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The United States cannot afford to send humans anywhere beyond the space station — especially Mars — unless it wants to spend more money.

“You just can’t get there,” Sally Ride, the former astronaut, said over and over again on Wednesday as she presented calculations of the costs and timetables of various proposed space missions, ranging from establishing a base on the Moon to touring asteroids to landing on Mars.

Dr. Ride told a meeting of a panel that is investigating options for the future of the space program that she was still looking for proof that a human exploration program could be undertaken under the National Aeronautics and Space Administration’s present budget.

In an afternoon of rambling discussion and argument on a stage at the International Trade Center in Washington, Norman Augustine, former chief executive of Lockheed Martin and chairman of the panel, said, “If we do want a strong space program, we might have to face up to investing more.”

NASA convened the panel in response to a request by President Obama and the Office of Science and Technology Policy in May. They have 19 days left, Dr. Augustine said, to present to Mr. Obama options for human spaceflight. Should NASA continue on the road set by President George W. Bush aimed at a base on the Moon or so something else? This was their last scheduled public meeting.

Among the options the committee has to consider is whether to retire the space shuttle in 2010 as planned, or extend its life to 2011 or beyond, whether to dump the International Space Station in the ocean in 2016 (for which there is no money in the budget), whether to continue developing the Ares 1 and Ares 5 rockets to replace the shuttle, or to build something else — and, of course, where to go in these shiny new rockets.

Many committee members agreed that political considerations made it likely that the space station would survive and that the space shuttle would probably fly at least until 2011, and that some options should show that, but they argued about what other options should be in “the Chinese menu,” in the words of Jeff Greason, chief executive of XCOR Aerospace.

Unable to fit anything into the official budget, Dr. Ride and her colleagues tried to see how various programs would fit into an “unconstrained budget,” which would be allowed to overshoot it by up to $3 billion a year, then grow with inflation.

The best fit in that case was something called “Deep Space,” which would involve flybys of asteroids, the Moon or Mars and other interesting places in deep space, but not necessarily landing on the Moon or Mars. Under that plan, Dr. Ride reported, there could be missions every other year in the 2020s past asteroids and Mars and even a landing on the Moon by 2029 or 2030.

As the afternoon wore on, the participants wrestled with whether to retain the goal of a direct flight to Mars.

Mr. Greason said that he had dreamed of going to Mars his whole life, but that making a “dash” for Mars would be destructive of the dream, leading to its abandonment the way Americans abandoned the Moon. “I want to go to Mars, but not this way,” he said. “I want to go the right way.”

But Bohdan Bejmuk, a former Boeing manager and aerospace consultant who helped develop the space shuttle, said, “By God, I think we should go to Mars.”

Leroy Chiao, a former astronaut, also argued for keeping Mars as an option. “Let the decision makers know what it would it cost,” he said.

In the end, the committee agreed to treat Mars not as an option, but as the end goal of all options.