Integral and Rosetta on show in Turin
23 November 1999In 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 o 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.