Space planes—winged aircraft that can leave the clouds behind and ascend into orbit—darted through the dreams of the Space Age's visionaries.
A piloted trip to the heavens, and a comfy airport runway landing on return, seemed inevitable and desirable in the Age of Moon Landings and the "Right Stuff." (See "Early Manned Spaceflight".)
And while the 2011 retirement of NASA's space shuttle, which glided to runway landings, seemed to dim prospects for space planes, the vehicles have recently reappeared in U.S. government plans and in proposals from private space firms.
Earlier this month, the U.S. Defense Advanced Research Projects Agency—the Defense Department’s future-focused technology arm—proposed an award of $14 million for an “XS-1 spaceplane.” The plane would place satellites that weigh up to 4,000 pounds (1,800 kilograms) into orbit at a cost of $5 million per launch, about ten times less than it costs now with a conventional rocket such as the Orbital Science Corporation's Minotaur 4.
Blame Buck Rogers
The idea of a space plane has influenced everything from Buck Rogers to NASA's space shuttle and has survived setbacks that would have likely killed off any other technology, says science historian Roger Launius of the Smithsonian's National Air and Space Museum in Washington, D.C. (See "Shuttle History".)
DARPA's announcement said the defense agency seeks "a fully reusable unmanned vehicle that would provide aircraft-like access to space" and that could fly ten times in ten days.
But some space experts say ambitions for space planes say as much about engineers' hopes and dreams as they do about any hard-headed practicalities of rocket science.
"Why did the space shuttle have to have wings? It didn't have to," Launius says. "That tells us something about how technologies are driven by ideas and culture, as much as the rational reasons we pretend explain things."
The linkage of rockets to wings took flight in the popular and scientific imagination in science fiction stories as the shape of spaceships in the 1920s, just as regular airplane travel was getting under way, Launius writes in a historical overview in the current Centaurus history journal.
The winged space rocket "became a powerful icon of spaceflight," Launius writes, engraved into comics with the 1928 debut of Buck Rogers in an issue of Amazing Stories that led to a long-running comic strip, radio series, and films.
Austrian aerospace designer Eugen Sänger's 1938 design for a "Silbervogel" (Silverbird) space plane also widely influenced engineers: A Caltech lecture on the design inspired the rocket research team that later formed NASA's Jet Propulsion Laboratory in Pasadena, California.
Indeed, until the Russian launch of Sputnik, the first spacecraft launched into orbit, aboard a rocket in 1957, the space plane remained the dominant approach to space advocated by spaceflight enthusiasts, Launius says.
By 1961, however, the U.S. government realized that it was only going to win the moon race with the Soviet Union with rockets, starting with Project Mercury's "Man in a Can" launches of space capsules into orbit.
A much-lamented rocket-launched space plane, the $410 million X-20 "Dyna-Soar," was cancelled by the Defense Department in 1963. "It is, without question, one of the most memorable vehicles never flown," says Launius.
But plans for a space plane were revived when the Apollo moon landings ended and NASA threw aside its massive Saturn V rockets for the space shuttle. A limited kind of space plane, NASA envisioned a "space truck" that could perform runway landings, offering quick turnarounds to allow new launches.
Space Shuttle Disappointments
NASA's budget office originally promised the U.S. Congress that the space shuttle would cheaply and reliably send cargo into orbit: $10.4 million per launch in 1972.
Space shuttle launches averaged about $1.5 billion each and the top year, 1985, for shuttle missions saw nine lift off from NASA's Kennedy Space Center. The next year, the Challenger disaster showed the space agency the foolhardiness of even that tempo of launches.
Then, in 2011, after 133 missions and the two deadly accidents that in total killed 14 astronauts, the space agency retired the space shuttle.
The much-debated decision, largely the result of the investigation looking into the 2003 Columbia disaster, seemed to kill off the idea of space planes. NASA is now planning to build a giant rocket for its future manned missions.
"The idea of a winged space plane won't die, though," Launius says. "That may be a good thing. With crazy ideas in history, maybe 99 times out of 100, they don't pay off. But the one time that they do, they pay for everything else."
On the other hand, he says it’s remarkable how much interest in space planes came simply from the view among engineers, historically, that flying a plane into space is simply a more "elegant" way to travel.
In the Centaurus study, Launius details how spacecraft designers repeatedly returned to the idea that landing from space on a runway, ready for a quick trip to the Officers Club, was simply seen as a more refined way to travel. This compared favorably to splashing down in the ocean in a space capsule to await a undignified retrieval from a cramped space capsule by the U.S. Navy.
"That shows the power of an idea to push engineering reality," Launius says.
Economics has a way of undermining even the most fondly held dream, and critics have long pointed to shortfalls in a good rationale for the space shuttle and other space planes.
"Underneath it all is really the holy grail of cheap access to space," says economist Henry Hertzfeld of the Space Policy Institute at George Washington University. "I don't see us having that now. And I don't see us having it coming forward, regardless of how you try to get into space."
In theory, a reusable space plane would be cheaper than a throwaway rocket; it would just need to be refueled for each flight and would relieve the Navy of responsibility for retrieving astronauts after each return trip to Earth.
To those ends, space entrepreneurs have recently proposed the "Lynx", a piloted space plane meant to carry two people on a half-hour suborbital flight some 62 miles (100 kilometers) high, and the "Dream Chaser,” a NASA-funded vehicle with a "lifting body" design that resembles a smaller space shuttle.
The U.S. Air Force has also launched an unmanned mini-space shuttle called the X-37B three times in recent years on classified landings.
At the end of the day, though, Hertzfeld says space plane technology still ultimately relies on rockets to get into space.
Space planes won’t be a cheap way to send stuff into orbit, he says, as long as the chemical energy of rockets remains the only way to get into space. The rocket remains the costly part of the launch.
When it comes to space planes, Hertzfeld says, "I'm left with the feeling that we, as a society, will continue to try to build one and will find various ways to convince ourselves that we really have a space plane.”
“Even if it is at its core just a 'dressed-up' rocket."
DARPA might harbor some of the same concerns. The defense technology agency left open the option of a space capsule, not a space plane, meeting its XS-1 requirements.
"How it’s configured, how it gets up and how it gets back are pretty much all on the table,” said DARPA's Jess Sponable, in a statement. "We're looking for the most creative yet practical solutions possible."