You're probably here because Find_Orb refused to show you some bits of data for a spacecraft-based observation (such as angular and radial velocity), and told you to look here for more info. It does that because by default, it simply can't compute that information, because it doesn't know what the spacecraft's velocity was at that time. Fear not, though; a workaround to add those velocities to the astrometry shown below.
Find_Orb will always know the position of an observer at the time of observation. If it's a "normal", ground-based observer, the program can do the usual math to take the observer's latitude/longitude, the known orientation of the earth, and figure out both position and velocity.
But for a spacecraft-based observation (from WISE or STEREO-A/B or others), the position can't just be computed. It's (usually) supplied using a scheme for encoding spacecraft positions used by the MPC. Under that scheme, the position is supplied on a second 80-byte record, such as
0414PK16J030 2S2016 05 11.73557 16 45 16.92 -18 23 51.3 9.3 T @0334C49 0414PK16J030 2s2016 05 11.73557 2 +0.92722889 +1.56624638 +0.67757352 @0334C49
with the second line giving the Cartesian coordinates of the spacecraft at that time, relative to the geocenter.
However, that only tells you the spacecraft position, not the velocity.
If you want to know the apparent angular velocity of the object as seen
by the spacecraft, or analyze timing errors or such, you're out of
luck. The
ADES format originally lacked a way to specify the spacecraft velocity,
but this was added in the 2022 version with
<pos1>-4531.3607016</pos1>
<pos2>-4505.7747238</pos2>
<pos3>2634.58943354</pos3>
<vel1>5.7317012679</vel1>
<vel2>-4.4881705657</vel2>
<vel3>2.1747779316</vel3>
<obsTime>2021-05-31T17:13:12.605Z</obsTime>
To get positions and/or velocities, you can cut/paste or upload astrometry (80-column or ADES) into my spacecraft offset adding tool. This will add spacecraft positions if those are missing. If you give it 80-column data, velocities will be added as comment lines. If you give it ADES data, vel# data as in the above will be added.
The positions and velocities come from JPL's Horizons system. You can look here for the C source code used for this service.
For 'traditional' 80-column data, the modified astrometry will look something like this :
COM add_off ver 2022 Dec 07, run Mon Sep 11 12:13:07 2023 COM vel (km/s) 2016 05 11.73557 -51.5292038 +25.8416189 +11.1465683 C49 0414PK16J030 2S2016 05 11.73557 16 45 16.92 -18 23 51.3 9.3 T @0334C49 0414PK16J030 2s2016 05 11.73557 2 +0.92722889 +1.56624638 +0.67757352 @0334C49 COM vel (km/s) 2016 05 11.74598 -51.5342103 +25.8328473 +11.1427764 C49 0414PK16J030 2S2016 05 11.74598 16 45 13.14 -18 24 39.0 9.0 T @0334C49 0414PK16J030 2s2016 05 11.74598 2 +0.92691906 +1.56640172 +0.67764053 @0334C49 COM 2 positions set by add_off; 0 failed in 0.01 seconds
The velocity will be provided for each spacecraft observation, as a "comment" just above the astrometry. Find_Orb will parse that appropriately, and you'll get actual angular motion, radial velocity, and along-track and cross-track residuals for the observations. In short, they will be handled just like any ground-based observation.