How APT Processes Solar System Targets

How, in general, does APT determine the schedulabity of Solar System targets?

When APT was first released, the Visit Planner assumed that anything related to a planet (the planet itself, a moon, a surface feature, etc.) had the ephemeris for the planet. Comets and Asteroids were not supported at all. Furthermore, any observing constraints specified as Solar System Target Windows (e.g. angular separations, orbital longitudes, CMLs) were ignored by the Visit Planner for all targets - even ones in planetary systems.

Currently, as long as there is an internet connection, APT will use MOSS (Moving Object Support System) to compute a precise ephemeris for each target regardless of its location. Targets in planetary systems are no longer approximated by the ephemeris of their parent planet. Asteroids and comets are now fully supported. Solar System Target Windows are now computed for all targets and displayed as the Moving Target constraint in the Visit Planner.

How does MOSS processing in APT work?

When you run the Visit Planner on any visit which observes a solar system target, APT will first automatically attempt to run MOSS. No special effort is needed on the part of the user. This requires an internet connection, and can take some time, from as little as a minute for a simple target or up to possibly 10 minutes for a more complicated target. If you have multiple visits with complicated targets you may wish to run a single visit through the Visit Planner first, to see how long it will take.

When will MOSS reprocess?

If you rerun the Visit Planner after making a change to a solar system target, that target will automatically be reprocessed first with MOSS. But if you rerun the Visit Planner without having made a change to the target, MOSS will not be rerun.

Error conditions

Syntax errors (denoted by red Xs) in a solar system target specification should be corrected before attempting to run the Visit Planner. If you neglect to do this APT will not run the MOSS system.

During MOSS processing if you get this pop up message:
 Unable to contact STScI submission server. Please check your network
 connection. If you are behind a firewall try turning on the 'Force
 HTTP' option in the APT Preferences.
it could mean one of three things:
  1. You are not connected to the internet.

    If this is the case and you can simply plug back into the internet and click the OK button on the pop up. Processing should proceed.

  2. Your firewall is interfering with the connection.

    This is identical to the issue that some people have with accessing the address database and submitting.

    Note that if you end up having to use "Force HTTP" to get around firewall issues you could end up with a time out error for sufficiently complicated targets.

  3. The MOSS server is down.

    If this is the case then you should send e-mail to and let us know that the server for MOSS in APT appears to be down.
After you acknowledge the error generated by one of the above three failures, Visit Planner processing will continue. It will attempt to run MOSS once more (in case the problem has been corrected), and if that is not successful, it will fall back to using MOSS products from a prior run (if available) or, finally, using the default planet ephemerides that were used for all solar system targets prior to the release of APT 15.2.
Last modified: May 14, 2013.