Radiation Shielding and Magnetic Sails

The Royal Astronomical Society’s recent meeting was laden with interesting papers, enough so that, with the added distraction of Gliese 581 c, I find myself still clearing out the backlog of newsworthy items. Otherwise, Centauri Dreams would have examined Ruth Bamford’s work on radiation shielding much earlier. Bamford (Rutherford Appleton Laboratory) and team are working on a magnetic shield that would protect against dangerous cosmic rays and radiation. The work is significant because the radiation threat is real, and our current methods of dealing with it are inadequate for long-range space missions.

Consider the International Space Station, where a chamber built for the purpose of radiation protection is available. The method works for the intermittent periods when solar radiation is intense (as from major flares), but such a chamber adds substantially to the mass of a spacecraft, becoming impractical on missions beyond Earth orbit. The new plan is to create an artificial magnetosphere using superconductors and magnetic confinement techniques, a deflector shield that could be deployed not only on space vehicles but around bases on the Moon or beyond.

A deployed radiation shield

Image: An artificial magnetosphere could be generated around manned space craft en route to the Moon or Mars to protect the occupants from the potentially lethal radiation in space from the Sun. A superconducting ring on board such a space craft could produce a magnetic field, or mini-magnetosphere, similar to the Earth’s, which would create a Star Trek like ‘deflector or plasma shield.’ Credit: Ruth Bamford/Rutherford Appleton Laboratory.

Start thinking about the outer planets and radiation shielding becomes critical. Nor is it just a concern for the long journey there and back. We’d like to know a lot more about the major Jovian moons, for example, especially Europa because of its probable ocean beneath the ice. Callisto, too, shows some signs of possessing an ocean. But if a human presence is to be established anywhere near these worlds, it will have to reckon with Jupiter’s radiation belts. How radiation shielding plays out will have much to say about the kinds of missions we can mount near Jupiter.

Finally, we can speculate on how some of these technologies may eventually come together. We’ve talked about magnetic sail concepts in which a spacecraft generates a magnetic ‘bubble’ in order to ride the solar wind to the outer planets. More advanced designs might one day use beamed energy to reach speeds that could make an interstellar crossing possible within a human lifetime. Our prowess with artificial magnetospheres may have much to teach us not only about shielding but propulsion, which is why this work has implications not only within our own Solar System but for the longer missions that will follow.

A Conference on Warp Drive

If we ever develop a true ‘warp drive’ that can take us to the stars well within a human lifetime, we’ll probably look back at Miguel Alcubierre as the theorist who took a science fictional idea fully into the realm of scientific calculation. The physicist’s 1994 paper (reference below) suggests that manipulating the spacetime continuum itself could allow a spacecraft to move within a ‘bubble’ enclosed by the warp. It would never break the light barrier but would ride on the spacetime distortion to arrive at its destination as if it had. “A propulsion mechanism based on such a local distortion of spacetime,” wrote Alcubierre, “just begs to be given the familiar name of the ‘warp drive’ of science fiction.”

It’s quite a notion, isn’t it? In essence, you want to create more spacetime behind your bubble while contracting what’s in front of it. The British Interplanetary Society notes that Alcubierre’s original paper has inspired about fifty publications probing the intricacies of the concept. One of the most troubling is a paper by Michael Pfenning and Larry Ford which raises the question of energy. In their view, the Alcubierre drive would demand more energy than is available in the entire universe. Chris Van den Broeck later produced a variation demanding no more than the energy output of a single star, so I guess we’re making progress of sorts.

Clearly, we have a long way to go before any spacecraft powered by a warp drive becomes feasible, if it ever does (and we haven’t even started talking about negative energy yet). It’s heartening, though, to see that the BIS is putting out a call for papers for a symposium on the matter to be held later this year. From the announcement:

In an effort to generate interest in solving some of the technical problems a symposium is being organised with the intention of focussing on four main themes: The Current Status of the Warp Drive Proposal; Quantum Field Constraints; Photon Propagation through the Warp Field; Alternative Faster than Light Drives. Where the latter may be based upon alternative versions of Einstein’s gravity such as Brans-Dicke theory or Yilmaz theory, or based upon alternative suggestions for interstellar travel such as the Krasnikov tube and wormholes.

The address for submissions: 27/29 South Lambeth Road, London SW8 1SZ, or via email to mail@bis-spaceflight.com; full details are in the link above. Needless to say, this is the kind of effort that the Breakthrough Propulsion Physics program would have mounted if NASA had continued its funding, and it is a reminder of how far the space program in the US has wandered away from theoretical subjects like these in its quest to keep Space Shuttles and the ISS flying. But that, I suppose, is an argument for another day.

The papers mentioned above are Alcubierre, “The Warp Drive: Hyper-Fast Travel Within General Relativity,” Classical and Quantum Gravity 11 (May 1994): L73-L77; Pfenning and Ford, “The Unphysical Nature of ‘Warp Drive,'” Classical and Quantum Gravity 14 (1997): 1743-51; and van Den Broeck, “A ‘Warp Drive’ with More Reasonable Total Energy Requirements,” Classical and Quantum Gravity 16 (1999), 3973-79.

Related: New Scientist looks at another way to travel vast distances quickly (in this case, perhaps between individual universes): the wormhole. Are black holes now under study actually wormholes? Physicists Thibault Damour (Institut des Hautes Etudes Scientifiques, France) and Sergey Solodukhin (International University Bremen, Germany) make the case for this interpretation. Click here for more.

Gerald Nordley: Doubts on Gliese 581 c

We’d all like Gliese 581 c to be as Earth-like as possible, but not everyone puts high odds on the planet being even potentially habitable. In an e-mail discussion circulating among space professionals, Gerald Nordley took issue with the ‘terrestrial world’ concept and pointed out how the results of Stephane Udry and the Geneva exoplanet team shouldn’t be taken too far. Nordley, a retired Air Force astronautical engineer, is a familiar name to those who follow interstellar studies from his work in the Journal of the British Interplanetary Society as well as his essays in venues like Analog. He is also the author of numerous science fiction stories.

Here are Nordley’s comments, reprinted with permission:

Udry et al., make a good case for a planet being there, but the rest looks speculative at best. The planet has a minimum mass of 5 Earths, the “1.5 Earth radius” is based on a density assumption with no data behind it, and the planet’s insolation is about 2.44 times the Earth’s (L/a2 = 0.013/.0732). The effective temperatures calculated didn’t reference any atmosphere model. A similar calculation for Earth gets you about 256K (-17C), depending on albedo. They used a Venus-like albedo to get down to 273K — actually not bad for the Venusian upper atmosphere. Of course, we all know what the surface of Venus is like.

If an awful lot of things break the right way, well, maybe a terrestrial planet. But in my crystal ball G 581c is a rather hot mini-Uranus.

The next planet out has an insolation of 20% Earth’s. If it (big if!) were of similar density to the Earth, it would have a surface radius and gravity roughly twice as high as high as Earth’s. And even if the top of the atmosphere were much colder, if it were a few bars deep, the lapse rate would produce a liquid water surface.

Nordley’s thoughts come at a time when Greg Laughlin (UC-Santa Cruz) has pegged the odds on Gliese 581 c harboring “a clement surface or a temperate ocean-atmospheric interface” at a thousand to one against. Which is not to downplay the significance of the Gliese 581 c discovery, but only to point out that there is a wide gap between the actual facts we have on this planet and the speculation they have provoked. We can learn more through continuing observations — and we can’t rule out the possibility of a transit, which would help immensly.

So just what is the significance of Gliese 581 c? Whether or not it turns out to be habitable, this planet represents the first time we’ve ever looked at a world where all the pieces could fall into place. And the new planet should energize further investigation, quickening the pulse not only of those already involved in the search, but in a public that shows signs of becoming excited again about deep space exploration. That makes the outlook for the next few years in exoplanet studies more promising than ever, because Gliese 581 c is only the first of many terrestrial world candidates to come.

Administrative: RSS Feed Glitch

Some of you have reported getting only a summary rather than the full text from the Centauri Dreams RSS feed today. I think the problem is fixed, but if it persists, please let me know. Ah, the joys of administration…

A Gliese Moment

Exoplanets are a niche topic for many people, rarely brought to mind except to note an occasional discovery before moving on to the rest of the day’s news. But Gliese 581 c is causing ripples. Yesterday, BBC radio host Eddie Mair referred to it as ‘the planet everyone is talking about.’ And last night on my regular walk I passed a neighbor I run into almost every evening. He was standing in his yard looking west under a sky dominated by an incredibly bright Venus. This is a man I have known for years, and not once in that time have we spoken about astronomy. But on this night, he said “So how do you pronounce G-l-i-e-s-e?”

I’ve always said ‘Glee-see,’ but as astronomer Wilhelm Gliese was German, the proper way to say it really should be ‘Glee-zuh’. Gliese (1915-1993) first came to my attention about twenty years ago when I was trying to work out the odds of picking up accidental radio emissions from civilizations near the Sun. The Gliese Catalog of Nearby Stars told me what was where, all known stars within 25 parsecs of the Sun.

That seemed pretty esoteric too, but this morning I passed another neighbor (I walk a lot, usually three or four miles a day). The sky was soft, tawny, criss-crossed with contrails and promising rain by evening. We exchanged pleasantries and talked about the new planet. What got her going was my use of the word ‘nearby.’ “You say it’s a nearby star. How long would it take to get there?” I told her 20 years if we could move at the speed of light and her eyes widened. “If that’s nearby,” she said, “I’d hate to know what you consider far away!” We both laughed and looked into the sky, shaking our heads at the sheer scale of things.

Maybe I’ve coined a new term — a ‘Gliese moment’ — that describes what happens when a formerly niche topic suddenly goes mainstream. In any case, what an opportunity to get people not normally involved with astronomy to acquaint themselves with what the exoplanet hunt is really about. This past decade of ‘hot Jupiters’ and outer system giants is giving way to a period when planets not much larger than ours will be swimming into view. Give us another decade and we may be looking at reflected light off a planet with an atmosphere, oceans and clear signs of life.

My unexpected conversations on this topic have completely delighted me. Because what I am picking up is the palpable sense of awe as people leave their daily concerns behind for a moment and start to think about just how big the universe is, where we might fit in it, and what else we might find as we push ever further out toward stars like Gliese 581. This new world was like finding an unexpected gift at the door, one that made these two people, both nearing retirement, feel enchanted with the cosmos again. As for me, Gliese 581 c, that distant world under a dim red sun, warm in places and maybe water-laden, has put a definite spring in my step. The hunt for terrestrial exoplanets has only begun.