Even NASA will admit it: The age when space exploration was the exclusive province of governments is over. A number of newly formed companies are promising suborbital tourist flights within the next five to ten years, entrepreneur Robert Bigelow is outlining plans for an orbiting space hotel, and Internet billionaires right and left are sinking fistfuls of cash into space startups.
Rational exuberance? Perhaps. But there are still a number of things standing in the way of private enterprise in space. The main problems? Cost and reliability.
Click here for a slide show of other problems that need to be solved.
After decades of space launches, it's become cheaper to get off the Earth. The cost of launching one pound of payload into orbit currently ranges from around a couple thousand dollars for low-Earth orbit (about 250 miles above the Earth's surface) to $10,000 and above for geosynchronous orbit (22,300 miles above the Earth's surface). Those prices represent a decrease of over 35% since 1990, according to the Bethesda, Md.-based consultancy Futron. But they’ve got to fall a lot further before anyone starts trying to mine the moon (see: "Galactic Gold Mine?").
The costs of launching people into orbit, which have barely budged in decades, will have to fall, too. And demonstrable improvements in vehicle safety will be in order, especially for human passengers. What will all that take?
Nuts, Bolts And Batteries
Rocket fuel is currently the No. 1 reason that space travel is so expensive. Orbital flights, which must propel vehicles past the atmosphere into outer space, require a particularly large amount of it. The problem becomes less acute once they've cleared the atmosphere, but the high speeds required to escape the Earth's gravitational field (more than 6.8 miles per second) necessitate an enormous amount of energy.
At the moment, that energy is supplied by engines, which run on the combustion of chemicals--basically a controlled explosion. Finding just the right mixture is a delicate balance; some of the cheaper chemical fuels aren't as efficient, and each pound of fuel that a rocket has to carry into space adds to the weight it must lift off the ground.
Nuclear propulsion systems may offer a less costly alternative. As early as the late 1950s, a scientist named Freeman Dyson designed a space carrier that would use a series of timed atomic detonations to propel itself through the atmosphere. Sound absurd? Many prominent physicists of Dyson's day were convinced that it could work, but the Nuclear Test Ban Treaty of 1963 outlawed the testing that the project would have required.
Some contemporary researchers still harbor hopes that there may be safer ways to harness nuclear energy. For the most part, though, their proposals call for activating nuclear reactors only after the vehicles have reached low-Earth orbit.
"Nuclear-propelled rockets should only be used well away from the Earth," says Charles Oman, a senior research engineer at MIT's department of Aeronautics and Astronautics.
Other launch techniques have been suggested, including electrical propulsion, laser propulsion and even magnets. But these approaches, according to Oman and others, are decades away at best.
For the suborbital space flights of the sort that billionaire Richard Branson's Virgin Galactic hopes to run, energy won't be as costly. The vehicles reach about 50 miles above the Earth, so they have no need to clear the gravitational field and require much less fuel. Still, finding a cheaper energy source could cut costs substantially. Michael Kelly, co-founder and chairman of San Bernardino, Calif.-based Kelly Space and Technology, suggests that it's possible to reach suborbital space using jet propulsion engines akin to those used on airplanes, rather than rockets.
"It's a very complicated engineering challenge," he says. "But from a propellant-expenditure perspective, you'd be saving a lot of money."
Risky Business
Cost may be the major barrier to widespread commercial space endeavors, but eventually, as MIT Aeronautics and Astronautics professor Larry Hoffman points out, "you're going to have to deal with risk."
It can't be eliminated, but it can be reduced. Engineers will have to incorporate a lot of redundancy into spacecraft designs, so that if a component fails, another one will kick in. Costs, of course, will go up. But so will safety--and reliability. Balancing the two is the trick.
Another way to reduce space-related risks is simply flying. A lot. The Federal Aviation Administration currently requires that aviation companies perform anywhere from a couple dozen to a couple hundred test flights on new commercial airplane models before they are allowed to carry paying customers. Last February, the FAA announced it would evaluate the number of test flights required for commercial suborbital space flights on a case-by-case basis.
Transportation to and from outer space has a ways to go until it is cheap enough and robust enough to sustain widespread commercial space exploration, and many scientists believe that the true way forward will be in partnerships between public and private entities. How long will that take? Hard to say.
"Space is a wonderful frontier," says aerospace industry analyst Howard Rubel of New York-based Jefferies and Co. "But every time you get close to it, the horizon recedes in the distance."