WASHINGTON - At NASA's request, scientists have given the space agency a detailed wish list of missions they hope to see conducted over the next 30 years.
The proposals range from something as down to earth as a satellite to measure all our planet's rainfall to a far-out mission looking back to the dawn of time.
That venture would send a spacecraft, the Big Bang Observer, to study the explosion that astronomers believe gave birth to the universe roughly 13.7 billion years ago.
The goal of the latter mission is to "determine what powered the Big Bang and how the universe began and evolved," said Paul Hertz, a senior scientist in NASA's Office of Space Science.
Another mission on the list would use a "solar sail," propelled only by light rays from the sun, to explore interstellar space beyond our solar system.
Yet another project would station "sentinels" between the Earth and sun to watch for solar storms that affect our atmosphere and threaten astronauts' safety. The aim is to "forecast all-clear periods for space explorers near Earth," said Tim Killeen, director of the National Center for Atmospheric Research in Boulder, Colo.
These proposals and dozens more are in a set of six "road maps" prepared by scientific and technical advisory committees from NASA, the commercial space industry and universities. The Space Studies Board of the National Academy of Sciences is analyzing the road maps, which NASA will put together in a Strategic Science Plan this summer, in time to be considered in next year's federal budget request.
"This is the science we'd like to do," Hertz told the board recently. He acknowledged, however, that money problems are likely to delay or cancel some of the scientists' favorite projects.
NASA is pondering how many of the ideas can be squeezed into the agency's tight budget. Future scientific missions are supposed to total no more than about $6 billion annually - about what NASA is spending on science this year.
Exact costs for most of the projects aren't yet available, but they fall into three categories: missions costing $300 million to $500 million, $500 million to $800 million, and up to $2.8 billion.
For example, launching a craft to land on Titan - Saturn's largest moon, which has an atmosphere that might resemble early Earth's - would cost $1.4 billion to $2.8 billion.
Projects that would further President Bush's vision for human exploration of the moon and Mars are also competing for NASA's limited resources. That exploration will cost about $3 billion in fiscal year 2007. Some researchers fear the manned missions will gobble up money they'd rather see spent on science. Others think that exploration and science can complement and support one another.
Killeen, a physicist who leads one of the road map teams, called the proposals "science enabling exploration."
Each of the road maps is divided into three 10-year phases ending in 2015, 2025 and 2035. Each phase is more ambitious and difficult than the one before. For instance, the Big Bang Observer wouldn't be built until after 2025.
The third phase would end around the time that humans would land on Mars under Bush's plan. Road map planners said a lot of scientific work was necessary before a manned Mars expedition would be possible. Satellites must monitor lethal radiation from the sun and deep space, and methods must be found to extract water and other materials on the Martian surface.
Attempting to land on Mars without a lot of advance research would be "a very risky business," Killeen said.
Even if a future president or Congress scrapped the Moon-Mars expeditions, scientists said, their road maps would still be useful for purely scientific space missions. "We don't see that that would change our plans [or] lead us to a drastically different outcome," Killeen told the Space Studies Board.
Despite the obstacles and expense, committee members hope the road maps will light the way to discoveries even more astonishing than scientists have made in the last 30 years.
"Science is now poised to answer some of humanity's deepest questions, such as how the universe came into being; how it formed the galaxies, stars and planets that set the stage for life; and whether there is life on other worlds," a NASA statement on the road maps said.
For more information, visit www.nasa.gov/about/strategic _roadmaps.html online.
Here are some of the projects NASA might undertake within the next 30 years:
The James Webb Space Telescope would succeed the Hubble Space Telescope.
The Terrestrial Planet Finder would locate Earth-like planets around other stars that might harbor life.
The Big Bang Observer would study the first burst of "inflation" believed to have started the universe and its continuing expansion.
The Interstellar Probe would study the gas and dust filling space between the stars.
The Black Hole Finder Probe would study the creation and evolution of the objects so dense that nothing can escape them.
The Black Hole Imager would observe material as it falls into a black hole.
The Joint Dark Energy Mission would study the force driving the universe to expand.
The Laser Interferometer Space Antenna: Three spacecraft separated by 3 million miles would catch "gravity waves," ripples in space left over from the big bang at the birth of the universe.
Sun-Solar System Great Observatory: Multiple satellites stationed between the Earth and the sun would study the star's effect on our planet.
The JUNO spacecraft would orbit Jupiter and observe what goes on inside the solar system's largest planet.
The Europa Lander would study the ice-covered moon of Jupiter for evidence of possible life.
Titan Explorer would land on and study the composition of Saturn's biggest moon.
Venus Surface Explorer would study the planet's makeup.
The Mars Science Laboratory would conduct studies preparatory to a human landing.
The Mars Sample Return would bring Martian soil and rocks back to Earth for scientific analysis.