As NASA marks the 25th anniversary of space shuttle flight, the agency is applying the lessons learned with that program toward development of a replacement vehicle that more closely resembles the crew-carrying capsules of the Apollo era.

The space shuttle Columbia ushered in NASA’s shuttle era on April 12, 1981, when it launched on STS-1 with astronauts John Young and Robert Crippen aboard.

A quarter century later, the aging shuttle fleet is destined for retirement in 2010 and the space agency is designing a wingless capsule dubbed the Crew Exploration Vehicle (CEV) to carry astronauts back to the Moon by 2020. The $104 billion CEV, which also will ferry astronaut crews to and from the international space station, is expected to debut no later than 2014.

“The shuttle was a ‘do everything for everybody’ vehicle,” Scott Horowitz, associate administrator of NASA’s Exploration Systems Mission Directorate, said in an interview . “We built a reusable spacecraft, which had never been done before. But it was more difficult to do than many people imagined.”

Horowitz said NASA is taking lessons from the shuttle’s two tragic failures — the loss of 14 astronauts during Columbia’s 2003 failed re-entry and the Challenger launch accident of 1986 — and the agency’s spectacular successes, such as the Apollo Moon effort, to push ahead with its new human-carrying spacecraft.

“The shuttle showed us how to operate routinely in space and reaffirmed that going into [orbit] is difficult,” he added.

Hard Lessons Learned

NASA biggest lesson from its 114 shuttle flights so far — which it learned the hard way through accidents and sacrifice — is that astronauts need a quick and dependable means of escape in case of a launch or landing emergency.

“We learned we need to have a dedicated vehicle to launch crew with a robust escape system,” Horowitz said.

During Columbia’s STS-1 mission and three subsequent test flights, all of which were flown by two-astronaut crews, the orbiter carried ejection seats for commander and pilot should they need to bail out of the vehicle — after first blowing the roof off the cockpit — at key moments.

“Truthfully, I’m not sure that they could have handled many contingencies,” Crippen said of the ejection seats, adding that it’s unlikely they could have handled extreme failures like the Columbia or Challenger incidents. “With this [new] vehicle, we’ll be able to put in an escape system that we weren’t able to do with shuttle.”

The CEV is expected to feature escape rockets capable of wrenching the capsule away from its launch vehicle if something goes wrong during liftoff . Its broad, stubby heat shield concept is reminiscent of NASA’s Mercury, Gemini and Apollo programs, and is still employed by Russian and Chinese re-entry vehicles today.

“We do know that those launch escape systems work,” said Roger Launius, a former NASA historian and chairman of the Division of Space History at the Smithsonian Institution’s National Air and Space Museum in Washington . “We tested them unmanned on Mercury and Apollo, and the Russians have aborted twice in launches and succeeded in bringing the crew back.”

For some astronaut veterans, an attractive feature of a capsule-based CEV approach is the added distance it provides between crews and the main engines down at the bottom of the launch vehicle . During shuttle launches, astronauts sit in a crew compartment separated from the three main engines by an 18-meter payload bay.

“We always worried most about those and blowing the back end off the ship,” former astronaut Tom Jones, a veteran of four shuttle flights, said in an interview . “If you had an engine explode on the way to orbit, it would probably have damaged the orbiter to the point that it couldn’t return safely, and then the crew is lost.”

In addition, with the capsule on top, the astronauts need not worry about foam insulation or other debris striking their spacecraft during launch, Jones said.

“We can at least look at the way the shuttle was fatally flawed, and make the CEV bulletproof to those threats,” he added.

At the same time, however, there are elements of the shuttle that NASA wants to keep as it makes the shift back to an Apollo-like capsule. The agency intends to base the rockets that will launch the CEV as well as Moon-bound cargo loads on the space shuttle’s solid rocket boosters and external fuel tank.

The Tradeoff

In going back to the future with its capsule-based CEV approach, NASA is giving up some of the space shuttle’s unique capabilities, many of which stem largely from its catch-all design. These shuttle-unique capabilities include repairing satellites and telescopes on orbit and returning tons of hardware to Earth from the space station .

“It’s a remarkable vehicle [and] it does things that no other vehicle has ever done, and may not do for awhile,” NASA shuttle program chief Wayne Hale said in an interview. “It has its limitations and we as a spacefaring people should have been building the next generation shuttle long ago … I think it will be well past time for the shuttle to retire when we roll it into the Smithsonian.”

Launius, however, said he is concerned that NASA may spend years developing the CEV, only to be stymied after the shuttle is retired and left without a dedicated human spaceflight capability.

“The landscape right now is littered with would-be shuttle replacement programs,” Launius said, referring to past NASA and Pentagon projects like the National Aerospace Plane, the Orbital Space Plane, the X-33 and others. “Each of those projects ran aground for a variety of reasons, usually technological or financial … and in each of those times they hit the reset button.”

The challenges, Launius said, are very real for NASA’s CEV . “I hope they’re able to move forward with CEV and bring it online,” he said.