I'm using skyfield to compute the relative distance of planets to Earth as a function of time (as described on the skyfield home page). It works great and now I'm trying to implement Earth=>comet distance (e.g. 67P/ Tchouri).
I've found at NASA JPL, a way to create Spice SPK files for comets (here) but it produces xsp files that I cannot seem to read with the load command from skyfield.
Another possibility I considered is to use orbital information as suggested for pyephem (see here) but I don't know how to read them in Skyfield.
I also saw that comets were on the roadmap for skyfield coding sprint so that's maybe my answer but if you know a way to make it work with the current version that would be very helpful.
Skyfield did gain support for comets! You can find the details here:
https://rhodesmill.org/skyfield/kepler-orbits.html#comets
Adapting the code from the documentation, here is the distance to a comet from the Minor Planet Center database:
from skyfield.api import load
from skyfield.constants import GM_SUN_Pitjeva_2005_km3_s2 as GM_SUN
from skyfield.data import mpc
ts = load.timescale()
eph = load('de421.bsp')
sun, earth = eph['sun'], eph['earth']
with load.open(mpc.COMET_URL) as f:
comets = mpc.load_comets_dataframe(f)
comets = comets.set_index('designation', drop=False)
row = comets.loc['1P/Halley']
comet = sun + mpc.comet_orbit(row, ts, GM_SUN)
t = ts.utc(2020, 10, 17)
ra, dec, distance = earth.at(t).observe(comet).radec()
print('Distance in AU:', distance.au)
I see the result:
Distance in AU: 35.22790002485247