President Bush's Jan. 14 speech painted broad brushstrokes of his plan to put humans back on the Moon and send them to Mars. He will depend on NASA and a new commission to sketch in the details.

The Big Questions

There is no set price tag. After the shuttle fleet is retired and the space station completed in 2010, about $6 billion of NASA's current annual budget of $15.5 billion will be diverted to the new program. Meanwhile, Bush has asked for an additional $1 billion spread over the next five years.

Other funds could come from curtailing other space agency activities, but no details were provided.

That depends of course on whom you ask. Lost in much of the discussion on this point is the fact that America already spends $15.5 billion per year on space exploration, less than 1 percent of the overall federal budget. The vast bulk of the new project's financing, at least over the next decade, will come from shifting some of these funds.

The increase Bush asked for amounts to, on average, $200 million per year for each of the next five years. That is a key number that should be considered in any water cooler debates about the merits of space exploration.

Critics argue that not enough money will be available to accomplish what Bush envisions. "It's never going to happen," said Robert Park, a physicist at the University of Maryland and director of the Washington office of the American Physical Society. "The price tag will scare Congress off and the robots are doing so well it's going to be hard to justify sending a human."

Other scientists said the gradual approach to increased funding is sensible.

"I think this is the best thing that has happened to the space program in decades," said Rep. Dave Weldon (R-Fla.), whose district comprises much of Florida's Space Coast. "When you really look back over the last 30 years we've had a lack of clarity, purpose and direction. George W. Bush laid out a plan that I think is doable from a financial and political side as well."

There's also a lot of wait-and-see. The White House stresses that other NASA programs will be adjusted and better aligned towards long-term exploration. Astronomers are anxious whether any robotic or telescopic missions will suffer.

Details will come with the President's 2005 budget, to be submitted to Congress next month.

That's a philosophical argument that cannot be answered -- or, rather, each person has his or her own answer. Many scientists (and citizens) see space exploration as an important piece of overall federal spending. Others would prefer NASA's budget be capped or cut, though the latter opinion is not often voiced in debates over space spending.

Among experts, the debate centers on whether whether robots or humans are more efficient at exploring other worlds.

Robert Park, a physicist at the University of Maryland and director of the Washington office of the American Physical Society, estimates robotic exploration costs about 1 percent of the price of sending humans.

Ken Edgett, a geologist at Malin Space Science System, uses a robot to explore Mars. He helps operate the orbiting Mars Global Surveyor.

"The only way we're ever going to understand Mars and its history is to have people there doing the work," Edgett says.

Supporters also stress that space exploration inspires the nation, and generates useful medical and industrial spinoff technology. Others see little or no point in human spaceflight, which is more expensive on a per-mission basis, and often these critics instead favor robotic spaceflight and remote observing (as with the Hubble Space Telescope).

This remains to be seen. The White House's position is that "impact stemming from the Shuttle's retirement and the new focus on exploration will depend on what type of vehicle systems and skills will be needed in the future. It is premature to speculate on specific job impact. In general, the requirements of the new vision will have a very positive impact on the aerospace sector and related sectors, and the vision will help attract talented people to science and engineering fields."

Because humans need new destinations and ever-expanding horizons. That's one argument. Because only humans can unlock the mysteries of the red planet, including whether it does or ever did harbor life. Because going to Mars will inspire the nation's youth. And because the technology developed along the way will benefit all humanity.

Those are the main arguments. Critics don't buy them, of course, at least not if they cost too much.

This is perhaps the most contentious point of Bush's plan as far as scientists are concerned. The most enthusiastic supporters of human missions to Mars do not want to stop at the Moon first, as they see it as a possible dead-end detour that will suck up funds and political energy.

Some planetary scientists applauded Bush's step-by-step approach as the sort of reasonable, affordable vision that could get support of Congress and the people.

The Planetary Society, an advocacy group of scientists, favors continued robotic exploration and also putting humans on Mars. The group yesterday issued a statement in general support of Bush's vision but said it had not taken a position on the lunar step.

"Carl Sagan remarked, many years ago, that the Moon could end up a detour, rather than a stepping stone, to Mars. How lunar missions would lead to a Mars landing must be closely examined," said Louis Friedman, the society's executive director. "The essential requirement is to keep the focus on sending humans to Mars -- investigating conditions of life and habitability on that planet."

The White House maintains the Moon missions will be an "important demonstration of our ability to live and work on another world. We will assess technologies and the use of lunar resources, and we will build the skills and gain the experience that will enable us to conduct sustained exploration of other worlds."

Curiously, Bush never uttered the phrase "Moon base" or "permanent colony" in his speech, as many had anticipated. Instead he called for "extended human presence" with the goal of "living and working there for increasing periods of time."

Few scientists, politicians or space analysts would argue that NASA was in a rut. The shuttle Columbia disaster cast a dark cloud over the human spaceflight program. "Why spend $6 billion or so a year to dangerously circle the Earth?" many people wondered.

Some sort of reorganization was inevitable. The question in many minds was whether human spaceflight would ultimately be redirected, curtailed or halted.

The White House's position: "From the Apollo landings on the Moon, to robotic surveys of the Sun and the planets, to the compelling images captured by advanced space telescopes, U.S. achievements in space have revolutionized humanity's view of the universe and have inspired Americans and people around the world. As the world enters the second century of powered flight, it is time to articulate a new vision that will define and guide U.S. space exploration activities for the next several decades."

The Details

Under the plan, a robot would go to the Moon around 2008. The first manned flight would occur between 2015 and 2020.

No timetable was set. But you can bet it won't be before 2020, at least not if Bush's vision is carried out. If the White House and NASA think it'll take at least 12 years to get to the Moon, it seems reasonable to assume at least a few years more would be needed to mount a Mars mission, especially since the president stressed that financial and technological readiness would be evaluated at each step of the process.

Yes. But its fate is then unclear. The Bush plan calls for retiring the shuttle fleet after the station is completed in 2010.

There will likely be a gap -- perhaps four years -- when America has no space-ready vehicles. Presumably Americans could not then get to the station except aboard Russian ships.

Meantime, Bush said work aboard the space station would be redirected to study medical effects of space flight in support of the vision. Medical research is now part of a host of science activities aboard the station.

America's next space ship is not yet designed. Bush called for a vehicle that could take astronauts to the Moon.

Some analysts worried that the shuttle would be replaced by an Orbital Space Plane (OSP) with obvious limitations. The White House's position is that this won't be the case. A new Crew Exploration Vehicle "will have different requirements and will be developed for the exploration mission. It may be able to perform some functions the OSP would have performed, but its design will be centered on exploration."

Bush was clear on this point: "The Crew Exploration Vehicle will be capable of ferrying astronauts and scientists to the Space Station after the shuttle is retired," he said in his speech. "But the main purpose of this spacecraft will be to carry astronauts beyond our orbit to other worlds. This will be the first spacecraft of its kind since the Apollo Command Module."

Maybe. Bush said human trips to the Moon would serve to test ways to get beyond it. He was clear that Mars is not the only ultimate destination. "Today I announce a new plan to explore space and extend a human presence across our solar system," he said. "We do not know where this journey will end, yet we know this: human beings are headed into the cosmos."

Some scientists think asteroid mining (many asteroids are rich in metals) could become commercially profitable.

White House position: "Other potential destinations include asteroids, the moons of Jupiter, and deep space sites suitable for large observatories."

The implication of "large observatories" is that of huge telescopes on the Moon, where there are no clouds or blurring atmosphere.

Yes. But it is not clear if commercialism of space will extend beyond the supportive roles that aerospace companies have always played in human spaceflight (by getting NASA funding to build the machines).

The White House position: "NASA will vigorously pursue commercial and private sector participation in exploration."

Some analysts think space needs to be opened up to exploration led by private industry and supported by NASA, from advertising to lunar hotels and perhaps even space reality television. No such plans were mentioned by Bush.

The president hopes so, as do scientists and space analysts who see shared space missions as an opportunity to bring nations together.

"We'll invite other nations to share the challenges and opportunities of this new era of discovery," Bush said. "The vision I outline today is a journey, not a race, and I call on other nations to join us on this journey, in a spirit of cooperation and friendship."

No. Bush the senior laid out a vision of sending humans to Mars, then a huge price tag was applied -- $500 billion. The reasons for the vision were not laid out as well as with Bush the junior. And the cost this time around was, perhaps wisely, not presented as a lump sum.

The White House position: "This vision sets the nation on a sustainable course of long-term exploration. It is not predicated on getting to a particular destination by a particular date, nor is it solely focused on human exploration."

There are several ideas for getting to Mars with less than $250 billion nowadays, even as cheaply as $30 billion by one account. But many critics think it will cost much more.

No. The Apollo program was a race. Bush said this is not a race but is a journey. Apollo was driven partly by fear and in the interest of national security and was given a comparatively huge budget for the era. The new vision is driven by exploration and a desire to achieve and, as Bush presented it, with only incremental increases for space agency funding.

The White House position: "The new vision shares the same spirit of opening a new frontier that inspired the Apollo program. But this initiative will be based on the sustainable allocation of a reasonable resource level over the long-term. It will involve both humans and robots and will advance our knowledge of multiple destinations in parallel, including the Moon, Mars, Jupiter's moons, asteroids, and planets around other solar systems. The vision is not driven by a single destination or a particular timeline."

The Apollo program is estimated to have cost about $150 billion to $175 billion in today's dollars, all crammed into a few years.