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Coach-class tickets for space?

Scientists discuss new ideas for high-performance, low-cost space transportation

April 7, 1999: Getting there is half the fun, goes the old saw about travel. But in space travel, it's the cost, an expensive ticket that chains most plans for exploration to the Earth.

Cutting the cost will take "looking in strange places for the right answers," says Gary Lyles director of the Advanced Space Transportation Program at NASA's Marshall Space Flight Center. Lyles spoke at the opening of the 10th annual Advanced Propulsion Research Workshop held by NASA, Marshall, the Jet Propulsion Laboratory, and the American Institute of Aeronautics and Astronautics.

Right: A uranium oxide specimen glows not from fission but from the heat of sintering, processing a powder into a robust alloy. This is part of research effort by the University of Florida to develop advanced materials to encase nuclear fuels should the nation decide to use nuclear power in planetary propulsion. (NASA)

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Lyles said that NASA Administrator Dan Goldin has established "stretch goals - in fact, they seem to be impossible." But they are essential to enabling affordable exploration of the solar system by more than a robot or two a year.

"It all comes down to high (performance) margins in the propulsion system" that will allow launch of larger, heavier payloads at low costs. "We want space transportation to be like flying an airplane," with costs down to $10 to put a pound of payload in orbit, and reusable "hands-off, no maintenance" vehicles that can fly more than 100 times a year. Transportation from Earth orbit to the planets is more expensive.

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Lyles compared the development of transportation systems to the 17th century quest to develop a means of determining longitude so mariners could sail across the ocean and make accurate landfall. What became the earliest government-sponsored research effort - a prize offered by the British Parliament in 1714 - thwarted the mental giants of the day - including Sir Isaac Newton. It was solved in 1761 by a self-educated clock maker, John Harrison of Yorkshire, England. Accurate timekeeping allowed mariners to fix their position with an accuracy of a few miles, and revolutionized seafaring and the preindustrial world.

Some years later, an artist who had once ridiculed the idea of solving the longitude problem called Harrison's clock a true work of beauty.

"We'll never get to the stars without that combination of simplicity and power" in rocketry designs, Lyles said. "Look for beauty, look for ideas from people you don't recognize."

Ad astra, per subversa

What does it take to be a rocket scientist? Math, physics, engineering - and an attitude.

"I believe that all the people in this room are subversives," Homer Hickam, a former NASA engineer, told the audience at the start of the Advanced Propulsion Research Workshop. "We mean to beg, borrow, and steal whatever it takes to build the machines and leave this world behind and explore new ones."

Hickam has become a national figure through his best-selling autobiography, "The Rocket Boys," and the hit movie, "October Sky" (an anagram of "Rocket Boys"), describing his high school efforts to build rockets and join the space program. Although his NASA career involved computers and flight crew training, Hickam says he's a rocket scientist at heart, and just as subversive as he was when he was a kid in Coalwood, W. Va.

In his second book, "Return to the Moon" (due for release in June), Hickam has the lead character declaring that NASA is a subversive organization. While it can be a timid bureaucracy, he says, "Its charter is to develop the means so Americans can leave the planet."

The story in "Return" involves mining the lunar surface for helium 3 to power fusion reactors on Earth, a concept gaining support. Hickam urged the audience that the United States now lives in a cheap, fossil fuel-powered "energy bubble" that must be replaced by fusion power.

Hickam urged the "rocket scientists" in the audience to develop, within 15 years, a high-power, high-efficiency rocket that will allow exploration and development of the solar system.

"It will take grit and determination to build it," he said, "but once we get the first one flying, I'm convinced that there will be no holding Americans and the world's citizens from exploring the solar system." The alternative, he cautions, is to decay as Coalwood did when the coal mines ran out.

On to Mars

In the near term, one of the most attractive uses of advanced propulsion is manned exploration of Mars. Historically, most studies have invoked nuclear fission in order to get humans and their living quarters and exploration gear to Mars and back. During 1956-73, NASA and the Air Force studied nuclear rocket engines. The most advanced of these, the Nuclear Engine for Rocket Vehicle Applications (NERVA) would pump liquid hydrogen over a graphite core reactor to produce a superhot exhaust gas.

While nuclear fission poses a number of operating and environmental challenges, it is also more easily achieved than the other advanced concepts because it has been done, at least on the ground: NASA test fired the KIWI and ROVER ground test models several times in the 1970s.


Above: A university of Florida engineer checks on a uranium sintering experiment.

Through the 1990s, NASA has been developing and refining the Mars "design reference mission, the best estimation of how to put humans on Mars given existing or near-term technologies. In a sense they meet a challenge issued by Robert Zubrin and Richard Wagner, then with Martin Marietta, who thought the initial NASA design was too expensive and cumbersome. They proposed a non-nuclear, "live off the land" approach called Mars Direct which has become the concept to beat in design studies.

But Mars Direct imposes an unnecessary risk on the crew, argues Ben Donahue, a Boeing Space Systems engineer who analyzed the latest Design Reference Mission 3. The risk comes from having limited abort options during landing, Donahue argues. Instead, he recommends that the ascent stage of the Mars lander employ a 15,000-lb. thrust engine identical to three that would boost the mission from Earth orbit onward to Mars in the DRM-3 concept. Using the nuclear engine for just 15 minutes to ascend from Mars and head back to Earth imposes only 10 percent weight penalty on the mission, but replaces the automated Mars propellant refinery with a rocket engine that is being developed anyway.

NERVA is highly attractive for this mission because it is proven. Alternatives have been proposed and have adherents, but each has its own drawbacks, points out Dr. Michael Houts of NASA/Marshall. For example, Americium 242m has been proposed as an alternative to the uranium 235 used in NERVA. It is easier to split, but is extremely difficult to refine from plutonium waste - and even from more common, unusable isotopes of americium - and it's radioactive.     All rockets great and small. The workshops technical chair, Stephanie Liefer of the Jet Propulsion Laboratory, reminded the attendees that tiny rockets are needed for a number of special applications. JPL is studying ion engines (right; a "rocket test stand" is at left) that would be etched and built using the same tools that now make computer chips. These would be employed as thrusters for sensitive position and attitude adjustments of large deep-space telescopes searching for planets circling other worlds. (JPL)

"The big advantage of uranium systems is they're largely not radioactive at launch," an important environmental concern, Houts explained. "We don't see an advantage to going to that type of isotope (Am 242m)."

Another popular concept is deuterium-tritium fusion (heavy hydrogen and heavy-heavy hydrogen nuclei). Assuming that it can be harnessed, Houts said that "D-T" fusion would not breed as much tritium as it uses, and would rely on large quantities of tritium - costing $100 million/kilogram - brought up from Earth.

Finally, he noted that all of the alternative systems relay on large radiator panels to dump waste heat into space.

And beyond

All of it could become moot later in the 21st century if NASA succeeds with its Breakthrough Physics Program sponsored at Glenn Research Center in Cleveland, Ohio.

"We are looking today to go beyond the limits that are known in science," said manager Marc Millis, "and venture into the realm of the impossible." All grounded in physics, though. No magicians need apply. Over the past two years it has sponsored 39 papers by scientists describing what they foresee as the future, and now is in the middle of a rigorous peer review for its first round of research projects.

Left: Coming soon (?) to a star system near you. Or at least to today's sessions which will cover interstellar sails, among other topics.

Because the projects are in review, Millis could not describe the submissions, but he did review some of the credible papers that have been submitted to date. "Gravity shields give me the willies," he said. "You're jumping to a conclusion before you have any credible foundation."

The topics do sound like a "Dr. Who's Who" of science fiction concepts - like canceling inertia or forming wormholes - but they are rooted in demonstrated physical law. The ultimate objectives of the Breakthrough Physics Program are propulsion without rockets, maximum speed, and high energy yields, and one of the challenges will be translating a physical discovery into a working tool.

"An achievement of all three goals means we can send humans to the planets or the stars," Millis concluded.

Web links

MSFC Advanced Space Transportation Programs Office.

Leftover Instruments Will Pave Way for New Propulsion Test (March 22, 1998) Well understood and well used scientific insturments will help verify a new instrument as they all fly on JAWSAT.

Spacecraft may fly on "empty" (Jan. 22, 1999) Using a propulsive tether concept, spacecraft may be able to brake or boost their orbits without using onboard fuel. A NASA/Marshall project, named "ProSEDS," is slated to demonstrate braking, by accelerating an expended rocket toward re-entry.

Lecture series to cover Physics for the Third Millennium (Feb. 2, 1998) Lectures on science in the next century will be held at Marshall Space Flight Center during February 9-12, 1998. Relativistic physics, and next generation propulsion techniques are among the topics.


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