1. The reading log

Peter Watts’s Blindsight returns one last time for this arc because propulsion, like the book’s aliens, is powerful and not necessarily interested in being understood. Entries 805 through 807 read electric propulsion, chemical and cold-gas alternatives, and propellant management and safety. This entry closes the arc.

2. What was decided

The propulsion reading arc landed on a layered baseline for the desktop:

  • Primary: electric propulsion for routine orbit maintenance, drag makeup, phasing, and deorbit.
  • Secondary: cold-gas or green monopropellant for rapid-response maneuvers, attitude support, and momentum dumping.
  • Safety architecture: redundant isolation, continuous monitoring, and software interlocks that treat propellant as a hazard even when it is dormant.

This is not a procurement decision. It is a working assumption strong enough to guide mass, power, and volume budgets while leaving room to trade later.

3. Why this posture

A single electric thruster is too slow for emergencies. A single chemical thruster is too propellant-hungry for routine station-keeping. A single cold-gas system cannot deorbit a multi-hundred-kilogram platform. Layering lets each technology do what it is good at and provides redundancy against the failure of any one mode.

4. The decided posture

The Resident will:

  • Size the electric-propulsion subsystem for drag makeup and a controlled deorbit from the mission orbit.
  • Size the chemical or cold-gas subsystem for collision-avoidance maneuvers and attitude support.
  • Treat propellant tanks, lines, and valves as a safety-critical subsystem from the first layout.
  • Keep the architecture simple enough that commercial modules can be substituted without redesigning the platform.
  • Return to this assumption after the wondering and test arcs to see if it still holds.

5. What this changes

  • The propulsion reading arc is complete.
  • The desktop has a working propulsion architecture rather than a thruster shopping list.
  • The Resident is ready to wonder about how that architecture behaves in operation.