WASHINGTON — NASA officials are weighing whether they need two space shuttle launch pads to support the upcoming Hubble Space Telescope servicing mission or if they can get by with one launch pad, a shift that would help keep the planned July test flight of the Ares 1-X launch vehicle on schedule.

Before NASA can fly the Ares 1-X, a prototype of the Ares 1 crew launch vehicle slated to debut in 2015, the agency needs to make permanent modifications to one of the two space shuttle launch pads at Kennedy Space Center in Florida. However, the Hubble servicing mission as currently planned requires both pads to be available: one from which to launch the Space Shuttle Atlantis on the repair mission and one to launch Space Shuttle Endeavour on a rescue mission, should that become necessary.

Current plans call for having Atlantis and Endeavour occupy pads 39-A and 39-B, respectively, during preparations for the planned May 12 launch of the STS-125 Hubble servicing mission. But NASA officials now are considering launching Atlantis and then rolling Endeavour out to pad 39-A, said Jeff Hanley, Constellation program manager at NASA’s Johnson Space Center in Houston. This would make pad 39-B available to undergo the three to four months of modifications necessary to support the Ares 1-X flight, he told reporters in a Dec. 17 press briefing.

Constellation refers to the hardware NASA needs to replace the space shuttle, which is slated to retire in 2010, and return astronauts to the Moon.

To hold to the July 11 date for the Ares 1-X test flight, Hanley said he will need a decision by February as to whether the Hubble servicing mission will use just one launch pad.

Bill Gerstenmaier, NASA associate administrator for space operations, and John Shannon, space shuttle program manager, will decide whether Endeavour can be placed in ready status quickly after Atlantis lifts off, an option NASA officials previously said was not likely. The prospect of Ares 1-X being delayed again by the Hubble servicing mission prompted a second look at that option.

“I think I can confidently say if pad B is required for STS-125 in May ’09 that we will not launch Ares 1-X in July.” Hanley said. “We have some very close coordination going on with the shuttle team. We are trying to mitigate as much as we can the overlap that might occur should the shuttle team not be able to use single pad operations.”

Ares 1-X originally was scheduled to launch in April, but the flight was pushed to July after problems with Hubble’s onboard computer system delayed the servicing mission to the 18-year-old observatory to February. NASA later delayed the Hubble mission to May after a discovering glitch in one of Hubble’s spare parts.

While the Constellation team awaits a decision on the Ares 1-X test flight, it is working on other equipment modifications needed to support the Ares program. The team installed electronics on the shuttle’s mobile launcher platform, for example, even though that system has not been officially handed over to them, Hanley said.

“The team has been digging in and finding operations to do,” he said. “We’re looking for opportunities every chance we can get.”

NASA has embarked on an ambitious three-day roll out and launch schedule for Ares 1-X, which Hanley said he believes the team can meet, or at least come close to meeting.

Meanwhile, NASA is working toward other Constellation milestones, including an Ares 1 preliminary design review in the spring or early summer and release of the first phase of contracts for the heavy-lift Ares 5 launcher necessary to support the return of astronauts to the Moon. The final request for proposals will be issued the week of Dec. 21, said Doug Cooke, deputy associate administrator of the Exploration Systems Mission Directorate at NASA headquarters in Washington.

NASA also is seeking comment from industry on a draft request for proposals for the first phase of contracts for the Altair lander, which will be launched by Ares 5 and carry four astronauts to the lunar surface. That final request for proposals is expected in January.