Integral Engineering Model test campaign successfully completed
27 August 1999On 23 August 1999 ESA's new gamma-ray observatory, Integral, has passed a most important milestone in its development. The Engineering Model tests, which lasted more than a year and which were to verify that all satellite subsystems and instruments interface well and function as a system, were successfully completed.
Electrical hardware and software from contractors all over Europe was assembled and tested at Integral's prime contractor Alenia in Turin, Italy, to make up the spacecraft Engineering Model. Engineering Models of all four of Integral's scientific instruments that will gather radiation from exotic objects far away in space were sent to Alenia from Italy, France, Spain and Denmark. Would all the different parts together operate as planned? This was the question the engineers were eager to answer. They tested the complete satellite model consisting of the service module and the payload module that carries the scientific instruments. All electrical and software interfaces and all functions were thoroughly tested. The instruments operated together as expected and without cross-interferences. A couple of sensitivities were identified, but minor modifications will correct these. This is precisely the purpose of the Engineering Model - to demonstrate a sound design and to allow for small adjustments before testing of the Flight Model itself.
Instead of having a summer break, engineers at Alenia have been busy completing the last phase of the campaign which is testing for electromagnetic interference. Electromagnetic interference is a common problem in our everyday life. Every airline passenger is familiar with the instruction during take-off and landing to turn off all computers, headsets, radios and mobile phones as the electromagnetic waves radiated by these objects can interfere with the aircraft's electronics. Your vacuum cleaner may cause snow on your TV or your car radio may buzz when you drive under a power line. In satellites such interference can be fatal.
To verify the electromagnetic compatibility the engineers place the satellite into a special anechoic test chamber lined with black cones, which absorb electromagnetic radiation rather than to reflect them, thus simulating deep space. The electromagnetic emissions of the satellite were measured over a wide range of frequencies. Then the satellite was irradiated with electromagnetic radiation from various antennas and its proper function carefully monitored to ensure that the satellite will function safely in an environment which is even worse than what it will be exposed to in orbit.
The testing of the Engineering Model showed that all systems operate together well and demonstrated that the Integral satellite is strong enough to withstand electromagnetic interference. The few minor disturbances discovered during testing have been identified and will serve to ensure that the Flight Model is as perfect as possible. The campaign was completed on time and construction of the satellite is well on schedule for Integral's launch in 2001. But there is no respite for the busy engineers - preparations are already underway for the integration of the Flight Model itself.