 has been a pain for many missions trying to do this.”
Despite strict clean room controls on the ground, all space missions launch with some amount of contamination, which can outgas in orbit once heated by the sun. The high-energy laser aboard Aeolus could also lead to outgassing as it warms up materials inside the ALADIN instrument.
Engineers determined they could flush the ALADIN instrument with tiny injections of pure oxygen throughout the Aeolus mission. Two high-pressure tanks carrying a combined load of around 31 pounds (14 kilograms) of liquid oxygen will gradually supply the instrument once in space.
“We have a regulation system which takes the high pressure oxygen down to an extremely low pressure in orbit — 40 to 60 pascal — which is an incredibly light pressure, very few molecules,” Elfving said.
The amount of oxygen gas inside the instrument in space will be equivalent to the oxygen produced by a small plant indoors, according to ESA.
“But it is enough to cause combustion of this organic material which always remains on the optics,” Elfving said. “It helps to catalyze and burn away that, instead of carbonizing it and blackening the optics.
“Those two, I would say, have been the main challenges — laser-induced contamination and laser-induced damage,” he added. “For the rest, we are talking about stabilities in alignment of microns or nanometers, and that’s obviously a tough challenge, especially when we are pumping a lot of energy into the laser.
“That put us between a rock and a hard place,” Elfving said. “So it has taken us about 10 years to get from a prototype laser to a flight-worthy laser with a lifetime that meets our requirements. In the beginning, due to this laser-induced contamination, we lost about 50 percent of the energy within hours, and we now we have run a laser with absolutely no degradation for six months and beyond. So we’re very confident that have achieved the state of the art.”
Concerns about the sensitivity of the Aeolus satellite’s laser instrument drove managers to transport the spacecraft from Europe to the mission’s launch base in South America by ship instead of airplane. Engineers worried the pressure increase during an airplane’s descent would damage the instrument package on Aeolus.
There were no such concerns about a pressure decrease like the conditions the spacecraft encountered as it climbed into space.
Once the spacecraft arrived in French Guiana, teams fueled Aeolus and put the spacecraft through an extra step of cleaning. Technicians used a powerful ultraviolet torch to search for particles of dust residing on the satellite, then used a soft brush and vacuum cleaner to remove any contamination they found.
“This is a bit of a tedious task, but one that is necessary,” ESA said in a statement.
The Aeolus satellite was built by Airbus Defense and Space’s spacecraft manufacturing plant in Stevenage, England, and is based on the satellite design used by ESA’s Rosetta and Mars Express interplanetary probes. With its maneuvering fuel loaded, Aeolus weighed around 3,013 pounds (1,367 kilograms) at launch, according to Elfving.
Airbus Defense and Space’s division in Toulouse, France, developed the ALADIN instrument, and the laser transmitters were supplied by the Italian company Leonardo in Florence and Pomezia, Italy.
The launch was delayed an extra day from Tuesday to Wednesday to allow for more favorable high-altitude winds over the Guiana Space Center.
The early hours of Aeolus’s mission appeared to go according to plan. ESA officials said the satellite extended its power-generating solar panels on time, and the first three days of the mission will focus on activations of key spacecraft systems, putting the observatory into a stable configuration for testing.
“Then we start switching on the laser and the instrument,” Elfving said. “That will take around two weeks if it goes well, but it could take longer because there’s a lot of tuning and observing of this high-energy laser. We don’t want to damage anything if we have any wrong settings. In October, we expect to start collect