Faulty Component that Delayed ExoMars Affects Other ESA Programs

by

Updated at 10 a.m. EDT Sept. 23

PARIS — A defective batch of pressure gauges that forced a two-month delay in the launch of Europe’s ExoMars 2016 mission has disrupted multiple other programs but was identified early enough to prevent any of the leaky units from launching, the European Space Agency said Sept. 22.

In response to SpaceNews inquiries, ESA said the same pressure transducers whose suspected leaks forced the agency to delay, to March, the launch of the ExoMars mission have been removed or repaired on a half-dozen other missions — all in time to prevent in-orbit problems.

“Beyond ExoMars there is a whole group of missions affected, but for all of them there is adequate time to either repair the existing transducers or procure new ones,” the agency said in a statement.

“For the science program, BepiColombo [a mission to Mercury slated to launch in 2017] will fly these sensors but they have been procured prior to the lots that are affected, [so] no risk for BepiColombo,” the agency said. “Further, Solar Orbiter and Cheops are affected and will repair and exchange, respectively, the sensors with no impact on the overall mission planning.”

The Cheops exoplanet-hunting satellite and the Solar Orbiter sun-focused mission are scheduled for launch in 2017 and 2018, respectively.

The two-month delay in the launch, aboard a Russian Proton rocket, of the Euro-Russian ExoMars 2016 orbiter and entry, descent and landing module is a rare case in which the usual Mars launch window, which typically opens every two years, permits liftoffs just two months apart.

Rolf de Groot, head of ESA’s robotic exploration coordination office, said ExoMars 2016 will arrive in Mars orbit in October, around the same time as it would have were it launched in January.

The delay was caused by a component alert issued this summer by producer Moog Bradford of Heerle, the Netherlands, a unit of Aurora, New York-based Moog Inc. Moog Bradford did not immediately respond to requests for comment Sept. 22. The company’s U.S. headquarters said Moog would not discuss the issue without explicit customer approval.

The company, which says it has a zero-failure-in-orbit record, has nearly 500 pressure transducers on missions that have yet to be retired or have yet to launch. These missions include, in addition to ExoMars, Europe’s Galileo positioning, navigation and timing satellites; the new Small-Geo platform for telecommunications and other missions; the EarthCare Earth observation mission; and the Cygnus space station cargo carrier.

“For the science program, BepiColombo [above, a Mercury mission slated to launch in 2017] will fly these sensors but they have been procured prior to the lots that are affected, [so] no risk for BepiColombo,” ESA said. Credit: ESA artist’s concept
“For the science program, BepiColombo [above, a Mercury mission slated to launch in 2017] will fly these sensors but they have been procured prior to the lots that are affected, [so] no risk for BepiColombo,” ESA said. Credit: ESA artist’s concept

For ExoMars, the transducers, each weighing less than 1 kilogram, were to monitor pressure in the entry, descent and landing module’s helium pressurization tank and the hydrazine fuel tank.

ESA has decided to remove them, not replace them, given that their role is noncritical to the lander’s functioning.

De Groot said ExoMars’ Joint Steering Board, with Russia’s Roscosmos space agency and ESA, is scheduled to meet Sept. 24 at ESA’s European Space Research and Technology Centre in Noordwijk, Netherlands, to give final approval to the new launch schedule.

De Groot said ESA was informed this summer by ExoMars prime contractor Thales Alenia Space of France and Italy that a defective welding machine had left a series of transducers, all made in 2013, susceptible to leakage.

“We looked at the risk the transducers brought to the mission and decided not to accept it,” de Groot said in a Sept. 22 interview. “There was a high risk of mission failure during descent [to the Mars surface] in 2016.

“This was not something we discovered in testing. It was brought to the attention of the prime contractor by the manufacturer that the welding machine defect could produce cracks in the transducers. Whether these cracks would lead to leaks is something we would not learn until we were in the descent stage at Mars. That’s not when you want to find this out as it would have led to a full loss of mission.”

For a January launch, the ExoMars hardware would have been shipped to the Russian-run Baikonur Cosmodrome spaceport in Kazakhstan on Oct. 21. The new launch date of March 14-25 will allow the shipment to be delayed to early December.

De Groot said one advantage to moving to the later launch date is that it will allow for the ExoMars Trace Gas Orbiter’s high-resolution Colour and Stereo Surface Imaging System camera, which will be a late arrival, to be integrated onto the orbiter at Thales Alenia Space’s production facility rather than at the Baikonur launch base.

Walter Cugno, ExoMars program manager at Thales Alenia Space, said removing the transducers means dismantling a significant portion of the entry, descent and landing module. The company is now employing double shifts to complete the task and prepare for shipment to the launch site.

Cugno said Sept. 23 that ExoMars 2016, which has always been on a tight schedule, would have been ready for a late-October shipment if the transducer issue had not come up.

The entry, descent and landing module, powered by batteries, is expected to operate for only two or three days on the Martian surface. The European rover vehicle to launch as part of the ExoMars 2018 mission with Russia will carry a radioisotope heating unit to provide power and keep the rover’s instruments warm at night.