SOURCE is used to specify the source name. It is required for the first scan and whenever there is a change. The name must match, in a case-insensitive sense, one of the names of a source in the source catalogs (recall that 5 different names or aliases are allowed for each source).
SOURCE may be the name of a Solar System object. If so, if an EPHFILE: has been specified, and if the object is not in the source catalog, SCHED will determine the position and planetary motion of the object using a JPL ephemeris. This position is very good -- certainly good enough for use for pointing which is the primary use envisioned (note that much work would be required on the correlator to correlate planetary observations). There is a similar capability for pointing at satellites using orbital elements in SATFILE:.
The Solar System objects that SCHED understands are Mercury, Venus, Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, and Sun. Topocentric positions and rates will be provided for VLBA antennas if one of these is specified. Geocentric positions along with rates and horizontal parallax are provided for the PM cards for the VLA. Note that SCHED does not understand how to specify moving objects to antennas that don't use the VLA or VLBA control file types. Specifically, solar system sources are not currently supported for VEX output files.