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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: Research Attitude Determination Systems Filter Pertinent Reference Material from Previous Research 1/22/09 Kris Ezra Attitude

  2. Attitude Determination Systems • Task: Identify feasibility of using GPS and/or Earth based telemetry in LEO • Method: Compare GPS and an Earth based system • Trimble Advanced Navigation Sensor (TANS Vector) GPS sensor • Mini Dual Earth SENSOR (MiDES) Horizon Sensor • Results: • TANS Vector: Azimuth accuracy between 0.3 and 0.15 degrees RMS (pitch and roll error multiply by 1.5 to 2 depending on installation) • MiDES: Accuracy better than 0.06 degrees (3 Sigma 98.9%) Kris Ezra Attitude

  3. Other Issues and MiDES Specifications • No record of independently flown GPS Attitude Device  • High speed of parking orbit is outside specifications of TANS Vector device • MiDES will require other sensing units (i.e., reference gyros) • Performance Accuracy:   Better than 0.06 deg. 3 sig. • Operational Range:                  +/- 5.5 deg. • Weight:                           <1.4 Kg • Dimension: 5.39” x 5.39” x 5.17” (Roughly Cubic Shape) • Power Consumption :                   <800mW • Operating Temperature:     -20 to +60 deg. C 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. TANS Vector Specifications • Azimuth accuracy: • 1 meter baselines: 0.30 deg (RMS), typical, application dependent • 2 meter baselines: 0.15 deg (RMS), typical, application dependent • Pitch/Roll accuracy: • 1 meter baseline: 0.50 deg (RMS), typical, application dependent • 2 meter baseline: 0.25 deg (RMS), typical, application dependent • Position accuracy: • 25 meters horizontal, 95% of the time • 35 meters vertical, 95% of the time • Differential GPS (SA on or off with base station within 500 km) • less than 5 meters horizontal, 95% of the time • less than 8 meters vertical, 95% of the time • Velocity accuracy: • Steady-state conditions, without SA: 0.2 m/sec, RMS • Differential GPS: 0.1m/sec, RMS Kris Ezra Attitude

  6. TANS Vector Specifications • Dynamic capability: • Velocity: 400 m/sec • Acceleration: 4 g (39.2 m/sec2) • Jerk: 2g/s (20 m/sec3) • Temperature: • Operating: -40•C to +71•C • Non-operating: -55•C to +85•C • Prime power: • 9 to 28 Volts DC nominal (32 Volts maximum), nominal 4 Watts • Dimensions: • RPU: 127 mm x 241 mm x 56 mm (5" x 9.5" x 2.2") • Antenna: 96 mm x 102 mm x 13 mm (3.8" x 4.0" x 0.5" maximum) • Volume: • RPU: 1,714 cc (105 cubic inches) • Antenna: 127 cc maximum (7.8 cubic inches) Kris Ezra Attitude

  7. TANS Vector Specifications • Weight: • RPU: 1.42 Kg (3.1 pounds) • Antenna: 0.19 Kg (0.42 pounds) • Predicted Reliability: • The estimated reliability based on guidelines of MIL-HDBK-217F. For ground mobile and transport aircraft environments, calculated mean time between failures is greater than 5000 hours. Kris Ezra Attitude

  8. References Trimble Navigation Limited. “TANS VECTOR: GPS Attitude Determination System Specification and User’s Manual,” SunnyVale, CA. May 1995 SERVO.COM. “Mini-Dual Earth Sensor,” Acessed 21 Jan 2009, URL:http://www.servo.com/midestd.htm Cohen, C.E. et al. “Space Flight Tests of Attitude Determination Using GPS,” International Journal of Satellite Communications, Vol. 12, 427-433 (1994). Garrison, James. Personal Interview. 21 Jan 2009. Kris Ezra Attitude