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Attitude Determination in Low Earth Orbit

Attitude Determination in Low Earth Orbit

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Attitude Determination in Low Earth Orbit

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  1. 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. 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

  3. 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

  4. 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

  5. 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

  6. 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