PARIS — Mobile satellite services providerCommunications’ request that U.S. regulators loosen requirements for deorbiting the current Iridium satellite constellation will still permit the company to bring down all of its satellites within a few years of their retirement, company officials said.
And for most of the satellites, the post-retirement deorbit plan remains what it was from the start: They will be lowered to an elliptical orbit low enough to force them into the atmosphere to burn up within months, not years.
The U.S. Federal Communications Commission (FCC), which licenses Iridium’s operations, approved part of the company’s deorbit modification request for as many as 10 satellites, and rejected the request for similar dispensation for the entire 66-satellite constellation. Company officials said they have no problem with the FCC decision.
McLean, Virginia-based Iridium operates a fleet of 66 satellites, plus spares, in a circular orbit some 778 kilometers in altitude.
All the satellites are well beyond their planned retirement dates, but most still have more than enough fuel to accomplish the original deorbiting obligation. Iridium had promised the U.S. government that it would send the retiring satellites into an elliptical orbit with a perigee of 250 kilometers, from which they would be pulled by atmospheric drag into a destructive re-entry after having been “passivated” to eliminate stored energy sources such as charged batteries.
The deorbit plan is part of a broader, if only intermittently followed, suite of recommendations by the Inter-Agency space Debris Coordination Committee (IADC), a grouping of spacefaring nations, to mitigate the accumulation of space debris. Iridium’s exposure to space debris issues was driven home in 2007 when one of its satellites was struck by a retired Russian spacecraft, causing a large cloud of debris.
IADC guidelines advise operators of satellites in low Earth orbit, typically below 1,000 kilometers in altitude, to passivate their vehicles on retirement and place them into orbits from which they would re-enter the atmosphere within 25 years.
Given the large size of the Iridium constellation, the company and the FCC have set higher standards for Iridium.
Iridium plans to launch a second-generation constellation starting in mid-2015, with all 71 second-generation satellites to be in orbit by late 2017. As soon as the second-generation satellites are in place, the first-generation constellation will be deorbited, with the possible exception of a few spacecraft to be used as spares, Iridium has told the FCC.
But Iridium has said that for between seven and 10 first-generation satellites that have shifted orbital planes to fill coverage gaps, the remaining fuel will be insufficient to get them to the target 250-kilometer-perigee orbit.
Iridium asked the FCC to approve a new deorbit plan that would allow all first-generation satellites to be sent only to a 600-kilometer-perigee orbit. The company said even this higher orbit would assure atmospheric re-entry much quicker than 25 years.
Iridium Chief Operating Officer S. Scott Smith, in a Sept. 11 interview here during the World Satellite Business Week organized by Euroconsult, said that given the Iridium satellites’ drag coefficient, the time it would take to re-enter the atmosphere from 600 kilometers would be between three and 10 years, and perhaps far less.
Smith said Iridium was drifting the last of its in-orbit spares to an operating plane. Assuming the second-generation constellation stays on schedule, the first generation of satellites will be deorbited, most to the 250-kilometer orbit, in a short period of time in 2017.
In its July 31 decision, the FCC said seven Iridium satellites currently have insufficient fuel to get to the 250-kilometer orbit. These satellites, plus as many as three more likely to be in that condition in 2017, will be left to decay from 600 kilometers.
Smith and Iridium Chief Executive Matt Desch, in a separate interview, said the company has received all U.S. shipping and launch licenses needed to send the first two second-generation satellites to Russia for a June 2015 launch aboard a Russian-Ukrainian Dnepr rocket operated by ISC Kosmotras of Moscow. The shipment is expected to occur 45 days before the launch. The tensions between Russia and Ukraine, and between Russia and the West, have had no effect on the launch campaign, Smith and Desch said.
The Iridium second-generation satellites, 81 of them including spares, are being built by a team led byof France and Italy. Orbital Sciences Corp. of Dulles, Virginia, is handling final integration and testing, and the satellites will ship from Orbital’s facility in Gilbert, Arizona.