I am working on software that needs to parse an ephemeris file for the ISS. However, I cannot find any documentation for the particular format I have. The only mention I found is in this presentation, where on slide 5 it is described as a "TSA Ephemeris."
I did find a sample on the public internet here. The header looks like this:
PROP_MAN 11.0 2017 0.000 14212800.000 1296000.000 M50 FT FPS SEC
Looking at how the previous version of the software parsed the file, I've guessed that the numeric fields are:
0.000: epoch (seconds from start of year)
14212800.000start time (seconds from epoch)
1296000.000duration (seconds from start time)
The subsequent fields were ignored, but I believe they are:
M50: The reference frame: earth-centered inertial, equatorial, mean-of-date 1950 (see the ISS coordinate system reference)
FT FPS SEC: The units of the file
The records (lines) look like this:
14212800.000 -8535865.420155 -19320104.581130 -7028174.772018 17383.209720 -1082.297123 -18145.674503 907581.4
14212800.000: time (seconds from epoch)
-8535865.420155 -19320104.581130 -7028174.772018: position (feet)
17383.209720 -1082.297123 -18145.674503: velocity (feet per second)
907581.4: ignored, possibly spacecraft mass in pounds
I do have enough information to parse the file, but I'd like to know a bit more to make my parser more complete/robust:
- What is
PROP_MAN 11.0? If
11.0is a version, are there other versions I might encounter?
M50really the B1950 reference frame? (If so the existing software uses the wrong transformation.) What other reference frames are valid?
- What other units are valid?
- Do the time offsets count leap seconds in years that have them?
- Is the last data field actually the spacecraft mass? If so, then why does it change sometimes?