A malfunctioning propulsion system will delay AEHF-1's operational debut.
It then will take another three to four months checkout time before AEHF-1 is fully operational in late 2011, said Dave Madden, director of the Military Satellite Communications Wing at Los Angeles AFB, Calif.
The Air Force and its industry partners launched AEHF-1 into space on Aug. 14. Lockheed Martin is the prime contractor.
AEHF-1’s liquid apogee engine that was originally intended to thrust the spacecraft through its initial orbit-transfer maneuvers, shut down on Aug. 15 after failing to meet its expected acceleration. Officials attempted a second burn two days later, but the propulsion system shut down once more, said Madden during a teleconference with reporters Monday.
"From the performance data collected from the two aborted LAE burns, we believe the LAE is unusable, and at this point we have no plans to fire that engine again," Madden said.
Instead, officials have come up with a new plan that involves using six five-pound thrusters, known as monopropellant hydrazine thrusters, to push the satellite into a better orbit. Those thrusters, along with 12 0.2-pound thrusters that also make up the monopropellant system, typically are used only during the LAE burn to "settle acceleration and control authority," Madden said.
Once the satellite is in a better position, the third on-board propulsion system, known as the hall current thrusters, will kick in and bring AEHF-1 into its geosynchronous orbit. The HCTs also are used for repositioning maneuvers and station keeping, Madden said.
The Air Force already has approved the first segment of the orbit raising plan, which includes a number of burns over the course of a week using the five-pound thrusters. The first burn started on Aug. 29 and ran for about 40 minutes, Madden said. Over the next week, officials will run a series of additional burns intended to bring AEHF-1 into a parking/intermediate orbit roughly at an altitude of 950 kilometers above the Earth's surface.
"After each burn we will assess results, conduct new orbit determination, and make adjustments for subsequent burns as necessary. By moving to a higher perigee immediately, we will no longer need to fight the Earth's high-atmospheric drag," Madden said.
Despite previous technological problems with AEHF-1, Madden said the propulsion system has "always been clean." It's not clear what caused the failure, but officials are hoping a root cause analysis will reveal the answer. That analysis is expected to wrap up in about three weeks, he added.
"The problem could range all the way from the propulsion system up inside the spacecraft to a flaw inside the LAE engine. We really don't know the answer to that question right now. We just know it's not performing the way it's supposed to," Madden said.
As of now, AEHF-2 is still slated to launch in February 2011, but that could get pushed back pending the results of the analysis. If that happens, a busy launch schedule could present another challenge to officials looking to get back on the manifest quickly, Madden said.
AEHF-1 will have a 10-times increase in capacity over the aging Milstar satellite. The Air Force intends to purchase at least four AEHF spacecraft, which eventually will replace the five-satellite Milstar satellite.
Madden said he is confident AEHF will enter orbit before the Air Force loses the first Milstar.
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