BALTIMORE (AP) -- The moon has very little atmosphere, and lots of dust. Those are some of the things being considered this week at the home of the Hubble Space Telescope, where astronomers are discussing the opportunities offered by NASA's plan to return to the moon, including the possibility of a telescope on the lunar surface.

The moon is a large, stable platform with very little atmosphere to interfere with viewing the stars. However, the size of any lunar telescope; whether it would be built on Earth and unfold on arrival, or be assembled on the moon; and how it would be funded all remain to be decided.

Scott Horowitz, a NASA associate administrator, told the group the space agency is still early in the design stage for the next moon rockets and vehicles but wants significant capability to transport scientific instruments, living quarters and other cargo to the moon. "We're building a pickup truck and we're going to fill the bed with whatever we can,"

Of the about 125 metric ton launch vehicle being designed, about one quarter will be payload, Horowitz said.

"We're still trading off how much is available on the exploration lander for scientific payload, we still don't know the exact number," Horowitz said.

The meeting at the Space Telescope Science Institute on the campus of Johns Hopkins University, which coordinates the use of the orbiting Hubble, comes a week before NASA is to unveil its moon exploration strategy at a conference in Houston.

NASA is planning on using a new crew vehicle, the Orion, and new Ares rockets to return to the moon. NASA hopes to begin flying Orion with astronauts by 2014 and return to the moon no later than 2020.

Unlike the Apollo missions of the late 1960s and early 1970s, the new technology will enable NASA to reach any part of the moon, including areas that are constantly bathed in sunlight, which will allow for continuous solar power production, and areas that constantly face away from the earth, and its radio noise.

Shuttle astronaut John Grunsfeld, who has been assigned to lead the spacewalk that will repair the Hubble during a mission scheduled for 2008, also appeared at the conference. Conducting repairs on the Hubble in orbit around the Earth, and the possibility of moon-based telescopes are just the latest examples of distant and forbidding environments to which researchers have ventured in the name of science.

While some have criticized the limited amount of time available for research on space missions, Grunsfeld said about 18 percent is usually available for research. While that may seem like very little time, it is comparable to limitations faced by researchers in other harsh environments, such as the Antarctic, he said.

Paul Spudis of the Johns Hopkins Applied Physics Laboratory said the moon is full of advantages and hazards.