Alphasat reaches key ground-testing milestone

Two months' rigorous thermal testing of Inmarsat's next L-band satellite, Alphasat XL, has begun to simulate the severest conditions found in space.

The satellite, which will give Inmarsat an additional 7 MHz of L-band spectrum in the Europe, Middle East and Africa region, is being tested in a vacuum chamber at Astrium's centre in Toulouse, France.

Franco Carnevale, Inmarsat Vice President of Space Segment Engineering, described this phase as the most important milestone in Alphasat's ground testing programme.

Liquid nitrogen
The satellite has been placed in a black metal chamber 8 by 10 metres in size, where it will be subjected to the extreme cold and heat experienced in space.

The chamber also simulates the high vacuum experienced by the satellite in space – just 100 millionths of the atmospheric pressure found on the ground.

To replicate the severe cold faced when the satellite passes from direct sunlight into the Earth's shadow, the shroud of the chamber is pumped full of liquid nitrogen to lower the temperature to -173 deg C.

“We will also test the satellite in extreme heat of many 100s of degrees, but this easier to replicate than is extreme cold,” explained Franco.

Extreme temperatures
“This testing will continue until late January 2013 and its scope has three purposes. First, to prove the ability of the spacecraft's thermal controls to behave properly in space.

“Secondly, we want to simulate all the thermal regimes it will endure – including the equinoxes when for a period the sun does not illuminate the spacecraft and the solstices each year of its space life.

“Thirdly, we need to precipitate any latent failures of the avionics, mechanisms and thermal control systems. For this, we keep changing the temperatures in a process called thermal cycling consisting in changing the temperature of the spacecraft between hot and cold extremes. We use in excess of 1200 temperature sensors to ensure that at no time the spacecraft reaches critical temperature “For these critical operations the Inmarsat oversight team in Toulouse is ably supported by thermal experts from ESA.”

Greater redundancy
Alphasat is expected to be launched into space in mid-2013 on board Ariane 5 from French Guiana.

Part-funded by the European Space Agency, Alphasat has been designed to seamlessly augment our current Inmarsat-4 fleet, supporting the same BGAN, FleetBroadband and SwiftBroadband services

It will give Inmarsat's global L-band network increased capacity and redundancy, and will support, higher speed streaming services.