1. The ship that counts every kilogram of fuel

James S. A. Corey’s The Expanse returns as the recalled work because the Rocinante’s crew is constantly aware of remass, delta-v, and the burns that can and cannot be afforded. A LEO desktop is the same: every maneuver subtracts from a finite propellant budget, and some maneuvers are more propellant-efficient than others.

This entry wonders about maneuver planning and propellant conservation.

2. Drag makeup

Atmospheric drag slowly lowers a LEO spacecraft’s orbit. The platform must periodically reboost to maintain altitude. Options include:

  • Continuous low-thrust electric reboost: fire the electric thruster regularly to counteract drag.
  • Impulsive reboost burns: use chemical thrusters for larger, less frequent burns.
  • Altitude selection: choose an orbit where natural decay is slow enough that stationkeeping is minimal.
  • Reduced cross-section: orient the platform to present a smaller area to the atmosphere when not actively working.

The choice depends on thrust level, power availability, and how much propellant the platform can carry.

3. Collision avoidance geometry

A collision avoidance maneuver changes the orbit enough that the close approach no longer occurs. Common strategies include:

  • In-plane burn: raise or lower the orbit to change the arrival time at the conjunction point.
  • Out-of-plane burn: change the inclination or right ascension to miss the other object sideways.
  • Retrograde or prograde timing shift: arrive slightly earlier or later at the conjunction.

The most propellant-efficient option depends on the relative geometry and the uncertainty of the conjunction.

4. Propellant budgeting

Propellant is a hard constraint. The platform must budget for:

  • Routine stationkeeping over the mission life.
  • Collision avoidance maneuvers with a statistical reserve.
  • End-of-life deorbit or disposal.
  • Attitude control and momentum dumping if thrusters are used for those functions.
  • Margin for unexpected perturbations or failures.

A platform that spends its propellant on avoidable maneuvers may not have enough left for deorbit.

5. Optimizing maneuvers

The platform can reduce propellant use by:

  • Combining a reboost with a collision avoidance burn.
  • Executing avoidance maneuvers as early as possible, when smaller changes have larger effects.
  • Using electric propulsion for slow, efficient corrections.
  • Accepting a slightly higher conjunction probability when the object is small or the data is uncertain.

6. What limits this

  • Uncertainty in atmospheric density makes drag predictions imperfect.
  • Conjunction data has positional uncertainty that grows with time.
  • Customer payloads may require the platform to maintain a specific attitude or orbit during a maneuver window.
  • Regulatory requirements may mandate notification before any maneuver.

7. What this changes

  • Maneuver planning and propellant conservation are tightly coupled.
  • The desktop should optimize burns across stationkeeping, avoidance, and deorbit needs.
  • The next entry will ask what autonomous orbit maintenance needs from the desktop architecture.