balloonsare the current allocation. Together with military. This band is subject to astudy to allocate more permanent services here [40], which shall happen in 2018.

• 2.4 GHz.

The present services allocated in this band, to 2483.5 MHz, are the same asfor the 2.3 GHz-band, permanent radio, mobile radio, amateur radio, radioloca-tion. [39]. The area of use are short radio devices, wireless networks, amateurradio and military [40].

ITU, the International Telecommunications Unit, is the corresponding agencyto PTS working on an international scale. The ITU is a part of the UN. They is-sue regulations and recommendation to all authorities over the world whom areworking with communications, such as PTS. These regulations and recommen-dations are executed by each country’s own authority, and national deviationsmay occur.

For the 400MHz-band ITU have started an investigation regarding trans-missions on the 401-403 MHz bandwidth. This is to ensure that present servicesin that band, meteorology and Earth research, are not affected. This covers

Page 26


transmissions from Earth to space, and the investigation will be done to thenext World radio conference in 2019 [31]. On the last conference, 2015, ITUissued two regulations stating that the bands adjacent to 406-406.1 MHz shallbe controlled not to interfere with the distress signal located there. The 2.3GHzband has been harmonized across Europe to allow for the implementation of the5G technology for cellular networks.

To be able to perform international flights, as a circumpolar mission is, thefrequency plans for the relevant countries have been studied as well. These areNorway [5], Finland [56], Russia [25], Canada [41], and USA [11].

For the 400 MHz-band, USA does not provide any service in which high al-titude ballooning belongs. For 450 MHz, Canada does not provide any suitableservices. All countries supports aeronautical telemetry on the 2.3 GHz-band.Canada, Russia and Canada have this service prioritized for parts of the al-located bands. The frequency plans for 2.4 GHz are similar to Sweden’s, onlyUSA does not provide mobile radio until 2450 MHz.

4.2 Modulation

The modulation used today on EBASS is GMSK, Gaussian Minimum Shift key-ing. It is a special type of FSK. The definition of MSK is ”a continuous-phaseFSK with a minimum modulation index (h=0.5) that will produce orthogonalsignaling” [36]. GMSK is MSK filtered with a Gaussian filter to increase perfor-mance. According to senior engineer at Esrange, Alan Niva, it was chosen for itsperformance, while still being relatively simple. As it is a type of frequency-shiftkeying, no phase correlation is needed.

In [36] Davide Micheli goes through the basics of communication theory andmodulation techniques. Some of them are:

• BPSK/NRZ(theoretical): Is used as reference

• FQPSK-B: this is a type of OQPSK

• MSK: Minimum shift keying

• GMSK: Gaussian Minimum Shift Keying

• 8-PSK: 8-leveled PSK

He also goes through the ”Efficient Modulation Methods Study” performed atNASA/JPL, from which he presents the most interesting methods, and evaluatestheir results. The study focuses on the BER, the spectral density and the powercontainment of each modulation scheme. The power containment is a measureof how much power is contained in how much bandwidth. The more power inthe lesser amount of bandwidth the better [36].

Page 27


FQPSK-B and GMSK was shown to be the two top performing modula-tion methods. Both from Davide’s own material and from the study done byNASA/JPL. Especially for spectral density and power containment they outper-formed the other methods. In figures 15 and 16 are the relative power spectraldensity shown for each modulation method. Figure 17 shows the power loss inrespect to the bandwidth of the signal. Davide Micheli’s analysis of the studyis that FQPSK-B have to be investigated more, but there is all reason to do so.About the GMSK is said ”Clearly, space agencies interested in RF spectrumefficiency should seriously consider GMSK modulation” [36].

Figure 15: Relative power spectral density of GMSK compared with BP-SK/NRZ and MSK [36].

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Figure 16: Relative power spectral density of FQPSK compared with BP-SK/NRZ [36].

Figure 17: Relative power loss with respect to bandwidth [36].

The Consultative Committee for Space Data Systems, CCSDS, providesstandards for space operations and technology. Their reports where chosenas the communication link for a high altitude balloon have much in common

Page 29


with space missions, and to make sure the results are feasible for possible futureoperations for SSC, cubesats. In their document CCSDS recommendations forradio frequency and modulation systems, recommendations are made accordingto the data rate of the communication link. Options are 10 S/s(Sample/second)-20 kS/s low rate, 20 kS/s-200 kS/S modest rate, 200 kS/s-2 MS/s medium rate,2 MS/s-20 MS/s high rate, and 20 MS/s - very high rate [8]. The balloon systemwould go in the low and modest category.

For low and modest data rate, PSK modulation is recommended, consideringit is already a common method used for space agencies and its performance isgood enough. For medium data rates, the recommendation is QPSK/OQPSK,modulation, considering it is already a common method used for space agencies.For high data rate and above the recommendation is GMSK modulation, dueto its spectral efficiency [8].

4.3 Corona discharge prevention

As can be seen in section 3.3 the breakdown voltage is depending on the gas pres-sure and the gap distance. The worst case during the balloon mission is between10 and 20 km as the balloon passes through pressure levels which correspondsto the Paschen minimum for gaps between 0.026-0.1231 mm. Engineers at Es-range have experienced corona discharge in the RF filters during transmissionon these altitudes, and especially at 14 km. Even though transmission voltagesdoes not reach the breakdown voltage, voltages spikes further into the circuit iswhat causes the discharge.

The Corona discharge is also depending on the geometry of the electrodes.Sharp edges, corners or points make the field accumulate at these places andthus increasing the chance of a discharge [21] [37].

The power loss during transmission due to corona can be seen in [57]. Inthe case of a continuous wave the ionization rate of the electrons, in front of theantenna, is higher than the loss. As the density of ionized electrons increases, itreaches a point where the partially ionized gas, which now is a plasma, beginsto act as a reactive and absorptive medium for RF fields. This will affect themodifying field, which in this case is the transmitted electromagnetic field, and adecrease in power of that field occurs. This happens at a density of ne ≈ 104f2,where ne is electrons per cubic cm and f is the frequency in Mhz. This is knownas the critical density [57].

In [57] Taylor, Scharfman and Morita shows the complexity of calculatingthe breakdown voltage for corona discharge. They start from the electron con-tinuity equation, and since continuous wave is considered, the change in densityover time is 0. The continuity equation is solved for a 1-dimensional exampleof ionization between two infinite plates. The result from the parallel platesexample is used within an empirical relationship between the electric field andthe ionization rate, which results in equation

Page 30


E = p

(1 +

ω2

vc2

)1/2

3.75

[(D

pΛ2

)+ 6.4 · 104

]3/16

. (20)

Here p is pressure, ω is the angular frequency of the field, vc is the averagefrequency of electron collisions with neutrals, D is the diffusion coefficient, andΛ is the characteristic diffusion length. This shows that the breakdown onsetvoltage increases with increasing frequency. This was first discovered by RichardWoo, and is presented in his article RF voltage Breakdown in Coaxial Transmis-sion line [58]. The Woo curves is presented in figure 18 together with simulationresults from the Standard/Handbook for RF Ionization Breakdown Preventionin Spacecraft Components obtained with this semi-empirical equation [42]

E = 5.3 · p

(1 +

(2πf

p · 5.3

)2)0.5 [

L−2D

(1140

p

)2

+ 6.4 · 104

]1/5.34

. (21)

E is the electric field[V/cm], p is the pressure[Torr], LD is the diffusion length[cm],and f is the frequency[GHz].

Even though the curves are shifted in voltage level depending on the fre-quency of the electric field, they still show the same shape as the Paschen curvein figure 12. The Paschen minimum is found where vc = ω in equation 20.When following the curves to the right the pressure increases and vc

2 � ω2,and to the left the pressure decreases and ω2 � vc

2.

Figure 18: The Woo curves from [58] presented with simulation results from [42].

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4.3.1 Measures against corona discharge

As can be read from above the corona discharge is a complex phenomena anddepends on a lot of parameters. To completely prevent corona discharge fromhappening, the voltage levels of a system could be kept under the critical level.If this is done, no other parameters are important, as the strength of the electricfield would not be enough to ionize the gas enough for the corona discharge tooccur. As is shown in Paschen’s curve, figure 12, the minimum voltage levelhave to be reached for a breakdown.

In Insulation and dielectric breakdown design consideration in sub-atmosphericenvironments [16] Schweickart et. al writes that usually voltage levels betweenzero and 50 V are considered corona free. This is for DC to 500 MHz, and anenvironmental temperature not exceeding 250° C. This also accounts for no con-tamination of the components from neither use nor manufacturing. The articlealso says that as long as the electric field over the air gap does not exceed2000 V/mm no creepage and tracking should exist as long as good workmanshipis consistent trough out the manufacturing and handling of the components.When operating on this no-corona level it is important to practice good work-manship to not affect the components or circuits in such a way that coronacould occur anyway. This implies: [16]

• Contamination shall be avoided

• Small gaps between thinly insulated conductors shall be avoided

• Sharp edges shall be avoided

As the voltage level increases and approaches the values in figure 18 other de-sign aspects has to be taken into account to eliminate corona discharges. Whendesigning a system that operates close to the breakdown level the following isimportant: ( [16])

• Triple points, where the dielectric meets conductor in the presence ofgaseous dielectric, shall be avoided

• Flashover gaps could be lengthened to avoid critical distance

• Separation between high and low voltage circuits

• Make sure any sub-assemblies are designed and tested for the operatingenvironment

In the handbook for ionization prevention ( [42]), it is written that ”manyRF breakdown-related issues can be traced to a lack of standard processes foranalysis and test”. This handbook goes through the procedures required toensure the prevention of corona discharge. It points out that it is important togo trough all the equipment, which they list as well. And as soon as an aspect ofa mission is set, it shall be tested for corona discharge. Any subassemblies shallalso be tested as far as possible. The handbook also provides analytic tools toevaluate the equipment, such as the figure 18, shown above.

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4.4 on-board computers

In this section the results found for the computer systems presented in section 3.4are presented. Trade studies, based on least assessment, have been performedfor development boards and industry SBCs to find a good representation forboth systems.

All computers in this study have enough performance to perform as a on-board computer for the service system. What is presented in this section is theirability to fit into the service system as a whole and the features and possibilitiesthat come with each computer. The requirements presented in section 2.6 areused as guidelines.

As seen in section 3.1, a service system consists of a lot more functions thanonly the on-board computer. Such as sensors, GPS, transceiver, etc. Theseother necessary functions are assumed to be handled by external units. If thecomputer system would provide any of the functions provided by external units,this will be evaluated to the best ability of the author.

A simple thermal study of the four computers have been made in COM-SOL multiphysic. This gives a first indication of how they are affected by theenvironmental effects during a high altitude balloon flight. The method andvalues used have been obtained from the Master’s thesis Heat Transfer in Air-borne Equipment - Theoretical Model [6] by Beenish Batul, also performed atEsrange. The computers have been modeled as shown in figures 19, 22, 25, and28. Where the box is of the same size as is used for the simulation of EBASSin Beenish’s thesis. The box have 1 cm thick walls assumed to be made out ofstyrofoam, and the computers are placed in the center of the box on top of apodium made from steel plates. A transient study with two cases for a 7 hourflight has been performed, using real mission data as input parameters. Thehot case is for 9am during summer, and the cold case is for 11pm during winter.The sun’s position and ambient radiation have been considered for each case.The hot case have a lowest peak temperature of almost -57° C and a float tem-perature of -30° C, while the cold case have a lowest peak temperature of -69° Cand a float temperature of -50° C [6].

4.4.1 Development boards - Beaglebone Black

Chosen to be apart of the trade study was the Raspberry Pi [44], BeagleboneBlack [10], and the Intel Galileo gen 2 [29]. These computers were chosen as theyare well known, and they can run linux, which is of interest for programmingcapabilities. Specifications are presented in table 3.

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Table 3: Comparison table between then BeagleBone Black, the Raspberry Pi3 and the Intel Galileo Gen 2. [10] [46] [29]

Criteria BeagleBone Black Raspberry Pi 3 Intel Galileo Gen 2

Flashmemory

4 GB, 8 bit Embed-ded MMC

NaN 8 MB NOR

SD card MicroSD MicroSD MicroSDRAM SDRAM 512 MB

DDR3L1 GB LPDDR2 256 MB DDR3

CPU ARM Cortex-A81 GHz 2000 MIPS

4xARM Cortex-A53 1.2 GHz

Intel Quark SoCX1000 400 MHz

ADC 8 ch 12 bit NaN 6 ch 12 bitGPU NaN(graphics

engine)Broadcom Video-Core IV dualcore

NaN

Serial in-terface

UART via 6 pins UART via GPIO RS-232 UART viaGPIO

GPIO 2x46 pins 2x20 pins 20 pinsOpensource

Yes Partially Yes

This trade study lead to the choice of the Beaglebone Black. The Galileohave already been used for other purposes on Esrange. The involved engineerwas not satisfied with it and the advice was to let it be. The Raspberry Piis more directed towards media systems, than the Beaglebone Black. Table 3shows more RAM and GPU, features important for media handling. No ADCand low amount of GPIO, connectivity features important for an on-board com-puter. Raspberry Pi is only partially open source, while the Beablebone Black iscompletely open source. Little technical information can be found on the Rasp-berry Pi. Beaglebone Black provides complete data sheets, and schematics. TheBeaglebone Black is the most suitable computer, containing more appropriatefeatures for a on-board computer.

Figure 19 shows how the Beaglebone Black thermal simulation model lookslike. This figure shows a steady state simulation for a hot case with an ambienttemperature of -10° C and an ambient pressure of 300 Pa. The Beaglebone Blackis modeled as the box on the podium inside the box. The Beaglebone Blackdoes not come in any metal box, and due to this it has been modeled with theproperties of the PCB material FR4. Its power consumption is 5 W, and all ofthis is assumed to be dissipated as heat. The upper surface of the BeagleboneBlack has been chosen as heat source. It can be seen from the figures below,20 and 21, that the computer reaches a stable temperature during the missionduration. The results of the thermal simulations are presented in table 4. TheBeaglebone Black have a operational temperature range of -40° C to 90° C, andthe results in the table shows that it will stay in operating range during a 7

Page 34


hour balloon flight.

Table 4: The results from the thermal study of the Beaglebone Black.

Simulation Simulation temperature &pressure

Unit temperature

Cold case steady state -90° C, 400 hPa ca -32° CHot case steady state -10° C, 300 Pa ca 60° CCold case transient -50° C, 4.6 hPa (float) -13° C (stable)Hot case transient -30° C, 7.1 hPa (float) 47° C (stable)

Figure 19: Hot case steady state analysis of the Beaglebone Black, with anambient temperature of -10° C and an ambient pressure of 300 Pa.

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Figure 20: Transient analysis of the Beaglebone for a 7 hour balloon flight duringwinter. Temperature expressed in Kelvin.

Figure 21: Transient analysis of the Beaglebone for a 7 hour balloon flight duringsummer. Temperature expressed in Kelvin

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For a service system built around the Beaglebone Black the following featuresare assumed to be handled by external devices:

• Pyrotechnic equipment for balloon cutters

• All sensors, including load cell

• Transceiver, GPS, ATC, Satellite modem

• Power distribution

The Beaglebone Black lacks two features to fit as on-board computer; goodenough ADC performance, and standard connectors for serial communication.It provides 8 ADC channels with a resolution of 12 bits. The amount of channelsare not enough, and the resolution is to low. Only Ethernet and USB connectorsare mounted on the computer. The rest of the communication interfaces areprovided by the pin-connectors. The lacking features have to be provided byanother unit.

It is possible to buy pre-made COTS extension capes to the BeagleboneBlack. These capes are connected to the pins and can be stacked upon eachother, up to four pieces. Features such as ADC, relays, serial connectors, etc,are available. There exists converter capes to make use of capes made for otherbrands of development boards. Any connected cape is controlled an powered bythe Beaglebone Black. This is done through the pins. Communication is oftenperformed pin-to-pin, but cases using SPI or similar interfaces exists. Customdesign units could be designed to provide the missing features.

The Beaglebone Black comes pre-loaded with Linux ready to boot.

4 different publications where the Beaglebone Black has been involved havebeen analyzed. These have been found through the search of various differentdatabases using terms such as ”Beaglebone black on-board computer”, ”Bea-glebone Black UAV” and others.

The Beaglebone Black was a candidate as the flight computer for the ex-periment in this article by David Wayne et al [17], but a custom made solutionwith FPGAs was chosen instead. The purpose of the flight computer in thearticle is presented to be ”[the] interface with the host spacecraft, a data acqui-sition module to record the telemetry and optical detector data, and a modemto modulate the laser beacon”. The primary purpose of the flight computer isto ”record raw data sampled from the optical sensor”, and also transfer thisdata to the host spacecraft. The Beaglebone Black was not chosen as the otheralternative used FPGAs. As data modulation and sampling was the primarypurpose of the flight computer, and the FPGA technology is more capable ofperforming that, the choice was obvious. They write ”The FPGA would bedesired in the envisioned MRR payload to carry out the modem functionality”,which refers to the capabilities of the FPGA technology. Except for the dataacquisition task of the flight computer proposed, the purposes presented in thearticle are the same as for the on-board computer for the balloon.

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In [9] the Beaglebone Black has been chosen as on-board computer. It willalso control a camera and act as interface towards the RF-equipment. Thepurpose of the Beaglebone black is stated as follows ”BeagleBone Black is re-sponsible for the integration and coordination of high-frequency RF and pho-tography/camera module, through the relevant interface and high-frequencymodule integration, and implement relevant programs contain data transfer andhigh-frequency module under the relevant control procedures. ” This purposecontains control and interfacing, but no sampling or processing of data.

In [43] they describe how they have used the Beaglebone Black as the mainon-board computer for an autonomous Quadrotor. It is equipped with Wi-Fireceiver, GPS and camera, and it is responsible for building Robot OperatingSystem network, to communicate with the ground station. In addition to theBeaglebone Black, the STM320F28335 [28] is used as attitude processor. Thismicro controller will handle all attitude processing and control, and are con-nected to three units, which contains sensors for attitude measurements. TheTMS320F28335 is also responsible for driving the motors, according to the mea-surements to keep the quadrotor in the air. A notable difference in specificationsbetween the TMS320F28335 and the Beaglebone Black is processor speed, wherethe former has only 150 MHz, compared to the Beaglebone’s 1 GHz. Even so, itis the TMS320F28335 which performs the attitude determination and control.The reason for this is another noteworthy difference in specifications, namelythe amount of PWM and ADC channels. The TMS320F28335 have up to 24ADC channels(8 for each MUX) of 12 bit resolution and 24 PWM channels, ofwhich 6 are high resolution, typically 150 ps [28]. While the Beaglebone Blackonly has 8 channel with 12 bit resolution and just 3 PWM channels.

Another example where the Beaglebone Black has been used as main com-puter, is [19] about a vehicle avoidance system. The authors presents a solutionbased on the Beaglebone Black, in addition with a Raspberry Pi and an Ar-duino. In their proposed system, the Raspberry Pi is used to provide a graphicalinterface towards the user, and the Arduino is used to provide audio for the sys-tem. As main computer the Beaglebone Black will be connected to the sensorsvia CAN bus and digital interface, process this data, and communicate ade-quate information to the other computers. This system shows the strength ofthe Beaglebone Black; the processor power, and communication interfaces, butalso what it is lacking, graphical processing and analog outputs. In this system,a CAN bus expansion cape is connected to the Beaglebone Black to provide astandard physical interface.

4.4.2 Single-board computers - SBCT43

Five industry classed SBCs were identified as potential on-board computers.These have been found trough the search of industry classed computer used forcubesats, UAVs, and other control purposes.

• SBC-TM335 [14]

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• SBC-T43 [13]

• SBC-FX6 [12]

• Zynq-7020 [60]

• NanoMind A712D [24]

The SBC-TM335, SBC-T43, and SBC-FX6, are rugged single-board com-puters. Shock and vibration certified. Zynq-7020 is a system-on-module(SOM)with a CPU and an FPGA. The NanoMind A712D is special designed for cube-sat systems. These were compared to find the most suitable computer. Thiscomparison lead the the choice of the SBC-T43. Connectivity and flexibilitywere the important aspects.

The Zynq-7020 does not provide any standard connectors. A carrier boardor other attachment is required to access its features. The Zynq-7020 was dis-carded due to lack of connectivity. Table 5 lists some of the specifications of the4 remaining computers.

The NanoMind A712D have less computing power, memory and flexibilitythan the other three. Therefore it is discarded. The computing power andstorage capabilities are equal between the other three. The SBC-T43 providesthe most connectivity and flexibility(ADC, UART, SPI.) This makes the SBC-T43 most suitable choice for this study.

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Table 5: Comparison table of the NanoMind A712D, SBC-FX6, SBC-T43, andSBC-TM335 computers. [24], [12], [13], [14]

Criteria NanoMindA712D

SBC-FX6 SBC-T43 SBC-TM335

CPU ARM7TDMI8-40 MHz

Freescalei.MX6 singlecore Cortex-A9MPCore,1 GHz,

Sitara, ARMCortex-A9, 1 GHz/800 MHz

AM3352 CPU,275 MHz/AM3354 CPU600 MHz

RAM 2 MB static 256 MB-4 GB

128 MB-1 GB 128 MB-512 MB

Flash 4 MB data,4 MB code

128 MB-1 GB

128 MB-512 MB(eMMC 4 GB-32 GB)

128 MB-1 GB

Ethernet Na 100Base-T 1000/100/10 1000Base-TWiFi Na Yes Yes YesUSB 2.0 Na 5 2 5UART 1(USART) 0 3(up to) 0CAN 0 1 1 1MMC/SD/SDIO

MicroSD2 GB

MicroSD32 GB

MicroSD 32 GB MicroSD 32 GB

SPI 2 0 4(up to) 2(up to)I2C 2 busses 0 2(up to) 3(up to)GPIO 7 24 24 24ADC 6 ch 0 16 ch 12 bit 4 ch 12 bitPowerconsump-tion

0.23 W,3.3 V

Na (5-15 V) Na (3.3-5 V) 1-1.5 W,3.3 VDC

Figure 22 shows how the SBCT43 have been modeled in the thermal simu-lation, as the block on top of the podium in the middle of the box. For the hotcase it is assumed to dissipate about 15 W, and for the cold case 8 W. The uppersurface of the computer is modeled to be the heat source. The SBCT43 does notcome in any metal box, and due to this it has been modeled with the propertiesof the PCB material FR4. The steady state simulation in figure 22 is done for-10° C ambient temperature and 300 Pa ambient pressure. As can be seen fromthe graphs in figures 23 and 24 the computer reaches a steady temperature dur-ing the duration of the simulation. The results from the thermal simulations ofthe SBCT43 are presented in table 6. The temperature specifications for theSBC-T43 is -40° C to 85° C. These simulations shows that it does not exceedthese limits.

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Table 6: The results from the thermal study of the SBC-T43.


Unit temperature

Cold case steady state -90° C, 400 hPa ca -30° CHot case steady state -10° C, 300 Pa ca 77°CCold case transient -50° C, 4.6 hPa (float) -2° C (stable)Hot case transient -30° C, 7.1 hPa (float) 55° C (stable)

Figure 22: Hot case steady state analysis of the SBCT43, with an ambienttemperature of -10° C and an ambient pressure of 300 Pa.

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Figure 23: Transient analysis of the SBCT43 for a 7 hour balloon flight duringwinter. Temperature expressed in Kelvin

Figure 24: Transient analysis of the SBCT43 for a 7 hour balloon flight duringsummer. Temperature expressed in Kelvin

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For a service system based on the SBC-T43 the following features are as-sumed to be handled by external devices:

• Pyrotechnic equipment for balloon cutters




The SBC-T43 is lacking two features to fit as on-board computer: goodenough ADC performance and standard connectors for serial communication.It provides 4 ADC channels with 12 bits resolution. The amount of channelsis not enough, and the resolution is to low. Connectors for Ethernet, USB,and HDMI are mounted on the board. The other communication interfaces areaccessible through the pin connectors. The lacking features have to be providedby another unit.

The SBC-T43 consists of two parts, one SOM, the CM-T43, and the carrierboard, SB-T43. It is possible to design a new carrier board to the SOM, thatfeatures all connectors and the ADC performance required. An external unitutilizing the pin connectors, or any other connector available, could be designedto provide the lacking features.

The SBC-T43 can be pre-loaded with Linux and a Real-Time extension. Acouple of design features can be chosen by the customer upon purchase. SBC-T43 is available for 10 years. Full hardware and software support.

The trade study presented in the article about Astrobee [33] is performedto find the best Middle-Layer-Processor for the robot. The computers used, in-cluding the SBC-FX6 which was a part of the comparison performed above, areall similar to the SBCT43. The purpose of the middle layer is to act as interfacefor external devices requiring standardized connectors, for example cameras.But also to combine and handle sensor data and run navigation algorithms.These are similar to the purposes of the service system’s on-board computer.This trade study is made for System-on-Modules, and not complete single-boardcomputers. The computers are evaluated for the supported features alone, andnot for their physical connectors.

4.4.3 DAQ system UEIPAC

For this service system, the Cube chassi with three slots, and the DNA-AI-201-100, DNA-SL-501, and DNA-AO-308-350 I/O boards was chosen. Thisconfiguration have been used for the thermal simulations.

In figure 25 the UEIPAC is modeled as the block on top o the podium inthe middle of the box, with an ambient temperature of -10° C and an ambientpressure of 300 Pa. As the chassi is of metal the UEIPAC has been modeled

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as an aluminum block, which dissipates heat equally in all directions, 10.5 Wfor hot case and 9 W for cold case. This is done only to simplify the model forsimulation purposes, as to model the equipment as it is constructed would beto time consuming for the purpose of this study. As can be seen on the graphsin figures 26 and 27 the temperature of the UEIPAC keeps increasing for thehot case, while it ends up stable for the cold case. The results of the thermalsimulations are presented in table 7. The temperature specifications for theUIEPAC are -40° C to 85° C. As can be seen from the thermal simulations theUEIPAC does not exceed its operational temperature range.

Table 7: The results from the thermal study of the UEIPAC.


Unit temperature

Cold case steady state -90° C, 400 hPa ca -28° CHot case steady state -10° C, 300 Pa ca 52° CCold case transient -50° C, 4.6 hPa (float) -2° C (stable)Hot case transient -30° C, 7.1 hPa (float) 36° C (increasing)

Figure 25: Hot case steady state analysis of the UEIPAC.

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Figure 26: Transient analysis of the UEIPAC for a 7 hour balloon flight duringwinter.

Figure 27: Transient analysis of the UEIPAC for a 7 hour balloon flight duringsummer.

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For service system based on the UEIPAC the following features are assumedto be handled by external devices:

• Pyrotechnic equipment for balloon termination




The configuration of I/O boards used have the following specifications:

DNA-AI-201-100 24 channel ADC with 16 bit res-olution, 100 kS/s

DNA-SL-501 4 full duplex RS-232/RS-485DNA-AO-308-350 8 channels with 16 bit resolution,

max values 10 V and 50 mA

The UEIPAC is lacking one feature to make it as on-board computer: stan-dard serial communication connector. The connector to the serial interfaceboard is a 37-D connectors. Standard size connectors have to be provided by aconverter. A simple connector converter, that divides the communications linesinto single connectors, is needed. A D-37 to four D-9 converter cable is availablefrom UEI.

The UEIPAC can be pre-loaded with Linux and Xenomai Real-Time exten-sions, or VxWorks. Cross compiler for eclipse is available. It is available for 10years, as is the I/O boards. Full hardware and software support available.

The I/O boards can be exchanged in the matter of minutes, and the stan-dardized interface, D-sub, towards the boards allow for easy configuration andinstallation of the rest of the equipment on-board. The processor registers whatboard is connected via the board’s EEPROM, and controls both the boards andtheir power supply. The UEIPAC does already contain software to operate theI/O boards connected, and thus an user application only have to call the rightfunctions to access the connected boards. The system does however inflict asingle-point of failure, as the processor in the chassi is the only thing that keepthe boards operational.

The UEIPAC have been used for the COLBERT treadmill [55] that was sentto the ISS by NASA in 2009. Its purpose is to control and perform measurementson the treadmill while the astronauts are using it. One task is to measure theimpact forces upon the treadmill from the astronauts, which is done by readingaccelerometers and load cells. It has also been used for a military ULV(ULV)providing control and sensor interfaces. 6 different I/O boards was used forthis [54].

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4.4.4 Custom Designed Control System - DHS boards

The configuration of modules chosen for the service system is the PCDU board,the TMTC board, the Spider support board, the FLIP board, and the THERMboard. The thermal simulation have been performed for this set up.

In figure 28 the thermal model of the DHS board is shown for a hot casesteady state simulation, with an ambient temperature of -10° C and an ambientpressure of 300 Pa. This model has been made after the configuration exampleshown above, with 5 boards to complete the service system. They have beenstacked on top of each other because of simplicity. The boards have been mod-eled as aluminum boxes, as they are put in metal cases when mounted. Forthe hot case 25 W and the cold case 14 W power dissipation is simulated, equalin all directions. As can be seen in figures 29 and 30 the temperature of thesystem increases during the whole duration of the simulation. The results ofthe thermal simulations is presented in table 8. No definite number s availablefor temperature operating range, so industry temperature operating range isassumed, -40° C to 80° C. As can bee sen from the simulation results the systemis within operating range during the whole simulation.

Table 8: The results from the thermal study of the DHS system.


Unit temperature

Cold case steady state -90° C, 400 hPa ca 2° CHot case steady state -10° C, 300 Pa ca 75° CCold case transient -50° C, 4.6 hPa (float) 35° C (increasing)Hot case transient -30° C, 7.1 hPa (float) 55° C (increasing)

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Figure 28: Hot case steady state analysis of the DHS boards.

Figure 29: Transient analysis of the DHS boards for a 7 hour balloon flightduring winter.

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Figure 30: Transient analysis of the DHS boards for a 7 hour balloon flightduring summer.

For service system using the DHS boards as on-board computer the followingfeatures are assumed to be handled by external devices:




The configuration of the DHS boards used have the following specifications:

FLIP 16 ADC channels with a resolu-tion of 16 bits

THERM 48 temperature sensors, PT1000and PT100

SPIDER Provides pyrotechnic cutters

The DHS system software applications have been written using CMX RTOS.A possible transition to FreeRTOS may take place in the future.

The PCDU, the TMTC and the Spider support board have been flown inconfiguration on the SPIDER/LEEWAVES sounding rocket mission launchedfrom Esrange [47]. For this mission the three DHS boards were connected to thepayload in different ways. The PCDU provided power and the Spider support

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board was connected to the pyro equipment on the payload. The TMTC boardwas connected to the payload to provide umbilical control of the payload onground. No communication between the payload and the TMTC board tookplace during flight [47].

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4.5 Concept service system

The requirements presented in section 2.6 gives a picture of how the architectureof the service system shall look like. In this section the resulting service systemwhen following the requirements are presented. Hardware and software. Thisresult is used in the analysis to find the most suitable solution. The resultfrom each requirements are presented and compiled in the end. Shall is a strictrequirement, meaning it shall be followed, could is an example that could beused.

• R 1:

The service system shall be made out of industrial components. These have longlongevity and if a model would be discontinued similar options are available.This would ensure the availability for many years.

• R 2:

The service system shall be compared with EBASS to make sure no functionsare left out.

• R 3:

Even though it shall be designed to endure a high altitude balloon flight the sizeand geometry shall be efficient. This could be a square box with attachmentsin each corners.

• R 4:

Standard connectors shall be used, and different interfaces for different purposesto make it simple. The software shall provide buttons for all functions.

• R 5:

The system shall be divided into different modules according to their physi-cal function. A bus with standard connectors can be used and allow for anyconfiguration.

• R 6:

The interfaces shall be standard and the design open for others to use.

• R 7:

Dual communication lines could be used, and each module should provideenough functions to control the service system. Such as processor and memory.

• R 8:

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All modules shall be able to take over the control of the service system. Withdifferent modules available other service requirements can be met.

• R 9:

The distribution of the power to the service system shall not be a part of thesystem itself.

• R 10:

A common design for all modules would lead to a faster design process as onlyrequirements and design specification have to be stated to the manufacturerwhen new modules shall be produced.

• R 11:

No connections shall be offered to customer systems, as long as it is not a partof the service system.

• R 12:

The common physical design shall allow for flexible mounting capabilities. Aseach module run their own software, only the service application controllingthe service system have to be adjusted to the modules used. With the useof EEPROMs with configuration data, the service application can be writtenfor many modules and just activate sections corresponding to the connectedmodules.

• R 13:

The functions of each module shall be chosen in such a way that as many mod-ules as possible can be used independent of the platform.

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Figure 31: The modules of the concept service system connected via a bus.

From the result above a possible configuration of Module 1, Module 2 andmodule 3 is shown in figure 31. Each board have the same design; processor,memory and interfaces. The use of a communication bus and two possibleconnections on each board allow for many different configurations. Which inturns simplifies placement of the system. Redundancy is implemented as everyboard work individually, and their functionality is not depending on any othermodule. As the processor, memory and communication interface is identical,each module is as capable of controlling the service system. This gives muchreliability and makes the system fail-safe.

As each module, including software, can be handled individually, the workon one module does not affect another. This allow resources to be shifted,while still some parts of the project is going on. This makes the project workmore efficient as resources can be put on more urgent measures when needed.Test and repair could also be done on individual modules, if the tests allow it.Reconfiguration is also simplified, as if one module is damage it is just exchangedfor an identical without notice.

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The design allows for simple development of new modules, as only the func-tional part have to be changed. This also allow partners to SSC to design theirown modules. With this design, as many modules as possible can be madeplatform independent, and be used for various purposes.

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5 Analysis

The different subjects covered so far are just some of the design challenges onefaces when developing a new service system for high altitude balloons. Thetheory presented in section 3 and the results in section 4 are combined andcompared to be able to give a well founded suggestion to SSC what to do withtheir new system. Where equally good equipment or methods are found, thechoice that is most suitable to the operations at Esrange will be identified andchosen.

5.1 Frequency

As the theory in section 3.2.1 describes the Free-space path loss increases withfrequency. 450 MHz have a FSPL of 139.5 dB and for 2.3 GHz it is 153.6 dB.This is an increase in FSPL of 14.1dB. As 3dB represents a doubling, thiscorresponds to a 4.3 times increment in loss. For a ground station this is not animportant number as power is not an issue, but for the balloon it is. Since theballoon is a limited power system, an increase of transmission losses means thatan already stressed resource, power, will get even more stressed. The increasedtransmission power required have to be compensated, either by produced power,e.g. from solar panels, or stored power, ie by bringing more batteries.

As one studies the corona discharge phenomena in section 3.3 it can be seenthat during a high altitude balloon mission the balloon travels through a veryexposed region. During this region the Paschen minimum is satisfied for a rangeof gap distances which can be found in electronics. In section 4.3 it is describedand shown, in figure 18, how the threshold power for corona increases with fre-quency. The simulation curves from equation 21 shows that for a frequency of400 MHz, the threshold power is about 50 w, and for 2.3 GHz it is about 500 w.As explained the corona discharge can cause power losses for antennas duringtransmission [57].

The frequency allocation in Sweden is similar to the other countries’ alongthe Arctic circle, with a few exceptions. The possible frequency bands availablewas identified as the 400 MHz, 450 MHz, 2.3 GHz, and 2.4 GHz. The 400 MHz,450 MHz, and 2.4 GHz were also given as advice by a contact at PTS. The2.4 GHz band is not an option as the ELINK is already operating on that band.It is the payload communication system. The ELINK system is a special ex-ception to the usual regulations when it comes to Wi-Fi. The ELINK com-munication link is basically a regular Wi-Fi network, but with a super chargedtransmitter(compared to the ones operating in our houses). This band is notas available in the other countries, as the other bands are. Since the E-LINKis an exception to the regular use of this bands, Wi-Fi networks, such an ex-ception can’t be accounted for internationally. There are no indications thatthe two lower bands will be changed during the next 10 years, and thus furtheroperation in these bands are possible. As long as uplink and downlink are notswitched. 2.3 GHz is interesting as this band will undergo changes in the coming

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years. As for now temporarily permissions have been used for sounding rocketsand some balloon missions, but as this band is up for allocation in 2018 it couldbe possible to get a frequency band dedicated to high altitude services. The2.3 GHz band is open for aeronautical telemetry in all countries along the arcticcircle. This could simplify the use of ground station support in other countriesduring international missions.

Even though the physics have a big effect on the communication link, themost important aspects to consider is the frequency spectrum allocation plan.If this does not include the wanted service, there will not be any radio commu-nication link. As the 400 MHZ and 450 MHz will be available for a long time,it is the suggestion from the author that SSC keep using these. Both as itsimplifies the use of hardware as much is already suited for these bands, butalso that the loss during communication is less. But, to keep looking forwardSSC should investigate the possibility to get a dedicated frequency band in the2.3 GHz band. The present operations is these bands will be easier as no tem-porary permissions have to be applied for. This is also an international validfrequency for aeronautical telemetry, which could simplify communication dur-ing international missions, or have international customer bring their equipmentto Esrange.

5.2 Modulation

The theory in section 3.2.2 describes the basics of the different modulationmethods. It is mentioned how the characteristics of the signal can influence thechoice of transmitter amplifier. For amplitude modulation only linear amplifierscan be used. These are less efficient than non-linear amplifiers. As can be usedfor both frequency and phase modulation. If one compares the expressions foramplitude modulation and frequency/phase modulation from equations 11 and13. It can be seen that any power put into the message does not effect the powerof the modulated signal for frequency/phase modulation, but for amplitude itdoes. m, which is the modulation index, affects the amplitude of the carrierfor amplitude modulation, but only the phase in frequency/phase modulation.Thus any power put into the information transmitted, is not used to affect thepower of the signal.

The spectral density and power containment are important measures to getas much as possible out of the available bandwidth. And as shown by Davidein [36] the best performing modulation schemes for this is GMSK and FQPSK-B. Even though he presents other methods it is the GMSK which he encouragesagencies to use if spectral efficiency is a concern to them, which it often is.Davide Micheli’s results are confirmed by the CCSDS document CCSDS rec-ommendation for radio frequency and modulation systems [8]. Depending onthe link performance CCSDS recommend different modulations. As spectralefficiency is more important for higher bit rates GMSK is recommended forcommunication links with a data rate above 2 MS/s. The recommendations for

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lower data rates are base upon the argument ”this method is already commonand good enough to be used”.

Spectral density is very important and since Esrange is already using GMSK,there is no reason to abandon that method for another modulation scheme. Asit is the among the best and most efficient methods. It would be a step backto chose another type(if not FQPSK-B is chosen). From the recommendationsof CCSDS it may be overkill to use GMSK for such communication link, as thedata rate is only 38 kb/s, but their opinion to use what is most convenient forthe agencies is another argument to keep it. Further benefits with GMSK is theavailability to use non-linear amplifiers, which saves power on-board the balloon,compared to linear ones. The spectral efficiency of GMSK makes it possible touse Frequency Division Multiplexing Access to communicate over several links atthe same time. With an efficient utilization of the bandwidth, each channel canhave less bandwidth. And less space between each channel would be requiredas the power outside one bandwidth is very low. With GMSK Esrange havea modulation method which can be used for many different purposes and datarates, and communications can be used for more demanding platforms.

With the increasing use of SDR, and the fact that SSC does have a PhDstudent working on an SDR solution for the company, is something that alsoencourages the use of GMSK [45]. Obviously it will take some time to get anSDR system to work properly, but a high altitude balloon is a good platformto test and develop such a system on. When the SDR communication system isworking properly, the scaling procedure to adapt it to other frequencies or datarates is not that challenging. Then SSC have a system they can use on manyplatforms, with the best performance available.

5.3 Corona discharge

The corona discharge is a complex phenomena and depends on several variables.And to be able to answer the question if Esrange can do anything to preventcorona, one shall consider what was written in section 4.3. Namely that theengineers at Esrange had experienced corona in the RF filters, and not at theantenna. If the system is kept as it is today, then there’s only one real solu-tion to this problem; buy better filters. Filters that are more suitable to thevoltage levels of the service system. Why couldn’t Esrange just increase thefrequency, as it is shown in figure 18 that the threshold voltage depends onfrequency one might ask. To change frequency is not to solve the problem, itis to move it to another source. An increase in transmission frequency wouldresult in increasing Free-space path losses, which in turns means higher trans-mit power and higher voltage levels within the filter. A change in frequencywould not only require a change of on-board hardware but force an exchangeof the ground station equipment as well. If one studies the two equations forFree-space path loss(6) and corona initiation voltage(20), one can see that thefrequency have the same relationship in both of them, f2, but the term in the

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corona onset voltage equation is also squared-rooted. If one compare the pic-tures of the corona onset voltage(18) and the FSPL(7) the increase in Free-pathloss is much greater than the increase of onset power. The increase in onsetpower is about 10 times, 10 dB, 102.7/101.7, and the increase in FSPL is about26 times, 14 dB, 2.32 ·1015/(8.89 ·1013). Even though the antenna gain increaseswith frequency, it must be more than 4 dB for the power to not reach the onsetvoltage. If one have an antenna for 2.3 GHz, which have a higher gain then4 dB, then an increase in frequency from 400 MHz, would eliminate corona dis-charge. At the antenna, which was not the problem. If a voltage spike occurssomewhere else in the circuit, corona might still occur. There might be cavities,sharp edges or gaps, in the system as it is now, that have the right parametersfor corona as the power in the system have increased. Parts or details thatfor a lower power level never were an issue. Thus a new system with higherfrequencies can’t just be built from the old one, but it also have to undergo alot of testing. As was described in section 4.3, every aspect of a mission must betested an evaluated for corona discharge. As from this reasoning, increasing thetransmission frequency is not a feasible solution to eliminate corona. The sim-plest way, and cheapest when taking working hours into account, is to make surethat the filters, where corona had occurred, are exchanged by even better filters.

A solution to overcome corona discharge is to pressurize the equipment, soit never reaches the critical values. This method has already been utilized atEsrange and has not been covered during this study.

As a change in frequency is disregarded as a solution to this problem, onehas to rely on the hardware to solve the problem. since SSC doesn’t buildany systems by them self, they can only make sure that the manufacturersknow what they are doing to prevent corona. A complete specification listof environmental characteristics and operating values must be provided to themanufacturer to be able to solve the problem. As was stated in [42] manycorona incidents occur due to an inadequate handling or manufacturing of theequipment, and this responsibility lies not at SSC’s hands until implementation.SSC must also ensure that test procedures are standardized, also mentionedin [42], to ensure that the complete setup is corona free. If corona dischargeoccurs, there shall be procedures to identify the parameters involved, so thefailing specification can be fixed.

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5.4 Service System and On-board computer

The engineers at Esrange are very satisfied with the EBASS service system,section 3.1.1. This is because it does what needs to be done by a high altitudeservice system, not more nor less. This accurate performance capabilities is aresult from the custom design approach of the whole system. Each subsystemhave been manufactured to be a part of the EBASS. This makes the system verycompact as the functionalities are integrated with the design. It also makes thesystem very dedicated to one purpose only.

The NOSYCA system, section 3.1.2, has much redundancy due to new con-straints on the operating agency to officially prove that they protect the flyinggoods, the overflown population and environment. Even though the NOSYCAis a very complex system, it has features such as internal communication viaWi-Fi, that should be adopted. As well as the ability to use an interface(theSIREN) if a third part would like to fly with the new service system, but onlybe able to communicate with their own unit. This could also be a way to testnew equipment, without having to interact with the regular operation at all.For the user it would act as a separate communication link.

The results of the thermal simulation, section 4.4, shows that non of thecomputers reaches temperatures outside their operating range. The Beaglebonegets the coldest, as it dissipates less heat. These simulation does not ensure thatthe computers won’t reach other temperatures, but rather gives an indication ifthey can be used or not.

It is possible to build a service system around any of the four computersystems. And if one must chose one system that shall fly on balloon as soon aspossible, the answer is the UEIPAC. This is one of the two(DHS is the other)systems which can provide all necessary functions without the need for customdesigned units. Be aware that this is the choice, for a fast solution, not the best.

The UEIPAC have been used for autonomous vehicles, as seen in [54], andis capable of high resolution measurements and actuation. The analysis is thatthe UEIPAC is designed for systems where the data acquisition is the primeobjective, and control and processing comes second. This is motivated by theconnections available on the UEIPAC chassi(not provided by the I/O boards)and the inability to put the unit, or individual I/O boards in stand by-mode.Only Ethernet and USB connectors are available, and thus any serial commu-nication have to be provided by the I/O boards. It is not possible to turn ofindividual I/O boards, when they are not used. To save power the whole unitwould have to be turned off. The UEIPAC is the most expensive system to buyfrom a vendor. The example configuration in section 4.4.3 costs about 19000 sek,only for the I/O boards. The serial interface board is only chosen to enable aninterface towards radio and other external units, and it costs about 5550 sek.That is just to make serial communication available. The sample rate of theADC I/O boards is much higher than what is required for the service system.As is the resolution of the analog output board too. The cost of this system ispaid for many features which cannot be utilized on the balloon. The UEIPAC

Page 59


is a single-point of failure, as the I/O boards only can be accessed through theprocessor within the chassi. If any error would cause the processor to malfunc-tion this would completely disable the use of the functions of the I/O boards.This could be compared with the DHS system, where each module have theirown micro-processor, which would run disregarding of the status of the mainprocessor. The design intentions of the UEIPAC, high cost and the single-pointof failure are the reasons why the UEIPAC is not recommended to be used forthe service system.

It has been noted during this study that the development boards(which aresingle-board computers) and the industry single board computers are in factvery similar. The Beaglebone Black and the SBC-T43 both falls short on thesame aspects, ADC performance and available connectors. When comparing thetwo computers head to head, appendix A, their performances are similar, withlittle difference in available features. Both computers would require at leastone additional unit to provide analog-to-digital converters, but also standardinterface for serial communication. This is something that is common for all thesingle-board computers in this study. This can also be seen on the applicationswhere the computers have been used. For the Beaglebone Black, neither of theapplications include data acquisition. It was even discarded as on-board com-puter as it could not perform this task good enough. This is probably becauseas one buys a single-board computer, it is not to perform high resolution mea-surements. If so, a DAQ system like the UEIPAC is more interesting. One shallnot forget when comparing with the MFB, that it is not a COTS single-boardcomputer but custom designed for the service system. Utilizing features fromboth SBCs and DAQ systems. The Beaglebone Black barely costs 8%, 600 sek,of the SBC-T43, 7540 sek(both the system-on-module and carrier board). Thisdifference in price cannot be identified in the performance. The SBC-T43 isclassified for shock and vibrations, which costs money, but does not make upfor the price difference. And as can be seen on the applications where the Bea-glebone has been used, it has been launched to space on a rocket where vibrationand shock are present. Much of the price for the SBC-T43 can be seen on thesupport given, and the reliability ensured by the company. One shall take intoaccount that the Beaglebone Black is a mass produced unit, and thus the man-ufacturing processes have been adjusted and improved many times to performa reliable result. Due to the cost of the SBC-T43, for the same performanceas the Beaglebone, it is not recommended as on-board computer for the newservice system.

The Beaglebone Black requires at least one extra unit to provide ADC ca-pabilities and serial connectors. Although extension capes are available, theydo not provide the performance needed to justify their use. In only one of thecases where the Beaglebone Black have been used for applications similar to theservice system, had COTS capes been used. This was for a communication in-terface. The serial interface unit would need a controller if more than one serialinterface shall be used. The pins on the Beaglebone Black are multi-purpose,

Page 60


and their function is controlled by the processor. The same pin(s) is used forboth SPI, I2C, UART, and CAN, and thus the serial connector cannot justbe relayed to this pin, but the information flow from each physical connectormust be supervised. Otherwise simultaneous transmissions could come fromtwo different sources to the same pin, in different voltage levels too, resultingin miss-communication as best. A micro-processor could be used to control theinformation flow in the interface unit, and provide the Beaglebone Black withthe data upon request. A memory to store application data and save communi-cating data could also be included on the unit. The ADC unit would also needa micro-processor for control. As the conversion is performed at the unit, theBeaglebone have to request what data to be converted and send to it. A mem-ory to store application data and measurements could also be included on theunit. This system, with the Beaglebone Black controlling external units, whichare running their own program, is similar to the concept system described insection 4.5.

The Beaglebone Service system does also resemble the DHS service system.Individual modules with different functions and a common communication inter-face between the modules. Both the DHS system and the proposed BeagleboneBlack system fit on the description of the concept service system built from thepresent requirements. However, the Beaglebone Black is a fictive system, whilethe DHS system does exists. This leads to the analysis that the BeagleboneBlack is not to recommend to be used for a service system. As the DHS systemcan be used without major manufacturing needed, but the Beaglebone Blacksystem have to be developed first. Another reason is that it is considered unnec-essary to have two similar service systems within the company, as this increasesthe cost for basically the same function.

The idea of using the Beaglebone Black however shall not be thrown to thetrash, as it is too much value to not take advantage of. The possibilities itoffers, for that price, are remarkable. With the use of little power and space, itprovides processing, control and storage of data to any unit which can utilizeserial communication, on various interfaces.

Even if the DHS system can be used for balloons right away, it is not done ina smooth way. Five different modules being used shows that they are not opti-mized for the purpose. The functions of the present modules are heavily aimedtoward sounding rocket operations. The PCDU and the TMTC are perfect forthe service system, and the TMTC does already have GMSK as a potentialmodulation method. But the balloon control function and measurements wouldhave to be fitted into one or two modules. This is something that can be donewhile the present setup is already in use. It can be test flown to identify moreaspects which needs a change to work for balloon operations as well. And assoon as the new modules are available these can quickly be exchanged and im-plemented in the system. Other benefits with the design of the DHS system isthe redundant bus, a feature also mentioned in the concept system. And thereis no single-point of failure within the system.

This analysis shows that to use COTS products for the service system would

Page 61


either require an expensive, probably over performing unit, or at least the useof custom made units to some extend. Or to use a complete custom designedsolution. The analysis have been done that money is better spent on customunits, as this gives back more to the company than just a piece of hardware. Aproduct that can be sold or worked with as the company pleases.

Page 62


6 Conclusion

The conclusion from the analysis regarding what frequencies SSC Science ser-vices’ new service system for high altitude ballooning shall use for commu-nication are the 400 MHz-band and the 450 MHz-band. These are the samefrequencies that are used with the present service system. This is a result formthe analysis of the frequency allocation plan for Sweden, decided by PTS. Fromthe theory of Free-space path loss, it has been seen that this loss increases withincreasing frequency. Thus a lower frequency is better for a balloon, which is alimited power system.

The 2.3 GHz-band was identified as a candidate frequency, but is more inter-esting from a international point of view. It is used for aeronautical telemetryin the countries along the arctic circle. SSC are encouraged to work to get a fre-quency band within the 2.3GHz-band dedicated for high altitude services. Thiswould be possible as this band is under development due to the implementationof 5G cellular network. This could open up new possibilities for SSC.

The fact that GMSK modulation is already used for the service systemcommunication link is only for the good of SSC. GMSK is among the best mod-ulation method when it comes to spectral efficiency. An aspect important foragencies working with space communication. It is recommended by the Consul-tative Committee for Space Data Systems for communication links with highdata rate, above 2 MS/s. GMSK can be used for other applications within thecompany as well. SSC science division shall keep using the GMSK as modula-tion scheme.

The conclusion from the analysis of the corona discharge and how to pre-vent it is that SSC can only affect this problem indirect. The corona appearswithin or between components, design characteristics which SSC is not involvedin. The corona phenomenon must be involved in the early stages of the designprocess, to enable a better result in the end. Standardized requirements to en-sure manufacturers have all the correct specifications needed, and standardizedtests to verify the components are what SSC can do to prevent corona discharge.

The best computer system for the new service system is the in-house designedDHS system. This computer system had the most resemblance with the conceptservice system. The other computer systems would lead to a similar solution,but with more work or for a higher cost. The DHS project also provides goodintentions for the company.

The Beaglebone Black has been identified to have too much value for thatamount of money to not be used. It can improve present systems by providingprocessing and storage capabilities, over simple serial interfaces.

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7 Future Work

The next step in the development of the service system is to complete therequirements documents. This must be done to truly be able to evaluate thespecifications at the DHS system. Such an evaluation must be done as thesystem only has been used on sounding rockets. From these requirements it ispossible to evaluate each individual model and its function.

While the requirements documents are being completed, it is possible toactually fly the present DHS modules on the balloon. The compatibility can betested, and the practical experience with the system can be used when evaluatingthe functions of the modules.

The requirements and practical experience can be used to identify the non-balloon compatible features of the system. In this way the work towards newmodules can begin. A system evaluation could also be done, to find featureswhich could have been done different to make the DHS system more cross-platform.

When the above mentioned work is done, especially the requirements, thework with the preliminary design of the entire service system can begin.

Page 64


Page 65


A Specification table

Name

Company

Type of boardSize

Weight

Open source

CPUG

PURAM

BeagleBone BlackBeaglebone

Development board

86.4x53.3mm

39.68gYes

Sitara AM335BZCZ100,

ARM Cortex-A8, 1G

Hz,2000M

IPS

Grapgic engine,

SGX530 3D, 20M

Polygons/S

SDRAM 512M

BDDR3L 800M

Hz

Rasperry pi 3 Model B

RaspberryFoundation

Development board

85x56mm

PartiallyBroadcom

BCM2387

chipset, 1.2GHz quadcore

arm cortex-A53

Dual CoreVideoCoreIV M

ultimiedia Co-

Processor

1GB LPDDR2

CM-FX6

CompuLab

Computer-on-m

odule75x65m

m33g(withoutheat-plate)

Freescale i.MX6 single

core Cortex-A9MPCore, 1

GHz, 512kB I/D shared L2

cache. Dual/quad optionsavailable

Yes256M

B, 512MB,

1GB, 2G

B, 4GB,

DDR3-1066, 16-64bit bus

SB-FX6Com

puLabCarrier board

160x160mm

Same specs as for CM

-FX6

CM-T43

CompuLab

Computer-on-M

odule36x68m

m12g

Texas Instruments Sitara

AM4379 ARM

Cortex-A9,1G

Hz/AM4376 ARM

Cortex-A9,800M

Hz(Programm

ableReal-Tim

e Coprocessor)

PowerVR SGX530

GPU

DRAM 128M

B,512M

B, 1GB,

DDR3-800, 32bitdata bus. Boot-loader SPI NO

R2M

B

SB-T43Com

puLabCarrier board

150x130mm

145gSam

e specs as for CM-

T43Sam

e specs as forCM

-T43

CM-T335

CompuLab

Computer-on-M

odule68x30m

m33g

Texas Instruments

AM3352 CPU,

275MHz/AM

3354 CPU600M

Hz, 32KB (L1) +256KB (L2) cache

PowerVR SGX 530

DRAM 128M

B,256M

B,512MB,

DDR3-1066, 16bit bus

SB-T335Com

puLabCarrier board

130x96mm

Same specs as for CM

-T335

Same specs as for

CM-T335

Zynq-7020Xilinx

Hybrid System-on-

Chip19x19m

mDual-core ARM

Cortex-A9M

PCores, 2.5DMIPS/M

Hz,667/766/866M

Hz

Controller forDRAM

up to32kB. Interfacefor SRAM

up to64kB

NanoMind A712D

GO

MSpace

On-board com

puter90x95m

mAtm

el ARM7TDM

I, 8-40M

Hz2M

B static

UEIPACUEI

DAQ system

Depends onchassi

Depends onchassi

Freescale 8347, 400 MHz,

32-bit

Notes*

*****

Precludes 1 UART port1 Ethernet port is m

utually exclusive with the mini-PCIe socket

Page 66


FlashStorage

EEPROM

ADCJTAG

I2C(port)CAN(port)

UART(port)SPI(port)

RS232/RS485(port)4G

B, 8bit Embedded

MM

CM

icroSD4KB

8ch 12bitO

ptional 20-pinCTI

3(pin)2(pin)

6(pin)2(pin)

MicroSD

Boot flash, 2MB, SPI

NOR,

reprogramm

able.NAND 128M

B-1GB,

8bit.

SSD 8-32GB,

trough SATA. Upto 3M

MC/SD/SDIO

interfaces (3Vlevels)

IEEE P1149.1,1149.6 (standardJTAG

)

3 interfacesUp to 2 CAN businterfaces(FlexCAN), 3.3V

Up to 5,com

patible withRS232-F, 3.3V.

Up to 51 RS232, Rrx/txonly(RS232)*

SD/microSD socket

Sata interface, 7-pin vertical.M

icroSD socket

CAN busdriver(100-m

ilheader)

Up to 2 RS232/485ports, rx/tx only(RJ-11)

SLC NAND 128MB-

512MB. eM

MC 4G

B-32G

B

Up to 3M

MC/SD/SDIO

12 bit 16channels

Up to 2Up to 2 CAN businterfaces, 3.3V

Up to 6, 3.3VUp to 4

MM

C/SD/SDIOinterface, SDsocket

12 bit 16channel(100-m

ilheader)

Up to 2 (100-m

il header)CAN busdriver(100-m

ilheader)

serial debug,UART-to-USB(m

icroUSB).Up to 3,3.3V(100-m

ilheader)

Up to 2 (100-m

il header)Serial debug RS232transceiver(ultra-m

iniserial connector)***

128MB-1G

B NANDSLC, 8 bit.

Up to 3M

MC/SD/SDIO

,up to 32G

B

12 bit up to 8channels

IEEE 1149.1,1149.6, 1149,7.

Up to 3Up to 2, 3.3Vlevels

Up to 6 TIA/IEA-232-F com

patibleUp to 2

MicroSD socket

Up to 4 generalpurpose ADCinput

CAN busdriver(100-m

ilheader)

2 RS-232 ports

Support for NAND,Q

uad-SPI, paralleldata bus, parallelNO

R up to 64MB.

2 Level 1 caches,32kB each. Level2 cache 256kB. 22.0 SD/SDIOcontrollers

17 channels, 12bit, dual sam

pling2 m

aster andslave

2 CAN 2.0Bcontrollers

2 UARTS2 full-duplex

4MB data. 4M

B codeM

icroSD up to2G

B6 channels

Yes2 separatebusses

1No (1 USART)

2 channels

32MB(16M

B for userapplications).

256MB(128

available for SW).

SDcards up to32G

B.

Provided by I/Oboard


Debug port on chassi.Provided by I/O

board

Mutually exclusive with serial debug port via USB

Page 67


PWM

USBEthernet(port)

HDMI

Wi-Fi

BluetoothPCI

GPIO

ExtensionsO

SPow

er(socket)3

2.0 Client mini USB,

2.0 Host Type A10/100 (RJ45)

microHDM

I,16b,1280x1024

2x46Yes

Linux, Android,W

indowsEm

bedded CE,Q

NX, ThreadX

5W, 5VDC

(5.5mm

)

4x2.0 USB10/100 ()

Yes802.11 b/g/n LAN,inbuilt antenna

4.12x20

YesRaspbian,W

indows 10 IOT

CORE, Ubuntu,

RISC OS, Linux

12.5W, 5V

(microUSB)

42.0 O

TG m

icroUSB, 4Host type A

1000Base-TEthernet interfaceim

plemented

Yes802.11b/g/n.Connector forexternal antenna

3.0+HSPCI-ExpressG

en 2.0interface

Up to 112(shared withotherfunctions)

Linux, Yocto,Android, W

indowsCE

Active: 2.0-6.0W,

3.3-5.5VDC

1 OTG

MicroUSB. 4

Host type A2 1000 BaseTEthernet port(RJ-45)**

YesW

iFi 802.11b/g/n.Connector forexternal antenna

3.0+HSM

ini-PCIesocket**

Up to 24 (100-m

il header)Sam

e as CM-FX6

5-15V

62.0 host/device. 2.0host

21000/100/10Mbps

Ethernet port

Dual-band, dual-antenna 2x2M

IMO

802.11ac/a/b/g/nW

iFi interface

4.0Up to133(sharedwith otherfunctions)

Linux, Yocto, U-Boot

3.3-5.0V

2.0 OTG

microUSB. 2

2.0 type-A21000/100/10M

bpsEthernet port

Dual-band, dual-antenna 2x2M

IMO

802.11ac/a/b/g/nW

iFi interface

4.0Up to 24 (100-m

il header)Sam

e as CM-T43

8-15V

1 OTG

USB 2.0. 4host USB2.0(Precludes O

TGm

ode)

1000 Base-TEthernet

WiFi 802.11b/g/n.

Connector forexternal antenna

4.0Up to65(shared withotherfunctions)

Linux, Android,W

indows CE1-1.5W

, 3.3VDC

1 2.0 OTG

microUSB.

4 2.0 host type-ARJ-45 connector

Connector for2.4G

Hz antennaUp to 24 (100-m

il header)Unregulated 10-16V

2 USB 2.0 OTG

2 10/100/1000 tri-m

ode EthernetM

AC peripherals

Up to 118 bits

3 3.3-5V +-3A7 bit

FreeRTOS, eCO

S0.23W

3.3V


2.010/100/1000Base-T

Provided byI/O

boardLinux, W

xWorks

9-36V

Page 68


Operating tem

pShock & Vibration

Price-40 - 90

67.4$ for 1(without tax)

-40 - 9050G

/20ms, 20G

/0-600Hz

780.5$ for 1,6244$ for 10

-40 - 8550G

/20ms, 20G

/0-600Hz

444$ for 1,2960$ for 10

-40 - 8550G

/20ms, 20G

/0-600Hz

490$ for 1,3920$ for 10

-40 - 8550G

/20ms, 20G

/0-600Hz

393$ for 1,2620$ for 10

-40 - 8550G

/20ms, 20G

/0-600Hz

281.25$ for 1,2250$ for 10

-40 - 8550G

/20ms, 20G

/0-600Hz

249$ for 1,1660$ for 10

125.3$ for 1

-45 - 85

-40 - 85M

IL-STD-810G, IEC

60068-2-27/ MIL-STD-

810G, IEC 60068-2-

64, IEC 60068-2-6)

Page 69


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https://www.raspberrypi.org/blog/pi-in-the-sky-2/

https://www.raspberrypi.org/blog/pi-in-the-sky-2/

http://www.antenna-theory.com/basics/friis.php

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