1. The ship that always had somewhere else to point

James S. A. Corey’s Leviathan Wakes, the first novel of The Expanse, returns as the recalled work because every ship in that universe is constantly choosing an orientation: main engine thrust, maneuvering thrusters, communications laser, radar, PDC coverage, docking collar. The Canterbury and the Rocinante do not have the luxury of a single preferred attitude; they trade between them according to the immediate threat and mission. A LEO desktop is less dramatic but faces the same queue of pointing requests.

This entry wonders how the platform chooses what to point at.

2. The queue of targets

At any moment the desktop has several valid pointing targets:

  • Sun: to charge batteries and warm the right surfaces.
  • Nadir: for Earth observation payloads and some thermal radiator geometries.
  • Ground station or relay satellite: for high-rate communications.
  • Payload target: a specific point on Earth, a star, or another spacecraft.
  • Ram or anti-ram: for minimum or maximum drag, or to orient a thermal shield.
  • A safe attitude: Sun-pointing, or a known stable orientation after a fault.

Each target is legitimate. They cannot all be satisfied at once. The communications antenna wants one direction, the camera wants another, and the solar panels want a third. The question is not whether to point, but who wins and for how long.

3. Selection as an optimization problem

One way to frame the problem is as a constrained optimization over a planning horizon. The platform knows the future positions of the Sun, Earth, ground stations, and targets from its orbit propagator. It can score each candidate attitude by:

  • power collected;
  • data downlink opportunity;
  • payload observation value;
  • thermal margin;
  • momentum accumulation;
  • time until the next chance to satisfy each request.

Hard constraints include Sun keep-out cones for sensitive instruments, occlusion by Earth or the spacecraft’s own structure, and actuator rate limits. Soft constraints express customer priorities and contractual deadlines. The scheduler picks the attitude trajectory that maximizes total mission value over the horizon while respecting the hard limits.

4. Selection as a policy problem

Optimization is elegant but fragile if the model is wrong. A simpler policy hierarchy may be more trustworthy:

  1. Safety first: if power, thermal, or momentum margins are critical, go to safe mode.
  2. Committed obligations next: scheduled ground passes and customer observations have fixed windows.
  3. Opportunistic tasks last: extra power generation, calibration, or secondary imaging fill the gaps.

The policy can be overridden by ground command, but the default should be autonomous. A hybrid approach uses the policy to choose among coarse modes and optimization to plan the slews within each mode.

5. What this changes

  • The desktop needs a model of future geometric events, not just current state.
  • Pointing decisions should be driven by mission value, not by fixed priorities.
  • Conflicts between power, communications, and payload pointing are normal and must be resolved automatically.
  • The next entry will wonder about resolving those conflicts and managing momentum while doing so.