Citation
Abstract
The accuracy of tracking measurements using very long baseline interferometry (VLBI) is seriously limited due to angular and temporal separation between the calibration and spacecraft measurements. Same-beam interferometry, in which the calibration source is in the same primary beam as the spacecraft being observed, eliminates temporal effects and, because of the reduced angular separation between the calibrator and the spacecraft, considerably reduces calibration errors. With the current measurement methods, this requires having a suitable calibration source with enough signal strength within the primary beam of the antennas used for the interferometry measurements. Normally such sources are not available because of the low density number of suitable strong calibration sources. However, there are many more weaker calibration sources, and it may be possible to use a combined signal from a number of weaker sources within the primary beam of the antennas if a single strong source is not available within the primary beam at any time. The probability of having enough combined total signal increases considerably if we accept using multiple calibration sources. The expected accuracy of a tracking measurement using a signal from multiple calibration sources should be similar to the accuracy expected with a single calibration source within the beam, if the total combined signal from the individual weaker sources is similar to the desired single source. An important point that is worth noting here is that if we want to take advantage of utilizing same-beam interferometry for accurate spacecraft tracking most of the time, then the diameter of the DSN Array antennas should be limited to as small a value as practical to give a large field of view. This will enable having suitable calibration source(s) within the primary beam of the antennas. Considering practical aspects, it appears that the diameter for a DSN Array antenna should be limited to a maximum of about 12 m.
Keywords
Details
- Volume
- 42-171
- Published
- November 15, 2007
- Pages
- 1–6
- File Size
- 69.9 KB