1. AAE450 Spring 2009 Attitude Determination in Low Earth Orbit Description: Determine Attitude Accuracy Upper and Lower Bound Recommend Addition of Sun Sensor 2/5/09 Kris Ezra Attitude 1

2. AAE450 Spring 2009 Attitude Determination Systems  Task: Find upper and lower bounds on attitude accuracy to determine necessary sensory equipment  Method: Make simplifying assumptions and choose limiting environment –Assume communications constrain attitude, not transfer trajectory –Assume spherical earth and circular orbit  Results: Upper bound on accuracy extremely high, lower extremely low (Upper: 1.451x10 -17 Degrees, Lower: 24.992 Degrees) –Recommend assume accuracy requirements ~0.5 degree –MiDES: Accuracy better than 0.06 degrees (3 Sigma 98.9%) not necessary –Recommend Sun Sensor for Solar Arrays and Despin Kris Ezra Attitude 2

3. AAE450 Spring 2009 Sun Sensor Recommendation  Valley Forge Composites Sensor –Performance Accuracy: +1 Degree –Operational Range: 100 x 50 degrees –Weight: ~0.35 kg –Dimension: TBD (very small) –Power Consumption : 2.5 Watts Peak –Operating Temperature: ~ -20 to +60 deg. C  Total Attitude Determination Mass (Including Star Sensor): ~3.55 kg Kris Ezra Attitude 3

4. AAE450 Spring 2009 MiDES Specifications  Performance Accuracy: Better than 0.06 deg. 3 sig.  Operational Range: +/- 5.5 deg.  Mechanical Interface  Weight: <1.4 Kg  Mounting: Mounting flange at base  Alignment: One unit pre-aligned  Dimension: 5.39” x 5.39” x 5.17”  Electrical Interface  Power Input: 28 Volts DC +7/-6 VDC  Power Consumption : <800mW  Environment  Operating Temperature: -20 to +60 deg. C Kris Ezra Attitude 4

5. AAE450 Spring 2009 Star Sensor Specifications  Performance Accuracy: 15 arcseconds  Mass: <3.2 Kg  Dimension: 32 x 32 x 16 (cm)  Power Consumption : 10.2 W  Operating Temperature: -40 to +60 deg. C  Cost: 400,000 (Part of larger package) Kris Ezra Attitude 5

6. AAE450 Spring 2009 References SERVO.COM. “Mini-Dual Earth Sensor,” Acessed 21 Jan 2009, URL:http://www.servo.com/midestd.htm Garrison, James. Personal Interview. 21 Jan 2009. Valley Forge Composite technologies. “Sun Sensors,” Accessed 3 Feb 2009, URL: http://www.vlyf.com/aerospace/sun-sensors/ Kris Ezra Attitude 6