`orbitforge stationkeep`

Synopsis


orbitforge stationkeep --constellation <PATH> [OPTIONS]

Description

Estimates the propulsive cost of holding a constellation in place over a multi-year horizon, and reports whether the propellant you have covers it.

Two strategies are available, and they model different physics:

Strategy	Fights	Typical regime
`leo`	Atmospheric drag lowering the semi-major axis	Low Earth orbit
`geo`	East-west longitude drift and luni-solar inclination drift	Geostationary

This is a budgeting tool for design trades, not a maneuver planner. For actual burns see maneuver and target.

Options

Common options.
Parameter	Type	Unit	Default	Required	Description
`--constellation`	path	n/a	—	Yes	Path to a constellation JSON file.
`--years`	float	years	`5`	No	Budget horizon.
`--strategy`	enum	n/a	`leo`	No	`leo` for drag makeup on the mean semi-major axis, `geo` for east-west and north-south box keeping.
`--isp-s`	float	s	`220`	No	Thruster specific impulse. Sets how much delta-v a kilogram of propellant buys.
`--fuel-kg`	float	kg	`20`	No	Usable propellant per satellite.
`--dry-mass-kg`	float	kg	`240`	No	Dry mass per satellite.
`--json`	path	n/a	—	No	Write per-satellite reports and the fleet aggregate.

LEO strategy only.
Parameter	Type	Unit	Default	Required	Description
`--deadband-km`	float	km	`1`	No	Mean semi-major-axis deadband half-width. The orbit is allowed to decay this far before a correction fires.
`--cdam`	float	m^2/kg	`0.01`	No	Ballistic coefficient, Cd times A over m. The dominant input; see the warning below.

GEO strategy only.
Parameter	Type	Unit	Default	Required	Description
`--slot-longitude-deg-east`	float	deg east	`0`	No	Assigned orbital slot longitude.
`--ew-deadband-deg`	float	deg	`0.05`	No	East-west longitude deadband half-width.
`--ns-deadband-deg`	float	deg	`0.05`	No	North-south inclination deadband half-width.
`--ns-drift-deg-per-year`	float	deg/year	`0.85`	No	Luni-solar inclination drift rate.

Worked example

A 60-satellite Walker shell at 550 km, budgeted over five years:


orbitforge stationkeep \
  --constellation demo.json \
  --years 5 --strategy leo --cdam 0.02


Station-keeping budget for `demo`: 60 satellites over 5.0 years.
Per satellite: 10.43 m/s/yr (1.242 kg/yr propellant), capacity 172.7 m/s.
  drag-makeup: 10.43 m/s/yr, 1.096 m/s per cycle every 38.4 days
Fleet: 580.4 m/s/yr total delta-v, 69.17 kg/yr propellant.
Fuel margin covers the full horizon.

Reading the output

Figure	Value	Meaning
Per satellite	10.43 m/s/yr	Annual delta-v to hold the deadband
Propellant	1.242 kg/yr	That delta-v converted through the rocket equation at the given specific impulse and dry mass
Capacity	172.7 m/s	Total delta-v the loaded propellant provides
Cycle	1.096 m/s every 38.4 days	One correction burn’s size and how often it fires
Fleet	580.4 m/s/yr, 69.17 kg/yr	Fleet totals, useful for logistics rather than for spacecraft sizing
Verdict	Covers the full horizon	172.7 m/s capacity against 52.2 m/s needed over 5 years

The cycle line is the operationally useful one. It says a satellite fires roughly every five and a half weeks, which sets how often the ground segment must plan and execute maintenance across 60 spacecraft.

Capacity divided by annual cost gives the real lifetime limit: 172.7 divided by 10.43 is about 16.6 years of station keeping, comfortably beyond the five-year horizon.

The parameter that dominates

In LEO, delta-v scales roughly linearly with the ballistic coefficient --cdam. Doubling it doubles the propellant. The default of 0.01 m^2/kg is a placeholder, not an estimate of your spacecraft.

A budget produced with a guessed ballistic coefficient is a guess with extra decimal places. Compute it from the actual drag area, drag coefficient, and mass, and state the value alongside the result.

Atmospheric density is itself uncertain by tens of percent and varies strongly with solar activity, so treat the output as a range rather than a value. A common practice is to run the budget at the expected and at an elevated density assumption, and size propellant for the latter.

orbitforge stationkeep