A GPS Flight Computer – Michael CastleA GPS Flight Computer – Michael CastleAIAA Responsive Space Conference – Redondo Beach, CA April 2003AIAA Responsive Space Conference – Redondo Beach, CA April 2003

1. GPS Flight Computer concepts2. SiRFStar2e/LP Block Diagram 3. Flight Computer Concepts4. SiRFStar2e/LP System overview5. Flight computer system diagram 6. Test Flights7. Trajectory Simulation8. Sub-orbital Repeater / Imaging

application9. Applications for GPS flight computer10.Future Developments

GPS Flight Computer Overview

GPS Flight Computer Concepts Flight Computer Concepts

SiRF GPS has enough processor power to act as a flight computer for sounding rockets (50MHz)

Controls vehicle attitude with fins Logging, Flight Termination and recovery 1Hz/10Hz update rate requires new type

of steering algorithm vs. typical 50Hz rate Small sounding rockets improved

performance from subsonic trajectory and GPS attitude corrections

New applications for sounding rockets Reduces costs of expendable stages

I/O lines

Servo Control

SiRF GPSFlight controlcode

SiRFStar2e/LP System DiagramSiRFStar2e/LP System Diagram

ARM7TDMI50MHz

2Kx32 Cache

BusInterfaceUnit

System Timer32Kx32 SRAM

BridgeUnit

GPS EngineTrack Accelerator WAAS Beacon

UART x 2SPI port

ASB 16/32

Battery Backed RAM

GPS Flight Computer System DiagramGPS Flight Computer System Diagram

TelemetryTransceiver

SiRF GPS RTC + SRAM

Servo Control

Serial PortIIC/ADC

Flash Memory+extra RAM

Up to 40 I/O lines

Attitude Sensors

Test FlightsTest Flights

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•Oscillating flight as GPS •updating at 1Hz•Damped oscillations

•When launch rail canted•GPS recovers to vertical

•Future flights will improve control loops, and add mid-flight corrections

SiRF GPS User Interface simplifies SiRF GPS User Interface simplifies implementation of flight computerimplementation of flight computer

Structured s/w for easy design User Interface into GPS code, no need to write

GPS code etc. User tasks can be real time, as user can control

interrupts, and task scheduling User task scheduler, 10Hz interrupt rate Allows easy code migration, multiple tasks

running Ground support code available 2 UARTs, SPI bus for high speed telemetry GPIOs to control telemetry/AtoDs/etc Spare RAM for user code, and a complex lookup

tables, matrix manipulation Guidance Navigation and Control system (GN&C)

does not use gyros/accelerometers

Software OverviewSoftware Overview

GPS Core Object code

Start-Up

UI Event Handler

SiRF Protocol (I/O)

NMEA Protocol (I/O)

RTCM Protocol (I)

User Interface

ISR Routines

Scheduler

User Tasks

SiRF Tasks

Memory SRAM Access Routines, Battery backed RAM

Protocol Functions

Physical I/O Device

Module Interface MI Events

MI Get/Set functions

TASKING

UART

MI Utility functions

USER1 Protocol (I/O)

Attitude Correction codeAttitude Correction code•Attitude ControlIf ((VelNed.Vn>1)||(VelNed.Vn<-1) steern=(VelNed.Vn)*8; //scale to servo range 10-150 If ((VelNed.Vn>1)||(VelNed.Ve<-1) steere=(VelNed.Ve)*8;•Provides flight termination capabilitydrift=(Ltp.Lat-latzone); //0.1 degree lat is 11.1km at 53N if ((drift>0.1) || (drift<-0.1)) count1s=ALARM; drift=(Ltp.Lon-lonzone); //0.2 degree lon is 13.2km at 53N if ((drift>0.2) || (drift<-0.2)) count1s=ALARM;

Trajectory Simulation for GPS Flight ComputerTrajectory Simulation for GPS Flight Computer

Lightweight top stage completes task Fire top stage, (possibly separate from fins) Re-orient for top stage firing, then separate

from steering inter-stage coupler Coast with GPS attitude corrections when

subsonic Separate stages,Recovery of bottom stage Accelerate to supersonic, stage separation at

50km Sub-sonic through lower atmosphere to 30km,

with GPS attitude corrections Booster lift-off or air-launched depending on

application.

Sub-Orbital Repeater / Imaging Sub-Orbital Repeater / Imaging beneath cloud cover Applicationbeneath cloud cover Application

•GPS recovery of lower stages

•Top stage flies to destination using GPS at high altitude

• Provides high altitude repeater for data

•Glide to destination, deploy balloon under clouds and relays images.

1st stage to 60km

Glide to destination

Sub-Orbital TrajectorySub-Orbital Trajectory

GPS Flight Computer ApplicationsGPS Flight Computer Applications

Sub-orbital applications– Rapid response imaging– Search and Rescue– Atmospheric/Weather research– Research/Educational payloads– Rocket development– Data relay/ bandwidth fill-in

Very low cost (<$1M!) Proving sub-systems for space

Have sounding rockets been forgotten?