radec

ssapy.compute.radec(orbit, time, obsPos=None, obsVel=None, observer=None, propagator=KeplerianPropagator(), obsAngleCorrection=None, rate=False)[source][source]

Calculate observed right ascension, declination, and slant range of orbiting objects as viewed at specified times and positions.

Parameters:

  • orbit (Orbit or list of Orbit (n,)) – Orbit(s) for which to calculate ra and dec.

  • time (array_like or astropy.time.Time (m,)) – If float (array), then should correspond to GPS seconds; i.e., seconds since 1980-01-06 00:00:00 UTC

  • obsPos (array_like (m, 3), optional) – Positions of observers at given times.

  • obsVel (array_like (m, 3), optional) – Velocity of observers at given times.

  • observer (Observer or list of Observers (m,), optional) – Observer(s) used to calculate obsPos.

  • propagator (Propagator, optional) – The propagator instance to use.

  • rate (bool) – If True, return additionally the time derivatives of the quantity, times cos(dec) in the case of right ascension.

  • obsAngleCorrection ({None, "linear", "exact"}, optional) – Correct actual angle to observed angle, meaning account for light-time delay, and aberration due to the observer’s velocity. None means don’t do any correction. “linear” means do an aberration correction and first order light-time correction. “exact” means do an aberration correction and iteratively solve for the exact light-time correction. (The “linear” correction is almost always sufficiently accurate).

Notes

Exactly 1 of obsPos and observer must be supplied. observer and obsPos follow similar broadcasting rules as detailed below explicitly only for obsPos.

The length of time and obsPos must match or be broadcastable to match. If orbit is scalar-valued (an Orbit instead of a list of Orbit), then that dimension will be squeezed out in the return value. Likewise, if both time and obsPos are scalar, that dimension will be squeezed out.

For Keplerian orbit propagation it is more efficient to use a “vector Orbit” instead of a list of single scalar Orbits.

When doing light time corrections, the time argument is the arrival time of the photons at the observer, as opposed to the emission time at the satellite.

Returns:

  • ra, dec (array_like (n, m)) – Right ascension and declination in radians.

  • range (array_like (n, m)) – (Slant) range in meters.

  • If rate, also

  • raRate (array_like (n, m)) – Time derivatives of right ascension times cos(dec), rad / sec.

  • decRate (array_like (n, m)) – Time derivative of declination, rad / sec.

  • rangeRate (array_like (n, m)) – Time derivative of range, meter / s.