faster way to observe()?

I’ve got code that calculates the ra/dec of an asteroid from the position of a satellite, but it runs slowly (~0.15sec per observe()), and I was wondering if my code could be rewritten in a faster way. Eventually, I’d like to be able to run it for a large project that would need many observe() calls (10^10 observe() calls per asteroid, for 500k asteroids).

import io
from skyfield.api import load
from skyfield.data.mpc import load_mpcorb_dataframe
from skyfield.data.mpc import mpcorb_orbit
from skyfield.constants import GM_SUN_Pitjeva_2005_km3_s2 as GM_SUN
from skyfield.toposlib import Topos

sc_lats  = [...] # list of satellite latitudes, degs
sc_lons  = [...] # list of satellite longitudes, degs
sc_alts  = [...] # list of satellite altitudes, meters
sc_times = [...] # list of times, astropy.time.Time objects

# asteroid Eunomia from Minor Planet Center's MPCORB.DAT
ast    = 15
a_line = '00015    5.2   0.15 K20CH  60.84584   98.61793  292.93525   11.75338  0.1863457  0.22921812   2.6442555  0 MPO530953  2394  79 1851-2020 0.55 M-v 38h MPCW       0000     (15) Eunomia            20200107'

eph    = load( 'de430.bsp' )
sun    = eph['sun'  ]
earth  = eph['earth']
a_line = io.BytesIO( a_line.encode('utf-8') )
a_info = load_mpcorb_dataframe( a_line )
a_info = a_info.set_index('designation_packed')
a_info = a_info.loc['%05d'%ast]
ts     = load.timescale()
a_pos  = sun + mpcorb_orbit( a_info, ts, GM_SUN )

for i in range( len(sc_lats) ) : # 1e10 loops per asteroid
  fermi = earth + Topos( latitude_degrees=sc_lats[i], longitude_degrees=sc_lons[i], elevation_m=sc_alts[i] )
                                         # 0.00036 sec per call  (earth+Topos())
  t1    = ts.from_astropy( sc_times[i] ) # 0.00024 sec per call
  raw   = fermi.at(t1)                   # 0.0024  sec per call
  raw   = raw.observe(a_pos)             # 0.15    sec per call :(
  rdd   = raw.radec()                    # 0.00007 sec per call
  print('final ra/dec/dist:',rdd)

I’m pretty sure it would run faster if numpy arrays were used in the underlying code, but I recognize implementing those changes would be a large amount work for the devs. Is there any way I can speed up the quoted code?

[craigim]

Most satellite TLEs are published at least once per week. So if you’re searching through 10 years of satellite data on, say, https://space-track.org, you can pull all TLEs for a particular satellite for the past 10 years (be sure to read the terms of service before pulling that much data). Each TLE has an epoch date around which it’s good for at least a couple weeks. Depending on how precise you need, you could pick one TLE per month and do your calculation over 120 1-month windows using a contemporary TLE. Not as good as doing it all at one go, but certainly better than doing it for each individual time point.

[brandon-rhodes]

Since the underlying request behind this issue is now identical to #532, I am going to close this issue so I don’t wind up tracking two issues about the same feature, and also to try to keep future discussion centralized in one place (as otherwise I sometimes have trouble tracking down on which issue an earlier comment was made). Hopefully the next few months will see progress!