#16: CHEOPS IS READY FOR FLIGHT11 March 2019
CHEOPS in the clean room. Credit: ESA – S. CorvajaRecent months on the CHEOPS mission have seen the completion of spacecraft testing and the conclusion of a very important review, which determined that the satellite is ready to fly. (...)
Following the completion of the environmental test campaign, several functional tests have been performed to demonstrate that all individual sub-systems (e.g. solar arrays, propulsion module, science instrument, etc.) operate correctly and continue to do their job when linked together at system level. Functional testing can uncover defects that have previously remained undetected, and are performed to confirm that the spacecraft has not been affected following the stresses of, for example, transport or environmental testing.
As an example, specific tests were executed to monitor the fitness of the solar arrays. Not only was it necessary to confirm the original condition of the solar cells, it was also important to determine whether any damage had been sustained during the environment test campaign, particularly the vibration and acoustic test activities.
To this aim, Electro-Luminescence (ELM) testing was carried out before and after the environmental tests. ELM testing exploits the fact that solar cells, which normally convert light to electricity, can also operate 'in reverse', emitting light efficiently if a current is applied to them when functioning correctly. Defective cells do not do so, and they can be singled out in images. An additional test, illuminating the solar arrays, was carried out to measure their output: a short, bright flash was used to light up the photovoltaic cells, and the voltage and current generated at the maximum power point were compared to known reference values.
Certain functional tests are critical for safety. For example, a global leakage test was performed by filling the tank, valves and piping with inert helium to make sure there will not be leaks in the propulsion module when it is filled with propellant. The safety of the propulsion subsystem was demonstrated by installing the spacecraft in a sealed enclosure and monitoring any increases in helium concentration within the enclosure.
Other tests involved mission-critical procedures, such as ensuring the one-shot, frangible bolt will break on demand – as planned – to open the baffle cover and allow light to enter the telescope once in orbit.
At the very end of the test campaign, when no significant modifications of the flight hardware could be expected, accurate measurements of the mass, centre of gravity and inertial properties of CHEOPS were made. These measurements allow an accurate analysis of the launcher trajectory and satellite separation, and will improve the precision of the manoeuvres that the Attitude and Orbit Control System will execute during operations. (...)
http://sci.esa.int/cheops/61203-16-cheops-is-ready-for-flight/