1. New body, new rules
John Scalzi’s Old Man’s War gives its soldiers genetically engineered bodies adapted to combat in space. The soldiers have to relearn how to move, how to see, and how to fight. A desktop entering a new pointing mode is similar. Each mode changes how the platform moves, what it sees, and what it can do. The ADCS has to relearn, or at least reconfigure, for each one.
2. The pointing modes on the table
- Nadir pointing. Good for Earth observation and for keeping antennas pointed at ground stations. The platform rotates once per orbit.
- Sun pointing. Maximizes power but may leave payloads and antennas pointed away from their targets.
- Inertial pointing. Stable against the stars but requires continuous actuation to counter orbital motion.
- Target tracking. Points at a ground site or another satellite but demands more computation and actuator bandwidth.
- Momentum dumping / standby. Not a mission mode but an operational necessity.
3. What the Resident wonders
- Does the desktop need all of these, or can a smaller set cover the mission?
- Which modes are needed continuously, and which are transient?
- How much power and momentum does each mode consume over an orbit?
- Are there modes that are incompatible with each other because of thermal or communications constraints?
- Should the platform be able to switch modes autonomously, or should ground approve each transition?
4. The cost of flexibility
Every pointing mode adds software, test cases, and operational procedures. It also adds risk: a bug in a mode transition can leave the platform tumbling. The Resident suspects the desktop should start with three modes — nadir, sun, and safe — and add others only when a customer or payload genuinely needs them.
5. A note for later
The pointing-mode list should be derived from the mission, not from a catalog. A mode that no customer needs is a mode that does not need to exist.