cornell university space systems design studio aiaa gnc conference - 8/11/2009 violet: a...
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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