QUOTE (elakdawalla @ Oct 24 2005, 11:06 AM)
Excuse my ignorance, but what is the SPICE ekernel and how do you access it?
It's not exactly easy to use, generally requiring writing programs in FORTRAN or C. As far as I know NASA hasn't provided an easy to use public interface to the ekernel data. Here are the steps needed:
- go to
http://naif.jpl.nasa.gov/naif/toolkit.html and download the appropriate toolkit (for C, FORTRAN or IDL)
- after installing the toolkit a library (e.g., libcspice.a) will be available for linking programs to, as well as a few pre-compiled utilities
- To use the toolkit, data in the form of what SPICE calls "kernels" need to be downloaded from the NAIF website. For Cassini, these are at
ftp://naif.jpl.nasa.gov/pub/naif/CASSINI/- Once the required kernels are assembled (a tricky process) then programs can be written to do things like give the position of the spacecraft, planets. moons, etc. There are some tutorials at:
http://naif.jpl.nasa.gov/naif/tutorials.html- As for the ekernels ("event kernels"), they give information as to the science plan activities and objectives, notes, etc. The ekernels are accessed with a query language much like SQL. For example, here a some queries used:
select observation_id,sequence,observation_title,science_objective,subsystem,notes from cassini_sp_observation
select begin_time,end_time,pointing_agreement,primary_pointing,request_id,request_title
req_description,secondary_pointing,sequence,subsystem from cassini_sp_request where request_id = \"%s\
Luckily, the Cassini project has pretty detailed ekernels. The Mars Reconnaissance Orbiter project in contrast has elected not to fund ekernel development. Maybe it has something to do with the former being a classic NASA project and the latter run by Lockheed?