The price of a putting human feet on the moon again is beyond sky-high. By Richard Sammon, Senior Associate Editor November 1, 2009 The national space agency's biggest dreamers and best engineers are still aiming for a return manned mission to the moon by 2020 followed by a pioneering mission to Mars a decade or so later. That's their official goal in theory and one sanctioned by Congress. But the cost estimates are simply crushing, and mounting federal deficits will require the agency to rein in its biggest plans by a galactic scale or two. Look for lots more attention to be lavished on unmanned space science in the next decade.Early cost estimates of about $1 trillion over 25 years to return to the moon and later plant a flag on Mars are causing more than a few budget migraines, and the technological challenges of the ambitious project are myriad and steep. The cost alone will prompt the Obama administration, under pressure to show spending restraint in an era of towering deficits, to reassess and sharply curb back the entire Moon-Mars space travel program while the program is still in its early stages, although several billion dollars have already been poured into it in research, testing and development of rockets. NASA's fiscal 2010 budget is about $18.7 billion, and space science experts say another $3 billion to $5 billion in each of the next few years -- followed by many more billions in 5-10 years -- will be needed to meet the 2020 moon return goal. Then literally hundreds of billions more would be needed to go to Mars and back in the following 15 or so years, and commitments on spending that money would need to be made in advance. That's becoming a huge red flag in Congress. Advertisement Look for the debate over manned vs. unmanned space exploration to get more fuel this week as NASA flight-tests its Ares 1-X rocket, the developmental rocket that is part of the agency's Constellation program intended to replace the aging space shuttles and keep alive U.S. manned space exploration. The space shuttles will be retired in the next three to five years, well past their original retirement date at the end of 2010. The manned space program, as envisioned by Constellation, won't be scrapped entirely by Congress. Much work has already been done, and support is spread fairly broadly throughout Congress. A good deal of the work is done in states with large congressional influence: Texas, California, New York, Virginia and others. The manned space program will be curtailed, though, and probably sharply. The Moon-Mars project will probably remain a stated goal for the agency, but only a goal. That will allow some research to continue but without full-scale funding to go with it. Manned space missions in the next couple decades, via the Constellation program, may not involve the moon or Mars at all, but perhaps near-earth objects, such as asteroids and comet flybys and space station and satellite servicing -- not as ambitious as a Moon-Mars mission, but far more cost conscious. Advertisement About one-half of NASA's budget is spent on human space endeavor work, from the rockets and the engineers to the astronauts and the space centers, the Constellation program and work with dozens of contractors. In comparison, about one-fifth of the agency budget is spent on unmanned or robotic space exploration missions - far smaller in proportion. But the unmanned missions are gaining favor, not only because they are more economical but because they also produce very good science and technology innovation and have less risk associated with them. NASA is currently managing 65 robotic space probe missions -- from the Hubble Telescope to space radiation probes and interplanetary craft - and another 40 unmanned probes are in various stages of development. Several planned probes aim to learn more about the sun and its composition, about sun spots and sun flares and solar radiation in the solar system affecting Earth and the planets. Others will study so-called dark matter in the universe, and others will search for more planets in distant solar systems. As talk of Moon and Mars begins to fade in light of the cost, look for more attention and funding on the unmanned missions. That will be a benefit for a variety of contractors that work on smaller-scale unmanned probes, including Alliant Techsystems, Wyle Laboratories, InDyne, Jacobs Engineering Group and ITT. Advertisement The typical unmanned space mission costs $300 million, start to finish. For comparison, that is less than the cost of one shuttle flight to the International Space Station, which is still seven shuttle trips away from being complete and which is expected to end its service life in 2016-2017. That's about the time the Constellation program should be operational, even if the Moon-Mars project has been shelved by then.