Where's the Edge?

NASA's Advanced Space Transportation Program looks at ways to turn science fiction into reality.

April 11, 2000 -- Where's the edge of knowledge? Where does science turn into science fiction? Will humans ever travel to another star system? Or are we doomed to only experience another star's warmth vicariously through our robots?

The answers to these questions are always changing. One hundred years ago travel to the moon -- by means of Jules Verne's cannon ship -- was fiction. Today, travel to the moon is science history! Ninety years ago, John Carter traveled to Mars in Edgar Rice Burroughs' imagination. Today, we are actually designing the technologies and ships to visit the red planet.

Right: Advanced plasma engines that produce high-power jets of ionized gas are one of many options for travel to the planets. (NASA/Marshall) [more information from Science@NASA]

But where do we stand in our quest for interstellar travel?

That's a little more problematic. We can imagine a voyage to Mars, to asteroids or even to the moons of Jupiter with today's technology, because those are relatively nearby (astronomically speaking). A travel time of 6 months or even several years to these worlds is something that our technology and our human physiology can support.

But when you start talking about travel to even the nearest star, you run into two implacable facts. First, the universe is a big place. Second, humans don't live very long. (A third implacable fact is the cosmic speed limit first recognized by Einstein -- 186,000 miles/sec, it's the law!)

Consider some facts about our current space transportation technology. If somehow you could modify the Space Shuttle or build a new version based on updated chemical rocket engines, you could talk about a manned Mars round trip in about 450 days. If you built a nuclear rocket (powered by a fission reactor operated only beyond earth orbit), you could cut that travel time by maybe a factor of two or three. Or you could go two or three times farther in 450 days. That would put you about half way to Jupiter.

With a Shuttle-class chemical rocket, then, a round trip to Jupiter would take you about 3 years, minimum. And that's assuming that you could pack all the consumables (food, water, air, etc.) into a nuclear rocket for the crew. But Jupiter is in our backyard, comparatively speaking! Pluto is roughly 10 times farther from Earth than Jupiter. Ten times beyond Jupiter puts you in the Kuiper Belt where comets are thought to "hang out" when they're not zipping into the near solar system to brighten our skies. The nearest stars are more than 10,000 times farther than the Kuiper Belt.

Left: A fusion-powered spaceship starts braking into orbit around Titan, Saturn's methane-shrouded moon and a possible harbor for extraterrestrial life. Basic research on fusion rocket technology is one of many areas of inquiry in NASA's Advanced Space Transportation Program. (NASA/Marshall)

So when you calculate how long it would take with a nuclear rocket to travel to the nearest star on a manned mission, and you include enough consumables to keep the crew alive, you quickly see that it requires multiple generations of the crew. Even fusion or antimatter rockets would only reduce the travel times by factors of 10 to 300, still multiple generations of human life.

What's the answer? Right now, the answer is fiction. We don't know how to do such a mission. But there are clues. And there are theories that suggest that there may be ways to travel between stars within a human lifespan. Well-respected scientists are beginning to ask questions that could lead to basic principles. A new area of scientific research has begun within the Marshall Space Flight Center's Advanced Space Transportation Program (ASTP) to begin to address some of the problems associated with interstellar travel. Part of the ASTP's many research activities is called the Breakthrough Propulsion Physics (BPP) Project. Managed by Glenn Research Center's Marc Millis, BPP has begun awarding small contracts to various scientists to perform theoretical and laboratory research into breakthroughs that might lead to new methods of propulsion.

"Our project has three challenges we'd like to solve," says Millis. "First we'd like to discover new propulsion methods that eliminate or dramatically reduce the need for propellant. All of today's spacecraft requires that we expel mass out the back to provide forward thrust. Having to carry that mass places a severe penalty on the system because in addition to accelerating the vehicle, you have to propel the propellant. We are looking for approaches to accelerate vehicles by other means.

"Second, we'd like to discover how to attain the ultimate achievable speeds to dramatically reduce travel times. This includes faster-than-light travel if it turns out to be physically possible. People don't live long enough to poke around the galaxy at sub-light speeds! Third, we'd like to discover fundamentally new methods of on-board energy generation to power these propulsion devices. We have to understand the physics of energy exchange to understand the physics of breakthrough propulsion."

Right: It may look like something out of Area 51, but this is a serious attempt at spacecraft design from Rensselaer Polytechnic Institute. The microwave Lightcraft being studied by Professor Leik Myrabo and his students is shaped that way because that's how the physics works. [more information from Science@NASA]

BPP has been officially underway since 1996, but only in 1999 did the project receive funds to move from mere surveys into supporting actual research. The first round of projects is now underway. Given reasonable progress, more research will follow and promising results will be further developed. "Consider this," says Millis. "Today we have rocks on the Earth that were carried here from the moon. Forty years ago, that was science fiction!

"Who knows what new knowledge is out there waiting to be found? I personally believe there is plenty of room for more advances - advances that will take us from what was once fiction to routine fact. We start by simply asking the right questions."

Related Links:

April 6, 1999: Ion Propulsion -- 50 Years in the Making - The concept of ion propulsion, currently being demonstrated on the Deep Space 1 mission, goes back to the very beginning of NASA and beyond.

April 6, 1999: Far Out Space Propulsion Conference Blasts Off - Atoms locked in snow, a teaspoon from the heart of the sun, and the stuff that drives a starship will be on the agenda of an advanced space propulsion conference that opens today in Huntsville.

April 7, 1999: Darwinian Design - Survival of the Fittest Spacecraft

April 7, 1999: Coach-class tickets for space? - Scientists discuss new ideas for high-performance, low-cost space transportation

April 8, 1999: Setting Sail for the Stars - Cracking the whip and unfurling gray sails are among new techniques under discussion at the 1999 Advanced Propulsion Research Workshop

April 12, 1999: Reaching for the stars - Scientists examine using antimatter and fusion to propel future spacecraft.

April 16, 1999: Riding the Highways of Light - Science mimics science fiction as a Rensselaer Professor builds and tests a working model flying disc. The disc, or "Lightcraft," is an early prototype for Earth-friendly spacecraft of the future. 

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