Orbiting VLBI Link Stability for 97 June

For the VLBI observations using the Green Bank Earth Station, the experiment is summarized and the link stability is plotted below. The plots of link stability indicate the difference between the predicted and measured 14.2 GHz downlink from HALCA. This down link frequency difference is expected to be different from zero, due to errors in the satellite orbit prediction and troposhere and ionospheric effects. The frequency errors are typically on the order of a few Herz, indicating the frequency error at the satellite is a few parts in 15,000,000,000.

The frequency residuals are used to produce a time corrections file applied to the data at correllators and by the JPL orbit determination group to calculate the satellite orbital parameters.

For each tracking pass below, two plots are produced:
Residual Frequency
The difference between the predicted and measured down link frequency is ploted versus time. (The Time axis is truncated MJD, which is MJD - 50000.). The difference is usually a few Hertz, indicating the satellite orbit prediction is very good. The frequency is slope of a linear fit to the downlink cycles during a two second interval.
RMS Frequency
The uncertainty of the slope of the linear fit to the downlink cycles indicates the quality of the two way link to the satellite. Typically, the RMS level is better than 0.02 Hz.

97 June 01 -- VT800 -- 1156+295

No fringes were found in this VLBA experiment. The HALCA/VSOP downlink was not commanded until 06h18m, but unfortunately there were troubles with the station software which delayed data recording until almost 06h30m. The VLBA stopped observations at 06h30m. Green bank Tracking ran from 97 June 01 05h28m to 06h41m.

97 June 14 -- VT804 -- 1124-186

Fringes were found in this L-band experiment (1648 and 1664 MHz). Green Bank Tracking ran from 97 Jun 14 10h22 to 10h50m. Data were recorded on both VLBA and S2 Tape.

97 June 14 -- VT151 -- 1124-186

Fringes were found in this L-band VLBA experiment. Green Bank Tracking ran from 97 JUN 14 19h35m to 23h36m.

97 June 19 -- VT154 -- 1730-130

Fringes were detected in this experiment. The VLBA recording was done automatically. The operators were present only for the beginning of this tracking pass. Green Bank Tracking ran from 97 JUN 19 02h30m to 5h12m.

97 June 22 -- VT805 -- 1730-130

Tracking pass appeared successful. The S2 recording was manually started. The pass in Green Bank was on 97 June 22 from 8h39m to 9h19m. The cryogenically cooled Ku band front-end had warmed before this pass, but the signal-to-noise ratio on the link allowed good two way link to the satellite.

97 June 26 -- VT806 -- 3C273

The tracking pass appeared successful, except that the frequency residuals were larger than usual. Tracking in Green Bank runs from 97 June 26 21h42m to 2h17m.

97 June 27 -- VT806 -- 3C273

Tracking in Green Bank runs from 97 June 27 5h56 to 9h09m.

Other Web Sites

Return to the NRAO Green Bank Tracking Station page.

VSOP/HALCA has a home page. The VLBA Correlator NRAO Socorro is developing other hardware and software for the NASA OVLBI project. There is a Space VLBA Correlator home page as well.

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
Last update: 97 July 2