Huygens communications package under investigation

During an extensive in-flight end-to-end telecommunications test conducted in early February 2000,
characteristics of ESA’s Huygens-Cassini communications link were observed which had not been
previously measured. The test was a more extensive calibration at system level than the one which had
previously been undertaken.

The outcome of the link characteristics would be that not all the data generated during the
descent and landing would be decoded by the Huygens receivers on-board Cassini.

Following the discovery, extensive ground testing of the link was performed in early September using the ground testbed located at ESA’s operations centre (ESOC) at Darmstadt (D). These tests have confirmed that the existing link would not support full data recovery under the currently planned mission scenario.

These results have been fully discussed with the NASA/JPL Cassini Program Office with a view to identifying scenarios to enable full data recovery during the mission. Several options are currently under study between the Cassini/Huygens team which would allow the science of the Huygens mission to be fully realised. A plan of action is intended to be in place by Summer 2001 by which time all options will have been thoroughly reviewed and tested and the optimal course of action identified.

ESA’s Director of Science, R. M. Bonnet, has initiated an enquiry board to ascertain why these link characteristics were not identified prior to launch and to ensure that the Huygens science will be fully realised and that future ESA missions utilising similar hardware are alerted to the problem.

Note for Editors

The link margins are degraded due to Doppler shift on the data sub-carrier being outside the bandwidth of the receiver phase-lock loop. In essence this means that there could be up to 10dB extra loss in the link compared to that assumed for the mission. Verification before launch was achieved by a mix of analysis and ground testing, this parameter was not isolated during the verification process.

Potential options for recovering the situation range from a greater fly-by distance, slower orbiter approach to tracking of the probe, all of which would lead to an increased signal level with a reduced Doppler shift enabling the data signal to remain with the existing Huygens receiver phase lock loop bandwidth. Such changes to the baseline mission scenario need full risk assessment and agreement of both NASA and ESA.

The selected scenario will take full account of the need to maintain the unique science objectives of the Cassini/Huygens mission.

For more information, please contact:

Mr. Hugo MarÈe
ESA Science Programme Communication Service
ESTEC, Netherlands

Tel: +31 (0)71 565 4604
Fax: +31 (0)71 565 7236

ESA Headquarters, Paris Tel: +33 (0)1 53 69 7106
Fax: +33 (0)1 53 69 7690