The TESS Full Frame Images each have an individual WCS. This is because, as TESS orbits the earth which orbits the sun, stars in the focal plane are aberrated in time and position. The FFI for each frame has a slightly different WCS to account for this. It is sometimes useful to have this updated, aberrated WCS. An example would be solar system objects, which can change their position in the focal plane significantly over a sector.

An ideal feature might let us do something like this;

WCS.from_archive(sector=1, camera=1, ccd=1, cadence_number=100)

To get the WCS for a particular frame. A stretch goal would be

WCS.from_archive(sector=1, camera=1, ccd=1, time="2020-07-25T10:20:01")

Which would have to somehow interpolate the WCS to the correct time, and would need to check the time was within the requested sector.

tesswcs uses information from the FFI fits files from TESS, which have been munged into data cubes by MAST and hosted in the cloud. The files to run tesswcs are created based on information scraped out of those files using tessrip. tessrip is under-development and isn't stable enough to be a dependency.

We need a way to
a) document how the files are made
b) create new files as TESS continues to observe
c) potentially have a CI action to create new files every few months