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The Challenges of the Journey |
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A Force Field for Astronauts? Researchers are reviving an old but wild idea to protect astronauts from Space radiation |
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A New Kind of Solar Storm High-energy particles from the Sun have just picked up speed |
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Mysterious Cancer Researchers agree that space radiation can cause cancer. They're just not sure how. |
| Solar super-sail could reach Mars in a
month 29 January 2005 NewScientist.com news service Celeste Biever A LICK of paint could help a spacecraft powered by a solar sail get from Earth to Mars in just one month, seven times faster than the craft that took the rovers Spirit and Opportunity to the Red Planet. Gregory Benford of the University of California, Irvine, and his brother James, who runs aerospace research firm Microwave Sciences in Lafayette, California, envisage beaming microwave energy up from Earth to boil off volatile molecules from a specially formulated paint applied to the sail. The recoil of the molecules as they streamed off the sail would give it a significant kick that would help the craft on its way. "It's a different way of thinking about propulsion," Gregory Benford says. "We leave the engine on the ground." Solar sails are in essence nothing more than giant mirrors. Photons of light from the sun bounce off the surface, giving the sail a gentle push. It was while developing a solar sail five years ago that the brothers stumbled upon their idea for enhancing the effect. The pair were testing a very thin carbon-mesh sail by firing microwaves at it. To their surprise, the sail experienced a force several times stronger than they expected. They eventually worked out that the heat from the microwave beam was causing carbon monoxide gas to escape from the sail's surface, and that the recoil from the emerging gas molecules was giving the sail an extra push. |
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In a forthcoming issue of the journal Acta Astronautica, the Benfords explain how a sail covered with a paint designed to emit gas when it is heated might propel a spacecraft to Mars in just a month. A rocket would take the craft to low-Earth orbit, 300 kilometres up. After the craft unfurls a solar sail 100 metres across, a transmitter on Earth would fire microwaves at it to heat it up. The Benfords calculate a one-hour burst of microwaves could accelerate the craft to 60 kilometres per second, faster than any interplanetary spacecraft to date. The feat would require a 60-megawatt microwave beam with a similar diameter to the sail. It would also have to be capable of tracking the craft as it accelerated away. But this power level could not be delivered by any existing microwave transmission system. The deep-space communications network that NASA uses to communicate with Mars rovers and the Cassini probe now orbiting Saturn can only manage half a megawatt. The Benfords say the power could be ramped up in future and hope to persuade NASA to consider doing this as part of a future upgrade to the network. A further challenge is how to formulate the evaporating paint. The ideal material would lock up large amounts of a light gas like hydrogen and only release it at very high temperature, when the high speed of the gas molecules would maximise the recoil. Ideally all the paint would boil away, leaving a micrometre-thin sail to continue the voyage to Mars. "It's pretty cool," says Geoffrey Landis, a physicist at NASA's Glenn Research Center in Cleveland, Ohio. "There are obviously some details to be worked out here, but in a fundamental way the idea makes sense." |
| 5 Ways to Get to Mars By Michael Behar Wired Magazine Dec 2004 Big dumb rockets? Solar sails? The pros and cons on the engine options Chemical propulsion The classic approach - lots of fire and smoke. Kerosene-burning engines put men on the moon, and chemical propulsion could get you to Mars, but it'll feel like the scenic route. It's six months one way, and your return window doesn't open for another 18. Total time away from home: 2.5 years. Pros: It's the devil you know. Big, dumb rockets like the ones used for Apollo could have put humans on Mars by 1990. If we want to leave soon, this is how. Cons: Speed, or lack thereof. Chemical propulsion is slow for interplanetary distances, and after 60 years of development, they're about as fast as they're going to get. Antimatter propulsion Star Trek was on the right track. An engine fueled by antimatter could attain 19,000 miles a second. Trips to Mars in days or even hours are possible - if you can survive the warp-speed acceleration. Pros: Very, very fast. With this under the hood, you just have time for a nod to the Red Planet as you head out to Alpha Centauri. Cons: The fuel costs more than the national debt. Not to mention that it would take 1,000 grams of antimatter to get to Mars and current worldwide production is only about 10 nanograms a year. Nuclear thermal propulsion Also known as nuclear thermal rockets, this has twice the performance of chemical engines. Liquid hydrogen is pumped through the core of a reactor, and the resulting white-hot gas blasts out a nozzle yielding plenty of horsepower. Pros: It's build-it-and-go technology that could get you to Mars in a few months. You can even use it to generate electricity along the way. Cons: Mostly political. Environmental watchdogs fear contamination here on Earth. Solar sail A giant solar collector - 5 micrometers thick and 3 miles long on a side - captures the kinetic energy of photons in sunlight, carrying the ship through the inner solar system like an America's Cup yacht. Pros: No onboard fuel means unlimited operation. You could fly to Mars and tack back to Earth as many times as you want. Cons: Sunlight may be free, but it's not very high torque. Expect a leisurely cruise - a couple of years one way - unless you use a big power laser on Earth to give it a shove. Ion propulsion There are several ion engines on the drawing board. The most promising for a Mars mission is nuclear electric propulsion. Inside the unit, electrons are stripped from xenon fuel, leaving behind a swarm of positively charged ions rarin' to go. A negatively charged grid in the back of the engine accelerates them, creating thrust. Pros: Fuel efficiency is so good that you can accelerate for weeks, instead of minutes, resulting in high top speeds. You could make it to Mars in a couple of months with one of these babies. Cons: An engine big enough for a human mission would be a major power hog. One design calls for three nuclear reactors putting out a total of 12 megawatts, enough to power a small town. Michael Behar wrote about fire science in issue 12.10. |
