How I set These Up

[theskyhound]

Hi Greg,

Back when BMD & I were trying to use a set of elements for a close pass, I tried to input elements from HORIZONS at 6 hr intervals. ST4v (4.0j R2) would only keep the first one that I entered & entering a new one was ignored. It also seemed that after a new set of elements was entered, all of the precalcs used to speed up plotting on the charts got repeated each time. With my MP database this took some time & I ended up with the same epoch date anyway - a waste of time. Can't add an element set from the MPC for different times because they only provide their 'standard' epoch time, like 2021 July 4 or the NEAs at Today's Epoch as options. Trying to add elements directly into the MP DB was an old method that you thought was eliminated, but we wiley users tried anyway  .

Would it be feasible to use a set of 3 osculating elements pre-, at & post-close approach taken from the HORIZONS system & interpolate between them during the pass? It would complicate the ephemeris calculations, but since it's only needed for the object of interest, it shouldn't be time prohibitive. As noted above this is a very niche application, so understandibly not a priority. I don't know how well interpolation of positions calculated from 2 sets of elements would work. Possibly weighting the results based on the time difference between the element epochs & the time for the calculation could work.

Cool stuff,

Phil S.

I outlined the reasons why it would fail to add a new orbit: unless something is broken, the "new" orbit won't be recognized as new unless the numbers don't match. It is possible that the orbit simply didn't change enough. By the way, precalculating the elements doesn't take that long. What takes a long time is when the databases used to plot minor planets on the charts, which are separated by epoch for speed, have to be re-sorted. But this should only happen when a new orbit has been successfully added or updated. I suspect the latter was the issue for you. Unfortunately the amount of coding required to insert the new orbit is a lot, but maybe someday.

I don't understand what you are asking regarding calculating osculating elements... are you suggesting that SkyTools have an n-body calculation built into it to take into account perturbations? If so, that's not a minor thing at all....

I do wonder if you guys aren't taking this to an unnecessary extreme. It is important to recognize that there are many reasons for an orbit to be inaccurate during a close pass. Most orbits simply aren't determined well enough! That is the primary reason for the asteroids to plot off-line, or more commonly, early or late, not the perturbations.  In all but the very closest passes, adding the perturbations should be unnecessary. As they say, you can't polish a turd. Unless the object has really good astrometry that goes back at least for many months, if not years, it may not be worth the trouble to use different sets of elements, unless it is passing very close (say, withing the earth-moon distance). Even then, for most I would think a set of three elements: before, closest, and after, should suffice.