by Stephen Ashworth
Physicist Eugene Parker has an article on cosmic rays in the March 2006 issue of Scientific American. He asserts that long-term exposure to cosmic rays is extremely detrimental to human health, and surveys possible shielding strategies for future astronauts on interplanetary missions, currently under development at a NASA workshop. A matter shield would require at least a 5-metre-thick layer of water, adding hundreds or thousands of tonnes to a spacecraft's mass. A magnetic shield would have to be so strong that it would create its own health risks. An electrostatic shield would not only not work, but make the problem worse.
Unlike charged particles originating from the Sun, cosmic rays are about a thousand times more energetic, which is why shielding adequate to protect astronauts from solar flares is useless when it comes to cosmic rays.
Parker concludes that the only likely solution involves space medicine capable of enhancing the ability of cells to heal themselves after cosmic ray hits. His article ends with the rather wistful comment that it would be a pity if "the romance of space travel" had to come to an end as a result of the cosmic ray danger making long-duration spaceflight medically impossible.
He seems to think that the problem applies with equal force on a planetary surface. This is clearly wrong: any planetary body will automatically shield astronauts from half the cosmic ray flux. As for the other half, Parker comments that a base on the Moon or Mars would have to bury itself under tonnes of regolith to provide shielding. But there is nothing odd about this. Any permanent enclosed structure on an airless or nearly airless world, built from local materials, would need to have a thick roof in order to balance its internal air pressure, which would automatically reduce the cosmic ray flux to Earth sea-level intensity.
George Musser of the Scientific American's staff has been running a blog on this subject to which anyone can comment -- see: http://blog.sciam.com/index.php?title=getting_nuked_on_the_way_to_mars
Two responses in particular caught my attention, and I'm sure Scientific American won't mind if I reproduce them here (in full).
Comment from: Theodore Rockwell
Thanks for Eugene Parker's excellent "Shielding Space Travelers" (March 2006). It clearly explains many aspects of this important problem. But it does, by implication, perpetuate some persistent myths.
1. It states that NASA is studying this problem by "investigating precisely how radiation batters DNA," and notes that one-third of an astronaut's DNA would be "sliced by cosmic rays every year." This sounds catastrophic, but DNA damage is not the problem. We all suffer about a million DNA damage-events per day in each cell (on the average) just from routine metabolism. Granted that each radiation damage event is apt to be more severe than metabolic damage (e.g. two or more branches of the DNA broken), the total DNA damage from radiation will still be trivial compared with DNA damage from normal metabolism.
2. Whether a body survives this damage depends on how effectively the repair process and other body defenses work. A fatal dose of radiation results from overwhelming the defense mechanisms, rather than from excessive DNA damage. It's roughly analogous to "catching a cold." Your mother was right to tell you to keep warm and dry (to protect the immune system) and not worry about picking up a few additional germs off door-knobs. Your cells are always exposed to germs -- and radiation.
3. The idea that even a tolerable level of radiation will eventually lead to cancer is based on the false premise that every single ray or particle hitting the body causes damage, and that damage accumulates until death. This idea, repeatedly repudiated by the data, was adopted for administrative convenience in the early days of nuclear power, based on concern over genetic damage. When it was seen that even at the very high radiation doses experienced by the Japanese A-bomb survivors, there was no evidence of genetic damage from radiation in humans, the concept was hurriedly transferred to cancer, where it makes no sense at all.
4. Parker notes that "chemicals that improve the resistance of laboratory rats to radiation damage are themselves toxic." Of course! As noted by Paracelsus in 1540, "Nothing is poison but the dose makes it so." Chemicals that are toxic at high doses are often beneficial at tolerable doses. Like smallpox vaccinations, like exercise and whiskey and sunshine and other forms of radiation. A significant (but tolerable) dose of radiation received quickly will generally stimulate the body's repair mechanisms, leaving not a damaged body, but a more radiation-resistant body.
It's true that current radiation protection regulations and practice are based on the discredited notice that one should reduce even the lowest radiation levels. This is justified as "prudent," but it is not good science to assume that nature works differently than we know it to be. For nuclear power plants, this situation creates unwarranted fears and huge wastes of money. For space travel, it could make the difference between failure and success.
Theodore Rockwell, February 16, 2006
N.B. Theodore Rockwell has been directly involved in nuclear power for nearly 60 years. He is a member of the Health Physics Society, a Fellow of the American Nuclear Society and a vice president and founding director of an international non-profit organization of independent radiation experts committed to bringing radiation policy into line with the best scientific data and theory. See his biog on http://members.authorsguild.net/tedrockwell.
Comment from: Paul Blue
If only we'd thrown our scientists and engineers at Mars during the 60s and 70s, when the Cold War meant that America had to get there first, no matter what. We seem now to be so dogged down with problems that I fear it will never happen.
Would we have sent men to the moon if we knew then what we know now? I fear the answer to that question is no, and therein lies the true problem.
February 17, 2006
If Theodore Rockwell is right, that means that cosmic rays pose effectively no problem whatsoever to human health, since, unlike solar radiation, they are roughly constant in intensity (though their intensity does vary slightly over the solar cycle with variations in the Sun's magnetic field).
But given the current climate of "the precautionary principle" and safety at all costs, it will probably take some years of experience of long-duration exposure to spaceflight conditions by professionals (and the odd daredevil entrepreneur) before the public will accept this.
-- Stephen Ashworth
My article "Europe's Martian Dream" has now been published in Spaceflight, April 2006 issue, p.136-39. Despite the editorial blue-pencilling of some of my more penetratingly critical comments on Europe's 2004 "Human Missions to Mars" design study, I think I have still succeeded in making it clear that the study failed to address its objectives.
It set out to provide an "overall architecture assessment" for a European approach to manned exploration of Mars. It proceeded from the initial assumptions that a European-designed Mars ship would use the Mars orbit rendezvous mission plan, would have a crew of 6, would not use local resources, and would not contemplate surface rendezvous.
In other words, it started by eliminating from its "overall assessment", without discussion, every option except those which could be guaranteed to produce an unrealistically large and expensive spacecraft. It then proceeded to design that spacecraft, and found that it would mean launching over 1400 tonnes into low Earth orbit, over a period of 4 years, for every single flight to Mars.
Needless to say, the study report does not venture any comment as to whether it thinks Mars exploration would be realistic if every single mission required more heavy-lift launches than the entire Apollo and Skylab programmes combined (25 launches, mostly of a revived Russian Energiya, as compared with 13 Saturn Vs and 9 Saturn IBs).
Is there a better way? Zubrin's "Mars Direct" plan is one obvious possibility. But it suffers from one drawback: it depends upon sustained political support for more than a decade, which is hard to achieve. Meanwhile, a letter of mine has been accepted for the May 2006 issue of Spaceflight, describing what I think is the way forward.
The Mars Society UK is playing a leading role in the European Mars Analogue Research Station project. As many people know, this series of stations was inaugurated by Robert Zubrin and members of the Mars Society in the US, whose first station, the Flashline Station on Devon Island in the Canadian Arctic, was commissioned on 28 July 2000.
Last December, the habitat for the European-organised branch of this project arrived in the UK (it had been manufactured in the US). Bo Maxwell and friends took delivery of two shipping containers. When they opened them they found that the hab's wall and roof panels had suffered considerable damage, both from having been stored outdoors in the US for two years, and from having been carelessly stowed in the containers, without any packaging to support them or hold them securely in place.
The plan is to put the hab on display in the UK for a while, before transporting it to Iceland for active use as a research station. The Mars Society UK is appealing for assistance repairing the damaged station -- both voluntary practical work and financial help.
With any offers of help, please contact: Bo Maxwell, President of the Mars Society UK, bo_maxwell(at)marssociety.org.uk.
The project should help to raise the public profile of Mars exploration in this part of the world. But whether it will have much impact on the spending priorities of Her Majesty's Government (total managed expenditure in 2005/06, a paltry 520 billion pounds) remains to be seen.
Thanks to David A. Hardy for pointing out that there are now two Clarke awards!
(1) The "Sir Arthur Clarke Awards", inaugurated 2005, recognise UK achievements in space in the spirit of the film industry's "Oscars". One major difference from the Hollywood awards is that nominations for the "Arthurs" come from the public. If people were "impressed, intrigued or inspired" by some aspect of space research, they were encouraged to submit their nominations to the award's website: http://www.clarkeawards.org/index.html
Winners for 2006 will be announced at the BROHP conference this month. The nominees include Sir Richard Branson, astronaut Michael Foale, David Parker (of BNSC and PPARC, and promoter of UK involvement in ESA's Aurora Project), David Williams (CEO of Avanti Screenmedia, for putting together a business package which set up a geostationary communications satellite programme), and many others.
(2) The "Arthur C. Clarke Awards" are for the best science fiction novel published in Britain during the previous calendar year. They have been awarded every year since 1987. See: http://www.literature-awards.com/arthur_c_clarke_awards.htm and http://www.appomattox.demon.co.uk/acca/
Previous winners include China Miéville (Iron Council, 2005), Neal Stephenson (Quicksilver, 2004), Christopher Priest (The Separation, 2003), Gwyneth Jones (Bold As Love, 2002), China Miéville (Perdido Street Station, 2001), and Bruce Sterling (Distraction, 2000). The first winner was Margaret Atwood for The Handmaid's Tale (1987). The shortlist for 2006 can be found at: http://www.appomattox.demon.co.uk/acca/shortlists.htm
Astronautical Evolution is an e-mail newsletter devoted to news and comment from an astronautical evolutionist perspective. To subscribe / unsubscribe / contribute / comment, please e-mail Stephen Ashworth, sa(at)astronist.demon.co.uk.
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