Big, bright fast mover (7482) 1994 PC1

[PMSchu]

Hi BMD,

Currently MPC's 'standard' epoch is 2022 Jan 21 0000 UTC & that's the epoch ST4v uses when it downloads MPCORB since mid-October 2021. At least that's the way it seems to work, Technoking can confirm this. If I understood what Greg was saying, ST4v will use the elements with the epoch from the MPC that are the farthest into the future, either 'Today's' or the 'Standard' & keep those & ignore the other.

Perhaps I've misunderstood something,

Phil S.

This isn't quite correct.

1. SkyTools accumulates orbital elements over time. The set of elements with an epoch that best matches the date of your calculation will be used.

2. In order to make the database efficient, orbital elements are sorted into different "standard epochs" when they are stored. This is a period of time, 200 days long, that orbits are sorted into. The epoch dates in general that you see from the MPC are typically these same standard epochs.

3. The complicating factor is that SkyTools will only store one set of orbital elements for each standard epoch. This is where it got tricky when it comes to NEOs, because the MPC started publishing elements at a standard epoch date in the future, and prior to the version 4.0j R8 update, SkyTools would only update the elements if the epoch was at a later time than the one already in the database.

In the update I changed how that works. There are now cases when a new set of elements will always overwrite the ones already stored for that epoch.

What this means in practice:

When you download the "MPC NEA Today" or "MPC Daily Update" from within SkyTools, the downloaded elements will always overwrite the current orbital elements for the current epoch. That way, you can always update your elements when a close pass is coming up (and the elements improve).

When you manually enter data, such as that from HORIZONS: if you edit an existing set of elements, this will always overwrite what was there before. If you create a new set of elements, be sure it has an epoch more recent than the one in the database. Otherwise it will not overwrite the one already there. Do not kludge the epoch. It must be accurate.

How do you tell things are ok?

1. Open The Minor Planets Database from the Data menu
2. Enter the designation of the minor planet under Designation and press the Enter key.
3. When it finds the minor planet, it will list all of the orbital elements by epoch. Double-click on any one to see the full data.
4. Ensure that there is no set of orbital elements for a date in the future, beyond the date of closest approach. If there is one, delete it, or replace it manually, by editing the data. To delete it, close the Osculating Elements dialog, right-click on the elements you wish to delete, and select Delete Element Set.

Thanks Greg,

I've been avoiding the download of MPCORB because of #2 in your list, but #3 after the R8 update fixes that issue. The number of MPs in the DB has been decreasing & is now down to <700k objects. When the MPC changed to the 2022 Jan 21 standard epoch all of the NEO known were updated to that epoch & didn't get the update for 'Today's Epoch'. I didn't notice that R8 fixed that.

Phil S.