Last Space Shuttle Rocket Boosters Delivered to NASA
The train carrying the final space shuttle solid rocket booster segments arrived in Florida May 27.

The last set of space shuttle rocket segments arrived in Florida Thursday after one final train ride from their Utah-based factory.

The rocket pieces were delivered to the Kennedy Space Center in Florida from Promontory, Utah, where they were refurbished by NASA contractor Alliant Techsystems (ATK).

The 149-foot (45-meter) boosters are actually reserve rockets that would only be used to launch a rescue mission if NASA's final scheduled shuttle flight on Endeavour runs into an emergency.

"I think there was a little bit of melancholy knowing that these were the last segments to come in," NASA spokesman George Diller told "They had a wonderful heritage, but on the other hand it kind of signifies the end of a very storied program for NASA."

Endeavour is currently scheduled to launch that final planned shuttle flight in late November. The mission, along with a September flight of Discovery, are NASA's last two shuttle missions remaining before the reusable space plane fleet hangs up its wings for good.

NASA's third space shuttle, Atlantis, landed at the Kennedy Space Center Wednesday to end its 32nd and final scheduled mission. It would be Atlantis that would use these last solid rocket boosters for the emergency flight, if one is required.

One last ride

The rocket parts were joined for the last stretch of the train ride by NASA and ATK officials, including shuttle launch director Mike Leinbach and astronaut Mike Massimino.

"I think this is a very historic moment," ATK spokeswoman Jessica Rye said in a phone interview. "It gives the team an opportunity to travel with the hardware they?ve worked so hard over the years to manufacture or manage."

ATK has been building and processing the solid rocket boosters that help propel space shuttles to orbit since the start of the program nearly 30 years ago.

"I think it was sort of a bittersweet occasion as we pulled into the train station," Rye said. "ATK is so proud of the legacy that we have in serving our space shuttle program. For us it was just a wonderful opportunity to reminisce and share stories about the legacy of the solid rocket boosters throughout the program."

The boosters were redesigned after the 1986 shuttle Challenger disaster, when an O-ring on the right SRB failed to seal, causing the loss of the vehicle and its seven-member crew.

Since then there have been no major issues associated with the solid rocket boosters.

 "They really turned out to be quite reliable in the long run, particularly after they were redesigned after Challenger," Diller said.

Shuttle booster stack-up

These last rocket segments will be assembled into the twin solid rocket boosters (SRBs) this summer to ready Atlantis for its potential STS-135 rescue flight.

However, there is a slight chance that NASA will shift this backup mission to a full-fledged final shuttle flight to deliver extra hardware to the International Space Station (ISS). NASA and some members of Congress have been lobbying for such a shuttle flight addition.

"This new mission, STS-135, would be flown with a minimum crew of four astronauts and would provide critical spare parts and logistics for long-term ISS operations," Florida senator Bill Nelson wrote in a letter to President Barack Obama.

Nelson pointed out other benefits of an additional flight, such as helping to transition the shuttle workforce to new activities. "It will also guarantee U.S. access to space for a longer period of time, and thereby help to close the spaceflight gap until a new domestic capability is provided."

Whether or not Atlantis flies once more to space, NASA still wants to fully prepare the shuttle just in case of an emergency with Endeavour.

The booster segments arrived Thursday at NASA's rail yard in Titusville, Fla., and were transported to their final destination at the agency's Kennedy Space Center in Cape Canaveral, Fla. Friday morning.

After initial processing and inspections, the pieces will be stacked into the four-segment boosters that will be strapped to the sides of Atlantis.

The solid rocket boosters work in concert with the shuttle's liquid-powered main engines to loft the spaceship to orbit.

About two minutes after liftoff the SRBs are jettisoned from the shuttle and land by parachute in the Atlantic Ocean. The spent SRBs are then recovered by boat and reloaded with propellant to be used for later missions.

"They have only become better over time as we have found additional ways to make them safe and effective," Diller said.