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HASP Student Payload Application for 2010

Payload Title:

Hatchling I BalloonSat

Payload Class:

Small

Institution:

Embry-Riddle Aeronautical University

Submit Date:

December 18, 2009

Project Abstract

The Embry-Riddle HASP payload will provide a test bed for the multi-mission satellite

subsystems under development at ERAU for future proposed NanoSat- and CubeSat-class

spacecraft. This core satellite bus will consist of power, computer, and communications

subsystems. The bus is being developed to accommodate a variety of scientific payloads. For the

2010 HASP mission, a cooperative demonstration payload experiment under development by

Pima Community College Northwest Campus Science Department will be included. This

experiment will provide calibration of sun photometers, which is critically dependent on the

extraterrestrial (ET) constant, i.e. the intensity of sunlight at the top of the atmosphere using an

array of detectors.

Team Name:

ERAU HASP

Team or Project Website:

http://spacegrant.pr.erau.edu/programs.shtml

Student Team Leader Contact Information: Faculty Advisor Contact Information:

Name: Seth Guberman John “Jack” Crabtree

Department: Aerospace Engineering College of Engineering

Mailing

Address:

Embry-Riddle Aeronautical Univ

3700 Willow Creek Rd

#7382

Embry-Riddle Aeronautical University

3700 Willow Creek Rd

Bldg. 75 AXFAB

City, State,

Zip code:

Prescott, AZ 86301 Prescott, AZ 86301

e-mail: [email protected] [email protected]

Office

telephone:

(928) 458-5148 (928) 777-6916

Cell: (832) 657-5688 (928) 713-2756

FAX: (928) 777-6945

(928) 777-6945

http://mail.google.com/mail/?ui=2&ik=c6b3c35381&view=a

tt&th=122e1390dbbe97d3&attid=0.1.2&disp=inline&zw2010 HASP Proposal ERAU Hatchling I BalloonSat and PCC BrightStar Payload

Prepared by Seth Guberman

ABSTRACT

Embry-Riddle Aeronautical University’s submission for HASP 2010 is a test

bed for the multi-mission satellite subsystems currently in development

for future NanoSat- and CubeSat-class spacecraft. This satellite bus

consists of electrical power, onboard computer, and communications

subsystems and will support a variety of scientific payloads. For the

2010 HASP mission, a cooperative payload experiment under

development by Pima Community College Northwest Campus Science

Department will be included.

ERAU Hatchling I and PCC BrightStar 2

Introduction As part of Embry-Riddle Aeronautical University’s goal to have a satellite in orbit

in the next five years, and with experience stemming from past successful

balloon launches, development of the Hatchling I BalloonSat began in early

2009. Its three core satellite subsystems (electrical power, onboard computer,

and communications) comprise a bus that will provide support for a variety of

scientific experiments while meeting the dimensional constraints of a CubeSat-

class spacecraft. For the 2010 launch, a scientific payload developed by Pima

Community College Northwest Campus Science Department has been selected

for integration with Hatchling I’s core subsystems. In addition, a composite

structure is being fabricated to accommodate the payload and comply with

HASP requirements.

Payload Description The 2010 HASP submission consists of two main parts: the Hatchling I satellite bus

(developed by ERAU), and the BrightStar scientific payload (developed by

PCC). Because BrightStar is the science driving the mission, and likely of greater

interest to the members of the HASP administration, it will be discussed first.

PCC BrightStar The Earth’s atmosphere is a complex system that requires the application of

physics, chemistry, astronomy, and biology concepts to explain climate change

and global weather systems. Of particular importance to students in the

physical sciences is solar and terrestrial radiation. The question of what happens

when sunlight interacts with the atmosphere leads to the investigation of

terrestrial radiation reflected from Earth’s surface. Ground based measurements

of solar radiation are dependent on the knowledge of the extraterrestrial

constant, or ET. While many studies of the air mass above the surface of Earth

utilize an average value for ET (1350 W/m2 ), this may not be sufficient to explain

or understand captured data. In our previous HASP application we proposed

building a complex sensor head composed of 25 LEDs covering wavelengths

from the blue to the infrared. Significant changes have been made to this

design that reduces the complexity of the sensor head and its fabrication. The

goal of our experiment is to enable our students to measure solar radiation in the

absence of the Earth’s atmosphere and compare it to simultaneously made

ground-based measurements.

Proposed Experiment: Measurement of the Extraterrestrial Constant

The calibration of sun photometers is critically dependent on the extraterrestrial

constant (ET), i.e. the intensity of sunlight at the top of the Earth’s atmosphere.

Our experiment will determine the value of ET at altitude while making

simultaneous intensity measurements on the ground. By employing the Langley

method we will determine the air mass for three separate wavelengths and


compare our results to published data. The detector head will employ the use

of six LEDs covering three distinct wavelengths and allow for a redundancy of

two. The use of LEDs as light sensors was pioneered by Forrest Mims III1 and has become the key instrument for his climate studies worldwide2,3.

The schematic representation below shows the signal flow through our LED

sensor head to the BX-24 microprocessor within BrightStar. The output of the

microprocessor is then passed to the Hatchling I onboard computer, described

later in this document.

Figure 1: BrightStar Signal Flow

There are two significant challenges presented by using LEDs as light sensors in

the near space environment found on the HASP platform:

• The measurement of ET is based on normal incidence of radiation.

• LED output is sensitive to temperature and hence the LEDs require heating.

In our previous HASP proposal, the sensor head called for a dome populated

with LEDs and was allowed to rotate with three degrees of freedom. The correct

1 F. M. Mims III, An Inexpensive and Accurate Student Sun Photometer with Light-Emitting Diodes as Spectrally Selective

Detectors, Proceedings of the Third Annual GLOBE Conference, 232-239, August 1998.

2 Brooks, David R., Forrest M. Mims III, Arlene S. Levine, Dwayne Hinton, The GLOBE/GIFTS Water Vapor Monitoring Project: An Educator's Guide with Activities in Earth Sciences. NASA Publication EG-2003-12-06-LARC, 2003.

3 Forrest M. Mims III, "LED Sun Photometry," Optics & Photonics News 20, 32-38 (2009)

http://www.opticsinfobase.org/abstract.cfm?URI=OPN-20-9-32


position of the sensor head was to be driven by servomotors that were

controlled by the output of four photocells arranged in an x-y pattern that

sensed the coordinates of maximum radiation and moved the LED platform

accordingly. This proved to be extremely complex to fabricate and was

abandoned for a simpler and more effective design. The new design calls for a

flat plate set at a pre-determined angle with respect to the y-axis. Figure 2 is our

proof-of-concept model that was used to finalize the circuit board design. The

final version will be considerably smaller owing to the use of vendor-fabricated

boards that adhere to Hatchling I’s bus specification. This will allow for

uniformity of the electrical and physical connections and simplicity of

integration within the payload structure.

Figure 2: Prototype Sensor Array

The output of each Op Amp was maximized by field testing the board and

determining the correct value of the feedback resistor that yielded the highest

voltage. The integration of the sensor board with the A/D circuitry and power

busses was then performed to evaluate signal integrity. Careful placement of

voltage lines and the addition of filtering capacitors further reduced the noise.

Finally, test integration with Hatchling I’s circuitry was performed. Those results

are discussed later in this document.

An electrical schematic is shown in the Preliminary Drawings section of this

document.

Op Amps

LEDs


Sensor Head Rotation

A single servo will drive the array in a plane orthogonal to the y-axis as shown in

Figure 3. To avoid twisting problems on the cable from the heater/LED platform,

rotation will be 180 degrees clockwise immediately followed by 180 degree

counterclockwise rotation. This constitutes a single cycle and will be repeated

throughout the measurement process. The platform will sit above the planar

exterior of the structure and still conform to a maximum overall height of 30 cm.

The mass of the sensor head and heater assembly does not present a problem

for the servo. We have cold tested the servo for 1 hour at -50 oC both loaded

and unloaded with no problems. The addition of a low temperature lubricant to

the servo drive mechanism will ensure continuous operation in near space conditions.

A cross-section of the measuring assembly can be found Figure 3. The mounting

plate that holds the sensor board and heater assembly is a picture frame design

that minimizes the mass. Materials under consideration at this time are

aluminum or Delran. The attachment of the sensor board to the frame will be

done with screws of the same material as the frame.

Figure 3: BrightStar Cross-Section (dimensions in inches)


The design of the electronic boards (trays #1 and #2 above) has since changed

and will instead interface directly with Hatchling I’s main PCB stack to simplify

integration.

Sensor Attitude

Since in our simplified design we are only rotating the platform in one plane we

need to establish an angle for the LEDs that will ensure orthogonal incidence of

the solar radiation. Realizing that this direction is a function of month, day, time

of day and geographic location, we chose to use date of launch and Ft.

Sumner, New Mexico as our starting point. While data collection will commence

with lift-off, the data of interest will be collected when the balloon has reached

float altitude. Assuming we reach float by 11:00 am on September 6th, 2010,

with solar noon occurring at ~11:55:33 am MST, a sufficient number of

measurements will have been made. Should the launch be delayed or

postponed until the next day, the variation in solar noon times from day to day is

only 30 seconds per day. As long as the exact geographic position of the

payload is known, we can apply the appropriate correction value of the angle

at which the array must be set. For a launch date of September 6, 2010 the

angle is equal to 63o with respect to the horizon.

Thermal Considerations

The responsiveness of LEDs used as detectors is affected by temperature. As a

result we have added a heater to the back of the sensor head (see Figure 4).

Environmental testing of the LED array was performed to determine the

effectiveness of the heater assembly. Since we will only be making

measurements during the balloon’s first 6 hours, this will allow us to stay within the

allocated payload power budget of which the heater required 50% of that power.

A novel circuit was employed that used Zener diodes along with software to

control the duty cycle. Additionally, a stored record of the sensor head’s

temperature during the flight will enable us to apply minimal corrections to the

LED output upon analysis of the data. In near space the mechanisms for

thermal transfer are limited to direct conduction. The key aspect of this heater

design is a conformal pad made of metal and coated with a thin electrically

insulating sheet. The pad conforms to the topology of the reverse side of the

circuit board while providing excellent thermal transfer. The environmental test

chamber was held at -55 oC and 0.3 atm. The sensor board temperature never

went below 15 oC over a 1-hour period. We will continue these tests over longer

time periods to look for possible failure modes. Heating of the sensor board is

only required for ~5 hours while measurements are being made.


Figure 4: BrightStar Sensor Array Heater

Calculation of ET

The idea of a Langley plot follows directly from the Lambert-Beer Law defining

the transmittance of the atmosphere:

I = Io exp(-t/cos!)

Where I0 = intensity of the solar radiation at the top of the atmosphere,

I = intensity at the Earth’s surface,

t = atmospheric optical thickness, and

! = solar zenith angle.

Since the voltage measured by the LED sensors is directly proportional to the intensity, the above equation can be written as:

V = V0 exp(-t/cos!)

Defining M = 1/cos! as the “air mass” yields:

Ln V = - M t Ln V0

Heating Pad


Plotting ln(V) versus “air mass” yields a typical Langley plot (shown in Figure 5), and the y-intercept gives the value of the extra terrestrial constant.

Figure 5: Langley Plot

ERAU Hatchling I As previously stated, the main objective of the Hatchling I satellite bus is to

provide a standard set of core satellite subsystems (power, computer, and

communications) for implementation in future satellite projects. As such, the

PCBs are being designed with CubeSat dimensions in mind and have a 10 cm

by 10 cm square footprint. A PC/104 computer bus connector is employed as

the main electrical bus for the entire satellite.

Structure

For the HASP 2010 launch a structure is being fabricated to accommodate the

PCC BrightStar payload and conform to HASP standards. Figure 6 below shows

an exploded view of the HASP 2010 ERAU Hatchling I BaloonSat with the integrated PCC BrightStar scientific payload.


Figure 6: Hatchling I Exploded View

The outer structure is an E-glass/foam composite fabricated at ERAU using pre-

preg. An aluminum plate inside the bottom of the foam structure (shown below

the PCBs) spreads the stress from the mounting hardware to prevent tear-out at

high loads. The structure was tested in this configuration (with dummy mass

inside) at ERAU using a shaker table in step-mode (single shock) and remained

attached after 30-G lateral and vertical shocks were applied.

Electrical Power Subsystem (EPS)

A system of regulators and switches governs the flow of electrical power from

HASP and within the BalloonSat. The 30 VDC from HASP is converted to 8.3, 5,

and 3 VDC with 85% efficiency for the systems onboard Hatchling I. Switches

controlled by the onboard computer (OBC) turn individual components on and

off. Inline capacitors reduce the ripple to ±20 mV. A breadboard prototype of

the design has been built and tested, and PCB design and fabrication is nearing

completion. A schematic is included in the Preliminary Drawings section. The

power budget is in the Payload Specifications section.

Top plate w/ PCC

servo and rotating

sensor platform

E-glass/foam

composite exoskeleton

HASP

mounting plate

Aluminum spars

and mounting hardware

Main PCB stack


Onboard Computer Subsystem (OBC)

The Onboard Computer subsystem is responsible for collecting the data from

sensors and packaging the data for transmission via the communications

subsystem. Additionally, the OBC has the responsibility of maintaining some

aspect of “thermal control” of the BalloonSat through the use of temperature

sensors, resistive contact heaters, and an automatic thermostat control in the

main function block. The OBC must interface with two transceivers (HASP’s

provided communication and Hatchling I’s own communication), a GPS

module, PCC BrightStar, and several temperature sensors and heaters

throughout the BalloonSat. Two ATMega644P microcontrollers (each with two

independent serial UART ports) have been selected to provide the four

necessary serial UART connections (two each for HASP and Hatchling I

communications). One microcontroller interfaces with the transceivers, enable

switches, and temperature sensors. The other microcontroller is responsible for

collecting data from BrightStar and the GPS module. The microcontrollers

connect via the Serial Peripheral Interface (SPI) Protocol. The microcontrollers

are interrupt-driven meaning that when they receive data the main function is halted and the data handling function is called.

A breadboard prototype of the design has been built, programmed, and tested

to ensure proper communication with the transceivers, GPS module, and PCC

BrightStar. PCB design and fabrication is nearing completion. A schematic is included in the Preliminary Drawings section.

Communications Subsystem (COMM)

In addition to utilizing the wireless communication provided by HASP, Hatchling I

employs its own communications subsystem for certification for future flights. The

COMM handles wireless communications between Hatchling I and our own

ground station, allowing for both real-time downlink of data as well as uplink of

commands. This is accomplished through the 70 cm amateur radio band. This

particular band allows for reasonably small antennas while still allowing us to

easily receive the packets on standard amateur radio equipment. It will be

operating on 445.925 MHz and is frequency modulated. The whole system

consists of a small transceiver and a TNC (Terminal Node Controller). The TNC

interfaces with the OBC through a 4800 baud full duplex serial port. The packets

are formatted in the internationally recognized APRS format and transmitted

using AFSK at 1200 baud. The TNC handles all the packet formatting, routing,

and outputs audio that the radio transmits. It is also able to receive audio from

the radio, decode the packets, and output the data as a serial stream. In short,

the COMM transmits everything it receives from the OBC, and forwards

everything it receives from the ground station to the OBC. A 6-inch antenna

extends below the plane of the HASP mounting plate.

The COMM has been tested in conjunction with the OBC and BrightStar to verify

functionality. Similar systems have been flown successfully on past ERAU


balloon missions. PCB design and fabrication is nearing completion. Link rates are shown in Payload Specification section.

Team Management

Organizations Hatchling I is being developed outside of class by engineering undergraduate

students at Embry-Riddle Aeronautical University. The team is led by student

project manager Seth Guberman, with assistance from faculty advisors Jack

Crabtree and Dr. Ron Madler and funding from the Arizona Space Grant

Consortium. The chart below shows the ERAU team’s organization.

Figure 7: ERAU Organization

The experimental subsystem is subcontracted to students at Pima Community

College Northwest Campus Science Department, led by Stacy Harrison and

faculty advisors Mike Sompogna, Anthony Pitucco, and Denise Meeks. The following chart shows their organization.

Project Manager

Seth Guberman

OBC

Lead Cody Blevins

Zach Grey

MEC

Lead Adam Ritchie

Bryce Fox

EPS

Lead Greg

Winkleman

Brittany Griffin

COMM

Lead Elijah Brown

THRM

Lead Zach Grey

Cody Blevins

EXP1

PCC BrightStar

Faculty Advisor Jack Crabtree

Faculty Advisor Dr. Ron Madler


Figure 8: PCC Organization

Contact Information The chart below gives phone and email contact information for the principal leads.

Table 1: Contact Information

Name Phone Email

Seth Guberman (928) 458-5148 [email protected]

Stacy Harrison (520) 390-8374 [email protected]

Jack Crabtree (928) 777-6916 [email protected]

Mike Sampogna (520) 206-2157 [email protected]

Timeline A timeline of milestones up to this point and in the future is shown for reference on the next page.

Project Manager

Stacy Harrison

Electronics

Zack J

Mike I

Peter S

Amy G

Software

Zack J

Peter S

Structure

Zack J

Kyle R

Thermo

Peter K

Amy G

Kyle R

Faculty Advisor Mike

Sampogna

Faculty Advisor Anthony Pitucco

Faculty Advisor Denise Meeks

Faculty Advisor Forrest M. Mims III


Table 2: Project Schedule and Milestones

Date Item

July 30, 2009 System Requirements Review

September 1, 2009 Begin Preliminary Design and

Breadboarding

October 1, 2009 Preliminary Design Review

October 24, 2009 PCC Data Stream Test,

Structural Design Frozen

November 1, 2009 Subsystem Testing

December 1, 2009 Critical Design Review, Begin

PCB Layouts

December 18, 2009 Application Deadline

January 15, 2010 Flight Subsystem Assembly

February 15, 2010 Final PCC Integration and Test

March 1, 2010 Thermal and Vaccuum Test

May 1, 2010 Submit Payload Integration

and Flight Operations Plans

Launch Personnel A number of the students involved in the project are graduating seniors. To

ensure the continued success of the project, younger members are being

trained for the summer integration and flight. Exact personnel have not yet

been decided, but it is estimated that between seven and ten members will be

present for each event. Expect more details in the upcoming Payload

Integration and Test Plan and Flight Operations Plan documents.

Payload Specifications Much care is being taken to adhere to the standards dictated by HASP for the small class payload to secure a position on the 2010 launch.

Weight Budget The weight of the Hatchling I BalloonSat with PCC BrightStar onboard, including

all cabling and mounting hardware shall not exceed 3 kg. Mass budgeting (Table 3) is taking place to meet this requirement.


Table 3: Mass Budget (in grams)

Component Allocation Estimate Measurement

Structure 600 500 426

COMM 300 280 274

EPS 200 125 105

OBC 200 125 122

GPS 150 50 36

PCC 600 600 988

Heaters 100 100 X

Cables 350 300 X

Subtotal 2500 2080 1951

Margin 500 920 1049

Total 3000 3000 3000

The measured values are for prototype units (breadboards, etc). The number of

heaters has not yet been decided and will be dictated by thermal testing.

However, they are lightweight resistive contact heaters and do not greatly

affect the overall mass. PCC BrightStar was under-budgeted from the outset,

but thanks to our 500 g margin that was not an issue.

Power Budget The incoming 30 VDC (0.5 A) electrical power from HASP is distributed as

needed by the Hatchling I EPS. Assuming 85% efficiency of our main regulators

(verified in test) that leaves 12.75 W for use by the BalloonSat and its subsystems.

Table 4: Power Budget

Component 3.3V (mA) 5V (mA) 8.3V (mA) Power (mW)

Linear Regulator

(1.7V drop)

48 0 0 81.6

GPS 48 0 0 158.4

OBC 0 40 0 200

COMM 0 400 0 2000

Relays (x5) 0 24 (x5) 0 120 (x5)

PCC 0 0 880 7304

Subtotal X X X 10344

Margin X X X 2406

Total X X X 12750

A margin of nearly 2.5 W is left for safety.


Other Specifications Other specifications requested by the HASP administration are given below in

Table 5.

Table 5: Miscellaneous Specifications

Specification Value

Footprint 15 cm x 15 cm

Height 26.9 cm

HASP Downlink 1200 baud

HASP Uplink 1200 baud

The HASP Downlink may be used simultaneously with or separate from the

onboard Hatchling I COMM. The external height of the structure including the

rotating sensor platform, but not the sensor head itself, is just under 27 cm. An

antenna for wireless communication will extend ~14 cm below the HASP

mounting plate. The overall height from the mounting plate to the top of the

sensor head will not exceed 30 cm. For more information refer to the structural

drawing in the Preliminary Drawings section.

Desired Position and Orientation No specific position is requested so long as a clear view of the sun (from the top

of the BaloonSat) without obstructions from HASP itself or any other payloads is

available. Of course a level platform (hopefully provided by HASP) is preferred

for the measurements made by BrightStar. The antenna should also have a clear line-of-sight path to the Earth below.

Integration Procedures We anticipate that the integration of Hatchling I to HASP will consist of fastening

the mounting plate to HASP itself and connecting the power and data cables to

the connections provided by HASP. The power-on command will be given to

verify that the Hatchling I systems and BrightStar respond appropriately. More

details will follow in the Payload Integration and Test Plan.


Functional Block Diagram Figure 9 shows the electrical connections within the Hatchling I BalloonSat.

Figure 9: Hatchling I Block Diagram

The thermal voltage required will be determined in testing at ERAU facilities later

and will likely consume the remainder of our power margin. If more power for

heating is needed, the Hatchling I COMM will be used less frequently, making

more power available to the heaters.

Preliminary Drawings For reference, this section provides the preliminary structural and electrical

schematics as they relate to previous topics.

Hatchling I

EPS

Hatchling I

OBC

HASP

COMM

Hatchling I

COMM

Hatchling I

Thermal

PCC

BrightStar

Hatchling I

GPS

BrightStar sensor electronics

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