ESA Science News

In Turin today the Italian satellite builder Alenia Aerospazio presented two
ESA spacecraft that will explore the near and far Universe: Integral, the
gamma-ray observatory, will gather the most energetic radiation coming
from distant objects. Rosetta, the comet chaser, will bring new insights in the
formation of our solar system.

In the company’s large clean rooms in Turin journalists could have a look at
the impressive models of the scientific satellites and get an idea of the
elaborate test campaigns that engineers need to complete in order to reduce the
risk of failure at launch or in space.

Integral integration started

For Integral, the International Gamma-Ray Astrophysics Laboratory, the
integration of the real satellite began this autumn, to be ready for a launch in
October 2001. The spacecraft is basically made up of two parts, the Service
Module and the Payload Module. In Alenia Aerospazio’s clean room integration
of the so-called Flight Model of the Service Module is well under way.

The Service Module is the lower part of the spacecraft and houses the satellite
systems including solar power generation, telecommunications and attitude
control systems. It consists of a central cone providing the interface with the
launcher surrounded by side panels containing the service elements. To keep
the costs low, the engineers made maximum reuse of hard ware developed for
ESA’s X-ray satellite XMM, due for launch this December. “The principle of
reusing hardware of XMM worked beautifully”, said Integral Project Manager
Kai Clausen. “That really is a success story.”

The flight units for the Integral Service Module are built by different
European companies and will be delivered to the Turin plant within this year.
First tests of the Service Module are expected for February 2000. As ESA’s
industrial prime contractor for the Integral mission Alenia Aerospazio is
responsible for the design, integration and testing of the satellite.

Next to the Integral Service Module a 4-m high, H-shaped black structure is
waiting for further integration. This is the backbone of the Payload Module,
the upper part of the satellite, which will carry the scientific instruments
and associated electronic equipment. It is made of strong and stiff composite
material. The instruments are provided and financed by consortia led by
scientists in different European countries. In return the scientists will get
precious observation time. ESA will also get the Integral launcher, a Russian
Proton, for free in return of one fourth of the observation time.

Besides the Integral Flight Model the visitors of Alenia Aerospazio could view
two Integral Models exclusively built for testing. The Structural Thermal
Model (STM) looks almost the same as the real spacecraft. Last year the STM
test campaign showed that the satellite would meet the stringent mechanical
and thermal requirements.

The Engineering Model (EM) was built to verify that all satellite subsystems
and instruments interface well and function as a system. This test campaign
was successfully completed in August and
demonstrated that the Integral satellite functions and is strong enough to
withstand electromagnetic interference. Meanwhile the models of the
scientific instruments of the Integral EM have been taken away and sent back
to the research institutes that provided them. The delivery of the real
instruments for the Flight Model is expected throughout the period May to
September 2000.

Rosetta model completed

In addition to Integral another ESA satellite was on show in Turin. 24
November was the final opportunity to view the Rosetta spacecraft’s
Structural and Thermal Model before it is packed and sent to ESTEC in the
Netherlands for testing.

For the past three and a half months the 1.4 tonne STM of Rosetta has been
painstakingly assembled by technicians at the Turin plant of Alenia
Aerospazio. “They have done a fantastic job,” said Rosetta Project Manager,
Bruno Gardini. “We are delighted with the way they have overcome all
difficulties to complete the STM on time.”

The box-like STM structure, 2.8 m high and more than 2 m wide, is
practically identical in size and shape to the spacecraft which will set off for
Comet Wirtanen in 2003. For example, the STM has the same thermal
blankets that will protect the flight model against the temperature extremes
of deep space. The scientific instruments,
although not functional, are high-fidelity replicas of the flight hardware.

However, there are some significant differences. For example, there is only
one deployable solar array (the other is a dummy), the
electronics boxes are empty and only one attitude thruster works. Although
the fuel tanks can be pressurised, they will be filled with water instead of
propellant during vibration testing.

The next stage on Rosetta’s long road to launch will be transportation of the
STM to Noordwijk during a five-day trek across Europe. But this will not be
the end of Alenia’s involvement in the programme. The next step will be the
integration of the Engineering Model of the spacecraft, which will start in
March next year. As with Integral, this second model of the spacecraft will be
an electrically functional model and will verify that all the electronics and the
onboard computers will work together properly.

As Assembly, Integration and Verification contractor for the Rosetta
programme, Alenia Aerospazio will eventually be responsible for the final
assembly and testing of the flight model before it sets off on its eleven year
odyssey to chase a comet.


* More about Integral
* More about Rosetta
* Alenia Aerospazio

[NOTE: Images supporting this release are available at]