WASHINGTON and NEW YORK — House lawmakers expressed confidence in the safety of NASA’s planned Ares 1 rocket and questioned whether alternative launchers and spacecraft could provide the same level of assurance sooner than the systems the agency is developing to replace the space shuttle.

During a Dec. 2 hearing, Rep. Gabrielle Giffords (D-Ariz.), chairwoman of the House Science and Technology space and aeronautics subcommittee, said the predicted safety of alternatives to NASA’s Orion Crew Exploration Vehicle and its Ares 1 launcher offers no compelling reason for NASA to change course. Orion and Ares 1, in development for the past five years, would replace the space shuttle as part of NASA’s Moon-focused Constellation program.

“Based on what we heard today, I see no justification for a change in direction on safety-related grounds,” Giffords said after hearing more than two hours of testimony from NASA officials, independent experts and a lone representative of the nascent commercial spaceflight industry.

Giffords, who is married to NASA astronaut Mark Kelly, said the hearing would inform future discussions on NASA’s manned space exploration plans. The current approach is under scrutiny by the White House, which received a review of NASA’s exploration goals from a committee of independent experts in October.

Meanwhile, NASA has set aside $50 million to support development of commercial vehicles capable of transporting crews to the international space station after the space shuttle fleet is retired. In its report, the White House-appointed committee recommended that NASA invest about $5 billion in commercial crew-carrying spacecraft.

Giffords said the commercial sector should not be in competition with the Constellation program, and that NASA will rely on private industry to develop systems capable of carrying cargo to the space station. She said NASA must continue to improve safety on Ares and Orion, as well as on promising commercial vehicles that could ferry astronauts to and from low Earth orbit. She stressed that NASA must set guidelines for commercial vehicles before astronauts can ride them into space.

“Much has been said about the potential for future plans in recent months, but there has been precious little discussion about safety,” she said in opening remarks.

NASA plans to fly five more shuttle missions in 2010 before retiring its three remaining orbiters to make way for Orion and Ares 1. The agency launched a suborbital test flight in late October of a prototype Ares rocket.

“Simply put, safety is a top priority in NASA’s Constellation program,” said Jeff Hanley, who leads that effort for the space agency.

NASA’s space shuttle program aims for a safety threshold that allows for a 1-in-100 chance of a launch accident. Astronauts and NASA officials want to boost that safety margin to a 1-in-1,000 chance for any future vehicles, said Tom Stafford, a retired U.S. Air Force lieutenant general who flew missions on NASA’s Gemini and Apollo spacecraft.

Unlike the space shuttles, the Ares 1 rocket will have a launch abort system designed to whisk Orion and its crew to safety in the event of an emergency at liftoff.

Orion and Ares are slated to begin operations in 2015, but the independent committee’s report stated that, given NASA’s available budget, the new vehicles will not be ready until 2017. Commercial crew vehicles, the committee stated, could be ready by 2016.

Two U.S. companies, Space Exploration Technologies (SpaceX) of Hawthorne, Calif., and Orbital Sciences Corp. of Dulles, Va., are building space station logistics vessels under contracts with NASA. Both companies have expressed interest in upgrading those capsules to carry astronaut crews.

Bryan O’Connor, a veteran shuttle commander and NASA’s safety chief, said the agency has provided its safety requirements to those firms, but formal discussions over human-rating a commercial spacecraft have not begun. The agency plans to use some federal stimulus funds to develop concise technical requirements for commercial crew capsules, as well as set up some form of oversight, he added.

“The longer we wait to start that process of commercial crew activities, the longer it will take us in terms of shortening any gap,” Brett Alexander, head of the Commercial Spaceflight Federation, told the House subcommittee. Alexander was referring to the anticipated time gap between the shuttle fleet’s retirement and the advent of its replacement system.

Alexander said that while the U.S. Federal Aviation Administration (FAA) will likely regulate commercially built manned spacecraft, NASA as the customer would have to tailor its requirements for crew vehicles to fit those private vehicles.

“There is no cookie-cutter approach to safety in space, nor is it a given,” said John Marshall, a member of NASA’s independent Aerospace Safety Advisory Panel (ASAP), during the hearing. “The ASAP strongly believes that specific criteria should be developed to establish how safe is safe enough.”

O’Connor said it took NASA about eight months to tailor its human-rated safety requirements to the in-house Orion spacecraft and its Ares 1 rocket. It took three years before NASA engineers were comfortable enough with Russia’s Soyuz vehicle to allow astronauts to fly on it. Today, Soyuz spacecraft are the standard ferry ships for space station crews.

It would take up to six years, O’Connor said, to adapt Orion to fly on a different rocket such as the Atlas 5 or Delta 4 Heavy boosters currently used to launch satellites to orbit.

But Alexander stressed that the six-year estimate is for Orion only. A smaller, commercially built crewed spacecraft could take as little as three years to meld with NASA’s guidelines, he said.