Successful deployment tests for Rosetta
The hectic schedule of ground tests on ESA’s comet chaser has
continued in recent weeks as engineers at the European Space
Research and Technology Centre (ESTEC) in the Netherlands put
the Rosetta spacecraft through its paces.
The latest phase of these critical pre-flight tests has involved
checks of the various arrays and booms that will be extended from
the cube-shaped body of the Rosetta orbiter during its eight-year
trek to Comet Wirtanen.
Most critical of all were the deployment tests on the two giant
solar wings that will power Rosetta throughout its 10-year
mission to deep space and back. These arrays, each 14 metres in
length, are covered with more than 22,000 specially developed
silicon cells that are designed to operate in conditions of low
sunlight and low temperature up to five times the Earth’s distance
from the Sun.
The ‘minus-y’ array, located to the left of the dish-shaped high
gain antenna, was the first to be unfolded. This was followed a
day later by deployment of the ‘plus-y’ array on the opposite
side of the spacecraft.
Held in place by six Kevlar cables — a necessary means for the
hold-down of the arrays during launch — each solar array was
released after commands sent via the spacecraft activated the
deployment sequence. ‘Thermal knives’ severed the cables in turn
by heating them to a temperature of several hundreds of degrees
Celsius.
After the sixth cable was cut, the array began to unfold like a
giant accordion. Attached to a huge deployment rig specially
developed by Dutch Space (formerly Fokker), the five panels in
each array were gradually extended to their full length across
the clean room. In order to simulate the zero gravity conditions
of outer space, the weight of the arrays was supported by a mass
compensation device equipped with dozens of springs.
"Both tests went very well and there was a big round of
applause when they were successfully completed," said Walter
Pinter-Krainer, Principal AIV Systems Engineer for Rosetta.
Confident that their spacecraft’s powerhouse would deploy properly
after launch, the engineers went on to check out Rosetta’s other
movable parts. First came a partial deployment of the 2.2-metre-
diameter communications dish, when three explosive charges known
as pyros were fired to release the antenna from its stowed launch
position.
The engineers also had to retreat to the safety of an observation
area in the clean room for the firing of more pyros during the
deployment of the upper and lower experiment booms on the orbiter.
Each two-metre-long boom carries probes and other equipment that
will investigate the magnetic field and particle environment
around Comet Wirtanen.
The fifth and final deployment test involved the release of a
wire antenna to be used by the CONSERT experiment. After another
explosive charge was fired, this unusual, H-shaped aerial was
gently unfolded, suspended beneath five helium balloons in order
to simulate the weightlessness of space. Once again, the trial
was completed without a hitch.
"All of the deployment tests were very successful," commented
Walter Pinter-Krainer. "These were crucial moments in our test
programme and we were very happy to see everything working so
well."
Rosetta will be launched in just over six months’ time. The Ariane
5 launch from Kourou in French Guiana is scheduled for the night
of 12-13 January 2003.
USEFUL LINKS FOR THIS STORY
* 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=30222&ooid=30223]
CONSERT antenna deployment. The balloons allow the absence of
gravity to be simulated.
[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=30222&ooid=30224]
One wing fully deployed, the other one is in the stowed position.
[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=30222&ooid=30225]
One wing fully deployed.
