Cluster FM7 gets a long-distance call
28 May 1999
How can anyone be sure that communications between the four satellites and the Earth will not break down once the Cluster II spacecraft are placed in orbit? The obvious answer is to test the system and see whether itworks.This is exactly what has been taking place during a series of System Validation Tests over the past four days (25-28 May). Engineers at the European Space Operations Centre (ESOC) in Darmstadt, Germany, have been communicating with the Flight Model (FM) 7 spacecraft, 300 km away at the Friedrichshafen facilities of Dornier Satelliten Systeme.
The aim has been to test and validate as closely as possible the communications loop which will be established after launch next summer. During the two year mission, instructions from the ground will be transmitted to the Cluster II spacecraft by controllers at ESOC, and data from the spacecraft will be sent back to ESOC.
This loop has been replicated with FM7 by sending data at 64 kilobits per second through ISDN phone lines between ESOC and Friedrichshafen. The data is sent through a replica ground station (known as a network data interface unit) at the Dornier end of the link. It then appears on screens at the mission control centre in ESOC, where it is interpreted by the Cluster II Flight Control Team.
"The results have been excellent," said Manfred Warhaut, the ESOC Ground Segment Manager. "The system has performed exactly as anticipated, in particular the payload instruments."
"This is a very important test for us because we we have few opportunities for access to the spacecraft," he added. "It enables us to obtain 'end-to-end' validation of the ground segment system and also provides valuable hands-on experience for the members of the control team who have joined us since Cluster I."
A similar test has already been conducted for FM6, but this was completed using the old Cluster I procedures. The recent test is the first to use the updated experiment procedures which will be used for Cluster II.
Identical System Validation Tests will be conducted for FM8 at the end of September, and for FM5 in late November.
