Alex Ordway60 hours worked

Attitude Control Subsystem Component Selection and

Analysis

2

Design Drivers

• Meeting mission pointing requirements

• Meet power requirements

• Meet mass requirements

• Cost

• Miscellaneous Factors

3

Trade Study

• Sliding Mass vs. Tip Thruster Configuration– Idea behind sliding mass

4

Trade Study

• Sliding mass ACS offers– Low power consumption (24 W)– Reasonable mass (40 kg)– Low complexity– Smaller contribution to spacecraft MOI– Limitations

• Unknown torque provided until calculations are made• No roll capability

• Initially decided to use combination of sliding mass and tip thrusters

5

ADCS System Overview

• ADS– Goodrich HD1003 Star Tracker primary– Bradford Aerospace Sun Sensor secondary

• ACS– Four 10 kg sliding masses primary

• Driven by four Empire Magnetics CYVX-U21 motors

– Three Honeywell HR14 reaction wheels secondary

– Six Bradford Aero micro thrusters secondary• Dissipate residual momentum after sail release

6

ADS

• Primary– Decision to use star tracker

• Accuracy• Do not need slew rate afforded by other systems

– Goodrich HD1003 star tracker• 2 arc-sec pitch/yaw accuracy• 3.85 kg• 10 W power draw• -30°C - + 65 °C operational temp. range• $1M

– Not Chosen: Terma Space HE-5AS star tracker• Lower thermal thresholds (-20°C - +40°C)• Greater power draw (15W)

7

ADS

• Secondary– Two Bradford Aerospace sun sensors

• Backup system; performance not as crucial• Sensor located on opposite sides of craft• 0.365 kg each• 0.2 W each• -80°C - +90°C

8

ACS

• Sliding mass system– Why four masses?– FRONTAL PICTURE OF THINGAMAJIG HERE

9

ACS

• Sliding mass system– Four Empire Magnetics CYVX-U21 Step Motors

• Cryo/space rated• 1.5 kg each• 28 W power draw each 200 °C

• $55 K each• 42.4 N-cm torque

10

ACS

• Gear matching- load inertia decreases by the gear ratio squared. Show that this system does not need to be geared.

2

2

2170 (600sec)

20.00389

(10 )(0.00389 )

0.0389

ms

ms

m a

a

F ma kg

F N

11

ACS

• Three Honeywell HR14 reaction wheels– Mission application– Specifications

• 7.5 kg each• 66 W power draw each (at full speed)• -30ºC - +70ºC• 0.2 N-m torque• $200K each• Not selected

– Honeywell HR04– Bradford Aerospace W18

12

ACS

• Six Bradford micro thrusters– 0.4 kg each– 4.5 W power draw each– -30ºC - + 60ºC– 2000 N thrust

– Supplied through N2 tank

13

Attitude Control

• Conclusion– Robust ADCS

• Meets and exceeds mission requirements• Marriage of simplicity and effectiveness• Redundancies against the unexpected