But no one in the aerospace field really knows the degree of risk aboard Mir. Hopes, wishes and the importance of the larger goal -- literally, peace on Earth and a new Moscow-Washington relationship -- have overwhelmed tough- minded analysis. The stage is set for new surprises ranging from irritating nuisances to shocking, life-threatening emergencies.

In pressing forward, NASA is being true to its enthusiastic "can-do" spirit. But it is giving short shrift to an equally critical aspect of its traditional culture: commitment to sound engineering assessments and to the goal of provable safety. Indeed, in evaluating the safety of Mir, NASA is beyond its sphere of competence. Here is a space vehicle outside its control and largely outside its knowledge, operating amid external factors NASA has never had to deal with before, such as the economic decay of the Russian space industry and the inadequate Russian historical documentation of past safety-related events.

NASA justly prides itself on the problem-solving virtuosity of its government/industry team of real-life "rocket scientists." They've made a habit of achieving impossible things, from traveling to the moon to deploying interplanetary robots to running an operational fleet of space shuttles. All are technological marvels unrivaled on this planet. Even in tough times, the NASA team has rebounded from disasters, regrouped and resumed its forward motion. Far from being "sunshine space travelers," they have been tough, resillent and persistent.

So when things really got tough aboard Mir, starting last February with a fire, NASA's instinct was to respond in its classic style. There was a barrage of enthusiastic problem-solving, a stiffening of institutional resolve to "complete the mission," and an unwavering commitment to goals that NASA considered crucial to the nation's, and even the planet's, future.

But this is not the proper approach to the challenge of Mir and the American role aboard it. NASA needs help from some independent "should-do" advisory group that is not caught up in the NASA problem-solving passion. Focused intensely upon the noble goals ahead of it, the agency now risks tripping disastrously over unseen obstacles in its path.

How, for example, is NASA supposed to deal with the financial and diplomatic uncertainties surrounding Russia's Baikonur Cosmodrome, the launch site in independent Kazakhstan, on which future joint missions will depend? Operations there are now threatened by Moscow's refusal to pay promised lease fees,

How does NASA expect to cope with the hemorrhage of experienced workers from the Russian space industry, as people with irreplaceable knowledge and skills wind up in other professions or, in alarming numbers, retired or dead? These are not the kinds of problems that NASA knows how to evaluate and solve.

Why continue the American visits to Mir? Is the diminishing value worth the growing risk? IS the technical capability to do something in space adequate justification for actually deciding to do it?

NASA and its advisory panels, committees of experts that evaluate night readiness, insist that Mir is safe and that American visits can proceed without abnormal risk. But the independence of these panels -- or their ability to resist the gung-ho NASA culture -- has been questioned even within NASA. They process information NASA alone gives them.

Certainly the track record of these advisory groups has been dismaying this year. In January, after certifying that Mir was safe, they sent Jerry Linenger off to the station, where he was nearly killed in a space fire and nearly poisoned in a space antifreeze leak. In May, in the wake of these life- threatening emergencies that had taken them totally by surprise, the same analysts approved the next flight -- for Michael Foale. At that time, a team of top American and Russian space managers solemnly signed a document that included this assurance: "The Mir complex is ready to support the beginning of the next increment of the U.S, mission with sufficient systems and redundancy to ensure a safe, healthy, and productive work environment."

Within weeks, new space disasters and breakdowns blind-sided these managers. Rarely have space prophecies been proven so wrong so quickly. Yet these same teams, with two strikes against them, have recently studied the situation again and reached the same conclusion for the expedition of David Wolf, which began Thursday night.

The latest studies, before Thursday's launch, do seem to have tried to assess basic Mir systems. But only their summaries, not their detailed findings, have been released, so it is impossible to judge their adequacy.

And as that safety-analysis task becomes less and less possible (so much of Mir is operating far out of the realm of prior experience), the mission's goals emerge as adequate justification for any risk.

In the end, we see risk itself being offered as proof of value. "All great tasks involve risk," we're told, and "Space flight is by its nature dangerous." These statements represent argument so non-logical that their purpose can only be to sway emotions, not persuade intellect.

Semantic gimmicks are in evidence with the use of phrases such as "cut and run" or "abandon" to describe the option to cease visiting Mir. If the United States stops this project, it is suggested, it will be because we "based on fear" and on an "outpouring of emotion."

Statistical tricks are in evidence when we are told that the risk on Mir is minor, compared with a rocket launch. This overlooks the duration of exposure to these dangers: nine minutes for the ride into orbit (mostly with reliable abort modes), versus four months aboard Mir. Even if the launch were a thousand times riskier than the orbital cruise, the greater cumulative danger would come from the visit to Mir, since it lasts 20,000 times longer.

Enthusiasm has become detached from reality, for example, in the claim that NASA has the responsibility of making the world see the United States as a "reliable partner" after years of American perfidy with foreign associates. We are told that partners do not run away when one gets into trouble, that the true test of a partnership is what one side does when the other runs into difficulty.

Actually, the Moscow-Washington agreements on which these last two American visits to Mir are based have already been violated -- and by the Russian side, as NASA's records prove.

In January 1996, NASA announced that the original Shuttle-Mir program (which comes to an end with the return of Foale aboard the shuttle launched Thursday) was being extended to two more visits to help the Russians in supplying Mir and also to provide them with some additional funding. In return, the Russians agreed to launch their already agreed-upon international Space Station (ISS) components on time, and to develop a heavy-class robot space supply ship for the station. As is known (see the press release on NASA's Web site) Russia has failed to live up to these agreements.

We are warned that if the United States drops out of its partnership with Mir (which never really existed, since we started the effort as a pure paying customer for specified services), the Russians will be tempted to drop out of their role in the ISS.

Last week in Houston, the Russian director of the Shuttle/Mir project hinted that anti-Western elements in Russia would seize upon such American treachery to force Russia out of the ISS. Old-timers among American kremlinologists should be getting a good laugh out of this recycled "hard liners in the Kremlin" argument, since for decades we were repeatedly told that we had to make negotiating concessions in order to empower the Moscow "good guys" in their internal power struggles. It was a gimmick then and it is a gimmick now.

Meanwhile, the space station is a good deal for the Russians and they would be foolish to let make-believe hurt feelings get in the way of cash flow and space technology access. Yuri Koptev, head of the Russian Space Agency, extols the arrangement in which Russia pays 15 percent of the price and gets 40 percent of the crew and 50 percent of the research resources. Walking out on that deal makes no sense.

NASA clearly wants to convince people it has done the job right, and it has indeed gone through the motions. But "safety" is a measurable feature of a system, based on knowledge of its components and its performance histories. The Mir safety assessments appeared, until recently, to consist mostly of reviews of past accidents and verification of countermeasures.

In other words, far from anticipating the kinds of things that might go wrong based on engineering analysis, these studies inspected the Band-Aids on things that had already gone wrong. The degree of improvement in the process remains impossible to judge. One test would be to see if the new procedures would have been able to forecast accurately the actual threats to the missions of Linenger and Foale as they really happened.

Considering the threat not only to Wolf's life, but to the entire embryonic U.S.-Russian space alliance, NASA should be true to its entire culture and resist temptations to let noble goals overwhelm sound technological judgment.

The price for imprudent behavior in the past has been high, measured in lost time, lost treasure, and, from time to time, lost lives.