How I set These Up

[bigmasterdrago]

Thanks for the clarification BMD. It can certainly be confusing keeping everything straight. Perhaps in the futire you can describe how you get elements at Today's epoch from Lowell. Can you do this for a single MP or a group of them?

An 8.5" error sounds pretty good considering the magnitude of some of the position errors that you've reported in the past. Is the good agreement because we're still some time away from the close approach?

A nice feature would be to be able to read a file with multiple elements sets at the same time & plug them all into the MP database at once. It would speed up the position calculations for close approachs.

Phil S.

Phil,
I sometimes have to force a download from Lowell as ST will say the elements have not changed since the last download. I did the force again today and when looking at the Minor Planet Database, all of the highlighted rocks have epoch dates of Oct. 9, not the 13th. Yesterday I independently downloaded a Lowell set from https://ftp.lowell.edu/pub/elgb/astorb.dat.gz. The epoch was 2459500.5 (13 Oct 2021 0UT). A similar download today gives the same epoch. In my mind, the only way to get an epoch date for any particular day/hour, is to us the Horizons interface and let JPL/Horizons make you a set of osculating elements to input into ST. This is what they do. Especially keeping up with the close approaches. The other software I use will create a daily set of osculating elements, but for SkyTools4v, I always use Horizons to make that set. I've not found a way to get the MPC elements to generate a correct location for a small rock passing inside the Moons orbit using ST although by downloading MPC NEA Today, will help. Only by using Horizons to generate a set of Osculating elements for the time I want to observe. It is the "Gold Standard". I've always used it as not only a sanity check, but to check against other software predictions.

I just noticed this morning in the Horizons Small-Body Database Lookup when searching 2021 TV10, a new link: "Earth Impact Risks"  https://ssd.jpl.nasa.gov/tools/sbdb_look...021%20TV10. I had not seen that addition prior.

Someone at Lowell mentioned, and I'll quote him: "The problem is the osculating elements are changing as a function of time, so one set done for time X and another done for X + 2 days (say) will both be “correct”, but the results downstream will be different.  Nowadays the computing is fast enough that one generates (as does JPL Horizons) elements and thus ephemerides for “now”.  (We do this also for very nearby objects.). In any case, for near-Earth approachers, you do not want to make an ephemeris until just before you need it because new observations are likely to come in and thus the ephemeris can shift a lot as a result of the object being so close (even if the elements per se hardly change).

    We don't update the Lowell database very often, so it would be a secondary source for very near objects.  Use JPL:  they are experts at this, and the system is maintained to a high state.  Part of their mission is to deal with potentially dangerous objects, so the team works on this behind tbe scenes continually."