Since the White House announced in February its new plan for NASA, canceling the Constellation program and putting a new emphasis on technology development and commercial providers, the future of the agency has been a subject of hot debate in the space community. NASA’s top two officials came to a major conference last week to defend–and debate–the agency’s new direction.

“I personally believe the president’s fiscal year 2011 budget and the request that goes with it is good for NASA, because it sets the agency on a sustainable path that’s tightly linked to our nation’s interests,” NASA Administrator Charles Bolden said in a dinner speech in Chicago at the International Space Development Conference (ISDC), the annual conference of the National Space Society (NSS). Bolden went on to say that the plan is “is the most authentically visionary policy for real human space exploration” since President John F. Kennedy announced a goal in 1961 of landing humans on the Moon by the end of the decade.

NASA Deputy Administrator Lori Garver, who served as executive director of NSS for several years in the 1990s, also defended the president’s plan in a luncheon speech at ISDC. “People have made a lot of rhetorical statements that this plan kills human spaceflight; in fact, it does the opposite,” she said, noting that Constellation was suffering from cost and schedule problems identified last year by the Augustine Committee.

Others at ISDC, though, were skeptical of some elements of the plan, including the decision to cancel the Ares I rocket that would have been used to launch the Orion crewed spacecraft. Scott Pace, a former NASA official who is now director of the Space Policy Institute of George Washington University, said at the conference it would be wise to retain Ares I as both a backup for proposed commercial crew providers as well as an investment in future heavy-lift rockets. Garver, engaging in an impromptu debate with Pace, disagreed, noting that the funding in the budget proposal for commercial crew programs “is not nearly enough” to complete Constellation if spent there instead.

Another critic of NASA’s new direction at ISDC was Robert Zubrin, president of the advocacy organization The Mars Society. While President Obama set a goal of a human mission to orbit Mars by the mid-2030s, that goal is too far in the future for Zubrin. “It basically means that they don’t have to start working on it while they’re in office,” he said.

At the end of her luncheon speech, Garver said she hoped that ISDC attendees, including members of the organization she once ran, would help advocate for the plan as Congress takes up the NASA budget in the coming months. “The space community should hopefully see that this our time,” she said.