The European Space Agency's (ESA) third and fourth Galileo navigation satellites have successfully completed thermal vacuum testing, bringing them closer to their scheduled launch in late September.
According to the agency, the third satellite completed its 20 day thermal vacuum testing in May at Thales Alenia Space Italy's plant in Rome, while the fourth finished the same tests early this month.
ESA Galileo IOV Satellite procurement manager Nigel Watts said that the two satellites were almost identical to the first two Galileo satellites launched on 21 October.
"We don't need to carry out full-scale qualification tests, because we already know from our in-orbit test campaign that the design performs to our expectations," he said.
"Instead, what we are carrying out is acceptance testing: checking the workmanship, performance and readiness to launch of these new satellites."
During the test, each of the satellites in operating condition, were placed into a vacuum chamber and air was pumped out, then the satellite's external surfaces were variously heated and cooled.
According to ESA, critical systems must be kept within a set temperature range.
Galileo thermal engineer Guido Barbagallo said: "Galileo's laser retroreflector on its exterior reached -110°C during the cold phase of testing."
Galileo satellite preserves its temperature range by deploying various procedures, which include multi-layer insulation, heaters, heat pipes depending on evaporating ammonia to transfer heat, and radiators to unload waste heat out into space.
The satellite's passive hydrogen maser atomic clock, located in the navigation panel, is claimed to be accurate to a second in three million years and is encased in multi-layer insulation to protect from the Sun.
"The passive hydrogen maser is mounted on a 3mm-thick aluminium plate to help hold a uniform temperature, with waste heat finally radiated to space from the external satellite surface," Guido added.
Image: The fourth Galileo satellite during thermal vacuum testing at Thales Alenia Space Italy's facility in Rome. Photo: courtesy of ESA/EADS Astrium - R Kieffer.