SETI bioastro: Fw: Critical Thermal Tests Begin For Rosetta Comet Chaser

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Date: Fri Feb 22 2002 - 08:47:16 PST

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Subject: Critical Thermal Tests Begin For Rosetta Comet Chaser

Critical thermal tests begin for Rosetta comet chaser
European Space Agency
February 21, 2002

With less than 11 months to launch, the most
advanced spacecraft ever to visit a comet is about to begin a
critical series of thermal tests at the European Space Research
and Technology Centre (ESTEC) in Noordwijk, the Netherlands.
These tests will play a vital role in ensuring the success of ESA's
Rosetta mission to unravel the mysteries of Comet Wirtanen.

During its 10-year, 5 billion kilometre mission of exploration,
the Rosetta spacecraft will be subjected to extreme temperature
changes as it flies from the benign environment of near-Earth
space to the dark depths of the Solar System beyond the asteroid belt.

In order to ensure that Rosetta will survive this hazardous trek -
the cosmic equivalent of travelling from the sizzling deserts of
North Africa to the frozen wastes of Antarctica - the spacecraft
has now been installed in the largest thermal vacuum chamber in
Europe, where every part of the Orbiter and Lander will be
alternately baked and frozen inside an airless room.

"These are the most critical tests in our entire pre-launch
programme because they reproduce the conditions that Rosetta
will experience in flight," said Rosetta Payload and Operations
Manager, Claude Berner.

The three-week-long series of thermal tortures began on 20
February, when engineers started the lengthy process of
removing air from the giant chamber. In order to create a vacuum
equivalent to that of deep space, this 'pumping down' was
expected to take more than one day.

Once the depressurisation is completed, the so-called 'thermal
balance - thermal vacuum' tests can begin. Perched on a gimbal
system - a table that can both tilt and rotate - the position of
the spacecraft will then be adjusted so that every phase of its
complex flight plan can be simulated.

"We will be working in three shifts, around the clock, to examine
the condition of the spacecraft during simulations of 15 different
mission phases," said Claude Berner. "This means we will have to
manoeuvre it into specific attitudes that represent critical parts of
the mission in terms of exposure to heat or cold."

During three circuits of the inner Solar System, the amount of
solar radiation reaching Rosetta will vary by as much as 25 times.
The period of maximum heating, which will take place near the
Earth, is simulated by using mirrors and powerful lamps. These
will expose different parts of the spacecraft to temperatures
exceeding 150C.

In order to simulate the cold of deep space, where the
temperature drops well below -100C, liquid nitrogen will be
pumped through pipes in the chamber walls. More than 100
active sensors will be monitoring the responses of the
spacecraft's systems and instruments during this punishing

"We want to make the tests as realistic as possible, so we are
testing the full flight configuration of Rosetta in the chamber,"
explained Claude Berner. "The spacecraft is blanketed by
layers of aluminised kapton that provide insulation against
extreme cold, while onboard radiators will be expected to
expel excess heat."

"We even have simulated propellant in the fuel tanks to see
whether any leakages occur," he added. "It is also important
to discover how much outgassing from the spacecraft
structure takes place as the temperature changes."

The Rosetta team expects the thermal tests to be
completed in the second week of March.

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