RS1 SESSION6 CASTLE 6005C

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A GPS Flight Computer – Michael Castle

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1. GPS Flight Computer concepts 2. SiRFStar2e/LP Block Diagram 3. Flight Computer Concepts

4. SiRFStar2e/LP System overview 5. Flight computer system diagram 6. Test Flights

7. Trajectory Simulation

8. Sub-orbital Repeater / Imaging application

9. Applications for GPS flight computer 10. Future Developments

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GPS

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

Servo Control SiRF GPS

Flight control

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SiRFStar2e/LP System Diagram

ARM7TDMI 50MHz

2Kx32 Cache

Bus

Interface Unit

System Timer 32Kx32 SRAM

Bridge Unit

GPS Engine

Track Accelerator WAAS

Beacon

UART x 2 SPI port

ASB _16/32

Battery

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GPS Flight Computer System Diagram

Telemetry Transceiver

SiRF GPS RTC + SRAM

Servo Control

Serial PortSerial Port

IIC/ADCIIC/ADC

Flash Memory +extra RAM

Up to 40 I/O lines

Attitude Sensors

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Test Flights

-10

•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

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SiRF GPS User Interface simplifies

implementation 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

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Software 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

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Attitude Correction code

•Attitude Control

If ((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 capability

drift=(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

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Trajectory 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

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Sub-Orbital Repeater / Imaging

beneath 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

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Sub-Orbital Trajectory

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GPS 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