How do you know that a satellite in space does exactly what you want it to do? You can’t have a close look at the spacecraft once it has been launched. A thorough and systematic series of tests must therefore be carried out before launch to make sure that the commands will have the desired effect and that the data sent by the satellite are correctly interpreted. This is what experts at the European Space Operations Centre (ESOC) at Darmstadt are now doing with Integral, ESA’s gamma-ray observatory. On 21 March 2000 the Integral team successfully completed the first phase of the so-called System Validation Tests. This proved that the Mission Operations Centre (MOC) will be able to control and monitor the spacecraft.
The team at Darmstadt was sending its commands to and receiving the telemetry data from the satellite that was located at Alenia at Turin, Italy, where Integral is integrated.
Every two or three minutes engineer Juan Pineiro, in Darmstadt, picked up a microphone and contacted his colleagues at Turin to announce the next step on an almost endless list of commands to be checked. On the computer screen in front of the engineer the new command was indicated. Only an expert would have any idea what the combination of letters and figures really meant. With one click of the mouse the engineer at ESOC in Darmstadt released the command that forced the satellite in Turin to switch on the Star Tracker, to switch off the battery charge or to initialise the electronics of the Sun Sensor. On a second screen on the right the expert was able to check if the command had been implemented successfully or if it had failed. Anomalies were listed in bright red. A third screen on the left showed the telemetry data of the satellite.
To enable the engineer to perform these tasks a support team at ESOC is needed — for example configuring the system for the tests or in charge of ESOC’s Ground Control Room that established the communication lines between Darmstadt and Turin.
"After two weeks of intense testing we could show that our control system works properly and will be able to perform the required functions", said Spacecraft Operations Manager Michael Schmidt. "We are very happy, it is really going well", added Integral Ground Segment Manager Paolo Maldari. "We have found a couple of small problems, but when we know where they come from we are confident that we can solve them."
For this first phase of System Validation Tests the emphasis was on the validation of the functions needed to handle the telemetry and telecommand data of the Service Module. The next phase that will start in two months will include also the execution of real operational scenarios, such as the Launch and Early Orbit Phase to validate the relevant flight procedures. At a later stage, when the Payload has been integrated, similar tests will be executed to ensure that the Mission Operations Centre will also be able to control the instruments on-board Integral.
The extensive pre-launch testing at ESOC is vital to guarantee a successful mission. The MOC in Darmstadt is the sole interface with the Integral satellite in space. "All commands to the spacecraft and instruments are generated at the MOC and all telemetry from the Integral satellite is routed to the MOC who is responsible for distributing it within the Integral Ground Segment, in accordance with the different needs", Paolo Maldari explained.
* More about Integral
* ESOC home page
* Alenia homepage
[Image 1:]
Typical set-up for the test execution.  Left Screen: Display of TM Data. Middle Screen: List of commands to be executed. Right Screen: List of commands that were executed and list of anomalies
[Image 2:]
Future INTEGRAL Control Room.