Unfortunately, it wasn't third time's a charm for the SpaceX CRS-3 mission to send an unmanned Dragon cargo ship to the International Space Station (ISS). In a statement today, SpaceX announced that the Monday launch of the Falcon 9 rocket has been rescheduled until April 18 because of a helium leak in the first stage. However, weather forecasts show conditions around Cape Canaveral deteriorating as the week progresses, so even that date is tentative.
This marks the third attempt to launch the CRS-3 mission and the third time that it has been scrubbed. The first delay was due to a contaminant found in the unpressurized cargo bay of the Dragon cargo ship, and the second occurred when a tracking radar was put out of action by a major malfunction.
The Dragon spacecraft had been scheduled to dock with the Earth-facing port on the Harmony module two days after launch. However, in the run up to Monday’s aborted launch, the ISS suffered a malfunction in an external computer called the Multiplexer/Demultiplexer (MDM). An emergency spacewalk is scheduled to repair this, but it is not clear whether this will cause a further delay for the docking of the cargo ship.
The Dragon spacecraft is carrying 2.5 tons (2.26 tonnes) of experiments and supplies to the ISS, including a new spacesuit and parts to repair the spacesuits already on the station. In addition, the Falcon 9 booster was scheduled to deploy microsatellites as part of the mission.
The rocket is also carrying landing legs for the first time on an operational launch mission. These are mainly intended to fly as dead weight to make sure the legs don’t interfere with flight operations or deploy prematurely. However, an experimental landing sequence will be carried out after second-stage separation ending in a pretend "landing" on the surface of the Atlantic Ocean, though SpaceX says that this maneuver has only a 30 to 40 percent chance of success.