cavsiopy: A Python package to calculate and visualize the pointing direction of the Radio Receiver Instrument on e-POP/Swarm-E and other satellite missions

The polarization characteristics of a radio wave observed by an
antenna on-board a spacecraft strongly depend on the geometry between the
receiving antenna pointing direction and the transmitting source. The
Radio Receiver Instrument (RRI) on the e-POP/ CASSIOPE/ Swarm-E satellite
consists of orthogonally crossed dipoles for radio frequency polarization
state measurements. Accurate information about the spacecraft
orientation/attitude and the antenna pointing direction are required for
resolving the true in-situ polarization characteristics of a received
radio signal. 'cavsiopy' is an open source Python package, which was
specifically developed to determine the look direction of the RRI
instrument on e-POP/ Swarm-E for HF radio wave propagation studies, but
can be applied to any satellite mission requiring accurate pointing
information. Given spacecraft position, attitude, and a target location,
the pointing direction and orientation of the RRI instrument with respect
to the target can be determined in various reference frames. 'cavsiopy'
supports the reference frames: Geocentric Equatorial Inertial J2000 (GEI
J2K), Earth Centred Earth Fixed (ECEF), International Terrestrial
Reference Frame (ITRF), geodetic North-East-Down, and geocentric
North-East-Center. Additionally, 'cavsiopy' contains routines for the
calculation of Swarm-E/ e-POP azimuth, elevation and orbital parameters,
as well as for the 2D/3D visualization of the geometry between the RRI and
the target. The functionality of 'cavsiopy' is presented along with
example routines and visualizations from the different attitude modes
typically used in RRI observations.