Designs for the Next Space Shuttle

When the space shuttle first launched on April 21, 1981, it opened a whole new era in space exploration for NASA. For the first time, the agency — and the world — had a space vehicle that could be recovered and used repeatedly.

Now, the tragic loss of Columbia may speed up the hunt for the next-generation shuttle — a task the aerospace industry has pursued almost since the current shuttle came into existence.

"The overall general consensus is that NASA needs to move forward in a new [launch] system," said Dennis Smith, a program manager involved with looking at next generation space vehicles at NASA's Marshall Center. "But we're early on in the process [of development]," he said during a teleconference with reporters today.

It's been NASA's call for cheaper, more capable, and safer spacecraft that has prompted the effort for a successor shuttle. And while many of the previous designs never got much past the drawing board, the attempts could help lead the industry and the U.S. space program to newer technologies for reaching the stars.

One example of the more recently attempted shuttle replacement efforts was the so-called Reusable Launch Vehicle, or RLV, program. Commissioned under President Clinton in 1994, the project hoped to develop a truly reusable space "plane."

The experimental shuttle design, dubbed the X-33 by Lockheed-Martin, would be a so-called single-stage-to-orbit vehicle. Launched vertically like the current shuttle, the X-33 would reach orbit using its own internal engines and fuel.

Once the mission was completed, it would glide back to land on a runway just like current shuttle. Its single-piece design meant that a working X-33 craft would need less work — and less expense — to prepare it for the next mission.

Technology Setbacks, Cost Overruns

It was hoped that the X-33 could save as much as 90 percent of current shuttle's launch costs.

But to lift the X-33, its payload and internal fuel without external assistance, designers turned to new rockets called aerospike engines that were supposed to propel the craft at up to 18 times the speed of sound. New lightweight, composite materials were supposed to keep the weight of the X-33 down as well.

Charles Vick, an analyst with space and defense think tank GlobalSecurity.org in Alexandria, Va., says that such immature technologies ultimately led to the X-33's downfall.

"[Advanced] materials for the fuel tank really struck out," says Vick, who notes that a fuel tank ruptured during ground testing in 1999 and caused massive delays and cost overruns.

After two years of redesign work — and a total investment of more than $1 billion — the project failed to produce a flying prototype and was subsequently canceled in 2001.

Pushing On

Still, NASA hasn't exactly given up on new launch systems.

Last November, NASA Administrator Sean O'Keefe announced a renewed effort to look at low-cost alternative spacecraft under a revamped program called the Space Launch Initiative, or SLI.

Rather than look for an outright shuttle replacement, the $4.5 billion program will study a variety of inexpensive options that would supplement the shuttle.

One such craft, the X-37 from Boeing, is designed along the lines of the X-33, using lightweight composite materials. However, rather than a single stage vehicle, the X-37 would be lofted into orbit using a large, disposable rocket booster.

Once in orbit, the craft could deploy satellites or conduct experiments in space for up to 21 days before gliding back down to Earth.

But what makes the X-37 a potential cost-saving vehicle? Unlike the shuttle, the X-37 will be a completely unmanned craft.

A True Space Taxi

For now, there are no plans to develop a completely robotic space shuttle. But if the technology works, elements may appear in another component of the SLI: the orbital space plane, or OSP.

Designs proposed by companies such as Northrop Grumman and Orbital Sciences Corp. envision the OSP craft to be shuttle-like, but roughly one-fourth the size of spacecraft such as the Columbia. OSPs would carry at most a crew of five and small cargo loads — typically supplies and scientific experiments that can be moved by the astronauts themselves.

GlobalSecurity's Vick says a smaller shuttle such as the OSP could be launched at the tip of cheap disposable rockets, such as the Delta 4. And such a small hybrid system would be "more reliable, and safer than any shuttle system that we have now," adds Vick.

What's more, industry and NASA advocates of the OSP concepts say smaller, lighter, and cheaper shuttles would be just the right vehicle for most missions to and from the orbiting International Space Station, or ISS. Instead of using the current, truck-like space shuttle, the OSP would operate as an efficient space "taxi," ferrying just the needed crews and supplies.

Still, such systems won't be able to carry large payloads — such as solar panels and other parts to help build out the ISS. So, new shuttles such as the OSP will be complementary crafts to the current fleet of NASA shuttles. And the first SLI prototypes, such as the X-37, aren't scheduled for any real tests until next year. That means a new launch vehicle probably won't be put to real-world use until 2006 at the earliest.