ISS glitch won’t delay SpaceX launch

Falcon 9 CRS 3 before launch

A SpaceX Falcon 9 v1.1 carrying a Dragon spacecraft on the pad at Cape Canaveral, Florida, on Sunday. NASA cleared the launch of the Dragon spacecraft, scheduled for Monday afternoon, despite the failure of a backup computer on the ISS. (credit: NASA)

The failure of a backup computer on the International Space Station (ISS) won’t further delay SpaceX’s next cargo mission to the station, which is still scheduled for launch Monday afternoon, officials said Sunday.

The potential for another delay for SpaceX’s third Commercial Resupply Services (CRS) mission to the station, designated SpaceX-3 or SpX-3 by NASA and CRS-3 by SpaceX, arose Friday evening when a backup Multiplexer-Demultiplexer (MDM) computer on the exterior of the station malfunctioned. The MDM backs up other computers used to control exterior systems on the station, including the solar arrays and a mobile transporter on the truss. NASA officials feared another failure could prevent the crew from berthing the Dragon to the station when it arrived there after launch.

At a briefing midday Sunday, NASA officials said they had worked out ways to ensure sufficient redundancy to proceed. “The team concluded the MMT [Mission Management Team meeting] with a go for SpaceX-3,” said Michael Suffredini, ISS program manager. The steps NASA will take will be to move the mobile transporter cart to a new position later today, and to put the solar arrays into a different configuration immediately after the launch to ensure they generate enough power but don’t interfere with the arrival and berthing of the spacecraft, in the event there was another computer failure between launch and Dragon arrival.

Suffredini said that the failed MDM will have to be replaced in a spacewalk, which would take place no earlier than April 22 should Dragon launch on time. The replacement of the MDM with a spare already on the station is a relatively straightforward repair, he said, taking no more than two and a half hours, and would be the only activity during the contingency spacewalk.

Launch is scheduled for Monday in an instantaneous launch window at 4:58:44 pm EDT (2058:44 GMT) Monday, with an 80-percent chance of acceptable weather at launch. Should the launch be delayed, the next opportunity is not until Friday because of orbital mechanics issues; the forecast then is only for a 40-percent chance of good weather.

One aspect of Monday’s launch beyond the delivery of the Dragon cargo spacecraft into orbit will be the test of the recovery of the Falcon 9 v1.1’s first stage. Hans Koenigsmann, vice president of mission assurance for SpaceX and the launch director for the mission, emphasized that the attempt to softly splash down the stage into the Atlantic Ocean is “completely experimental” with the odds of success of only 30 to 40 percent. “This is a really difficult maneuver,” he said of the recovery effort, which involves reentry and landing burns by the first stage after separating, with the water simulating a landing pad. If it works, he said, “we would be super thrilled.”

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