UPDATED Nov. 25 2:25 p.m. EST
PARIS — Globalstar Inc. has concluded an agreement with the builder of its 24 second-generation mobile communications satellites that likely will permit them to operate for 15 years in low Earth orbit even if they lose two of their four momentum wheels.
Under the agreement, announced by Globalstar Nov. 21, Thales Alenia Space of France and Italy will develop a software patch to be sent to the orbiting Globalstar satellites to overcome momentum-wheel failures that have taken one satellite out of service and threaten others.
Anthony J. Navarra, Globalstar’s president of global operations, said in a statement that the software upload “should enable the affected satellite to return to full service” and provide mobile voice and data communications for 15 years.
Covington, La.-based Globalstar has ordered 24 second-generation satellites from Thales Alenia Space. The first six of these were launched in October 2010. Shortly after launch, Globalstar discovered defective performance in the momentum wheels of one of these spacecraft, and indications that the same problem could affect the other five.
Momentum wheels permit satellites to maintain themselves stably in orbit. Each Globalstar satellite is equipped with four wheels; three are needed and one is a spare.
One of the Globalstar satellites has lost the use of two of its wheels and has been removed from service. The planned Thales Alenia Space software patch would permit a Globalstar satellite to operate with only two working reaction wheels.
Globalstar announced in early November that a momentum-wheel issue had cropped up on the second batch of six satellites, launched in July. The company said it was working with Thales and with momentum-wheel provider Goodrich Aerospace to determine the nature and extent of this anomaly and would, if necessary, delay the launch of the third batch of six satellites, planned for early December.
The Nov. 21 agreement with Thales Alenia Space places the proposed software solution into the Globalstar-Thales contract.
In a Nov. 22 statement in response to Space News inquiries, Globalstar said: “Thales and Goodrich have been working on identifying a proposed fix for a number of months but only recently was that proposal formalized, and an agreement signed. Thales believes they have a solution that will … allow us to bring our satellite back into service for its 15-year mission. The signed agreement establishes the commercial terms for the development of that solution.”
Michel Fiat, chief technical officer for Thales Alenia Space, said in a Nov. 21 statement that software upload to the orbiting Globalstar second-generation satellites will be conducted “after full validation on Thales Alenia Space software and avionics test benches.” Fiat said the same solution could be applied to others in the constellation.
Thales Alenia Space and Globalstar are continuing work on the 24-satellite delivery without taking into account their dispute over whether Globalstar has a right to order six more satellites under similar financial conditions. An arbitration panel, whose findings will be binding, is scheduled to review the issue Jan. 24.
In a Nov. 23 interview, Fiat said Thales Alenia Space and Goodrich have tentatively concluded that the momentum-wheel issue on the satellites launched in July “is of the same nature” as the problem encountered on the satellites launched in October 2010. He said that the inquiry has further determined that the problem will not get worse over the years, and that wheels functioning correctly after about a year likely will function normally for the planned 15-year service life.
“The board of inquiry we established with Goodrich has not completed its work,” Fiat said. “It is ongoing. We had said [after the wheel anomalies on the first satellites] that we had not been able to reproduce the anomaly on the ground, and were not totally certain of the root cause.
“The investigation had focused on a series of manufacturing and testing procedures not related to the design of the wheels. We thought we had addressed those issues given our conclusions as to the probable cause. In fact, if you look at the performance of the first batch [one satellite taken out of service with two defective reaction wheels] compared to the second, there is already less of a problem in the second batch. Goodrich is now refining root-cause scenarios that could conclusively explain the problem. We are looking at a series of options with our customer.
“The mode we have developed … permits us to fly with just two functioning wheels in most operating modes. If an unplanned satellite maneuver had to occur it would be more challenging, and our development plan is taking into account the options needed to confront this. But in the normal course of operations, the satellite can operate normally. Basically it means compensating for the loss of a wheel on one axis for all operating modes. At this stage we are very confident about being able to develop this solution.”
