The European delta-DOR correlator.
- Paper number
IAC-06-B3.1.05
- Author
Prof. Luciano Iess, University of Rome "La Sapienza", Italy
- Coauthor
Mr. Ricard Abello, European Space Agency/ESOC, Germany
- Coauthor
Dr. Alessandro Ardito, University of Rome "La Sapienza", Italy
- Coauthor
Dr. Giovanni Comoretto, INAF - National Institute for Astrophysics, Italy
- Coauthor
Mr. Marco Lanucara, European Space Agency/ESOC, Germany
- Coauthor
Dr. Roberto Maddè, European Space Agency/ESOC, Germany
- Coauthor
Mr. Mattia Mercolino, European Space Agency/ESOC, Germany
- Coauthor
Dr. Gabriele Rapino, University of Rome "La Sapienza", Italy
- Coauthor
Mr. Massimo Sensi, University of Rome "La Sapienza", Italy
- Coauthor
Prof. Paolo Tortora, University of Bologna, Italy
- Year
2006
- Abstract
The determination of the angular position of interplanetary probes by means of VLBI techniques has been pioneered by NASA over the past decade. This powerful method, usually called delta-Differential One-way Ranging (delta-DOR) or delta-VLBI, uses a quasar of known celestial coordinates to syncronize clocks at two ground antennas and phase delay measurements of the spacecraft signal to infer the angular position of the probe in the plane containing the baseline vector. By combining observations from multiple baselines and ground stations the spacecraft celestial coordinates are measured to an accuracy of a few nanoradians. Being almost independent from the dynamical model, delta-DOR is a valuable observable quantity for spacecraft navigation in the interplanetary cruise phase, where gravity gradients are small and single dish Doppler and range measurements are less effective in providing a good determination of the state vector. The European Sapce Agency and the University of Rome La Sapienza have undertaken the development of a software correlator for the analysis of delta-DOR data acquired by ESA 35-m deep space stations in New Norcia (Australia) and Cebreros (Spain). By using precise earth orientation parameters and a model of the spacecraft dynamics, the correlator determines the time delay in the arrival of the quasar and spacecraft wavefronts at the two intervening antennas. These quantities are then processed by an orbit determination code to improve the spacecraft ephemerides. The correlator has been validated using observations of the spacecraft Rosetta, Mars Express and Venus Express. By comparing the delta-DOR observations with the known orbit of Mars Express about the planet (determined to an accuracy of a few hundred meters from Doppler measurements), the residual delays are less than 0.5 ns, corresponding to a maximum angular error of 15 nanoradians (i.e. 2.25 km at 1 AU). A judicious choice of the reference quasar leads to significantly smaller residual delays. The attained precision is adequate for all anticipated navigational needs of ESA deep space probes.
- Abstract document
- Manuscript document
IAC-06-B3.1.05.pdf (🔒 authorized access only).
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