Impulse Maneuvers¶

Impulse maneuvers model instantaneous delta-V burns triggered by g-function zero-crossings during propagation. Each maneuver defines its own event function and firing condition.

ImpulseManeuver (Abstract)¶

Member	Description
`ComputeEventValue(StateVector)`	Scalar g-function evaluated at the current state
`EventCrossingDirection`	`CrossingDirection` that triggers the burn
`CheckPreconditions(StateVector)`	Optional additional constraints (returns `true` to allow firing)
`DeltaV`	Burn delta-V vector, in the inertial frame of the propagated state
`ThrustWindow`	Window of the equivalent finite burn (see below)
`ManeuverWindow`	Thrust window extended by the maneuver hold duration

Thrust Window Convention¶

The burn is impulsive: the propagated state receives the whole delta-V at the event epoch t. The library also reports the finite burn the impulse stands for. Its duration dt follows from the rocket equation (engine ISP, fuel flow and total mass), and the window is placed on [t - 0.666 dt, t + 0.334 dt]: two thirds of the burn before the impulse, one third after.

The end of ManeuverWindow is the earliest epoch at which the next maneuver of the chain may fire.

The two-thirds split dates back to the initial .NET implementation and no derivation of it is on record. The usual impulsive approximation of a finite burn centres the burn on the impulse (50 %). The value is kept unchanged for now; it will be revisited together with finite-thrust modelling.

Concrete Maneuvers¶

ApogeeHeightManeuver¶

Raises apogee height. Fires at perigee (r . v crosses zero from negative to positive).

PerigeeHeightManeuver¶

Raises perigee height. Fires at apogee (r . v crosses zero from positive to negative).

PhasingManeuver¶

Adjusts orbital period for phasing. Fires at perigee (r . v, negative to positive).

CombinedManeuver¶

Combined plane and apsis change. Fires at apogee (r . v, positive to negative) with an additional precondition that the apogee is aligned with the ascending node.

PlaneAlignmentManeuver¶

Changes orbital plane to match a target. Uses an adaptive crossing direction on the g-function r . h_target to fire at the nearest orbital node (ascending or descending).

ApsidalAlignmentManeuver¶

Rotates the line of apsides. Fires at the nearest orbit intersection point using the g-function r . (h x p) with negative-to-positive crossing.

Maneuver Chain¶

Maneuvers are linked in a chain on the spacecraft:

Leading attitudes execute immediately at the initial state.
The first ImpulseManeuver is wrapped in a ManeuverEventDetector.
When the event fires, the burn is applied and the chain advances to the next impulse maneuver.
The process repeats until all maneuvers in the chain have executed.

Example¶

// Raise the apogee radius to 42,164 km (meters), at the first perigee after J2000 TDB.
var maneuver = new ApogeeHeightManeuver(
    earth,
    Time.J2000TDB,
    TimeSpan.Zero,
    42164000.0,
    engine);

spacecraft.SetStandbyManeuver(maneuver);
var solution = spacecraft.Propagate(window, perturbingBodies, false, false, deltaT);