NASA's Antimatter Spaceships

If it works, unmanned spaceships could be flying throughout the solar system and interstellar space by the year 2040, says Gerald Smith, a retired Penn State University physics professor. And it's all possible under the current laws of physics. Nevertheless, Smith says, it will take "a great deal of research and development, and a few miracles along the way."

Natural antimatter was first discovered by American physicist Carl Anderson in 1933. He detected antiprotons in cosmic rays. But it wasn't until 1955 that scientists could create antiprotons in a laboratory. Even with today's technology, antimatter production is still an expensive, time-consuming process. With the most advanced equipment, the estimated cost of producing a single milligram of antimatter per year is prohibitive: $10 billion to $15 billion, Smith says. So from a practical standpoint, achieving propulsion through antimatter annihilation is still as futuristic as 23rd century physics a la "Star Trek."

More realistically--and cheaply--Smith proposes missions and spacecraft that would exploit the high-energy reaction between antimatter and hydrogen isotopes called deuterium and tritium, and a helium isotope called helium-3. "In order to do these missions, we clearly have to have nuclear energy as a source of power," Smith says. "The nearest-term nuclear energy source is nuclear fusion." That would make it possible to send unmanned probes to interstellar space to conduct data-gathering missions within a human's lifespan. Carrying out the same task with current rocket technology would take centuries.

"After building the engine, it would be very straightforward to build the spacecraft," Smith says. He already has a name for the nuclear craft: Aimstar, short for Antimatter Initiated Microfusion Starship. On its first mission, Aimstar would take a 220-pound probe to 10,000 Astronomical Units (AU). That's 931 billion miles from Earth--or so-called near interstellar space--10,000 times the distance between the Earth and the sun. The probe would finish its mission in 50 years.

Launching Aimstar

An expendable rocket, such as a Delta 4 or an Atlas 5, would be needed to launch Aimstar and its payload on an escape route from the solar system. Another option is to assemble the spacecraft on the International Space Station (ISS) and then launch it from there. To avoid contaminating the Earth's magnetosphere with nuclear particles--which could disrupt radio and satellite transmissions--Aimstar would start its engine only after reaching a safety distance of at least 600 miles from our planet. "Then it would go on an almost straight trajectory out of the solar system," Smith says. "We fire the engine for about four or five years and then it will coast for the remaining 45 years."

And while on its way to interstellar space, the spacecraft likely would perform a quick fly-by of Pluto. Smith believes the whole mission, as currently envisioned, may cost less than $1 billion. But to become possible, it would take more than money. Big technical hurdles must be addressed and overcome. Developing a nuclear-fusion engine and producing enough antimatter would be the most difficult challenges, Smith admits. Keeping antimatter stored for long periods of time, on the other hand, shouldn't be that hard. "Antimatter has been stored successfully for three months, and so there is no reason to think that with a little more effort we can't store it for three years," he says.

Once produced, antimatter must be preserved in special containers called Penning traps, where electrical and magnetic fields keep antimatter particles safely confined. Aimstar would rely on on-board traps for both storage and propulsion. To keep the nuclear fusion going, the spacecraft engine would need a total antimatter supply of 6 micrograms if used in combination with deuterium-tritium fuel, or 26 micrograms if deuterium-helium-3 is used. In the first case, the engine would burn for about three months, producing 33 megawatts of power. In the second, the burn would last 4-1/2 years, but would be far less powerful: 750 kilowatts. In all cases, the fuel would be injected at a rate of 42 nanograms per second, while uranium or lead would be used as a spark plug to start each of the 200 nuclear reactions per second.

The stream of atoms would be spewed through a nozzle in a fashion similar to that of conventional rockets. The final speed would reach about 200 million mph. Such high performance would make Aimstar look like a Porsche among spacecraft, Smith says, but its total weight would be only 1100 pounds, scientific payload included.

Despite the use of all this innovative technology, a scientific mission to 10,000 AU may not get the public too excited, Smith admits. After all, the spacecraft would get to interstellar space, but would not reach any stars or send back pictures of celestial bodies. Nevertheless, there would be radiation and particles to be studied and discoveries to be made about our own solar system and the universe. "You would be learning a great deal about ... our evolution after the big bang," Smith says. "This has a great deal to do with explaining or validating the big bang theory."

Smith says he hopes Aimstar will become reality, especially because a year ago NASA Administrator Dan Goldin (who's since resigned) said he wished to see a mission to deep space launched within 15 years. In fact, NASA is already working on a second-generation Penning trap that would increase the capability of storing antiprotons by 100 times, says George Schmidt, a propulsion engineer at Marshall Space Flight Center in Alabama.

Other projects include so-called decelerators that would make antiproton trapping easier, and the development of a smaller trap to demonstrate thrust production in parallel with Smith's Aimstar project. "All of those are big challenges, but probably the greatest challenge--no doubt--is the production of [antimatter] economically," Schmidt says. A new theoretical method being considered would make it possible to produce antimatter by exploiting energy fluctuations present in the vacuum "where virtual particles pop in and out of existence," Schmidt explains. But exploiting such energy to obtain propulsion is still "very hypothetical right now."

Pushing Physical Limits

While scientists try to push the limits of today's physics, and even look for loopholes around or within quantum mechanics to travel faster than light, Gerald Smith is convinced his projects--which also include manned exploration of the solar system--represent the only viable way, at least for now. He is even more skeptical about traveling through wormholes and time warps: "That's inventing new physics. This may be correct, but it's totally undocumented, and so this is theoretical physics at its best. My work is experimental physics at its best."

Smith's best is called ICAN-II: Ion Compressed Antimatter Nuclear, a propulsion system driving energy from small nuclear explosions and capable of pushing a gigantic, 800-ton spacecraft toward the outermost planets and reaches of the solar system (see lead illustration). "We have simply reinvented on the very, very small scale, the atomic bomb," Smith says. In short, instead of using huge bombs with the equivalent force of 100,000 tons of exploding TNT as a source of energy, Smith is proposing the use of 6-ounce pellets with an explosive force equivalent to that of 50 tons of TNT. Each pellet would be the size of a golf ball and would be made of concentric shells of uranium containing liquid hydrogen.

The idea is to use 200,000 of these pellets (with a total weight of 110 tons) exploding one per second to obtain a continuous nuclear fusion reaction. It would be triggered by a single microgram of antiprotons. The engine would generate 7 gigawatts of power, Smith says. The radiation produced by the fusion reaction would hit a hemispherical shield made of lead or carbon. The heat from each pellet exploding right at the focal point of the shield would make its atoms boil off, thus eroding the shield's surface at the rate of 1 micron per explosion. The resulting stream of atoms coming off the shell's surface would provide the thrust.

The size of the spacecraft--more than 200 ft. long--would require building it on the moon, then carrying it to a gravityfree point between the Earth and the moon and launching it from there. A spacecraft fired toward Mars using an ICAN-II engine would take about 40 days to reach its destination. Then the engine would be restarted to brake and enter into orbit around the red planet. Landing craft would use chemical engines to drop out of orbit, descend to the surface and then, after a 30-day excursion, go back to the mother ship. Another firing of the engine would send the spacecraft back toward Earth.

Before the astronauts could return to Earth, however, a stop on the moon would be required to decontaminate the spacecraft from any nuclear residuals. Finally, the crew would depart and dock with the ISS in Earth orbit--one last stop before the homecoming. Smith says the whole mission could be carried out for about $60 billion. Eventually, spacecraft using ICAN-II engines could be used to take astronauts on a 1-year flight around Jupiter. They would spend about three months observing the planet and its intriguing retinue of moons. Other missions would include putting a 110-ton, unmanned spacecraft into orbit around Pluto and a 400-ft.-dia. radio telescope to 550 AU--51 billion miles from Earth. That's the point where radiation coming from the Milky Way gets concentrated by the sun's gravity. Using this so-called gravitational lens effect, scientists should be able to peek at the very core of our galaxy.

These missions, fascinating as they sound, still would be a far cry from the quick interstellar trips envisioned by "Star Trek" creators and fans. Even the most intrepid physicists are skeptical about that type of space travel, especially given the need to overcome or circumvent the speed of light barrier. "Any time you have the possibility of faster-than-light travel, you also have to start worrying about the problem of time travel. And that really gets everyone scared because you start to sound like a refugee from a science-fiction convention," says Matt Viesser, a physicist at Washington University in St. Louis, Mo.

On the other hand, NASA's Schmidt believes only hyperfast transportation will make interstellar expeditions appealing, whereas solutions such as astronauts hibernating for decades do not. "I think people want to be able to do a significant number of things within the span of a human lifetime," he says. Both Schmidt and Viesser agree on the fact that today's physics does not allow much hope of using wormholes and warp drives as celestial shortcuts any time soon. Both researchers believe it might take hundreds of years, or even a thousand, before the necessary scientific breakthroughs make it possible. And both stress the need to keep an open mind and, at the same time, remain skeptical.

After all, as a fellow scientist warned Schmidt, "You don't want to open up your mind too much or else your brain will fall out."

The following article shows solar sails are very close. There's a team scheduled to fly a solar sail, I believe in July, from a Russian rocket launched by a sub

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A remarkable new carbon-fiber material is causing a revolution in the way scientists are thinking about laser and solar sails, according to engineers at NASA's Jet Propulsion Laboratory (JPL).

The fiber is a departure from solar sails of the past: it is about 200 times thicker than the thinnest solar sail materials, but so porous that it weighs the same.

"It's one of those things that comes along every so often that's kind of a technology breakthrough and at the same time, an honest-to-goodness paradigm shift," said Robert Frisbee, who analyzes advanced propulsion mission concepts at JPL.

"Always, I mean at least since the 1920s, people have thought of solar sails, laser sails, as basically being thinner and thinner sheets of solid material."

In space, solar sails would reflect photons of sunlight, thus harnessing their momentum. The sails, which could also be propelled by lasers, must be super-lightweight in order to benefit from the massless particles bouncing off their surfaces.

In addition, the sail surfaces must be tremendously reflective to maximize the propulsive force from the particles of sunlight.

Only in the past decade has it even been possible to manufacture sails that are thin enough, light enough and able to be coated with the proper reflective coating that sails require. But recent advances have finally made solar sails an option for certain featherweight spacecraft of the future.

Solar sails are now the propulsion method of choice for proposed NASA programs that strive to travel past the boundaries of the solar system, and to keep a gargantuan telescope hovering in space. Still, there is more work to be done.

The new carbon fiber mesh, which is developed by Energy Science Laboratories, Inc. in San Diego, California, could be the first step. The mesh is composed of a network of carbon fibers crisscross linked into a matrix that is mostly empty space. One hundred of these carbon fibers bunched together would make up a strand the size of a human hair.

A piece of rigid carbon sail material, made by Energy Science Laboratories, Inc. "floats" in the air above a model's hand. At 3 grams per square meter, the fiber is 25 times lighter than standard copier paper. (The finished product, which is about as thick as the cover of a hardback book, is lighter than all but the thinnest plastic sheeting. Even the thin plastic that wraps a cigarette pack, or a batch of index cards is heavier than this carbon fiber material, said Tim Knowles, president of Energy Science Laboratories.

"You know how when you finally get that crap off the index cards, it's clinging to your fingers, and you've got to sort of shake your hand to get rid of the wrapping? Well, that stuff has an area mass of 15 grams per square meter," Knowles said. "Our stuff has an area mass of about 5 [grams per square meter]."

There are a few problems with traditional sail membranes: these sheets tear easily, they require a relatively heavy support structure to stretch them out and keep them tensioned, and they can build up static electricity. Moreover, ultraviolet light degrades these membranes and they melt easily at high temperatures, so they can never get too close to the sun. Another drawback: they can't be propelled by high-energy lasers.

However, the carbon fiber mesh is 25 times lighter than a sheet of typical office paper the same size, yet rigid enough that you can pick up a piece at one corner and the sheet will not bend, Knowles said.

"It's really my candidate for magic."

"We're making things that are 10 times lighter than that little plastic, but they stand in your hands like a stiff cardboard plate. You can take the material and then pleat it -- zigzag pleat it -- and then hold this sort of stack with your hand on the table," he said. "But when you move your hand, it jumps up like a jack-in-the-box, and falls flat on the table and you can't even see where it was creased."

The fabric is receiving tremendous notice because of its promise to self-deploy. Instead of having complicated and cumbersome deployment mechanisms to unpack and stretch out films in space, this carbon scrub-pad material could be packed so that it pops out flat once it is released.

"It's really my candidate for magic," Frisbee said. "Now we've sort of turned everything on top of its head… It's like in the cartoons when the little light bulb goes on over the guy's head. It's got people thinking in new ways about an old problem."

The carbon fiber is also a great leap because it can tolerate temperatures as high as 4,500 degrees Fahrenheit (2,500 degrees Celsius). This gives it a great versatility and durability that other materials lack, said Charles Garner, a JPL senior engineer who works with solar sails.

"The dream would be then you can make these ultra-, ultra-lightweight solar sails out of carbon fiber that can be either taken very, very close to the sun to get a big kick, or can be hit with large amounts of laser power or microwave power," Garner said.

Recent experiments at JPL have demonstrated that lasers can indeed push this carbon material, which glows hot orange and white from the power of the laser beam, but keeps its integrity as a sail.

Henry Harris, a JPL engineer who is managing research into laser and microwave propulsion, said the materials are a huge advance.

"We got the temperature of the sail up to 2,600 degrees Centigrade (4,712 degrees Fahrenheit), which is really good news," Harris explained. "What it means is that it's like any kind of engine: we can run the engine at much higher power levels than we had previously anticipated because we're using advanced materials. And so that has tremendous implications for the future of interstellar spaceflight."

Implications, Knowles said, that do not end with solar sails.

"When you see the stiffness of these things you don't have to limit yourself to thinking about sails. They can be antennas, they can be propulsion systems like sails, or they can be support structures for other things that a spacecraft needs," such as solar cells, or optical sensors, or even flexible electronics circuits, he said.

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Antimatter Spaceships

BY STEFANO COLEDAN