Replan

POST/replan

Purpose

Answers the operational question after a satellite fails: what are the options, what does each cost, and how long does each take to restore service.

It returns several plans with a recommendation, so the trade is visible rather than decided for you.

Request

Like /resilience/*, this takes the shape of the problem rather than a constellation_id. There is no propagation involved; the question is combinatorial and economic.

Parameter	Type	Unit	Default	Required	Description
`a_ops_km`	number	km	—	Yes	Operational semi-major axis.
`inclination_deg`	number	deg	—	Yes	Operational inclination.
`phase_gap_deg`	number	deg	—	Yes	In-plane phase gap the failure opened.
`raan_gap_deg`	number	deg	—	Yes	Cross-plane gap, if the spare must change plane.
`in_plane_spares`	integer	count	—	Yes	Spares already in the affected plane.
`parking_spares`	integer	count	—	Yes	Spares held in a parking orbit.
`park_altitude_km`	number	km	—	Yes	Parking orbit altitude, which sets the raise cost.
`rephase_duration_days`	number	days	—	Yes	Time allowed for a rephase. Longer is cheaper in delta-v.
`replacement_lead_time_days`	number	days	—	Yes	Time to build and launch a replacement.
`replacement_sat_cost_usd`	number	USD	—	Yes	Cost of a replacement satellite.
`replacement_launch_cost_usd`	number	USD	—	Yes	Cost of a replacement launch.
`degradation_days`	number	days	—	Yes	How long degraded service is tolerable.
`revenue_at_risk_per_day_usd`	number	USD/day	—	Yes	Revenue exposed per day of degradation. This is what makes speed comparable to money.

Example


curl -s -X POST http://127.0.0.1:8080/replan \
  -H 'content-type: application/json' \
  -d '{
        "a_ops_km": 6928.0,
        "inclination_deg": 53.0,
        "phase_gap_deg": 30.0,
        "raan_gap_deg": 10.0,
        "in_plane_spares": 1,
        "parking_spares": 0,
        "park_altitude_km": 400.0,
        "rephase_duration_days": 6.0,
        "replacement_lead_time_days": 120.0,
        "replacement_sat_cost_usd": 1000000.0,
        "replacement_launch_cost_usd": 30000000.0,
        "degradation_days": 30.0,
        "revenue_at_risk_per_day_usd": 50000.0
      }'


{
  "recommended": {
    "actions": [
      {
        "ActivateInPlaneSpare": {
          "rephase": {
            "delta_a_km": -4.260819925470516,
            "delta_v_m_s": 4.664984976009534,
            "duration_days": 6.0
          }
        }
      }
    ],
    "restores": true,
    "time_to_restore_days": 6.0,
    "delta_v_m_s": 4.664984976009534,
    "cost_usd": 0.0,
    "revenue_at_risk_avoided_usd": 1200000.0
  },
  "plans": []
}

plans held three options in this run; only the recommendation is shown.

Reading the recommendation

Field	Value	Meaning
`restores`	true	This plan closes the gap. A plan that does not is still returned, for comparison
`time_to_restore_days`	6.0	How long until service is whole again
`delta_v_m_s`	4.66	Propellant cost, spent from the spare’s own budget
`cost_usd`	0.0	No new hardware and no new launch
`revenue_at_risk_avoided_usd`	1,200,000	24 days saved against the 30-day tolerance, at 50,000 per day

Why the spare wins

The recommendation activates an in-plane spare and rephases it, and the case for it is arithmetic rather than judgment:

Option	Cash cost	Time to restore	Revenue at risk
Activate in-plane spare	0	6 days	300,000
Replacement launch	31,000,000	120 days	1,500,000 at the daily rate, capped by tolerance

The spare costs nothing but 4.66 m/s of its own propellant and restores service in 6 days rather than 120. revenue_at_risk_avoided_usd quantifies exactly that difference.

cost_usd: 0.0 means no cash outlay. It is not free: the plan consumes 4.66 m/s from a spare that was carrying a fixed propellant budget, and it consumes the spare itself, so the plane now has none.

A recovery plan that leaves you with no spare has changed your resilience posture. Re-run /resilience/kfailure against the post-recovery fleet before treating the situation as closed.

The rephase is a drift maneuver

delta_a_km of -4.26 lowers the semi-major axis, which raises the orbital rate and lets the spare drift forward into the gap. After 6 days at the new rate it has closed 30 degrees of phase and circularizes again.

Lowering costs delta-v twice, once down and once back up, which is why rephase_duration_days matters: a longer allowance needs a smaller altitude offset and therefore less propellant. Speed and propellant trade directly.

Model basis: Recovery planning

Assumptions: Impulsive rephase maneuvers using a semi-major-axis offset to produce drift; delta-v from the two-body relation between semi-major axis and orbital rate; revenue at risk accrued linearly per day up to the degradation tolerance; replacement lead time and cost taken as supplied.
Validity range: In-plane rephasing and plane changes at the supplied gap sizes. A large `raan_gap_deg` makes a plane change dominate the budget, and at that point launching a replacement is usually cheaper.
Accuracy: Delta-v figures are first-order and exclude execution error and the perturbations acting during a multi-day drift. Cost comparison is only as good as the supplied revenue and replacement figures.
Reference: Standard phasing-maneuver relations; discounted revenue-at-risk comparison.