Rosetta passes compatibility test
17 July 2002Students approaching the conclusion of lengthy academic studies will have considerable sympathy with ESA's Rosetta spacecraft as the end-of-course examinations just keep on coming!
After successfully completing deployment tests on its solar arrays and booms at the end of May, ESA's comet chaser was moved into the Compact Test Range, a large test chamber at the European Space Research and Technology Centre (ESTEC) in the Netherlands, where it was subjected to an extensive electromagnetic compatibility (EMC) check.
In order to simulate the EMC environment during its long trek through deep space, Rosetta was placed inside a chamber lined with cones that absorb radio signals and prevent reflections. To avoid TV or radio interference, the walls of the chamber form a steel 'Faraday cage', impenetrable to electromagnetic signals from the outside world.
In this radiation-free environment, the ESTEC team was able to study the radio signals and electrical noise coming from the various systems on the spacecraft and to check whether they caused any electromagnetic interference with each other.
"Before a satellite is launched it is essential to ensure that the electrical and electronic equipment within a spacecraft functions correctly," explained Flemming Pedersen, one of the senior AIV engineers for Rosetta. "For example, it could be fatal if, when switching on one instrument, other instruments or systems such as the telecommunication links were disturbed or even disrupted."
Cocooned in the chamber
Like some alien creation, the spacecraft was cocooned in protective plastic foil while the engineers and scientists painstakingly prepared to switch on Rosetta's systems and payloads. At first, the see-through wrapping proved to be too tight and caused a minor interruption to the proceedings.
"Not enough air was flowing over the louvers (radiators), so the spacecraft was slowly getting too warm," explained Pedersen. "We had to partially open up the foil to improve the air circulation."
Once the temperature was under control, and the staff were cleared from the chamber, all was set to simulate the various phases of Rosetta's 10-year mission of exploration.
"For some of the time we were measuring the energy emitted by the spacecraft's high gain antenna, and this is hazardous, so the chamber was completely closed and everyone had to remain outside the chamber whilst the measurements were made," said Walter Pinter-Krainer, the Principal AIV systems engineer for Rosetta. "It would be like exposing the engineers to the radiation from thousands of mobile phones simultaneously."
The first series of tests studied how the spacecraft behaved in 'launch mode'. At this time Rosetta was in its launch configuration, with a minimum of systems active, while awaiting the lift-off of the Ariane-5 rocket. This was to ensure that signals from the spacecraft would not interfere with communications between the rocket and ground control during the launch phase.
Subsequent EMC tests took place when the spacecraft was at various levels of activity - from quiet periods when no science payload were operating to spells of hectic scientific investigation.
"We could switch on each instrument individually and measure the electromagnetic waves coming from it," explained Pedersen. "The rest of the instruments were put into listening mode to see if any of them detected any disturbance."
"On other occasions we switched on all of the instruments, including those on the Lander, in order to see whether we got any unexpected 'noise' or interference," he said.
"From this we can determine whether we need to switch a particular instrument off when we are making a very sensitive measurement with another instrument," he added.
"Since the entire set of Rosetta payload will not normally be operated simultaneously, the tests demonstrated that the spacecraft is very robust and capable of operating at higher data traffic loads than will ever be experienced in the actual mission."
"All of the EMC tests proved to be very successful," said Pedersen. "This was the last of the three big system validation tests and Rosetta passed with flying colours. We did not experience any unexpected measurements or major interference between the different instruments, and the results were within expectations for all of the tests."
Rosetta is scheduled for shipment to Kourou spaceport in French Guiana during early September. The Ariane-5 launch is scheduled for the night of 12-13 January 2003.