Orbiting VLBI Link Stability for 97 May
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 May 20 -- VT134 -- 1823+568
HALCA First Fringes with NRAO 140ft.
"First fringes" is the first alignment in time of astronomical signal
from HALCA throught the Green Bank Earth Station and the NRAO 140ft telescope
in Green Bank, WV. After this signal alignment, extreamly high angular
resolution images of the radio sources are made.
Observations from 97 May 20, 06h30m to 10h08m UTC.
97 May 22 -- VT136 -- 1519-273
HALCA First Fringes with NRAO VLBA.
Observations from 97 May 22, 03h06m to 06h20m UTC.
A detailed description of the observation can be obtained from
97 May 31 -- VT800 -- 1156+295
Fringes were found in this VLBA experiment. Unfortunately after the
first 10 minutes of this experiment, the
residual phase data were corrupted due to hardware problems.
Green bank Tracking ran from 97 May 31 21h02m to 23h27m.
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