1. 10/31/2006VSOP-2 Tracking Station Meeting 1 Lessons Learned From VSOP-1 Larry R. D’Addario JPL

2. 10/31/2006VSOP-2 Tracking Station Meeting 2 Operations Files The global schedule file was important. –The full schedule should be available to all mission elements, not sub-schedules for each. Mission operations should not produce multiple files with the same information but in different formats –Files specific to a mission element should be the responsibility of that element. –This includes, for example, orbit files (predicted and re-constructed). All files should be available to all mission elements, –even if they will normally be used by only one –For example, each tracking station log is needed mainly by one correlator, but should nevertheless be available to mission operations, other correlators, and other tracking stations. –This feature costs nothing extra, and no harm is done if it is never used, but if an interface not considered at the beginning is later found to be needed, it will be hard to add.

3. 10/31/2006VSOP-2 Tracking Station Meeting 3 Satellite Simulators Pre-launch compatibility tests,using a portable satellite simulator, were valuable for tracking station checkout in VSOP-1. –The simulator, built by the spacecraft designers, was brought to the tracking station sites for tests with the actual tracking station hardware. –An alternative might be for portable tracking station simulators, built by the station designers, to be brought to Japan for tests with the actual satellite hardware. Tracking stations also need a local satellite simulator for station verification at other times –after maintenance or modifications –perhaps before each pass

4. 10/31/2006VSOP-2 Tracking Station Meeting 4 GB Station Showing Sat Sim Connections

5. 10/31/2006VSOP-2 Tracking Station Meeting 5 Satellite Simulator Block Diagram

6. 10/31/2006VSOP-2 Tracking Station Meeting 6 Fault Detection Principle: Each mission element must check itself, and should not rely on feedback from other mission elements. Specifics: –Spacecraft health data should be transmitted from tracking stations to mission operations in raw form, allowing spacecraft experts to analyze it. Nevertheless, tracking stations may attempt to analyze the data and detect faults (and, indeed, they may need to do so in order to distinguish them from faults in the tracking station). Anomalies discovered should be logged. –Tracking stations should implement internal checks as much as possible, and should report detected faults or anomalies in their logs. They should not rely on correlators to analyze their data and report back. (In VSOP-1, an attempt was made to provide extra information in time correction files for this purpose. It was never used. Jon still owes me $20.)

7. 10/31/2006VSOP-2 Tracking Station Meeting 7 Time Correction The time correction file, generated by tracking stations and used during correlation, worked well for VSOP-1. Schemes that apply time corrections to the data in real time, or that create a closed-loop correction via the uplink signal, are risky and should not be attempted. Multi-frequency two-way timing signals would allow ambiguity resolution. Worth the trouble? VSOP-1 showed that the time transfer process did not degrade coherence of the ground-based H maser; hence an on-board H maser is not a reasonable alternative.

8. 10/31/2006VSOP-2 Tracking Station Meeting 8 Commonality It would be better to have just one design for the space- VLBI-specific components of all tracking stations. –In VSOP-1, there were three independent designs. It would be better to have just one kind of recording system for all tracking stations and all ground radio telescopes. It would be better to have only one correlator doing all VSOP-2 processing.