SpaceX CRS-3 Cleared for Friday Launch, Spacewalk on Wednesday

SpaceX will try again to launch its third operational cargo mission to the International Space Station (ISS) on Friday.  The launch window opens at 3:25 pm ET, but the weather forecast is poor.  Meanwhile, the ISS spacewalk needed to fix a broken computer on the exterior of the space station is now planned for Wednesday, April 23.

The SpaceX CRS-3 launch was scrubbed on Monday because a helium valve in the stage separation pneumatic system in the Falcon 9 first stage was not holding the correct pressure, the company said in a statement today.  It added that the launch could have gone ahead and relied on a backup check valve, but “SpaceX policy is not to launch with any known anomalies.”

The weather was great on Monday, but much has changed since then and the forecast for Friday is only 40 percent favorable.   NASA TV will cover the launch beginning at 2:15 pm ET and SpaceX will webcast it beginning at 2:45 pm ET.   If all goes as planned, the Dragon spacecraft with its load of cargo will arrive at the ISS Sunday morning, April 20, and be grappled by Canadarm2 at about 7:14 am ET.  NASA TV will cover the events beginning at 5:45 am ET.

One of the more interesting aspects of this launch is that SpaceX will test landing legs for the Falcon 9 first stage as a step towards eventually making the vehicle reusable.  This test will take place over the ocean so the vehicle will fall into the water, but only after SpaceX collects the data it needs to determine if the landing legs performed as expected.  A SpaceX official stressed that it is an experiment and the company is only 30-40 percent confident it will work.

If the weather or anything else interferes on Friday, SpaceX plans to try again on Saturday at 3:02 pm ET.

Meanwhile, NASA continues preparations for a “contingency” spacewalk (as opposed to a regularly scheduled spacewalk) to replace a malfunctioning computer called a Multiplexer-DeMultiplexer (MDM) on the outside of the space station.   NASA determined over the weekend that Dragon could be berthed to the ISS despite the malfunction; the primary MDM is working fine.  The MDMs control some of the robotic systems aboard ISS.   NASA astronauts Rick Mastracchio and Steve Swanson will perform the spacewalk on Wednesday, April 23, under the current plan.  NASA space station program manager Mike Suffredini described this as one of the easier tasks and the spacewalk is scheduled for only 2.5 hours.

If the SpaceX launch is scrubbed on Friday, however, NASA will move the spacewalk up to Sunday, April 20.