TargetType.OrbitalElements Property

TargetType.OrbitalElements (read-write, String)

MPC 1-line minor planet or comet elements for this Target, or specially formatted NEO Ephemerides (see remarks).

Syntax

TargetType.OrbitalElements [= String]

The property syntax has these parts:

Part	Description
Value (String)	MPC 1-line minor planet or comet elements for this Target, or specially formatted NEO Ephemerides (see remarks).

Remarks

One of three possible children of TargetType. Must not be specified in combination with Coordinates or Coordinates. The observatory will use the minor planet or cometary MPC 1-line Orbital Elements to calculate the position of the body at image acquisition time.

Alternatively, this tag may contain specially formatted NEO ephemerides. A near-earth object listed on the Minor Planet Center's Near Earth Object Confirmation Page (NEOCP) will not have orbital elements available. Instead, the MPC publishes short-term ephemerides on the NEOCP. You can retrieve the ephemerides for one or more NEOs and construct target specifications for each.

The format of NEO Ephemeris target specifications is strict. You must follow the directions explicitly or your plan will fail on the bad specifications.

You must set up the NEOCP ephemeris generator web page with the following options in order to get ephemeris lines in the expected format (all of these options are vital):

Geocentric observing point
Ephemeris Interval of 1 hour
Decimal coordinate format
Motions in "/hr
Separate RA and Dec coordinate rates (not sky rates!)
Full output (not brief!)

The length of the resulting ephemeris lines should be exactly 65 characters (ignoring any uncertainty hyperlinks that may be present!). If not, you picked the wrong options above. A typical ephemeris line from the MPC should like this (this is not the target specification format!):

2004 10 27 02    01.6915    -40.095    126.8  18.7  -69.29  -2.51

Once you have the NEO ephemerides displayed on your browser, select from 4 to 6 lines (spaced two hours apart) that will provide data for the entire night (so you don't have to know just when ACP will observe the NEO). Then build your OrbitalElements string as:

The first 35 characters of the first ephemeris line (Time, RA, Dec only)
A "|"
The first 35 characters of the next ephemeris line (use the one for 2 hours later than the first)
… and so on, for 4 to 6 lines.

This may seem complex, but once you get it, it's actually straightforward. Here is an example ACP plan target line for NEO A123456789 (hypothetical!) with 4 ephemeris records spaced 2 hours apart:

0        1         2         3         4         5         6         7         8         9         0         1         2         3         4
12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123
-----------------------------------------------------------------------------------------------------------------------------------------------
2004 10 27 02    01.6915    -40.095|2004 10 27 04    01.6834    -40.167|2004 10 27 06    01.6689    -40.301|2004 10 27 08    01.6721    -40.462

This target specification format is demanding of care and accuracy. The benefit is that your NEO images will be at precisely the coordinates predicted by the MPC, and if you use orbital tracking, your scope will move to track the motion of the NEO during the exposure.