Once each Galileo satellite has been completed, it is dispatched to the ESTEC Test Centre in Noordwijk, the Netherlands, where it undergoes acceptance testing to ensure its readiness for space.
This is the largest spacecraft testing site in Europe, with a full range of space simulation facilities under a single roof in cleanroom conditions.
Testing begins with a ‘mass property test’ – checking each satellite’s centre of gravity and mass are aligned within design specifications. The more precisely these are known, the more efficiently the satellite’s orientation can be controlled with thruster firings in orbit, potentially elongating their working life by conserving propellant.
Electromagnetic compatibility and antenna testing are performed within anechoic chambers, shielded from all external radio signals, to ensure the satellite’s systems work well together with cross-talk interference and that its multiple antennas will communicate with Earth as intended.
Each satellite must also undergo simulated launch conditions, beginning with acoustic testing in the Large European Acoustic Facility, LEAF, effectively the largest sound system in Europe. A quartet of noise horns are embedded in one wall of this 11 m-wide, 9 m-deep and 16.4 m-high chamber, generating sound by passing nitrogen gas through the horns, surpassing 140 decibels in all.
Accelerometers placed within the satellite check for potentially hazardous internal vibration during this trial by sound.
Each satellite is also vibrated on earthquake-strength shaker tables, simulating the violent forces of a rocket launch as data are gathered on the satellite’s response across hundreds of separate channels. Shock tests using the same tables recreate the moment of satellite separation from the launcher and dispenser.
Along with testing for launch, Galileo satellites must also be tested for space. Each satellite is placed inside a vacuum chamber for thermal-vacuum testing. Air is pumped out to create a space-quality vacuum at the same time as the temperature extremes in Galileo’s planned orbit are reproduced.
Thermal control is a critical design concern, seeking to maintain a set operating temperature within the body of the satellite. With no air to transfer heat, the opposing sides of satellites in space can become very hot and very cold simultaneously, depending on whether they are in sunlight or shadow.
But satellite systems and payloads – in Galileo’s case that includes two different types of atomic clocks accurate to a few billionths of a second – must still work perfectly. Thermal vacuum testing continues for a number of weeks with all satellite systems switched on.
Finally, once the satellite has passed all these tests, it is cleared to travel on to Europe’s Spaceport. It is placed within its protective air-conditioned container to be flown on to Kourou.
As the constellation is built up, new Galileo satellites will be undergoing testing at ESTEC on an ongoing basis.
Last update: 18 July 2014