ESA’s first Delta-DOR (DDOR) tracking campaign took place recently with VEX (Venus Express spacecraft) using the IFMS systems, developed for ESA by BAE Systems (UK) and MakaluMedia GmbH (Germany), at Cebreros and New Norcia on 20th and 23rd December and a NASA DDOR measurement (Goldstone and Canberra) was made around 12hr after the ESA one on the 23rd. The IFMS DDOR datasets were then processed by the new correlator from the University of Rome while the NASA ones were processed by the existing JPL correlator.
The circumstances were not ideal as the actual VEX location is not known and so it is only possible to compare these orbit solutions. But, using reasonable assumptions for the NASA and ESA DDOR weightings, the current outcome of data processing shows that ESA DDOR residual in these measurements is around 3ns. This corresponds to an angle of around 80nrad over the 11500 km baseline between the two ground stations. These results are already satisfying, but ESA expect to improve the accuracy with better tropospheric modelling: since the baseline is so long, an object in common view is necessarily low as seen from both ground stations and so tropospheric refraction is significant.
Further DDOR tests will be taking place in the next few months but the key objective of having an ESA DDOR capability in time for VEX orbit insertion (April 2006) now looks assured.
For more information about MakaluMedia activities, please contact Mr. Fausto Roveda or Mr. Matt Henderson at mail@makalumedia.com.