Citation
Abstract
The density of radio sources near the ecliptic in the astrometric JPL Very Long Baseline Interferometry (VLBI) catalog has been increased by over 50 percent since 1985, This density increase has been driven by the need for more sources for the VLBI navigation of the Magellan and Galileo spacecraft, but the sources also will be usable for Mars Observer and other future missions. Since the last catalog, including observations made through 1985, was published in 1988, a total of 21 radio sources has been added that fulfill the following criteria: (1) they lie within 10 deg of the ecliptic plane; (2) their correlated flux densities are above 0.2 Jy on at least one of the Deep Space Network intercontinental baselines at both 2.3 and 8.4 GHz; and (3) the source positions are known to better than 5 milliarcseconds (25 nanoradians). The density of such sources in the catalog has been increased from 15.6 per steradian to 25.2 per steradian. Ten more sources have been added that fulfill the last two criteria given above and lie between 10 deg and 20 deg from the ecliptic plane. Analysis shows that there may be ~70 more sources with correlated flux densities above 0.2 Jy that are within ~20 deg of the ecliptic. However, VLBI navigation observations of the new and prospective sources with the 250-kHz bandwidth of the current operational system will require the use of two 70-m antennas in most cases. Including both old and new sources, if two 34-m antennas are used, there will be usable navigation sources within 10 deg of a spacecraft in only 30 percent of the ecliptic, and sources within 20 deg of a spacecraft over 70 percent of the ecliptic. If one 70-m antenna were used along with a 34-m telescope, or if a somewhat wider bandwidth system such as the Mark II VLBI system (effective bandwidth of 1.8 MHz) were used with two 34-m antennas, usable navigation sources would be within 10 deg of a spacecraft over about 65 percent of the ecliptic. Within 20 deg of a spacecraft, usable sources would exist over 98 percent of the ecliptic.
Details
- Volume
- 42-100
- Published
- February 15, 1990
- Pages
- 274–300
- File Size
- 1.6 MB