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
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.
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
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:
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
- 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.
- 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.
- The MOSS server is down.
If this is the case then you should send e-mail to email@example.com
and let us know that the server for MOSS in APT appears to be down.
Last modified: May 14, 2013.