Station Software Guide

The Orbiting VLBI Tracking Station at NRAO Green Bank West Virginia, supports the Japanese HALCA/VSOP satellite as a part of the NASA/JPL Deep Space Network. The station also will support the Russian Radioastron mission. The tracking station runs semi-autonimously, requiring the operators to only periodically initiate a command sequence, mount/dismount VLBI tapes, and check system status.

Below, the inputs and outputs to the tracking station control computer are described, and the software methodology used for controlling the station outlined. In order to understand the software guide, a few terms are defined and and software design principles are given:


Methodology and Notes

The OVLBI software was developed based on the VLBA software system. In order to keep track of changes unique to OVLBI a methode of tracking the different software revisions was implimented using the SCCS system.


The input pre-processing, realtime tasks and output post processing are described in the following sections. The two station inputs from external sources are first processed "offline" before use in the "real-time" system.

There are 5 output file specifications, which are produced from the real-time logs and the phase residuals measured during the tracking pass.

Station Inputs

There are only two inputs to the station; a Space Radio-Telescope Schedule (SRS) file, and a satellite orbit prediction. The two station inputs are described by specifications between the tracking station and the other mission elements.

Real Time system

During tracking passes, all stations functions are coordinated by a single MVME147 single board computer. Many station tasks controlling the real-time operations run simultaenously.

At the beginning of tracking passes, all needed command files and satellite orbits are copied to the real-time hard drive. After the initial files are copied, then no offline files are needed during the tracking passes.

During the tracking pass, the real-time logs are copied offline every 15 minutes. If the site ethernet or some other offline component has failed, there should be no loss of real-time log data. Also during the tracking passes, the "status" file is regularly updated. The status file contains an ascii description of the station activites.

After the tracking pass, all the phase residual data are copied are copied offline. The final output files are created offline after the tracking pass has ended.

Station Outputs

The station outputs are created from the realtime logs and from the phase residuals measured during the pass. During the tracking passes, the HALCA telemetry data are extracted every 15 minutes and placed in an anonymous ftp area for "near-real-time" access to the state of the satellite.

All other offline data files are produced after the tracking pass is finished. The first step in creating the output data files is merging the 15 minute length logs into a single log file for the entire days log entries. Next the tracking pass for the day are summarized. The station operators generate the other output data files based on the tracking pass summary.

Offline Cron Jobs

Both of the station inputs are automatically retrieved from the source by offline system "cron" jobs, which periodically search for new station inputs. If new inputs are found, the cron jobs run to retrieve and process the inputs.

The station logs are automatically merged each day to produce a single log for the days events. The summary of tracking pass events is also generated by a cron job and e-mailed to the tracking station staff.

Software Methodology

The software methodology for realtime and offline have some similarities and differences. The station software is developed in a unix workstation envirionment. Almost all station code is written in C, and is extensively commented. Changes to all code and many documents are kept track of using the SCCS revision control system.

Software Documentation

Online documents describing the input specifications, designs, and user mannuals are kept with the Input, Realtime and Output descriptions. The primary interace documents are kept at ISAS . However, some clarifications to the specifications are kept in local documents.

Diagnostic Software

The use of diagnostic software is an important part of station maintainence. The regular use of plotting functions is needed to assure good quality link to the satellite is maintained.

Return to the station home page. The National Radio Astronomy Observatory (NRAO) is a facillity of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Last update: 97 July 1