Cape Canaveral, Fla. ? Trying to save the famed Hubble Space Telescope with a robot would cost $2 billion with just a 50-50 chance of success, an aerospace research group is advising NASA in the coming days.

And that thumbs-down is likely to be preceded by another potentially negative finding from the National Academy of Sciences, due to report today.

Both reports could spell doom for the popular, aging Hubble, whose fans have lobbied heavily to get it repaired to prolong its life and continue its stream of stunning and revealing pictures from space.

NASA requested the reviews of the National Academy and the Aerospace Corp., a California-based nonprofit research group, in hopes that a robotic repair could be made.

An Aerospace Corp. summary provided to the academy estimates a robotic Hubble mission would cost $2 billion and would take at least five years to be ready for launch. By then there would be a less than 40 percent chance that Hubble still would be functioning.

Less than three years would be needed to launch a shuttle mission to Hubble, for no more money and with the usual medium risk of mission success, the company said.

The full 100-page report is expected to come out this week or next, a company spokesman said.

In an interim report over the summer, a National Academy panel of scientists, aerospace experts and astronauts who have worked in orbit with Hubble urged NASA to keep its options open for one last service call by space shuttle astronauts. The panel did not rule out a robotic mission but noted its complexity and the technical challenges.

But NASA Administrator Sean O’Keefe has stuck by his guns that regardless of what the academy or the Aerospace Corp. says, no people will risk their lives to fix Hubble.

Today, the National Academy of Sciences will issue its final report on the subject.

“These reviews have tended to reinforce NASA’s sense that although (a robotic mission) is feasible, it will be extremely challenging and will require very disciplined management,” the space agency said in a statement Tuesday.

NASA will spend the coming year evaluating the robotic rescue plan and decide next summer whether to proceed. If nothing else, the space agency promises to launch a deorbit tug to guide Hubble down over the ocean — and not over populated areas — well before it would tumble in on its own during the next decade.