Momentum Wheels Get Rigorous Scrutiny on O3b Satellites
ROME — O3b Networks and its satellite prime contractor,, said they have gone to extraordinary lengths to ensure that a momentum-wheel defect that showed up on the recently launched second-generation satellites will not recur on the O3b system, which uses the same satellite design.
O3b Chief Technology Officer Brian Holz said his company has ordered a special series of tests for the wheels to be placed on O3b’s 12 planned satellites, to be launched starting next spring.
The tests on the first four satellites’ momentum wheels — each satellite has four of them — is scheduled for completion in January, Holz said Oct. 10 here during a briefing to analysts by O3b management.
O3b is using the same Goodrich ISR Systems momentum wheels as those aboard the second-generation Globalstar mobile communications satellites launched in 2010 and 2011.
Danbury, Conn.-based Goodrich, which has since been purchased by United Technologies Corp. of Hartford, Conn., is one of two main producers of satellite momentum wheels, the other being Honeywell Aerospace of Clearwater, Fla.
Industry officials say Honeywell’s momentum wheels are generally considered more expensive than Goodrich’s. Holz did not dispute that point but said cost was not the only issue in deciding on the Goodrich wheels.
Mobile satellite services providerCommunications of McLean, Va., turned to Honeywell for the momentum wheels on its Thales Alenia Space-built satellites, a decision that left Honeywell with a sizable order book, Holz said. Cannes, France-based Thales Alenia Space is building 81 Iridium satellites, along with 24 to 30 second-generation Globalstar spacecraft, of which 18 have been launched.
O3b’s constellation currently numbers 12 satellites, but the company is planning for more once the business delivers its initial results.
Concern for distributing an exceptional amount of business — Thales has 105 low and medium Earth orbiting satellites under construction now — also drove the O3b decision, Holz said. Another factor was that the Honeywell wheels are larger, which would have required a redesign of other satellite subsystems.
Having decided to stick with Goodrich, O3b directed Thales Alenia Space and Goodrich to make several changes in the wheels’ support structures, including heavier plating that joins the wheels to the satellite, Holz said.
The Aerospace Corp., a U.S. government-funded research center for U.S. Air Force space programs, was brought in for its expertise in system reliability. O3b required a special testing regime that, in two months, stressed the wheels to the equivalent of six months in orbit.
All O3b reaction wheels will be tested this way, Holz said, even though the end result is to cut the satellites’ in-orbit life expectancy by the same six months. O3b has sufficient margin in its satellites’ design to do this and still count on more than 10 years of service life, he said.
A Thales Alenia Space software upload, designed for Globalstar, should permit the Globalstar satellites affected by the momentum-wheel defect to operate with just two wheels, instead of the three normally required.
Finally, Holz and O3b Chief Executive Steve Collar said the company was invited into the board of inquiry looking into the Globalstar issue.
For O3b and Globalstar, the good news is that the Goodrich wheel issue appears to occur early on in the satellites’ life, judging from the Globalstar experience. In addition, Globalstar has reported no new momentum-wheel issues since the first couple, suggesting that the problem may have been solved.
“We are very confident that we will not have a problem here,” Holz said, adding that O3b, despite its startup nature and small size — nearing 100 full-time employees — has stationed seven people full-time at Thales Alenia Space’s Cannes facility. An additional three are at the manufacturer’s Toulouse, France, site, with two here, where the spacecraft are assembled.
O3b also has been able to enlist the support of technical personnel from satellite fleet operatorof Luxembourg, which is O3b’s major investor and has sent people to all three Thales Alenia Space production facilities on behalf of O3b.
Robert Carpentier, O3b customer manager at Thales Alenia Space, said the first batch of four satellites will be shipped to Europe’s Guiana Space Center in South America in February or March, in preparation for a late-spring launch aboard the European version of Russia’s Soyuz rocket.
Holz said the first O3b flight model completed its monthlong thermal vacuum testing at Thales Alenia Space in early October, and that the testing turned up no anomalies that will delay the launch.