AAE450 Spring 2009

Brian Erson Attitude Control Systems

Trans Lunar Phase

[Brian Erson] [Attitude]

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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 10-3 Nm• Drift error < 4 x 10-6 Nm• Total < 5.2 x 10-3 Nm

• Pointing Accuracy < .017 rad• Mass < 35 kg• Environment exposure

• Temperature -25 to +55C• Radiation Custom Hardening

• Power Requirement < 50 W• Lifetime > 2 years

*Assumption of Additive Property

[Brian Erson] [Attitude]

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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: $5600Estimated Thruster Cost: $100,000Total ACS cost: $505,600

[Brian Erson] [Attitude]

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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 speed 3000 rpm• Max Wheel Torque 12 mNm

• Drift Error = 1/3000 * 12 = 0.004 mNm

[Brian Erson] [Attitude]

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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]

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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]

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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, 2004.

• Longuski and Konig. A Survey of NongravitationalForces and Space Environmental Torques with Applications to the Galileo Spacecraft.AIAA/AAS AstrodynamicsConference: 9-11 Aug 1982.

• Valley Forge Composite Technologies, Lou Brothers, Owner <http://www.vlyf.com/aerospace/wheels/standard-wheels>

• 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]

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