Paul Verhoef, director of navigation at the European Space Agency, said the defects in the rubidium and hydrogen maser atomic clocks — two technologies, separate causes — on the Galileo satellites have been identified. A launch of four Galileo satellites is scheduled in December. Credit: ESA
LE BOURGET, France — The European Space Agency on June 22 signed a long-expected contract with OHB SE of Germany for eight more Galileo positioning, timing and navigation satellites, a contract that is about eight months late.
Valued at 324 million euros ($361 million), the contract stipulates that the eight spacecraft will be ready for launch by 2020, the date Galileo’s owner, the European Union’s executive commission, has set for full Galileo system service.
The contract, expected in late 2016, was delayed as the commission and the 22-nation European Space Agency (ESA) debated whether to maintain OHB as Galileo’s sole supplier or to award all or part of the contract to competitor Thales Alenia Space Italia.
In the event, the commission and ESA agreed that the savings realized from ordering recurrent-model spacecraft from OHB, and the schedule assurance this provided, outweighed arguments on behalf of dual sourcing.
Dual sourcing vs sole source
“Dual sourcing is always important but it needs to be weighed against other program requirements” including cost, said Paul Verhoef, ESA’s director of navigation. Verhoef said ESA and the commission may pursue dual sourcing for the next round of Galileo orders, when a new design will be used for the system’s second generation.
Verhoef has said in the past that dual sourcing in the case of Galileo is a bit of an illusion, since either prime contractor would rely on the same supply chain.
OHB’s partner in the Galileo work is Surrey Satellite Technology Ltd (SSTL) of Britain. Britain’s intention to exit the European Union in 2019 may or may not mean a British exit from European Commission-financed programs including Galileo.
But for now, Britain is a full EU member and Verhoef said there was never any doubt about whether SSTL could retain its role as payload builder for OHB, Verhoef said.
Verhoef said the main concern with the latest contract, called Batch 3, was that it came some eight months later than was scheduled. Subcontractors to OHB and SSTL were at risk of deploying staff to other projects.
“You cannot ask these guys just to keep people standing around for eight months waiting for an order,” Verhoef said.
Atomic clock issue resolved, repaired units arrive at OHB in July
The deployment of the Galileo constellation, eventually to include 30 satellites in medium-Earth orbit, has also been slowed by in-orbit failures on both types of Galileo atomic clocks:
The planned late-summer launch of four Galileo satellites aboard a European Ariane 5 rocket has slipped to mid-December to give satellite teams time to remove the clocks already integrated into Galileo satellites, replace any suspect hardware and then retest them before shipping them back to OHB’s Bremen, Germany, facility.
Government officials said Orolia Switzerland SA’s Spectratime division in Switzerland is expected to send two satellites’ worth of clocks — each satellite carries two rubidium and two hydrogen maser clocks — to OHB.
These will be integrated into the full satellites, retested and then sent to Europe’s Guiana Space Center spaceport in French Guiana to prepare for the December launch.
Both the rubidium and hydrogen maser atomic clocks on Galileo satellites have suffered failures, for different reasons. Credit: SSTL
China’s navsats spared atomic clock anomaly, but not India’s
Because the atomic clock anomalies occurred at about the same time on two clock designs, officials at first thought the problem’s cause was somewhere in the hardware ensemble around the clocks.
This turned out not to be true. For the rubidium clocks, the issue was a defective component that was produced for the OHB-built Galileo satellites but was not used for the earlier, in-orbit-validation satellites.
China’s Beidou navigation system also uses Spectratime rubidium clocks, but these came from a production series that predates the affected series.
“What’s remarkable here is that the component in question costs only a few dollars,” one government official said.
For the maser clocks, the problem relates to how they are operated in orbit. New operational practices have been instituted.
The Indian Regional Navigation Satellite System, however, has been affected by the same rubidium clock issue and has had to launch a replacement satellite earlier than planned as a result.
One government official said Indian and European authorities have compared clock data and determine that they were the suffering from the same problem. “The signatures were identical,” said the official. “We have kept them up to date on our testing.”
Verhoef said the clock issue has received enough attention in the past six months to assure that even a July arrival of the prequalified clocks at OHB will not threaten the satellites’ delivery in time for a December launch.