The Atlas 5 rocket spent over 90 straight hours on the launch pad for its first countdown test last week.

The Lockheed Martin Atlas 5 rocket is one step closer to its summertime inaugural launch following the successful countdown rehearsal and fueling tests conducted at Cape Canaveral's Complex 41 last week.

Known as a Wet Dress Rehearsal, or WDR, three of these countdown tests are planned over the next couple of months as pathfinder exercises to practice transporting the rocket to the pad, loading propellants and conducting simulated launch days for the control team.

The tests give engineers the chance to find any problems early so they can be resolved before the real launch day arrives.

Other than a few technical bugs that were uncovered with ground equipment, officials said the Atlas 5 rocket performed "flawlessly" during the crucial tests.

"The first one was a hit the first time out," John Karas, Lockheed Martin's vice president of Atlas Development, said of the successful 4 1/2-day test. "It exceeded everyone's wildest expectations."

Riding atop its 1.5-million pound mobile launching platform, the rocket was rolled from the new Vertical Integration Facility (VIF) to the open-air launch pad on Monday, March 11. The 1,800-foot trip takes about 20 minutes.

The Atlas 5 rocket leaves the VIF for the launch pad 1,800 feet way. Photo: Lockheed Martin

For a real launch day, the Atlas 5 will be moved to the pad just 11 hours before blastoff to be fueled up and readied for the final countdown. With such a short stay, a mobile service tower isn't needed at the pad.

Over the past two years, Complex 41 has been transformed from its legacy of launching Titan 4 rockets to supporting the next-generation Atlas 5. Adrian Laffitte, Lockheed Martin's Atlas launch director, says all that remains of the Titan 4 era is the flame ducts and four lightning protection towers.

After reaching the pad Monday, the first stage was loaded with RP-1 propellant, a highly refined kerosene.

Tuesday was spent working through some technical issues with ground systems.

On Wednesday, the launch team -- stationed in the new Atlas 5 Spaceflight Operations Center at Complex 41 -- oversaw the loading of the Centaur upper stage with its supplies of super-cold liquid oxygen and liquid hydrogen. The cryogenics were drained later that day.

Thursday saw the completion of a simulated launch day with the pumping of liquid oxygen into the Atlas 5's first stage. The countdown clock reached T-minus 4 minutes before the test was concluded and the liquid oxygen off-loaded.

The rocket rolls back to the VIF. Photo: Justin Ray/Spaceflight Now

Technicians spent Friday morning draining the RP-1 fuel from the first stage and readying the rocket for its return to the VIF building. The rollback was finished by lunchtime.

"The last piece of the Atlas 5 launch system left to test was the integration of vehicle and launch pad, which has now been verified to perform as designed and advertised," Karas said.

"Once again the entire Atlas 5 team has done a fabulous job achieving another critical program milestone," said Col. Bob Saxer, the Air Force's Evolved Expendable Launch Vehicle system program director. The Atlas 5 and Boeing's Delta 4 rockets are being developed in conjunction with the EELV program to usher in a new generation of U.S. launch vehicles.

"The technical challenges associated with bringing a brand new launch vehicle and launch pad to life are not insignificant. John Karas and the entire Atlas 5 technical team are to be commended for the outstanding job they've done; successfully tanking the entire vehicle, taking it to flight pressures, and counting down to T-minus 4 minutes during the first WDR is very impressive. I look forward with great anticipation to our first launch."

In all, the rocket spent over 90 hours standing on its launch pad, experiencing winds of up to 31 knots, rainshowers and even some lightning in the area. Since there is no protective service tower to enclose the rocket on the pad, the vehicle is designed to safely withstand over 60 knots of winds.

The Atlas 5 rocket sits on the open-air launch pad at Complex 41. The Vertical Integration Facility is the towering building to the left. Photo: Lockheed Martin

Karas said the next rehearsal will occur in about a month. Engineers will spend the next few weeks reviewing all the data gathered during this first test. The next WDR will also see the rocket fully fueled and clocks ticking down to T-0 seconds while the launch team practices countdown aborts and simulated problems.

This first Atlas 5 rocket, tail-number AV-001, will fly in what Lockheed Martin calls the 401-vehicle configuration. That means it will have a four-meter (14-foot) payload fairing nose cone, no strap-on solid rocket boosters and one Pratt & Whitney RL-10 engine on the Centaur upper stage. As with all Atlas 5 configurations, the first stage is made up of a "Common Core Booster" powered by a Russian RD-180 engine.

Standing 191 feet tall and capable of delivering 10,900 pounds of satellite cargo into geosynchronous transfer orbit, the 401-configuration will be the largest and most powerful version of the Atlas rocket to fly, surpassing the records set just last month with the inaugural Atlas 3B.

Launch of the first Atlas 5 has been delayed from its long-standing May 9 target date at the request of the mission's customer -- Eutelsat. The Hot Bird 6 direct broadcasting satellite won't be ready for launch until late June or early July.

Lockheed Martin has tentatively looked at July 8 as the new launch date.