October 22, 2012
Credit: Credit: United Launch Alliance
Amy Butler Cape Canaveral
U.S. rocket makers are refining a concept to dual-launch the next generation of Global Positioning System satellites, a move that could save $50 million per satellite compared to the traditional practice of dedicating a single booster to loft each spacecraft separately.
In the military space world, where some satellites can exceed $1 billion in cost, $50 million is not a lot of money. But the immense fiscal pressure being put on the Pentagon is compelling managers to consider pinching pennies wherever possible. This, combined with a solid record of performance from the United Launch Alliance's Atlas V and Delta IV vehicles, is driving officials at the Pentagon to consider taking the risk of stacking two GPS III satellites atop a single booster. Satellite manufacturers note that the cost avoidance can add up—a notional constellation of 30 could save $1.5 billion, they say.
GPS III, being developed by Lockheed Martin, is the ideal platform on which to try the dual-launch concept. Unlike other Pentagon satellite programs, the U.S. Air Force is buying GPS IIIs in large enough numbers to justify the non-recurring engineering for the new hardware and software for a dual launch. Air Force officials are considering this approach with satellites 9 and 10, though developers at ULA and Lockheed Martin suggest they could be ready to start with satellites 5 and 6.
The team is studying how to safely encapsulate and eject two spacecraft from atop a single booster. Options include relying on the satellites' onboard propulsion or developing a secondary vehicle for the orbital transfer, says Tony Taliancich, a ULA official.
The least risky and most affordable solution to maneuver the satellites into operational orbits will ultimately be using onboard propulsion, rather than relying on a secondary vehicle, says Keoki Jackson, vice president of navigation systems for Lockheed Martin. “This approach would also help mitigate ongoing space debris concerns, as no secondary vehicle would need to be jettisoned in high-traffic orbital areas.”
Unlike earlier GPS satellites, GPS III will not be directly injected into its operational orbit. The inherent propulsion capabilities of the A2100 platform on which GPS III is being built will allow for it to self-maneuver into orbit. “No modification would be needed for the satellite's onboard propulsion,” Jackson says. “To enable dual launch and successfully propel two satellites into separate orbital slots, we will just need to develop dual-channel communications units for each satellite, which will allow the ground system to distinguish between the two satellites during launch and orbit insertion.”
Jackson characterizes this communication system work as “low-risk,” and preliminary estimates suggest the cost of this work can be recovered in the first dual-launch mission.