Students 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.

USEFUL LINKS FOR THIS STORY

* Successful deployment tests for Rosetta
http://spdext.estec.esa.nl/content/news/index.cfm?aid=13&cid=36&oid=30222
* More about Rosetta
http://sci.esa.int/rosetta/

IMAGE CAPTIONS:

[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=30292&ooid=30295]
Rosetta was subjected to an extensive check in the Compact Test
Range. The Compact Test Range is a large test chamber at the
European Space Research and Technology Centre (ESTEC) in
Noordwijk, the Netherlands.

[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=30292&ooid=30293]
Rosetta cocooned in the Compact Test Range.