SpaceX Launch Time Set for 03:44 EDT 22 May 2012

If all goes as planned, SpaceX’s Falcon 9 rocket will lift off from Cape Canaveral in Florida at 3:44 A.M. Eastern Daylight Time tomorrow. The Falcon 9 will loft the company’s Dragon space capsule into orbit. The Dragon is slated to become the first privately operated spacecraft to rendezvous with the International Space Station, delivering a payload of crew rations and other cargo to the six astronauts on the station.

If the mission unfolds smoothly, SpaceX will begin regular deliveries of supplies to the space station. The company has agreed to send 12 cargo capsules to the space station over the next few years, at a total cost to NASA of $1.6 billion. Someday, a human-rated Dragon capsule could ferry astronauts, not just cargo, to and from orbit. But first the Falcon 9 rocket must get off the ground. _Sciam

Problems with last weekend's planned launch are being blamed on a faulty valve, which allowed pressures in the #5 engine combustion chamber to climb to marginally high levels -- automatically scrubbing the closely timed launch.

SpaceX has replaced a faulty valve that led to the aborted launch attempt early Saturday morning and is currently planning a second launch attempt at 3:44 a.m. EDT Tuesday, May 22. The first launch attempt was unsuccessful after a last-half-second shutoff occurred due to higher than acceptable pressure in the combustion chamber of one of the Falcon 9′s Merlin rocket engines.

After examining the problematic engine, SpaceX engineers were able to trace the high-pressure problem to a valve that controls the flow of nitrogen used to purge the engine before ignition. Using the inert nitrogen gas to purge rocket engines is common and has been used for decades. The nitrogen displaces gases and/or liquids, effectively cleaning the engine and preventing any volatile mixtures before ignition.

A check valve that allows the nitrogen purge prior to ignition in the Merlin engine was stuck open just before launch. This stuck valve allowed “liquid oxygen to flow from the main injector [for the rocket engine itself] into the gas generator injector” that generates hot turbine gas, which drives the turbopumps, according to SpaceX. The turbopumps (pictured) are basically very high-powered fuel and oxidizer pumps that deliver the liquids to the main combustion chamber of the rocket. The result was the turbopumps were operating at a slightly higher power level, resulting in the high pressure detected in the combustion chamber on engine five. _Wired

The more moving parts an engine contains, the more potential for such problems as apparently occurred. Potential hazards tend to expand exponentially at the kinds of pressures and temperatures which are normally found in and around rocket engines such as SpaceX's Merlin.

Here is a SpaceX flashback to 2003, containing a report on early tests and plans for the Merlin engine and the company. Such looks back are likely to prove nostalgic, should SpaceX achieve tomorrow morning's launch, and succeed in this and subsequent missions.