Cornell UniversitySpace Systems Design Studio

AIAA GNC Conference - 8/11/2009

Violet: A High-Agility Nanosatellite for Demonstrating Small Control-Moment Gyroscope Prototypes and Steering Laws

Slides and presentation by: David BjanesRajesh Atluri

SHOT II Post-Launch Presentation June 10-13th, 2010

Boulder, Colorado

Expected Results

We expect to store the following data on to the flash memory on the MCU board:

• Telemetry from sensors• GPS data signal by the GPS Receiver (RXer) Board

We expect to read flight data using a data parser application.

Expected Conclusions:

• Telemetry from sensors showed reasonable flight parameters.

• GPS data was logged accurately on to flash memory.

• GPS receiver picked up satellites.

Actual Results

Telemetry:• Low g Acc.: -0.5 to -1.5 g when within range of measure

• High g Acc.: -10 to -30 g varying greatly

• X & Y coupled compared to Z in both accelerometer sets

• Temp.: varied too much and recorded extreme values; periods of “stable,” realistic T ~ 25°C (+/- 5°) for ~10 seconds

GPS:• Recorded packets of raw data from receiver board

• Post-flight algorithm that searches for key header did not return meaningful data algorithm was operating with corrupt data

• Clue: even if antenna does not Rx, the YEAR field should say “1980”

Difference between Actual & Expected Results

Telemetry:

• Temp. sensor could be inherently damaged, become nonlinear at extremes, or interacted with other system in an unexpected way in flight

• Test data was mostly collected at room temp. ~ 20 °C

GPS:

• The packet structure was not as clear reading post-flight memory than during test corrupt bytes / interrupt timing

• MCU may not be fast enough to store raw GPS data, even with selective filtering of the RXer output

Conclusions• (Telemetry) How we interface sensors with CDH MCUs ought to work

• GPS test did not meet our intended goals:

• Did store the transmitted signal from RXer board

• RXer did not operate reliably with Mega32 MCU

• Impact on UN-6 Mission:

• Importance of the Interface Board to the GPS System

• IB’s program and serial interface takes some of the speed “pressure” off of CDH (MCUs) since RXer outputs at the fastest rate

• IB is the reason GPS data can be stored at a rate that minimizes the FC resources used for GPS (GPS IB speaks CUCP protocol)

• Lessons Learned

• Leave more time for debugging, integration of modules, and thorough testing

• The Right Hardware: getting the IB working properly OR having more memory on SHOT II would have made the MCU programming easier

GPS Receiver

GPS Receiver

CDH chip 1

GPS Interface

Board

Antenna Antenna

GPS Interface

Board

CDH chip 2