The Atlas 5 rocket arrives at the launch pad atop its mobile launch table. Photo: Lockheed Martin

Lockheed Martin's new Atlas 5 rocket has passed another key milestone on the road to its maiden voyage this July with the completion of a full launch day simulation.

Before dawn last Wednesday, May 15, the 191-foot tall rocket was moved atop a mobile transporter from its vertical hangar to the launch pad, signalling the start of the second so-called Wet Dress Rehearsal for Atlas 5.

As the day progressed, the launch team inside the new Atlas 5 Spaceflight Operations Center control room followed a countdown timeline very similar to the one for the rocket's inaugural flight. By late afternoon, super-cold liquid oxygen had been loaded into the first and second stages and liquid hydrogen propellant was nearly all aboard when a problem occurred.

Following a successful first countdown dress rehearsal in March, engineers changed a valve setting, believing it would be for the better. However, the change caused a rise in pressure that tripped up computer software monitoring the rocket, forcing a hold.

"We had made a change to try to make an improvement on the transfer line chilldown," Adrian Laffitte, Lockheed Martin's director of Atlas launch operations, said in an interview Saturday. "It was one of those things that worked the last time (but) let's see if we can make it better. The way we made the change, it created a back pressure that the software detected and immediately put us into a safe condition."

Already 14 hours into the countdown simulation, officials made the decision to basically scrub for the day and drain the cryogenics from the Atlas and Centaur stages.

The Atlas 5 Spaceflight Operations Center, or ASOC. Photo: Lockheed Martin

With analysis in hand to show what caused the glitch, the launch team changed the setting in preparation for another countdown attempt on Friday.

Fueling went well the second time around and the launch team guided the countdown to the T-minus 4 minute mark where a 10-minute hold was planned.

With all in readiness, clocks resumed ticking.

"We counted down from T-minus 4 and had a planned abort at T-45 seconds," Laffitte said.

The abort was designed to give the launch team practice in dealing with problems. The countdown was recycled to T-4 minutes and the rocket was put back into a launch posture for another try.

"We executed the abort, recycled and did count down from T-minute 4 all the way up to one second, aborted and recycled. Everything worked like a charm," said Laffitte.

"We executed two aborts and two recycles. There are over 500 redlines that we could get and we got none," Laffitte said of the parameters placed on systems to ensure all is working properly. "We were extremely happy."

The liquid oxygen and liquid hydrogen supplies were offloaded from the rocket Friday evening, and on Saturday the RP-1 kerosene fuel in the Atlas first stage that had been pumped into the rocket previously was drained. By mid-day Saturday, the rocket had completed the 1,800-foot roll back to its Vertical Integration Facility hangar to bring the Wet Dress Rehearsal No. 2 to a close.

Lockheed Martin officials have debated whether to do another full rehearsal between now and launch. Laffitte says a final one might be scheduled for late June.

Atlas 5 on the launch pad at sunset. Photo: Lockheed Martin

"From a technical point of view, we are happy we did two WDRs and we're pleased with all the technical data. But I think what we are going to end up doing is probably having what we call a Launch Campaign WDR with the customer."

The customer for the first Atlas 5 is Paris-based Eutelsat, which operates an orbiting fleet of commercial communications satellites. The company's Hot Bird 6 direct-to-home TV broadcasting satellite will ride the rocket into space.

The spacecraft is due to arrive from Europe on June 13 and be taken to a processing building for final pre-launch preparations.

While Hot Bird 6 is getting ready, the third countdown test could be performed, Laffitte said, giving the entire team one more opportunity to practice before the real launch day arrives.

Launch is still officially scheduled for July 8, with backup attempts available on July 9 and 10. But a couple-week delay may be in the offing.

Lockheed Martin has formally submitted a request to the Air Force-controlled Eastern Range at Cape Canaveral to take any open dates later in July.

The Range provides safety, tracking and communications services to all rocket and space shuttle launches from the Cape, and can only support one launch or major event at a time.

"We did put a request on the Range that said we want any dates between the 19th and 26th -- whatever becomes available," Laffitte confirmed.

"We want to give ourselves a little bit of contingency time," Laffitte explained. "It is just a matter of building a little bit of margin."

At present, the week of July 19th is all booked up on the Range with planned liftoff of space shuttle Columbia July 19 from Kennedy Space Center, followed by scheduled tests that need Range support involving Titan 4 and Delta 4 rockets for their upcoming summer launches.

The shuttle launch date has the potential of being delayed or the other rocket tests could also slip. Lockheed Martin's request would allow the Atlas 5 launch to fill whatever hole opens up on the Range.