Introduction to A Spaceship for Tomorrow
When the space shuttle was conceived in the 1970's, the dream of engineers was to create a new kind of spacecraft—one that could carry people and cargo into orbit, return to Earth, and then be used again repeatedly. They succeeded, but only partially.
In 1997, the National Aeronautics and Space Administration (NASA) and private aerospace companies were working to develop a space-launch vehicle that would operate more like an airplane. They envisioned a spacecraft that not only could be used repeatedly but would also be reliable and efficient enough to fly more frequently and at far less cost than the shuttle.
Why the Shuttle Is So Expensive to Launch
Of the shuttle's four major components, only one—the winged orbiter—is fully reusable. The large external fuel tank is jettisoned when empty, after eight minutes of flight, and it burns up as it reenters the atmosphere. The two booster rockets (at the sides of the external tank) are also jettisoned when empty, after only two minutes of flight. They then parachute into the ocean, where they are recovered. The rockets are later disassembled and refilled with solid propellant. But the recovery and refilling require so much special equipment and work that it would be nearly as economical to simply buy a set of throw-away rockets for each shuttle launching.
These and other difficulties make the shuttle an extremely expensive vehicle to fly—about $400 million per flight by the most conservative accounting. And that just covers the flight itself, not the satellites or laboratories that might be the cargo. So, more than 40 years after the dawn of the space age, single-use rockets remain cheaper to use than the shuttle.
Still, the idea of a single-use vehicle has always seemed wasteful. After all, what other mode of transportation throws away the vehicle with each trip? It has long been possible, in theory, to make a fully reusable, single-stage-to-orbit vehicle. But various factors, including the performance of engines and the materials available for fuel tanks and other structures, resulted in designs for vehicles that grew so big and expensive that they were impractical—at least if they were to carry any significant payload.
Technology Makes Reusable Spacecraft Viable
Some of these factors have changed in recent years, making the idea of a single-stage, reusable launch vehicle worth pursuing. Several key technologies have advanced since the shuttle was built. The development of certain composite materials (such as graphite-epoxy), stronger alloys (such as aluminum-lithium), and new ceramics make it possible to construct lightweight fuel tanks and better heat shields. Engines can be made lighter and more reliable. In addition, electromechanical flight-control systems are available to replace heavier, more troublesome hydraulic systems. And smaller, vastly more capable computers and more advanced navigational systems could streamline flight operations and maintenance.
Some of these technologies have already been applied in certain aircraft, including the B-2 bomber, the F-22 fighter, and the Boeing 777 jetliner. And some come from research begun in the 1980's to develop an aerospace plane, an airplane capable of flying into orbit.
An Experimental Craft
By the early 1990's, enthusiasts for a completely reusable spacecraft had persuaded the U.S. Department of Defense to test a vehicle to demonstrate that a single-stage-to-orbit rocket could be practical and inexpensive. The McDonnell Douglas Corporation built the first such vehicle, dubbed the Delta Clipper Experimental, or DC-X.
With its conical shape and its tail-first landings on a column of flame, the DC-X looked like something straight out of Buck Rogers. A ground crew of several dozen demonstrated that, after a flight, the DC-X could be ready to fly again the next day.
Teaming With Private Industry
It will take just such “aircraftlike” operations to slash the costs of space transportation. Many space experts believe that lower costs will bring new customers, even tourists, into space. But many of these experts also believe that costs can never be cut drastically until government lets the private sector sit in the pilot's seat.
To a large degree, NASA agrees with this viewpoint. In 1995, it announced that it wanted to help private industry develop a new experimental spacecraft, to be called the X-33. The hope was that this vehicle would demonstrate that space travel could be economically efficient. The target was to reduce the cost of launching a payload by 90 percent, to about $1,000 a pound. If this target could be reached, NASA speculated, perhaps private industry would want to build and maintain a fleet of commercial reusable launch vehicles (RLV's) on its own.
Although the RLV is sometimes portrayed as a replacement for the shuttle, that is not the goal for the vehicle. There is no urgency to replace the shuttle, because it was designed to easily fly another 15 years. With upgrading, it could fly until 2030. The goal for the RLV is simply to slash launch costs.
Lockheed Martin Wins NASA Bid
Three large aerospace companies were interested in developing the X-33. McDonnell Douglas proposed an enlarged version of its DC-X, called the DC-XA, or Clipper Graham. Rockwell International (teamed with Northrop Grumman) proposed a vehicle based on the shuttle orbiter, with many improvements. But in July 1996, NASA selected a plan by the Lockheed Martin Corporation because the plan used many technological innovations, and the company had promising ideas for an RLV to follow the X-33. Lockheed Martin's plan called for an RLV powered by a new engine called a linear aerospike engine. Instead of having the conventional cluster of cone-shaped rocket nozzles, this design has several nozzles arranged linearly along the edges of rectangular wedges. An automatic flight control system would independently adjust the throttles on each of the vehicle's seven engines. The plan also included a “lifting body” design, in which the vehicle is mostly body, with small wings. The large surface area of the X-33 would distribute the heat encountered upon reentry into Earth's atmosphere in such a way that a new type of metallic heat shield can be used.
The X-33 was to be 20.4 meters (67 feet) long and 20.7 meters (68 feet) wide. It was to fly 17,000 kilometers (11,000 miles) per hour—not fast enough to reach orbit. The first flight was expected in March 1999.
A Spaceship Named VentureStar
Lockheed Martin calls its concept of the RLV that would follow the X-33 the “VentureStar.” It would be similar to the X-33 but about twice as long and wide. It could carry up to 18,160 kilograms (40,000 pounds) in a large cargo bay. The first flight of the VentureStar could come as early as 2004.
Plans called for the VentureStar to be completely automated—the spacecraft would not carry a flight crew. Directions for each flight's mission would be programmed into the vehicle's on-board computer system. This automatic flight control system would control everything from engine operations to craft orientation to flight paths. People on the vehicle would be simply passengers. A separate capsule with a life-support system would carry them inside the RLV's cargo bay.
NASA already had flights to the International Space Station in mind for the RLV. Even if the RLV only took over the shuttle's role of carrying cargo to and from the station, it would be a big help, because it would make the station less dependent on the shuttle. That would, in turn, make the station cheaper to operate and free the shuttle to make only flights requiring astronauts. The space station was scheduled to be assembled in space between 1998 and 2002, during more than 40 missions involving the shuttle and Russian and European Space Agency vehicles.
Since its first flight in 1981, the space shuttle, despite its limitations, has been a very useful vehicle. The shuttle's crews have launched commercial and military satellites into space, repaired broken satellites (including the Hubble Space Telescope), and conducted a number of important scientific experiments. But in the future, the VentureStar or some other design for a fully reusable launch vehicle may make space transportation much more reliable and affordable. And such a vehicle may be the best way to maintain a vigorous presence in, and to expand the uses of, the final frontier.