how to implement satellite.at(time).is_sunlit(TLE)?

[dododo42]

First of all, I'd like to thank Brandon Rhodes for the awsome library.
I have just started using Python and it has already been so usefull.

Now, regarding the question:
I have the TLEs of a satellite which has mounted a sensor on it.
I need to retrieve some data about this sensor, such as if it can see the Sun or not.
I was planning to do this by myself, before noticing the existence of is_sunlit(ephemeris).
Unfortunately, the ephemeris of the satellite are not available, and I am working with TLEs only.
Is there a way to use is_sunlit() using the TLE as an input?
I tried to search for this through the documentation but I did not find anything.

At this point, my approach would be:

1. retrieve satellite position in ECI coordinates from TLE at time t
2. retrieve Sun long and lat at time t
3. check whether Earth is shadowing or not

Nonetheless, as there is a function which does exactly what I need, I wanted to be sure before implementing it.
Thanks in advance.

[dododo42]

I just realised that is_sunlit(ephemeris) refers to the ephemeris of the Sun.
The following code should return the right answer:

from skyfield.api import EarthSatellite, load
ts = load.timescale()
satellite = EarthSatellite(line1, line2, name, ts)
t = ts.utc(utc_date)
eph = load('de421.bsp')
sunlit = satellite.at(t).is_sunlit(eph)

Hoping I have not wasted anyone's time.

[brandon-rhodes]

Thank you for following up with the solution! Is there anywhere the documentation could have explained that more clearly, and made the purpose of the ephemeris argument clearer?

[dododo42]

As I come from more analytical environments, my mistake was not knowing that de421.bsp is a standard file for planets ephemiris.
I originally thought it was an example file of some object just to showcase how to use is_sunlit().
Nevertheless, I think the documentation is good already as it is. Only some inexperience from my side.