Space Colonization

How are we going to get there? Interstellar Propulsion

There are a number of interstellar propulsion systems on the drawing board today. They range from the practical using today's technology to the fantastical requiring great leaps in technological advancement to achieve. Here are a few of the more well known.

Project Orion, 1958

Nuclear bomb powered flight? Nuclear fission touted as the only known method of performing manned interstellar exploration with current technology by Wikipedia, the idea may still have merit. How it Works | Why it's Feasable

Bussard Interstellar Ramjet, 1960

This is probably the most well-known theoretical interstellar vehicle. Follow this link for a good discussion of the pros and cons of this 'might just be possible' design.

Project Daedalus, 1973

The challenge: use current or near-future technology, be able to reach its destination within a human lifetime, and be flexible enough in its design that it could be sent to any of a number of target stars. British Interplanetary Society's answer? Nuclear fusion, unmanned, 50 year flight to Barnard's Star.

Solar Sailing, 1984

Using the power of the sun to push us across space has been around for a long time. In 84 Robert Forward proposed a 65 GW laser to push us through interstellar distances.

Alcubierres Warp Drive, 1994

Warp because the theory is based on expanding (warping as in shape) the fabric of space-time behind the vessel, while contracting space-time in front of it. The actual ship would remain 'stationary' between the two warped spaces, which would relocate the ship potentially faster than light to another point on the space-time continuum.
Improvements to the Original Model

Deep Space 1, 1998

Ion propulsion is a technology that involves ionizing a gas to propel a craft. Instead of a spacecraft being propelled with standard chemicals, the gas xenon (which is like neon or helium, but heavier) is given an electrical charge, or ionized. It is then electrically accelerated to a speed of about 30 km/second. When xenon ions are emitted at such high speed as exhaust from a spacecraft, they push the spacecraft in the opposite direction. Deep Space 1 Home

Anti-Matter Drive, 2000

In October 2000, NASA scientists announced early designs for an antimatter engine that could generate enormous thrust with only small amounts of antimatter fueling it. Matter-antimatter propulsion will be the most efficient propulsion ever developed, because 100 percent of the mass of the matter and antimatter is converted into energy. When matter and antimatter collide, the energy released by their annihilation releases about 10 billion times the energy that chemical energy such as hydrogen and oxygen combustion, the kind used by the space shuttle, releases. Matter-antimatter reactions are 1,000 times more powerful than the nuclear fission produced in nuclear power plants and 300 times more powerful than nuclear fusion energy.

Cosmos 1, 2004

The first solar sail. The launch will be the culmination of the first international, privately funded space mission in history. Sponsored by the Planetary Society

Continuous Improvement

Scientists continue to look for more efficient ways of interplanetary propulsion. NASA engineers are dreaming up new ways to reach the final frontier more quickly and cheaply. Next spring, if all goes as planned, a private consortium will launch the world's first "solar sail," a spacecraft pushed along by the pressure of sunlight.

In 2006, NASA will send off the Dawn mission, powered by a novel engine that spits out charged electrical particles.

Farther in the future, scientists envision hurling interplanetary probes at Saturn or Neptune, letting the planet's atmosphere "brake" the spacecraft into orbit.

Even more wacky, a NASA team is working on a gigantic space slingshot a cable that would snatch probes coming from Earth and whip them along into space.

Many of these new technologies come from NASA's Marshall Space Flight Center in Huntsville, Ala., where a small group of engineers consider almost any idea for getting into space. In November 2004, they presented their best ideas to planetary scientists gathered in Louisville, Ky.

"This could be a new direction for a whole range of planetary exploration," said Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology. Right now, trips through the solar system are limited by how much chemical propellant spacecraft can carry. Missions with more fuel require bigger, more expensive launch vehicles. So engineers are trying to replace the Humvees of planetary exploration with more efficient vehicles.

Sailing away

Solar sails, for instance, are very lightweight, looking like nothing more than large fans made of tissue-thin foil. They are also extremely maneuverable; they can hover in one place or move out of traditional spacecraft orbits. The idea of solar sails has been around since the early 1970s, but only now are they becoming reality, said Louis Friedman, executive director of the Planetary Society, a nonprofit group devoted to solar system exploration. "Solar sailing is the only technology that we know of that could lead to interstellar travel," he said. Solar sails work because particles of sunlight bounce off the ultralight wings, gently pushing the spacecraft in a particular direction. Mission controllers sail the probe using sunlight pressure just as sailors control a boat using wind. NASA is working on solar-sail technology, but so far has only tested small-scale versions in vacuum chambers.

March 2005, the Planetary Society plans to launch the first-ever solar sail. If all goes as planned, the probe will launch, folded up, aboard a converted intercontinental ballistic missile from a submarine in the Barents Sea. After the external rocket stages drop away, the sail is designed to unfurl like a giant flower. With sunlight pushing its eight panels along, "Cosmos 1" will drift slowly through Earth orbit. If it works, the craft would be visible to the naked eye, appearing as a dot as bright as the full moon. "It will be a signal flare for the kind of world that all of our children deserve," said Ann Druyan, the widow of astronomer Carl Sagan and a driving force behind the project. Ms. Druyan runs Cosmos Studios, a production company that partnered with the Planetary Society and other donors to pay for the $4 million spacecraft.

But success isn't guaranteed. In 2001, an early test of Cosmos 1 failed when one of the upper rocket stages failed to separate from the missile, sending it and the attached probe crashing back to Earth. The missile had been improperly modified for suborbital flight; this spring's flight is designed to go into orbit and thus avoids the problem, Dr. Friedman said. The launch window opens March 1 and ends April 7; the exact date depends on the Russian navy.

Already working

Another idea for exploring the solar system ion propulsion is already in orbit, around the moon. SMART-1, a European Space Agency mission, reached the moon last week, powered by an ion propulsion engine. NASA's Deep Space 1 probe, using a similar engine, flew by Comet Borrelly in 2001, sending back the closest and best pictures ever taken of a comet. Ion propulsion relies on electricity, rather than chemistry, to get through space. A probe with ion propulsion uses solar panels to produce electrical energy, which then accelerates chemical propellants to provide thrust. Such engines aren't as powerful as traditional engines, but they burn for longer amounts of time, building up significant amounts of thrust. Deep Space 1's engine operated for more than six years more than 3 times longer than a traditional spacecraft engine, said Randy Baggett of the Marshall Space Flight Center. Its success paved the way for the Dawn mission, scheduled for a 2006 launch to the asteroids Ceres and Vesta.

Air brakes

Another chance to save fuel happens when a spacecraft reaches its target. For planets or moons with thick atmospheres, such as Saturn or Neptune, "aerocapture" might be one way to avoid burning lots of fuel to slow a spacecraft down. Several missions have already used a variant of aerocapture, dipping briefly into the atmosphere on each pass to "aerobrake" themselves over several orbits. In aerocapture, the probe would make a single pass, deep enough to be captured into orbit. "The faster you're coming in, the bigger the payoff," said Kirk Sorenson of NASA. But the probe can't come in so fast that it slingshots around the planet, or so deep that it burns up in the atmosphere. Aerocapture may sound far out, but it's nothing compared to the "momentum exchange tether" NASA is thinking about.

Wild sling

As currently envisioned, the 70-mile-long tether would orbit the Earth while spinning like a giant baton. Probes would be launched to meet the tether about 240 miles up. The spinning tether would clasp the probe briefly and hurl it outward, boosting it on a journey to the moon or Mars. After the throw, the tether would boost itself back to a higher orbit, ready for the next probe to throw. Such a tether would cost at least hundreds of millions of dollars to build and launch, but might save money in the long run by reducing launch costs for the probes it tosses. Slingshotting off the tether might give a spacecraft as much as a third of the energy needed to get to the moon, said Joseph Bonometti of the Marshall center. Of all the new technologies, he said, "we're the dark horse." NASA isn't sure exactly what the tether would look like. It would probably be made of a high-tech polymer material, with solar power stations strung along it like beads on a string. As for how it would actually catch the satellite "well, we're still working on that," said Mr. Bonometti.

Today's technological dreams, said MIT's Dr. Binzel, might soon fizzle out. Or one of them could just end up powering the next generation of space explorers.

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