It also increases the pressure on NASA Administrator Sean O'Keefe to lay out in greater detail the raft of questions that drove his decision last January to cancel the shuttle's planned servicing call to the orbiting telescope. For it is the safety of space shuttle flights, not the value of Hubble that is really at issue here.

Hubble was lifted into space as a shuttle cargo in 1990. Four times since, astronauts have repaired or upgraded the instruments onboard the telescope. A fifth shuttle servicing flight was being planned when, on Feb. 1, 2003, shuttle Columbia was destroyed during re-entry after a 16-day science mission that did not involve a rendezvous with the International Space Station.

In the aftermath of the disaster, the Columbia Accident Investigations Board reviewed mission control data and Columbia's wreckage and pinpointed that insulation foam shed during launch from the external fuel tank bolted to the winged orbiter was the cause of the accident.

The foam struck Columbia's left wing at about 500 miles per hour, punching a hole in the left wing's leading edge of reinforced carbon carbon panels. During the vehicle's descent, hot gases entered the hole, destroyed the wing and, eventually, the ship.

The CAIB laid out specific tasks for NASA to accomplish to get the shuttles flying in space again safely. The board presented NASA with 29 recommendations, 15 of which had to be met before the next launch, now set for sometime between March and May of 2005. They included eliminating the foam shedding, improved imaging of the climbing shuttles during launches, inspecting the spaceship in orbit to see if any damage was sustained, and developing ways to repair any damage.

O'Keefe has pledged the space agency will satisfy all of these recommendations before he authorizes the next flight.

The board also said the shuttle -- now more than three decades old -- remains a developmental vehicle and the risk of flying it in space -- and ways to mitigate those risks -- must be a continuing effort. The space agency agreed, but also has decided that when the space station assembly is completed, around 2010, the shuttle fleet will be retired.

The best risk mitigation strategy, NASA announced last spring, was to fly less.

As part of its return-to-flight planning, NASA decided to establish a safe haven concept in the event, despite its best efforts, the shuttle becomes critically damaged during lift-off and the damage is discovered after the space vehicle enters Earth orbit. The space station would serve as the haven.

Though not mentioned in the Columbia investigation report, NASA said this option would increase shuttle safety. Astronauts could have both more tools at their disposal and more time if they worked on a damaged shuttle while docked to the station. Equally important, should repairs fail, the crew could abandon the shuttle and stay on the station awaiting the launch of another shuttle or a Russian Soyuz spacecraft to bring them home.

NASA wants to stockpile extra provisions aboard the station as soon as shuttle missions resume, because no other cargo craft has the extra capacity. Also, the agency wants to store spare reinforced carbon panels and tiles, as well shuttle repair equipment. Both the crew of the station and the crew of the injured shuttle would pitch in for the repair effort.

NASA has looked at the fifth Hubble servicing mission in light of all these issues. The length of time a shuttle could spend in space during a Hubble trip would be significantly shorter due to limited stores of cryogenic oxygen on the orbiter, NASA said in an analysis released last spring. To make up for the limited time it could spend in space, a second shuttle would be prepared on an adjacent launch pad, standing by and ready for launch in case a rescue became necessary.

Even if a second rescue shuttle could be safely launched, however, its ability to rendezvous with the damaged craft would be questionable because a double-shuttle rendezvous has never been tested. NASA has said the procedure itself is dangerous.

A Hubble flight would not be able to take advantage of the space station or its equipment so engineers would have to design special tile and leading edge repair equipment just for that flight, including modifying the shuttle's robot arm for emergency use.

The arm would have to function as a boom-and-camera system to allow astronauts to inspect the entire area around their shuttle -- something that could be performed by the station crew in a safe-haven flight.

The challenges involved in developing such specialized equipment, as well as other, post-Columbia changes, have led NASA officials to determine the earliest they could safely perform a fifth Hubble mission would be spring 2007.

That is just about the time the telescope's batteries will start to die out. NASA has pointed out if any of the preparations for the specialized Hubble flight fall behind, even that date might not be achievable.

All of this is why O'Keefe made his controversial decision to cancel the flight, causing several members of Congress and a good-sized slice of the science community to fly into an uproar.

Sen. Barbara Mikulski, D-Md., was not happy with the decision. Last spring she asked the head of the CAIB, retired Navy Adm. Hal Gehman, to review the decision and address the issue of shuttle safety. He responded on March 5.

Reviewing the actual risk posed during a shuttle mission, Gehman said, for now, and in the foreseeable future, by far most of the risk in space flight is the launch, ascent, entry and landing phases. So, he said, to be safe, NASA should launch the shuttle as few times as possible before it is retired. Though he said it was not unsafe, he also said it was not safe, either, and he called for more studies.

With the political pressure mounting, O'Keefe asked the National Academies of Science to convene a panel to review the entire spectrum of safety issues, and also to evaluate a potential new option: Design a robotic servicing mission to do what the shuttle astronauts were planning to do.

In their preliminary report released last Tuesday, the panel, echoing Gehman, did not say whether the shuttle was safe. Instead, it urged evaluating the robotic option and advised O'Keefe to keep the shuttle mission option alive for the next year.

Thus, the committee members seem to have to come down on the side that concludes a Hubble servicing call would not be any more risky to astronauts than a station flight -- safe haven notwithstanding.

Politicians who had been howling in protest over O'Keefe's decision immediately embraced that part of the NAS report that kept the manned flight alive. Mikulski called the report enormously encouraging.

I support these recommendations, she said.

I wholeheartedly endorse its recommendations, added Rep. Sherwood Boehlert, R-N.Y., chair of the House Science Committee.

Several key Democrats on the committee also were supportive, including Reps. Bart Gordon of Tennessee, the ranking member of the committee, Nick Lampson of Texas and Mark Udall of Colorado. All support the idea of a shuttle flight to the Hubble -- if it can be proven to be safe.

Now what does NASA do?

The pressure has increased substantially to lay out repair protocols and a servicing scenario that could be accelerated in time to reach the Hubble before the 2007 anticipated cutoff of its batteries. The agency also must address all of the remaining shuttle safety issues that will need to be met before next year's resumed launch schedule -- including the repair equipment, camera-and-boom and other solo inspection procedures. The addition of the safe haven concept will almost certainly get a complete review by the agency, as well as in the NAS panel's final report later this summer.

Or, NASA must show why it would forego any of the Columbia panel's recommendations.

Some congressional staffers also think NASA needs to address the issue of whether the shuttle could -- or should -- ever fly again.

It (the NAS report) calls into question all of (O'Keefe's) logic in this decision, which we never fully understood anyway, said one staffer, who requested anonymity. Either that or just accept a higher level of risk on this flight.

Whatever the outcome, the NAS panel seems to be sending the ball back in NASA's court to find a way to get the shuttle back to space and fix the Hubble -- with either astronaut or robot elbow grease.

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