# Does SPICE function gftfov account for occultations?

I need to determine when an antenna on a spacecraft can see a ground station on Earth at particular epochs. I have generated all the necessary SPICE kernels necessary as well as using the NASA planetary ones and have been using the SPICE function gftfov to determine whether each antenna can see a particular ground station at a particular time given the coordinates of the ground station and the orientation of each antenna (with a boresight vector and boresight angle) as well as the ephemeris of the spacecraft. This has produced a number of results with an example below (not actual numbers but representative of what it looks like):

DSS49
Antenna H1: Coverage Windows = 5
Begin time (UTC): 12/08/2022 09:12:09
Stop time (UTC): 12/08/2022 09:29:18
Start time (UTC): 12/08/2022 09:51:47
Stop time (UTC): 12/09/2022 01:17:57
Start time (UTC): 12/09/2022 01:30:32
Stop time (UTC): 12/09/2022 02:13:26
Start time (UTC): 12/09/2022 02:31:50
Stop time (UTC): 12/09/2022 04:10:13
Start time (UTC): 12/09/2022 04:20:59
End time (UTC): 12/09/2021 04:21:49


However, I don't know whether this accounts for occultations -- namely blockage by the moon, which should happen when the spacecraft is in low lunar orbit and when it's undergoing descent. I know the SPICE function occult can handle occultations. If gftfov already includes the occultation restriction, that would be great. If not, is there an easy way to know whether a ground station is within fov of an antenna taking into account possible occultation?

## 1 Answer

Does SPICE function gftfov account for occultations?

Almost certainly not. The documentation does not indicate that gftfov does this. The documentation instead implies that this is purely a geometric calculation based on the field of view of the instrument and the position of the target, possibly with corrections for the shape of the target and corrections for aberration.

Occultations are extremely rare events. It's hard enough to find when the target object is in view to make that function worry about occultations.

• Thanks David! from what I see then, I'll have to filter the output of gftfov with the occultation restriction to remove the times where the line of sight is blocked by the moon. Correction on my statement earlier: this will only happen during LLO since during descent, we will have line of sight.
– Shen
Feb 14, 2021 at 19:44
• @Shen If you are working on one of the NASA Commercial Lunar Payload Services (CLPS) teams, congrats, but I probably need to stop discussions at this point. If you are working on one of the NASA Human Landing Systems (HLS) teams, also congrats, but once again, I probably need to stop discussions at this point. Feb 14, 2021 at 20:46