The National Aeronautics and Space Administration Authorization Act of 2005 (H.R. 3070), as originally introduced in the House by space and aeronautics subcommittee Chairman Ken Calvert (R-Calif.), included the following language in section (4)(b)(2) : “The Space Shuttle shall not be launched after December 31, 2010.”

Unfortunately, that language was removed by the full House Science Committee during markup of the bill. It should be reinserted prior to passage of the legislation.

Fixing a date certain for retirement of the orbiters is an important and necessary step forward in the execution of NASA’s new marching orders to move beyond low Earth orbit, to return to the Moon and go on to Mars. For real progress to be made beyond the current planning stage, that firm date must be set today — and engraved in stone — for a number of reasons.

Most often mentioned is the billions of dollars the orbiters cost the space agency on an annual basis, certainly a vital factor in terms of implementation of the new vision. Only with a definite deadline in place for retiring the orbiters can those funds be predictably and productively reprogrammed toward the new endeavor.

The enormous financial burden of operating the orbiters is at least exacerbated, if not overwhelmed, by very real safety considerations each time a shuttle flies. Each successive flight and every year that passes will see inevitable increases in cost directly related to safety. Should flight operations continue beyond 2010 the Columbia Accident Investigation Board (CAIB) report points out that the entire fleet must be recertified, which will no doubt result in large and perhaps excessive unforeseen expenses to update the vehicles.

If at that time we still have our eggs in the shuttle basket there will be real pressure to expend those additional funds.

Real human exploration, development and eventually the settlement of space are goals worthy of the thoughtful risk of human life. That said, crew safety must be the paramount consideration. It is a given that, before it is allowed to become operational, the next-generation human-rated space vehicle must demonstrate that it is considerably safer than the shuttle. That fact alone argues for the earliest possible retirement date for the three remaining shuttle orbiters.

Safety and expense are the two most often-cited reasons for retiring the orbiters at the earliest possible date. Beyond those is another essential consideration: The shuttles are fragile and complex machines that consume an inordinate amount of time and talent at NASA and in the industry in general.

Consider some basic productivity math: If each of the roughly 25,000 folks required to run the shuttle program works just 40 hours each week of the year, the result is a staggering 52 million hours of personnel time annually. Imagine the progress we might see in moving beyond low Earth orbit if those hours were spent in the service of that effort.

A fixed retirement date selected this far in advance will permit the orbiter work force to be retrained and otherwise transitioned in a timely and rational progression. On the other hand, an open-ended process leaves the door open to all sorts of variables in moving personnel from the old to the new.

Should a program-ending safety issue present itself before the transition plan is devised, ratified and initiated, the shuttle work force could face sudden and huge layoffs. In addition to the chaos caused in the lives of those workers, the nation could lose their collective years of experience and pool of skills as they are forced to accept jobs in other industries.

It is apparent that — in terms of funding, safety and human capital — retirement of the orbiters is both vital and inevitable if we wish to accomplish the goals set out in the Vision for Space Exploration.

However, even among those who say the shuttles must be retired, there is disagreement about the right milestone that should be used to define what initiates the retirement process. While many believe a date certain is the only answer, others prefer a more amorphous set of objectives tied to completion of the international space station (ISS). There are several challenges involved in that latter approach.

First, it is likely that using ISS full completion as the benchmark would take the orbiters past 2010, triggering the aforementioned recertification requirement that would be excessively costly in terms of dollars and effort.

Another challenge is that there is little agreement as to just how many flights would be required. Numbers as low as 15 to as many as 30 flights have been put forth by various stakeholders in the debate. Beyond that debate there is always the danger that “mission creep” could set in when using a flight rate method — the temptation to “add just one more” would be powerful. Once that occurs, adding a second, third or more flights becomes less strenuous to rationalize.

Setting a retirement date of Dec. 31, 2010, will better focus efforts to finish ISS in a timely and efficient manner. Having a fixed date will require ISS program managers to prepare a plan that makes the best use of each and every flight. It also will require them to look for new and innovative ways to decrease their dependence on the shuttle for routine resupply missions and other tasks.

If ISS is to remain viable beyond the end of the shuttle program, such innovation is obligatory. The time to find and enact those solutions is sooner rather than later. Facing an end date for the shuttle will spur their development.

The final argument against a fixed retirement date is made by those who contend that a gap in our human space access capability would have detrimental, even catastrophic consequences for NASA.

Such arguments are found wanting through an examination of history. The gap between Apollo and the shuttle was significantly longer than any currently contemplated between the shuttle and its successor, yet NASA did not close its doors. The gap in operations necessitated by the two horrible Challenger and Columbia tragedies also show that our space efforts can withstand downtime. The current stand-down clearly demonstrates that a temporary reliance on an international partner can serve to fill that gap without dire consequences to national security or pride.

Those periods of downtime do provide an important lesson: Future goals will come to fruition as long as there is a solid plan in place to bring them about. In the late 1970 s and early 1980 s anticipation of the shuttle program and the first reusable spacecraft overcame any attempts to end our human space program. After Challenger and Columbia, our collective determination to move forward led to a careful but consistent effort toward returning to orbit.

That is the lesson we should now take to heart. As long as we are moving down an evident path following a coherent plan, this nation will support the new goals for space exploration. Retiring the shuttle orbiters in 2010 is an integral part of that coherent plan and the first segment on that path. The time has come to set that date and stick to it.

Marc Schlather is president of ProSpace, a grassroots space policy organization.