NEW YORK — NASA has delayed the last flight of Space Shuttle Endeavour from July to November at the earliest to allow time to modify its cargo — a $1.5 billion science experiment — for a longer stay on the international space station.

Endeavour was initially targeted for a July 29 launch with a crew of six astronauts in order to deliver the Alpha Magnetic Spectrometer (AMS) to the space station.

The spectrometer will be installed on the exterior of the space station to study high-energy cosmic rays in the hunt for elusive antimatter and dark matter.

More than 200 researchers from 16 countries are working to build the Alpha Magnetic Spectrometer. The project is led by Nobel laureate physicist Samuel Ting of the Massachusetts Institute of Technology.

The researchers opted to replace a key part of the spectrometer — a strong superconducting magnet designed to last for several years until the cryogenic supply of liquid helium needed to keep it cool runs out — with a longer-lasting conventional magnet. The decision came after U.S. President Barack Obama announced in early February his intention to extend the international space station through at least 2020, instead of shutting it down around 2015.

“Given that the [space station] has been extended, the permanent magnet gives them a much longer science mission than the cryo-magnet,” said Mike Moses, NASA’s director of shuttle integration, last week. “From a thermal challenge standpoint, I think they’ll get a lot better science out of this other magnet.”

The spectrometer’s new magnet has flown before, during STS-91 space shuttle mission in 1998, mission scientists said.

The Alpha Magnetic Spectrometer is a 6,800-kilogram experiment that uses a powerful magnet to bend the path of incoming cosmic rays so that their component particles can be analyzed by detectors to see if there are protons, electrons and even anti-electrons (called positrons) that might signal the existence of dark matter.

NASA initially canceled the shuttle mission carrying the Alpha Magnetic Spectrometer to the space station in the wake of the 2003 Columbia shuttle disaster. But Congress later approved funding for an extra shuttle mission dedicated to delivering the powerful spectrometer to the station.

Top space shuttle program managers met April 23 and decided to delay Endeavour’s final mission to mid-November, according to NASA spokesman Kyle Herring.

“They basically made that decision to change their magnet, and it became pretty clear that they were not going to be able to support an end-of-July launch,” Herring said.

The move now makes Endeavour’s STS-134 mission NASA’s final space shuttle flight after nearly 30 years of orbiter flights since April 1981.

NASA’s next shuttle mission to fly will be Atlantis, which is slated to launch toward the space station May 14 carrying a new Russian science module for the nearly complete orbiting laboratory. That mission, STS-132, is the last flight of Atlantis.

Endeavour’s STS-134 flight was slated to be next in late July, followed by the final launch of Discovery — NASA’s oldest space shuttle — on Sept. 16.

Herring said that plans for Atlantis’ May launch are still on track. Discovery’s later STS-133 mission is also still targeted to lift off on Sept. 16, but potential delays associated with some spare station parts and the refit of an old cargo module to serve as a permanent closet on the space station could push that mission back as well.

There are other challenges to launching the Alpha Magnetic Spectrometer aboard Endeavour in November.

During much of that month, the space station will be flying in a so-called beta-angle cutout period in which unfavorable sun angles make it undesirable to send a shuttle to the orbiting laboratory because of power and heating concerns.

There also is a new crew launching toward the space station aboard a Russian Soyuz rocket in the late fall, and the European Space Agency plans to launch its second unmanned cargo ship to the orbiting laboratory around December. NASA also prefers not to fly space shuttle missions over Christmas and the New Year, adding yet another wrinkle if Endeavour cannot lift off in November.

NASA has been promised an extra $600 million in funding if any of its three remaining shuttle missions is delayed beyond September. That funding runs through December 2010.

NASA Deputy Administrator Lori Garver told Space News April 26 that if the final flight slips beyond the current budget year — which ends Sept. 30 — and Congress has not passed a 2011 appropriations bill by then, the agency will not be able to pay for the final flight. Until Congress approves the president’s 2011 budget request, “it’s not a done deal,” Garver said.

NASA spokesman John Yembrick said it is unlikely NASA will cancel the AMS flight.

“We basically have been told to safely fly out the manifest,” he told Space News Sept. 27. “This is something that we want to fly, it’s ready to fly, it’s configured to fly. They just need to swap out these magnets.”

Yembrick said AMS is not the only payload aboard the flight.

“There’s an ELC — an External Logistics Carrier — that puts external spares on the space station,” he said. “It’s a flight we want to do, and we consider AMS part of the international space station construction at this point.”

A congressional aide said if the AMS flight slips beyond this year, NASA could have a difficult time justifying the added expense. The $600 million included in NASA’s 2011 budget request for extended shuttle operations assumes the program will conduct its last flight by Dec. 31 — which is three months into the U.S. government’s 2011 budget year.

“If the AMS flight happens within the first three months of [fiscal year] 2011, then it matches up with the 2011 budget request and it’s covered,” the congressional aide said April 26. “But if it gets delayed beyond three months, there’s nothing in the 2011 proposal to cover it. The continuing resolution would continue to fund it and theoretically could continue to fund it for several months. But you’d be spending money above and beyond what the president requested, so there’d be parts of the budget that would have to get reallocated.”

Moses said that he is still confident that despite the delay to Endeavour’s final flight, NASA will be able to complete its last three shuttle flights by December.

“We’re still looking to finish out this calendar year,” Moses said.


Staff writer Amy Klamper contributed to this story from Washington.