SPK Type 10 Interpolation

[dahlend]

SPICE SPK kernels of type 10 are essentially lists of TLEs (Two Line Elements). Currently the kete implementation loads the current TLE and calculates the state of the object from that single TLE. In cSPICE, they load the closes two TLEs and perform interpolation between the two states. This has pros and cons. Pro:

• For well behaved orbits this is a good approximation

Con:

• Some objects, such as HST, have discontinuities in their orbits due to maneuvers. This makes the interpolation badly fit the orbits.

I had originally decided to not includes interpolation due to the HST issue, but I think it may be worth it for the small accuracy gain in the rest of the cases.

This will likely improve the SPHEREx kernel accuracy from about 30km at worst to maybe less than 10km? Thats a guess