WASHINGTON — The next few months will be a pivotal period for the U.S. manned space station, the testing ground and eventual frontier base camp for human expeditions to the moon and Mars.
Facing tough engineering problems, a budget bottleneck and a sweeping outside review of the management of the National Aeronautics and Space Administration, the space station is caught up in shifting currents of crossed purposes, many critics say.
"A lot of decisions they're going to have to make soon should have been made years ago," says Adam Gruen, project director of the Space Studies History Project under NASA contract.
When NASA landed men on the moon two decades ago, it was a one-time mission. The Apollo moon-shot hardware went into museum exhibits. The space station, however, is planned as NASA's first outpost of a permanent human presence in space. When NASA eventually lands astronauts on Mars, it will be part of a more sustained exploration.
This original vision of a space station as a way station to the planets dates to the 1920s. President Bush firmly embraced this ambitious space-faring vision a year ago, the first president to do so since the 1970s.
The space station was supposed to be built by now. Under the timetable set by President Ronald Reagan in 1984, the station would not yet have been launched and assembled in space, but it would have been ready on the ground.
Instead, NASA is at least two years away from contracting any actual construction for the station. Space policy-watchers outside NASA tend to blame the slowdown on underfunding stemming from lukewarm political support. NASA has sought to bolster political support by embracing a variety of sometimes conflicting purposes for the space station.
The station currently on NASA's blueprints is a manned laboratory geared to microgravity experiments, not a pit stop to space exploration. The station's structure, NASA asserts, can be adapted for space transit later.
"NASA has been flailing to find a mission for this space station," says Thomas Donahue, professor of planetary sciences at the University of Michigan.
The space agency may soon be pressed into some hard choices. Space-station engineers have run into difficult design problems. The most dramatic has just emerged. A NASA study completed this summer found that the space station would require about 3,300 hours of maintenance by space-walking astronauts every year, about 25 times the original goal of 130 hours. Even more daunting, some 6,200 hours of maintenance work would be required before the station is ready for human occupation.
Unless those hours can be brought down substantially through simplifying the design and using remotely operated robots, the station cannot be built, says space historian Howard McCurdy of American University in Washington.
Mr. McCurdy, and many other knowledgeable critics of NASA, say that the problem of "extravehicular activity" -- spacewalks -- can be solved.
But at the same time, NASA engineers must cut down the weight of the station while increasing the share of the power supply available for experiments.
These goals tend to work against each other, making them tough engineering issues.
NASA space-station spokesman Mark Hess says this is a normal stage in a big space project. The Apollo engineers took a couple of years, and the shuttle designers a year, to "get the weight back in the box," he says.
In November, space-station work groups were given maximum numbers for weight, volume, power use, outside maintenance and other limits. Each group, with a different part of the station, "weighs the blueprints" by adding up each wire, switch and panel. This phase should be complete by January, Mr. Hess says.
What is troubling, says Ray Williamson, a senior fellow at the Space Policy Institute at George Washington University and on leave from the congressional Office of Technology Assessment, is "why these things are arising at a stage when we've already spent $4 billion. They should have arisen a year or two ago."
Another pressure point for the space station is its budget. Administration and congressional aides are estimating that Congress appears likely to cut by $1.3 billion to $1.4 billion the $15.2 billion that the president has requested for NASA next year.
Since NASA's budget includes some politically popular projects, such as Earth-observation missions that may help discern the nature of global climate change, most expect the space station budget to be squeezed.
The space station represents a more sweeping transition for the space agency. NASA has been a research and development agency that staged massive missions and moved on. Even the shuttle program has moved from mission to mission as singular events. But running the space station requires a transition into a 24-hour, seven-day-a-week operations agency.