SAN FRANCISCO — When U.S. senators angrily denounced President Barack Obama’s 2011 NASA budget request, saying the plan to cancel the Constellation program leaves the United States without any clear goal for human spaceflight, NASA Administrator Charles Bolden responded that the ultimate goal is Mars.

Unlike the Apollo program with its clear timetable for reaching the Moon, however, Bolden said Mars was not a destination that could be reached within a decade.  “When we take on Mars, it is radically different from going to the Moon and it offers radically different challenges,” he said Feb. 24 during a hearing on NASA’s 2011 budget by the Senate Commerce science and space subcommittee. “I can’t provide a date certain for the first human mission to Mars because there are too many capabilities that we don’t have in our kit bag.”

To prepare to send astronauts to Mars, Bolden said the space agency would have to make significant investments in research to better understand the impact of radiation and long periods in low-gravity environments on the human body. In addition, NASA should develop spacecraft and launch vehicles capable of reaching the red planet quickly, he added.

“I would like to develop space technology that allows us to go to Mars in days not months … or a least to cut in half the time it would take us to travel there right now,” Bolden said. “We have got to invest in that technology.”

While senators generally endorsed Mars as a destination for human spaceflight, they also expressed concern that the Obama administration’s proposed cancellation of the Constellation program would cause irreparable harm to the space workforce.  “A significant upheaval in this workforce related to shuttle retirement is going to occur,” said Sen. Bill Nelson (D-Fla.), chairman of the subcommittee. “That massive loss of jobs is now exacerbated by the perception of the cancellation of Constellation and all the programs under it.”

To save some of those jobs, Nelson said the space agency should continue testing the Constellation program’s Ares I rocket and pursue a robust heavy-lift launch vehicle development effort. That type of activity would help NASA achieve its future exploration goals while making use of the nation’s dedicated and talented space workforce, he added.

Sen. David Vitter of Louisiana, the subcommittee’s ranking Republican, offered the most stinging criticism of the president’s plan. “This budget and the vision it represents would end our human spaceflight program as we know it and would surrender our world leadership in the area,” Vitter said. “I will fight with every ounce of energy I have to defeat this budget or anything like it. I believe there is great bipartisan support for that.”

Nelson said he also expected Congress to call for changes in the NASA budget, adding that his concerns were shared by his colleagues on the congressional committees responsible for appropriating funding for NASA programs.

While discussing his concern about job losses that would result from the proposed cuts in NASA’s human exploration program, Vitter asked Bolden what he says to “the NASA family,” the people who work for the space agency or private space companies. “I told them I don’t know how they feel,” Bolden responded, with tears in his eyes. “My kids are 38 and 33, they are out of school. I don’t know what a young engineer with a fifteen-year-old kid feels like right now. I know they are hurting.”

Both Nelson and Vitter also questioned NASA’s plan to rely on private space companies to develop the capabilities needed to offer transportation of astronauts and cargo to low-Earth orbit. Nelson cited safety concerns, while Vitter chided the administrator for offering a budget that would “cancel all major existing human spaceflight programs … with little more than a hope and prayer that commercial providers will eventually pick up the slack. There is no realistic hope that that can be done on a reasonable timeline. “

Bolden said he was confident that private companies would succeed in developing those spacecraft. “It my hope that by 2015, 2016, we will have enabled American industry to provide us with routine, reliable access to low-Earth orbit,” he said.

Vitter was particularly aggressive when asking Bolden whether NASA Deputy Administrator Lori Garver was the primary architect of the 2011 budget plan. Bolden replied that many individuals were involved in the budget process and declined to cite any specific architect, adding that if the panel wanted to blame someone, he would accept that blame. That response did little to appease Vitter who said he had heard speculation that Garver might one day be nominated to fill the post of NASA administrator. “Based on this budget, I would be a strong, fierce, active opponent of that,” he said.

Nelson, meanwhile, suggested that the White House Office of Management and Budget (OMB) was the real culprit. “I think OBM is running the space program because it designs the budget,” Nelson said. “The president has to take control. The president has to offer leadership.”

In his defense of the NASA spending plan, Bolden said the 2011 budget is not “a radical departure from the vision for human space exploration” as the senators suggested, but rather a more realistic course.  When he took over the job as NASA administrator in July, Bolden said the Constellation program included the goal of reaching the Moon and Mars but suffered from a lack of funding. “We didn’t have the assets to do it,” he said. “We now have the assets to make an orderly progression to getting humans to a place like Mars and I believe we can do it.”

Bolden added, “A vision without resources is a hallucination.” Vitter countered, “If vision without resources is a hallucination, resources without vision is a waste of time and money. That’s what I think this budget represents.”

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...