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Falcon 9 engine restart glitch blamed on thermal conditions

Posted: November 22, 2013

SpaceX says frozen fluid lines prevented the Falcon 9 rocket's second stage engine from re-igniting on a Sept. 29 test flight, but engineers are confident extra insulation will resolve the thermal problem on the Falcon 9's next mission set for liftoff Monday on the company's first launch to geostationary transfer orbit.

The Merlin 1D second stage engine nozzle glows during its first burn on the Falcon 9 rocket's Sept. 29 launch from Vandenberg Air Force Base, Calif. Credit: SpaceX
The aborted engine restart on the Falcon 9 test flight was caused when fluid lines for the second stage Merlin engine's igniter fluid froze after long exposure to cold oxygen, according to Emily Shanklin, a SpaceX spokesperson.

"This never happened on the ground, because ambient air kept the lines warm," Shanklin said in a statement. "We've added insulation and made sure that cold oxygen can't impinge on the lines.

SpaceX's Merlin engines use pyrophoric igniters with a hypergolic fluid called triethylaluminum-triethylborane, or TEA-TEB. The system allows an engine to restart multiple times on the ground or in flight without refurbishment.

The customer for the Falcon 9's next mission, Luxembourg-based SES, appears satisfied with the fix. The global satellite operator approved fueling of the SES 8 spacecraft and the satellite, already shrouded inside SpaceX's 17-foot-diameter payload fairing, is ready for attachment to the Falcon 9 rocket.

The SpaceX launch team rehearsed countdown procedures Thursday. Launch controllers filled the Falcon 9 rocket with liquid oxygen and kerosene propellants and checked the readiness of the launcher and ground systems before Monday's countdown.

The SES 8 mission logo. Credit: SpaceX
The mock countdown ended shortly before 5 p.m. EST (2200 GMT) with a brief firing of the Falcon rocket's nine Merlin 1D first stage engines, which powered up to more than a million pounds of thrust for a few seconds while restraints kept the rocket on the ground.

Called a static fire, Thursday's activity is a standard prelaunch test for SpaceX. The static fire Thursday was the first time SpaceX has exercised new launch pad systems installed since the last flight of a Falcon 9 rocket from Florida in March.

SpaceX's last launch on Sept. 29 from California was the maiden flight of the company's next-generation Falcon 9 rocket. Sporting upgraded Merlin engines, a new first stage engine cluster, lengthened propellant tanks and other improvements, the Falcon 9 deployed Canada's Cassiope space weather research satellite and a flock of secondary payloads into polar orbit after lifting off from Vandenberg Air Force Base, Calif.

The Falcon 9 rocket's second stage, powered by a Merlin 1D engine optimized for performance in the vacuum of space, completed the an initial burn required to place the launcher's satellites into orbit.

After releasing the mission's payloads, SpaceX programmed the second stage to restart its engine in a demonstration of a capability required by future flights, beginning with the launch of SES 8.

Photo of the Falcon 9's launch from Vandenberg Air Force Base, Calif. Credit: SpaceX
The SES 8 launch is the first mission of the improved Falcon 9 from Cape Canaveral, and it marks SpaceX's arrival in the global commercial launch services market. All of SpaceX's previous launches went to low Earth orbit a few hundred miles up. Monday's launch is heading for a maximum altitude of 22,300 miles.

SES inked the launch contract with SpaceX for SES 8 in March 2011.

The 7,055-pound SES 8 spacecraft was built by Orbital Sciences Corp. and is destined for a position in geostationary orbit at 95 degrees east longitude, where its 24 Ku-band transponders will broadcast direct-to-home television to customers across the Asia-Pacific.

SES 8 is the first Falcon 9 primary payload to require the Merlin engine restart capability. The launcher will put SES 8 into an elliptical geostationary transfer orbit, the drop-off point for most broadcasting satellites.

SpaceX and SES have not disclosed the exact orbit the Falcon 9 will target on Monday's mission.

SES 8 will use an on-board propulsion system to put itself into a circular geostationary orbit over the equator at an altitude of 22,300 miles. SES says the satellite will enter commercial service in the first quarter of 2014.

Follow Stephen Clark on Twitter: @StephenClark1.



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