`AntennaRadiationPressure`#

class AntennaRadiationPressure(origin: CelestialBody, spacecraft: Spacecraft, base_frame: Frame, emitters: list, t0: float = None, tf: float = None)#

Bases: DynamicModel

Recoil acceleration from power the spacecraft transmits: radio antennas and active instruments such as a LIDAR.

An emitter of radiated power \(P\) whose beam is a cone of half-power beamwidth \(\alpha_0\) around the boresight \(\hat{\mathbf{a}}_z\) pushes the spacecraft with

\[\mathbf{a}_k = -\frac{P_k}{m\,c}\, \cos^2\!\left(\frac{\alpha_{0,k}}{4}\right)\hat{\mathbf{a}}_{z,k}\]

where \(m\) is the spacecraft mass and \(c\) the speed of light. The factor \(\cos^2(\alpha_0/4)\) is the boresight share of the momentum of a beam spread uniformly over the cone; it is close to one for a high-gain antenna and about 0.91 for a 70 degree low-gain antenna. The total acceleration is

\[\mathbf{a}_\text{ant} = \eta_\text{ant} \sum_{k\,\text{on}} \mathbf{a}_k\]

with \(\eta_\text{ant}\) an estimable scale factor (default 1), read from the state under ("eta_antenna", spice_id).

Emitters. emitters is a list of dicts, each holding

"name": label;
"power": ArrayWUnits radiated power;
"hpbw": ArrayWUnits half-power beamwidth, within [0, 360) degrees;
"boresight": beam direction in the spacecraft frame;
"on_intervals" (optional): list of (start, end) pairs, in TDB seconds past J2000 or as EpochArray, when the emitter transmits (start <= t < end). Omitted or None means always on; an empty list means never on.

Quantities with units may also be given in their serialized form ({"values", "units"}), which is what emitters_to_dict() writes.

Attitude. Boresights are fixed in the spacecraft frame and reach the inertial frame through the spacecraft-fixed to inertial rotation \(C\) of DynamicalUtils, for the "CK", "inertialFixedAttitude" and "nadirPointingSun" values of Spacecraft.attitudeMode. Only in the last one, where the spacecraft \(-X\) axis points at the Sun and the Y axis follows the heliocentric velocity, does the acceleration depend on the state, through the rotation of the boresights, and the model reports depends_on_velocity.

Parameters:

originCelestialBody: Propagation origin. Used for the Sun-relative geometry of the nadirPointingSun attitude.
spacecraftSpacecraft: The emitting spacecraft. Its mass and attitude are read at evaluation time.
base_frameFrame: Inertial frame of the propagated state.
emitterslist of dict: The emitters, as described above.
t0, tffloat, optional: Propagation span in TDB seconds past J2000. When both are given and the frame is J2000, the Sun position is read from a Chebyshev ephemeris cache instead of SPICE.

Attributes:

depends_on_velocity: Whether the acceleration depends on the spacecraft velocity.
emitter_names: Emitter names, in the order of active_emitters().
emitters: The validated emitters.
frame: The inertial frame of the propagated state.
origin: The propagation origin.
origin_name: The name of the propagation origin.
param_name: State key of the estimable scale factor.
spacecraft: The emitting spacecraft.

Methods

`active_emitters`(epoch)	Which emitters transmit at `epoch`.
`compute_acceleration`(position, ...)	Antenna and instrument recoil acceleration.
`emitters_from_dict`(emitters)	Validate emitters and return them with live quantities.
`emitters_to_dict`(emitters)	Serialize emitters to plain JSON types.
`to_dict`()	Serialize this model's emitters; see `emitters_to_dict()`.

Raises:

InvalidEmitterError: If an emitter is malformed.
DynamicalUtils.InvalidAttitudeModeError: If the spacecraft attitude mode is not one of the three above.
DynamicalUtils.InvalidFixedAttitudeError: If an inertialFixedAttitude spacecraft has no 3x3 attitude.
DynamicalUtils.MissingVelocityError: If a nadirPointingSun spacecraft has no velocity in the state.

AntennaRadiationPressure#

`AntennaRadiationPressure`#