From SMAD (2011) - Section 29.1 Spacecraft Attitude Determination and Control Systems

Table of Contents

1.0 Component Selection

Per [CSDC-####] The selfie-cam must take a picture oncer per orbit. Assuming an ISS orbit, this leaves us with a 90 minute window to conduct the required maneuver. In a worst case scenario, this maneuver will likely consist of a 180$\degree$ rotation.

This gives us a slew rate of $180 /(90*60)=0.03\approx0.05 \deg/s$. Following Table 19-8 (Low Rates)

• Effect on Spacecraft
  • Minimal
• Effect on ADCS
  • Depending on spacecraft size, reaction wheels may be fully capable for slews
  • If reaction wheels not capable, thrusters will be necessary
  • Thrusters may be needed for other reasons: i.e., station-keeping

Per [CSDC-0420] The pointing accuracy $(3\sigma)$ required is 0.1 deg (secondary payload). Following Table 19-9 (< 0.1 deg)

• Effect on Spacecraft
  • 3-axis stabilization is necessary
  • May require articulated and vibration-isolated payload platform with separate sensors
• Effect on ADCS
  • Star sensor and better class of gyros
  • Control laws and computational needs more complex
  • Flexible body performance very important

2.0 Component Sizing

2.1 Reaction Wheels

2.1.1 Disturbance Rejection

Control torque, whether from reaction wheels or magnetic torquers, must equal worst-case anticipated disturbance torque plus some margin.

$$ T_C=(T_D)(Margin\space Factor) $$

2.1.2 Slew Torque

For max-acceleration slews with no resisting momentum (1/2 distance in 1/2 time).