NASA Administrator Mike Griffin chose not to focus on the elephant in the room Sept. 19 when he unveiled his blueprint for returning astronauts to the Moon by 2018, but he better than anyone else knows that it is not going to go away.

The elephant, of course, is the space shuttle program; more specifically, the cost of returning the orbiter fleet to flight next year, keeping it flying into 2010 and then putting it out to pasture. These final phases of the space shuttle program are all but certain to cost a lot more than anticipated when U.S. President George W. Bush unveiled his space exploration vision, complete with charts showing that it could be accomplished without major increases in NASA’s annual budget.

While briefing reporters on his space exploration architecture recently, Mr. Griffin acknowledged that budgetary pressures might force NASA to stretch out its timeline for developing the hardware for a return to the Moon. But that would be true even if all was well with the shuttle program. To assume that NASA will not encounter unanticipated cost growth in developing the Crew Exploration Vehicle, two shuttle-derived launchers and other hardware is to ignore history.

Restoring the shuttle program to normal operations following the Columbia disaster is proving extremely difficult. The recent flight of Space Shuttle Discovery on the first post-Columbia mission revealed that NASA has not solved the external-tank foam-shedding problem that led to the February 2003 accident, and the fleet is now grounded again at least until May.

NASA suffered another setback when Hurricane Katrina forced the closure of two agency facilities directly involved in the return-to-flight process.

NASA won’t say how much money it will need for the shuttle program beyond what has been budgeted between now and 2010, but by some estimates the agency will come up short by several billion dollars. With the overall Hurricane Katrina recovery costs likely to top $200 billion, and bills for the Iraq war continuing to mount, a substantial increase in NASA’s budget to cover its looming shuttle-shortfall is highly unlikely .

The U.S. government therefore faces a choice in civil space: it can scrap the shuttle now and have a reasonable shot at making the 2018 target date for returning to the Moon; or it can try and stick to the 2010 retirement date and defer substantial investments in exploration-related hardware until after that time. Under the latter scenario, a return to the Moon before 2020 becomes all but impossible, and even 2025 looks questionable.

For those eager to break out of the low Earth orbit rut that human spaceflight has been in for more than three decades, the answer is simple: NASA should cut its losses and retire the space shuttle fleet now.

But NASA does not operate in a vacuum, and two overarching realities make the early retirement option highly problematic. First, certain U.S. politicians are not ready to let go of the jobs and money the shuttle program brings to their districts, despite assurances that the Crew Exploration Vehicle and related efforts will quickly fill most of the void. Second, NASA has an obligation to launch European and Japanese hardware elements to the international space station.

The international problem is the tougher of the two. There are alternatives to getting new hardware to the station. Russia has launched station hardware in the past on Proton rockets, and the launchers NASA plans to develop for the lunar missions also would be able to launch hardware to the station. However, either of those options would mean additional delays and considerable expense for the space station partners who would need to redesign some of their hardware and keep expensive teams together years longer than planned.

The die-hard shuttle supporters in Congress ultimately can be swayed by the prospect of new development projects benefiting their constituents, but how is the United States supposed to tell its international space station partners that hardware in which they’ve invested billions of dollars either is going to be delayed further or never get off the ground?

To its credit, the Bush administration moved to open up some options on the space station program by asking Congress to amend the Iran Nonproliferation Act of 2000, which as now written bars NASA from buying human spaceflight hardware and services from Russia. The Senate has done its part by passing such an amendment, and the House should follow suit.

But access to Russian hardware is no panacea. Finding a way out of NASA’s budgetary quandary is going to take all of the creativity, leadership and diplomacy that the U.S. space agency and the White House can muster. In the end, the United States still may be forced to choose between deferring President Bush’s vision and doing damage to its international partnerships in space that will take a decade or more to mend.