- Other forms of state vector ephemerides, including those from NASA or the International Laser Ranging Service (ILRS).
The elements or state vectors are given in one of several reference frames. The most common ones are:
- EME2000 (The astrodynamical name for J2000)
- TEME (True Equator Mean Equinox, sort-of-but-not-quite equator of date). Space-Track TLEs are in TEME.
- ITRF (International Terrestrial Reference Frame, rotating with Earth)
- Availability of data, all of which is updated approximately daily:
- GP/TLE data are available from 18SPCS via the public website[1] for all satellites except secret US satellites, whose GP/TLE data are instead made available by hobbyists[2].
- The SP data from 18SPCS are available to operators by special arrangement with Space Force but not to the public.
- Such a special arrangement usually comes with restrictions that would be incompatible with our needs. Some researchers (e.g., M. Jah, UT Austin) have access to LEOLabs data for academic research, but they are in general not free.
- Some operators (notably Starlink, OneWeb, GPS) make their GP/TLE data available publicly. TLE versions of these data are available on T.S. Kelso’s Celestrak site[3].
- SP ephemeris files (several GByte per day) for SpaceX Starlink satellites are publicly available[4].
One of the conclusions from all our previous and current work is that our proposed PassPredict tools will need orbital information allowing for position accuracy of the order of an arcminute for imaging applications and general purpose evaluation. This is equivalent to knowing the position of a LEO satellite with a precision of ~ 200 m. For spectroscopy, the requirements would be even more stringent, on the order of an arcsecond or ~ 5 m. These levels of precision cannot be provided by the publicly available elements in GP/TLE format. However, the information is available to the spacecraft operators, possibly with an even higher precision.
We therefore recommend that the orbital parameters (suited to high fidelity models, with covariance/ uncertainty information) be reliably made available by the satellite operators to the observatories. Should the full precision orbital data be commercially sensitive information, they could of course be degraded/truncated, to a precision allowing for sub-arcminute uncertainty on the position. The detailed exchange of requirements resulting in such an arrangement can be part of the ongoing dialogue and cooperation between the astronomical community and the space industry.
- ↑ https://space-track.org
- ↑ notably https://www.prismnet.com/~mmcants/tles
- ↑ https://celestrak.com/NORAD/elements/supplemental
- ↑ https://space-track.org (under `Public Files')
