Station Software Inputs
Station Software Inputs
The two station inputs, the Space Radio-Telescope Schedule (SRS), and satellite orbit prediction, are described by specifications between the tracking station and the other mission elements. Below, a schematic diagram shows the relationships of the offline and realtime inputs:
The HALCA/VSOP control group at ISAS in Japan provids the SRS file for Green Bank and all other mission elements. The SRS file contains a high level summary of events for all mission elements. Each event in the schedule contains a precise time tag of when the event should be completed.
The SRS file is parsed by an OVLBI offline program called SCHEDCO, to schedule convert into the "command" syntax used by the OVLBI real-time control system.
The latest copy of the SRS specification is kept on-line. A users guide describes arguments provided to the program by the operators.
The JPL orbit determination groups provides twice weekly updates to the satellite orbit predictions. Each orbit prediction covers a one week period, and is provided in the "Spacecraft Planet Kernal" (SPK) format. The files is in a binary format and the Navigation Ansillary Information File (NAIF) software libraries are required in order to parse the predictions. An offline task, called ORBITCO, converts the binary satellite prediction into an ascii table of ranges, range rates, azimuths and elevations versus time.
The calculation of the satellite range, range rates, azimuth and elevation requires both accurate knowledge of the satellite and tracking station position. The tracking station position is determined from surveying relative to well known positions on the site and from precise calculations of the earth rotation model. The earth rotation model requires estimates of the difference UT1 and UTC and the number of leap seconds.
The orbit prediction format is described in the NAIF documents. Some information is kept online, in the form of programming guides. A users guide describes arguments provided to the program by the operators.
Return to the Station Software Guide. The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
glangsto@nrao.edu tminter@nrao.edu