Problem Two: Radiation Shielding
 
 

Long-term human residence in Space requires effective shielding against several different types of radiation. Radiation generally hurts people by destroying cells. Beyond a certain dosage, this leads to death within days or years. Most of the radiation from the Sun is removed by Earth's atmosphere because of collisions with air molecules, and converted to wavelengths with which our bodies are equipped to deal; yet we know that the higher-energy radiation such as the ultraviolet can harm humans. The solar radiation intensity at Earth's surface is only about a tenth of what is experienced in Space at Earth's orbit. The Earth's magnetic field also redirects and removes much of the charged-particle radiation approaching Earth.

A thick atmosphere of light molecules is an excellent protection against radiation. In fact, very light molecules such as hydrogen and helium are even better than heavier molecules to take out the higher-energy particles. Water is probably the most effective radiation shield of all. Unfortunately, there is no evident way of generating either a thick atmosphere (which requires strong gravity to hold it in place) or a blanket of water a couple of feet thick for habitats of any considerable size.

How do present-day astronauts survive? The answer is - they can't for very long. Their radiation dosage is carefully monitored, and when the dosage approaches a safe lifetime maximum, they must retire from space flight. The Space Shuttle, Mir and Space Station Freedom all provide some measure of shielding, but only against "routine" radiation. Solar "storms" or "flares" are very bad events from the radiation dosage point of view, and generally, Space flight is avoided when solar activity is at a peak. Veteran astronauts caught on Space Stations during such storms must spend their time inside specially-built chambers (generally made of plastic sheets, perhaps with some water bags around them) to ride out the storm - and be brought back to Earth as soon as possible. These are not options for long-term human habitats.

A much worse problem is posed by very high-energy particles called cosmic rays. These will interact with metals and generate a storm of secondary radiation particles scattered out of the metal atoms. Thus, aluminum and other metal shields can themselves turn lethal when hit by cosmic rays. The only known way to stop cosmic rays safely is by providing a sufficient thickness of matter for them to be slowed down. This can be done either using water or soil. The thickness of water needed is only of the order of several centimeters. The thickness of soil (lunar or earth) needed is roughly six feet (2 meters). Exotic coatings and materials are being developed to serve as lighter shields, but however light these are, the cumulative mass needed to shield a practical human settlement is still enormous. Since these materials require advanced manufacturing processes, they will have to be manufactured on Earth and shipped out - at enormous launch cost.

When large water reserves are found away from Earth, it will become practical to make shields from water. Until then, the best alternative is to make them out of lunar or asteroidal "regolith" (soil). Lunar - because lunar gravity is only 1/6 that of Earth, and there is no atmosphere, thus rendering impulse-type surface-mounted launchers practical (you don't face the problem of the launch vehicle burning up due to the high drag and friction of the atmosphere when it comes out of the launcher at high speed). Elsewhere, annular containers with hydrogen filling the annulus have been proposed as effective radiation shields. These may become practical as left-over hydrogen tanks from space missions are saved, and the boiloff needed to maintain liquid hydrogen in liquid form is also saved for use as low-pressure radiation shields. This is an alternative which we have not explored further.

These considerations dictate our present approach of designing the "city-building architecture" to use lunar-launched regolith for radiation shielding. We show that launchers which operate "all day" using solar energy can be developed on the Moon, to operate remotely without any long-term human presence.
 
 

References on Radiation Shielding and Habitat Construction from the 1970s:

1. O'Neill, Gerard K., "The High Frontier: Human Colonies in Space". William Morrow&Co, NY, 1977

2. Johnson, R.R., Verplank, W., O'Neill, G. K., : "Space Settlements: A Design Study". Report of NASA-ASEE Engineering Systems Design Summer Program, Ames RC, June-Aug. 1975. Web version, Dec. 1999 Globus, A., Yager, B., Sezen, T., Globus, R., http://lifesci3.arc.nasa.gov/SpaceSettlement/75SummerStudy/Design.html

3. The Low Dose Radiation Research Program of the U.S. Department of Energy COLLABORATIVE ENGINEERING METHODS FOR RADIATION SHIELD DESIGN http://www.lowdose.org/2001mtg/abstracts/singleterry.htm

4. NASA: "Stormy Space Weather" http://www.thursdaysclassroom.com/06jan00/article1a.html

5. NASA: "WEEK 6 Shielding the people in your space settlement from radiation" http://lifesci3.arc.nasa.gov/SpaceSettlement/teacher/course/page6.html

6. Wilson, J.W., Cuccinota, F.A., Miller, J., "Space Radiation Shielding Technology Workshop - An Overview". NASA Langley Research Center, March 15, 2001. http://sirest.larc.nasa.gov/workshop02/Overview.pdf

7. Tools for Nuclear Emergencies http://www.twotigersonline.com/products.html

8. NASA: "Orbital Space Settlements spreading life throughout the solar system" http://lifesci3.arc.nasa.gov/SpaceSettlement/

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Space settlement Annoted Bibliography from Al Globulus, NASA,updated 1995. Copied from: http://lifesci3.arc.nasa.gov/SpaceSettlement/bibliography.html
 

The books, articles, and other media mentioned are, in my opinion, some of the best references on space settlement and related disciplines. Most of them I have read, but a few have been recommended to me by others. I hope you find them helpful.

Last update: June 1995.

Space Settlement Books

* Space Settlements: A Design Study, NASA SP-413,1977. Summary of an early summer study of space settlements.
* Space Resources and Space Settlements, NASA SP-428, 1979. Detailed study of several space settlement design aspects, including life support systems and construction materials
* Humans in Space: 21st Century Frontiers, Harry L. Shipman, Plenum Press, 1989. A conservative, NASA insider view of space settlement with lots of good information. Shipman estimates that there is a 42% chance that space settlement is in our future.
* The Millennial Project: Colonizing the Galaxy in Eight Easy Steps, Marshal T. Savage; Little, Brown and Company, 1992. An awe inspiring vision of Life colonizing the galaxy in relatively small steps. There are decent back-of-the-envelope style 'proofs' of the feasibility of each step. But there's lots of work to fill in the holes. A non-profit group, the First Millennial Foundation, is trying to execute the ideas in this book.
* Colonies in Space, Heppenheimer, T.A.; Stackpole Books. A thorough description of space settlement design factors and construction.
* Space Colonies: A CoEvolution Book Ed. Stewart Brand; Whole Earth Catalog. This is the book that got me hooked on space settlement. A terrific debate on the pros and cons with some of the most far-out thinking in the field.
* Handbook for Space Colonists, Stine, G. Harry; Holt, Rinehart, and Winston, 1985. Discussion of space settlement design to accommodate human requirements.
* Pioneering the Space Frontier, Report of the National Commission on Space, Bantom Books, 1986. Projections of human activities in space well into the 21st century.
* The High Frontier--Human Colonies in Space, O'Neill, Gerard K.; Space Studies Institute Press, 1989 (reprint of the 1976 edition). Descriptions of space settlement designs, with some discussion of construction techniques and economics. Dr. O'Neill started modern space settlement design. He is, however, much better at physics than popular writing.
* The Space Enterprise Stine, G. Harry; Ace Books, 1980. Predicts how factories and industry will evolve in space, including supporting infrastructure and technologies.
* The Third Industrial Revolution, Stine, G. Harry; G. P. Putnam's Sons, 1975. Wide-ranging discussion of how industry will develop and operate in space.

Conference Proceedings
The Space Studies Institute, Princeton University, and the American Institute of Aeronautics and Astronautics (AIAA) have sponsored a biennial conference on space settlement at Princeton University for many years. With one exception, the proceedings are published by the AIAA.

* Space Manufacturing 9: The High Frontier, Accession, Development and Utilization. The 11th conference (1993). B. Faughanan, editor.
* Space Manufacturing 8: Energy and Materials from Space. The 10th conference (1991). B. Faughanan, G. Maryniak editors.
* Space Manufacturing 7: Space Resources to Improve Life on Earth. The 9th conference (1989). B. Faughanan, G. Maryniak editors.
* Space Manufacturing 6: Nonterrestrial Resources, Biosciences, and Space Engineering The 8th conference (1987). B. Faughanan, G. Maryniak editors.
* Space Manufacturing 5: Engineering with Lunar and Asteroidal Materials The 7th conference (1985). B. Faughanan, G. Maryniak editors.
* I don't have the 1983 conference proceedings. It was published by AAS.
* Space Manufacturing 4. The 5th conference (1981). J. Grey, L. A. Hamdan, editors.
* Space Manufacturing Facilities 3. The 4th conference (1979). J. Grey, L. A. Hamdan, editors.
* Space Manufacturing Facilities 2. The 3rd conference (1977). J. Grey, editor.
* Space Manufacturing Facilities (Space Colonies). The 1st and 2nd conference (1974 and 1975). J. Grey, editor.

Books on Background Subjects

* Introduction to Space: The Science of Spaceflight , Damon, Thomas; Orbit Book Company, Inc., 1989. Broad-based introductory material applicable to human activities in space; includes methods for calculating orbital parameters.
* Orbital Motion, Roy, A. E., Adam Hilger, Bristol and Philadelphia, 1988. Very good textbook on orbital dynamics. Assumes the readers knows calculus and elementary vector methods.
* Designing Places for People , Deasy, C. M.; Whitney Library of Design, 1985. Presentation of human behavioral issues for designers and architects of buildings and spaces.

Some of this page is copied from Spaceset materials provided by Anita Gale.

Space Settlement Home Page

Author: Al Globus