WASHINGTON — NASA’s space shuttle replacement program could be delayed by as much as four years due to inadequate funding, though additional money could minimize the schedule slip, according to an independent assessment by the Aerospace Corp., a government consultancy here.

“Aerospace believes that NASA is not properly funded to accomplish its current program of record. We think the schedule is going to slip,” Gary Pulliam, Aerospace Corp.’s vice president of civil and commercial operations, told members of a blue-ribbon commission tasked with reviewing NASA’s human spaceflight plans and providing a range of options to the White House in mid-August. The panel, led by former Lockheed Martin Chief Executive Norman Augustine, asked Aerospace Corp. to weigh in with an independent assessment of NASA’s Constellation program as part of its review.

Constellation refers not only to the shuttle replacement system, consisting of the Orion crew capsule and its Ares 1 launcher, but also to other hardware NASA needs to return astronauts to the Moon by 2020. The Ares 1-Orion system is scheduled to debut in March 2015, Pulliam said Ares 1-Orion could slip 18 months based solely on the White House’s 2010 budget request for the program. In addition, looming technical problems associated with the Ares 1 rocket could add another two years to the delay unless more money is made available to mitigate the risk.

The Aerospace Corp. also looked at the budget impact to Constellation of potentially extending the international space station program to 2020, Pulliam said. NASA’s current official plan is to de-orbit the station in 2016.

“From a perspective of needing to keep the station flying, and in the presence of the budget profile that is our baseline, the extension of [the international space station] to 2020 would result in another six months’ delay,” he told the 10-member panel during a July 29 day-long public meeting in Huntsville, Ala. Pulliam also said the current funding profile does not provide enough money to return humans to the Moon, though he said Aerospace Corp. is currently conducting a study of the cost and schedule for a robust human lunar return.

NASA’s current policy calls for a return to the Moon by 2020, a plan endorsed by U.S. President Barack Obama during his 2008 campaign.

As part of its study, Aerospace Corp. looked at a range of space transportation options, including the ability of private companies to launch humans into space.

“We recognize the value of COTS,” he said, referring to NASA’s Commercial Orbital Transportation Services program intended to incubate a commercial space station logistics and crew transportation service. “But it is a complement to exploration; it does not accomplish exploration.”

Pulliam also cautioned that, absent adequate funding, alternatives to Constellation are not necessarily any better, and that additional analysis is needed to ensure NASA does not “trade one insufficiently funded program for another insufficiently funded program.”

Pulliam’s talk was just one in a packed lineup of presentations to the Augustine panel, currently on a three-day tour of public meetings held in Texas, Alabama and Florida. In addition, there were presentations by members of subgroups within the blue-ribbon commission, including former Boeing rocket engineer Bo Bejmuk, whose team is charged with recommending launch vehicle options, and retired Air Force Gen. Lester Lyles, who is examining international and interagency cooperation