AAE450 Spring 2009 Brian Erson Attitude Control Systems Trans Lunar Phase [Brian Erson] [Attitude] 1

AAE450 Spring 2009 Attitude Control Systems (ACS) Relevant Requirements: Sum of torques on Craft* Space environmental torque< 2.4 x10 -4 Nm Thrust misalignment torque< 5.0 x Nm Drift error< 4 x Nm Total< 5.2 x Nm Pointing Accuracy<.017 rad Mass< 35 kg Environment exposure Temperature-25 to +55C RadiationCustom Hardening Power Requirement< 50 W Lifetime> 2 years * Assumption of Additive Property [Brian Erson] [Attitude] 2

AAE450 Spring 2009 Product Specifications Fulfilling Relevant Requirements Star Sensor VF STC 1, Valley Forge Composites Reaction Wheel Assembly VF MR 0.1, Valley Forge Composites Estimated propellant cost: $5600 Estimated Thruster Cost: $100,000 Total ACS cost:$505,600 [Brian Erson] [Attitude] 3

AAE450 Spring 2009 Backup Slide 1 Calculation of Thrust Misalignment Torque Estimate of Thrust at 1 kW~100 mN Estimate of Thrust misalignment~ 0.05 m Conservative Max Misalignment Torque ~ 5 mNm Calculation of Drift Error Tracking error from Reaction wheel spec sheet<1rpm Operating speed3000 rpm Max Wheel Torque 12 mNm Drift Error = 1/3000 * 12 = mNm [Brian Erson] [Attitude] 4

AAE450 Spring 2009 Backup Slide 2 Calculation of Mass Requirement (Ref, Smart-1 Lunar Probe) Reaction Wheel assembly~ 12 kg Sun Sensors~ 4 kg Angular rate sensors~ 0.3 kg Star Tracker~ 3 kg Total~ 19.3 kg ACS/Launch mass: 19.3/380 =.05 = 5% Conservative estimate of IMTLI: 700 kg * 5% Conservative estimate of ACS mass < 35 kg [Brian Erson] [Attitude] 5

AAE450 Spring 2009 Backup Slide 3 Calculation of Pointing Accuracy Max pointing error of SMART-1:60 arcminutes 1 arcminute = 1/60*deg 1 deg =.017 rad [Brian Erson] [Attitude] 6

AAE450 Spring 2009 Backup Slide 4 References: Berge, Bjork, Edfors, Jansson, et. Al., “The Attitude and Orbit Control System on the SMART-1 Lunar Probe”, Swedish Space Corporation, Solna, Sweden, Longuski and Konig. A Survey of NongravitationalForces and Space Environmental Torques with Applications to the Galileo Spacecraft.AIAA/AAS AstrodynamicsConference: 9-11 Aug Valley Forge Composite Technologies, Lou Brothers, Owner Waletzko, Brittany: Environmental Perturbing Forces and Effect on Attitude Control; 1/2009. Westerman, Solomon, School of Aeronautics and Astronautics, Purdue University, 1/2009. [Brian Erson] [Attitude] 7