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
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
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
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
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
to the NRAO Green Bank Tracking Station page.
VSOP/HALCA has a home page.
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
is a facillity of the
National Science Foundation
operated under cooperative agreement by
Associated Universities, Inc.
firstname.lastname@example.org Last update: 97 July 2