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March 04, 2013

SpaceX-2 Dragon Works out Thruster Problems

By Doug Mohney, Contributing Editor


The SpaceX (News - Alert) Dragon vehicle launched on March 1, 2012, and the second commercial space station supply mission appears to have cleared its thruster problems, leaving company officials and NASA cautiously optimistic that it will be able to continue its mission.

Dragon's thruster problems became apparent shortly after the vehicle had successfully detached from Falcon 9's second stage about 11 minutes into flight after a 10:10 a.m.ET launch from Cape Canaveral Air Force Station. Only one of the four clusters on the spacecraft had initialized, delaying deployment of solar panels and triggering a set of troubleshooting steps to assess the health of the vehicle and what could be wrong with the thrusters.

During the troubleshooting process, SpaceX decided to deploy the solar panels despite having only one thruster pack on-line.   Engineers were concerned that a drop in temperatures would affect deployment down the line, but the action proved to be a help.

SpaceX CEO and co-founder Elon Musk said he wanted to be careful about assigning a root cause to the thruster problem, but one possibility appeared to be some sort of blockage in the oxidizer pressure lines or a stuck valve as a "preliminary guess." A combination of cycling and "pressure hammering" valves appears to have unblocked the valves.

By the time SpaceX and NASA convened a 3 p.m. conference call, pressurization levels on all tanks were "nominal," said Musk, with pods 1 and 4 enabled and 2 and 3 being brought on line.

Minutes after the conference call ended at 4:04 pm. , Musk tweeted, " Thruster pods one through four are now operating nominally. Preparing to raise orbit. All systems green."

NASA officials William Gerstenmaier and Mike Suffredini both praised the SpaceX operations team for the professional job in handling the spacecraft as it focused on keeping the Dragon stable and healthy while they worked on the thruster issue.

Dragon's balky thrusters delayed a series of burns to even out its insertion orbit and start a careful approach toward the International Space Station (ISS) that would have resulted in a rendezvous and berthing on Saturday.  

NASA officials wouldn't commit to a date when a new rendezvous between Dragon and station wouldn't occur, but suggested one reporter "not to go to sleep" on Sunday.

Flight safety rules require that Dragon have three fully working thruster packs before making a close approach to ISS. NASA and SpaceX will be able to observer the operation of the thrusters over the next day as the vehicle conducts its approach to the station and conducts attitude control firings.

 If both parties are convinced the thruster systems are now stable and reliable, NASA will then give a green light for a rendezvous. Suffredini said there's a "number of days" available for a rendezvous in March while Musk said Dragon is good for "at least a month" on orbit.




Edited by Brooke Neuman



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