November 7, 2013
ESA’s Next Pair Of Galileo Satellites Undergo Crucial Testing
April Flowers for redOrbit.com - Your Universe Online
At a technical center in the Netherlands, the European Space Agency's (ESA) next pair of Galileo satellites have been the focus of a busy fall season. The satellites are undergoing a continuing, full-scale campaign to ensure their readiness for space.
The first of the pair of satellites is halfway through a five-week immersion in vacuum and temperature extremes. This "thermal-vacuum" testing mimics the conditions the satellites will face in space. It takes place inside a 14 foot-diameter stainless steel vacuum chamber called "Phenix." The sides of an inner box called the "thermal tent" are heated to simulate the Sun's radiation or cooled down by liquid nitrogen to create the chill of Sunless space.
Currently, there are four Galileo satellites in orbit and, along with the new pair, a projected 22 total "Full Operational Capacity" satellites will be launched as part of this program.
In mid-August, the second of the new pair joined its twin at ESA's European Space Research and Technology Center in Noordwijk, which is the largest spacecraft testing site in Europe. The Center has a full range of space simulation facilities under a single roof in clean room conditions.
This satellite first underwent a "mass property test" that verified that its center of gravity and mass are aligned within design specifications. The more precisely these measurements are known, the more efficiently the satellite's orientation can be controlled with thruster firings in orbit. The thruster firings potentially elongate their working life by conserving propellant.
The first of the two satellites left the wider universe behind in the Maxwell Test Chamber, with shielded walls blocking out all electrical signals, and with spiky, radio-absorbing "anechoic" material lining the chamber, enabling electromagnetic compatibility testing
The satellite, isolated within the chamber as though floating in space, could be switched on to check all its systems can operate together without interference.
In September, the second satellite underwent acoustic testing in the Large European Acoustic Facility, LEAF, effectively the largest sound system in Europe. The first satellite passed this same testing just a few weeks earlier.
For the acoustic testing, a quartet of noise horns are embedded in one wall of this 36-foot-wide, 29-foot-deep and approximately 54-foot-high chamber. The sounds are generated by passing nitrogen gas through the horns, surpassing 140 decibels in all.
The researchers placed accelerometers inside the satellite to check for potentially hazardous internal vibration during this trial. The satellite was then vibrated on the shaker tables to simulate the violent forces of a rocket launch.
Data was gathered across hundreds of channels as up-and-down vibration on the QUAD shaker was followed by side-to-side movement on the horizontal shaker.