Some questions and answers about President Bush's plan to send astronauts to the moon and later to Mars.

Q: What is the president proposing?

A: To send astronauts back to the moon and establish an "extended presence" there. Later in this century, astronauts would be sent on to Mars.

Q: How much will this cost?

A: The president is proposing to add $1 billion to NASA's budget over the next five years and to redirect funds now in the space agency budget toward the moon-Mars plan. But that will be just the startup funds for an effort that will take decades and hundreds of billions of dollars to complete.

Q: What is planned for the moon?

A: The plan calls for exploration of the lunar surface by robot craft by 2008 and the landing of astronauts there as early as 2015 "with the goal of living and working there for increasingly extended periods."

Q: How will astronauts get to the moon?

A: The president is calling for development of a new spacecraft, to be called the Crew Exploration Vehicle (search), which will be able to fly to the moon. The first manned launch of the new craft would be no later than 2014. The craft could also be used to ferry people between Earth and the International Space Station (search).

Q: When will astronauts go to the moon?

A: As early as 2015 and no later than 2020.

Q: What will astronauts do on the moon?

A: Mine resources from the lunar soil, including perhaps rocket fuel from helium-3 (search) and from suspected water deposits. Astronauts could use the moon to develop skills and technologies for use on other missions, such as to Mars. The moon, which has gravity one-sixth that of Earth, could also be used as an assembly stage and launch site for a Mars expedition.

Q: What happens to the space shuttle?

A: Flaws detected in the shuttle after the Columbia accident last year will be corrected and the winged craft will then be used to complete construction of the International Space Station. The shuttle will be retired by the end of this decade.

Q: What happens to the International Space Station?

A: Construction of the station with the space shuttle will be completed by 2010, fulfilling the U.S. commitment to the 15 partner nations. U.S. research on the orbiting laboratory will then focus on the effects of long-term space flight on the human body.

Q: When will astronauts go to Mars?

A: No firm date has been announced, but some administration officials suggested it would be after 2030.

Q: How will astronauts get to Mars?

A: The president's plan does not mention any plans for a spacecraft capable of going to Mars and landing there. Presumably, another craft would have to be designed, built and tested before a Mars expedition could be mounted.

Q: What other technology will be needed?

A: Experts suggest that extended expeditions to the moon and Mars will need some form of atom electrical power. Such systems are now being developed by NASA. The agency is also working on an electric-ion rocket engine that could accelerate the months-long journey between the Earth and Mars. For an extended stay on the moon and Mars, NASA will also need to develop shelters that could be transported, landed and installed. Extended stays also may require a system to protect astronauts from exposure to cosmic and solar radiation.