European Space Agency ESA tests
CHEOPS satellite with Unistats
Since the early days of space travel in the first half of the 20th century, scientists have gained many fascinating insights into our universe. The milestones of space exploration, such as Neil Armstrong’s first steps on the moon in 1969, are simply unforgettable. But space still conceals many secrets.
In neighbouring solar systems there are countless planets, which we know almost nothing about. They are outside the gravitational influence of our sun and orbit other stars. This is why they are known as extra-solar planets or “exoplanets”. Up to now, we have only been able to research the characteristics of planets in our own solar system using existing examination methods, and the characteristics of planets in other systems remained a mystery.
The European Space Agency (ESA) has now initiated a mission to deliver findings about these exoplanets – CHEOPS (Characterisation of ExOPlanet Satellites). Working closely with a research institute in Switzerland, they have developed a 300 kg optical telescope with a 30-centimetre aperture and a length of 1.2 metres.
Since 2017, the telescope has been collecting information about the previously unknown exoplanets using the “transit method”: If a planet travels in front of its central star, the latter’s brightness decreases because of the shadow cast by the planet. This process is observed by the telescope in the transit method. The diameter of the planet is derived from the reduction in brightness. Using earth-based instrumentation and another method – the “radial velocity method”, we can also determine the mass of the planets. If you know the diameter and mass, you can calculate the density. This then provides information about whether the planet consists of gas, ice, or rock. So, CHEOPS can help us gather a number of important indicators about previously unknown planets in other solar systems.
Vacuum chambers for simulating space
For the success of the CHEOPS mission, it is absolutely critical that the telescope operates extremely precisely and reliably. This requires exact preparation with a variety of tests. These can only be carried out on earth in simulation chambers which recreate the conditions found in space. For the tests on the CHEOPS telescope, a vacuum chamber was used, which was specifically designed for this challenging application.
High technical requirements
The space simulation chamber used to prepare the telescope for deployment in space must meet a high level of requirements:
- Create conditions similar to those found in space
- High temperature spectrum for instrument tests at
- extreme temperatures
- Rapid temperature change
- Low exhaust chamber surfaces in the vacuum
- Surfaces without particle release for tests under clean room conditions
The vacuum experts at our clients developed a 5.5 tonne calibration and vacuum chamber for the CHEOPS telescope. All the specific requirements for the application were considered right from the start. This means the necessary conditions can be created in order to test and calibrate the telescope and its components under realistic conditions.
Accurate preparation of the chambers began even before the actual delivery. As no reflections should appear on the chamber walls during the optical tests of the telescope components, the interior is coated with a special, black paint. In addition, this paint is optimised for absorption of the heat radiation from the test objects. During the tests in a vacuum, no chemical substances may be released from the interior coating in the chamber. Because of this, the vacuum specialists built the chamber fully before delivery, commissioned it, and heated it to 160 degrees Celsius for several weeks to expel gas from the chamber surfaces.
At the end of this process, the chamber was taken apart again and transported to the end user, along with three Huber temperature control units and the necessary vacuum accessories. In the cleanroom lab at the research institute the telescope components were gradually exposed to temperatures from -80 °C to +140 °C in the vacuum. Later on, the structural model and then the flight instrumentation were also tested in the chamber.
Demanding vacuum system
The thermal vacuum chamber is three metres long, with diameter of 1.8 metres. The two halves of the chamber can be easily moved apart and together using a rail system. Using the integrated vacuum and valve technology, the chamber can be evacuated to UHV pressure. The interior surfaces of the chamber are electropolished, so they are reflective.
An optical table is positioned in the centre of the chamber to support the telescope. A temperature-controlled shroud surrounds the whole test volume and screens the telescope from the walls of the vacuum chamber. Facing the test object, the shroud is coated with special black paint which
means it is optimised for the lowest possible level of
absorption and gas emission. The paint “swallows” the heat radiation from the sample in the same way as space does.
Using cleanroom-compatible insulated heating, the chamber can be heated up to +160 °C. The two Unistats pump a special thermal fluid through channels in the interior an facilitate cooling to -90 °C. The highly accurate regulating technology in the Unistats allows temperature control of the thermal fluid to a few hundredths of a degree.
This vacuum chamber delivers the basis for another, significant step in space exploration. It represents universal test equipment which can also be used beyond the CHEOPS project for future satellite missions.
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