As for a safe haven, that could be met by launching the Hubble mission just before a planned station mission, the report says.

Here is the schedule for the year's six remaining shuttle flights after the Hubble mission in April:

Despite the tragic loss of the space shuttle Columbia, he said, he judged Hubble missions as little more risky than other shuttle flights.

In other words, he said, NASA should simply "do the best you can" on a Hubble mission.

"We have to make some hard choices about whether a Hubble mission is worth it now, when moving ahead is likely to have an adverse impact on other programs."

With the diversion of money toward the exploration program, "it is entirely possible that they will cancel" the 2006 Hubble mission, Dr. Beckwith said.

We are also encouraged by preliminary assessments of alternative options for the instruments that would have flown on a Hubble mission.

Instead, the bureaucratic fear of a shuttle program failure is the main factor in NASA's reluctance to support a Hubble mission.

After several delays, the final Hubble mission, STS-125 was successfully completed in May 2009.

A Hubble mission may be marginally more risky than a flight to the space station, but that risk is surely worth taking for the scientific payoff.