Galactic Cosmic Rays (GCR) – The 800 Pound Gorilla

The most recent issue of Science News (18 December 2010) has the following notes from 17 December 1960:

HEAVY SHIELD UNNECESSARY — Heavy shielding as protection for an astronaut against space radiations may not be necessary, at least for trips of less than 50 hours and at distances not greater than 618 miles from earth…. [B]iological specimens were encased in different types of metal to test their effectiveness as shielding materials. Some specimens were shielded only by the thin aluminum covering of the specimen capsule and the comparatively thin shell of the recovery capsule. Radiation dosimeters showed that aluminum provided better shielding properties than lead and that any heavy metal such as gold or lead becomes a hazard during a solar flare as high energy protons interact with these heavy metals to create damaging X-rays.

However, if you want to travel to the Moon or journey anywhere within the Solar System, Galactic Cosmic Radiation will require that the human crew is protected. Let’s take a look at the problem and the research required to test and implement solutions.


The GCR problem arises from interstellar atomic nuclei traveling near the speed of light striking the structure of a spacecraft. The resulting shower of secondary particles cause radiation damage. The Earth is protected by the Van Allen belts and a deep atmosphere. Brief journeys such as an Apollo mission does not expose the astronaut to dangerous dosages. However, astronauts on such a journey are at risk from Solar flares (Solar Particle Events – SPE). SPEs can be mitigated with layers of hydrogen rich materials such as polyethylene or water. GCRs, however, require spaceships on long journeys of more than 100 days, or habitats on the Lunar or Martian surface, to be surrounded by tens of meters of water for passive protection, or magnetic shields for active protection. Either solution is extremely heavy and makes space flight prohibitive in terms of propellant requirements.

The following sections discuss each aspect and provide references for further reading about the problem

The Source of GCR

Galactic Cosmic Rays come from outside our Solar System, but from within our galaxy, the Milky Way. They are comprised of atomic nuclei that have been stripped of their electrons. These nuclei can be any element. Common elements are carbon, oxygen, magnesium, silicon, and iron with similar abundances as the Solar System. Lithium, Berylium and Boron are overabundant relative to the Solar System ratios.

The Shielding Problem

Early on, it was suggested that cosmic rays could penetrate the Apollo spacecraft. From “Biomedical Results of Apollo” section IV, chapter 2, Apollo Light Flash Investigations we have the following account:

Crewmembers of the Apollo 11 mission were the first astronauts to describe an unusual visual phenomenon associated with space flight. During transearth coast, both the Commander and the Lunar Module Pilot reported seeing faint spots or flashes of light when the cabin was dark and they had become dark-adapted. It is believed that these light flashes result from high energy, heavy cosmic rays penetrating the Command Module structure and the crew members’ eyes. These particles are thought to be capable of producing, visual sensations through interaction with the retina, either by direct deposition of ionization energy in the retina or through creation of visible light via the Cerenkov effect.

When Galactic Cosmic Rays collide with another atom, such as those contained in the Aluminum, Stainless Steel or Titanium structures of a spacecraft, they can create a shower of secondary particles, These secondary particles cause radiation damage in living organisms (humans).

The problem is creating sufficiently powerful barriers to these extremely energetic nuclei.

Researching Solutions

  • Passive Shielding – At least for solar flares (SPE), some solutions are easier than the GCR problem.
  • Active Shielding
  • Fast Passage to avoid exposure (VASIMR propelled craft). A proposal for vapor core reactors integrated with VASIMR engines.
  • A proposal for studying radiation and other factors associated with long term human occupation of space.
  • NASA’s Space Radiation Program in association with the Brookhaven National Laboratories.
  • In 2008, the National Academies of Science published Managing Space Radiation Risk in the New Era of Space Exploration, which included chapter 6: Findings and Recommendations
  • From the Summary in Radiation Shielding Simulation For Interplanetary Manned Missions
      Inflatable Habitat + shielding

    • Hadronic interactions are significant, systematics is under control
    • The shielding capabilities of an inflatable habitat are comparable to a conventional rigid structure – Water / polyethylene are equivalent
    • Shielding thickness optimisation involves complex physics effects
    • An additional shielding layer, enclosing a special shelter zone, is effective against SPE
      Moon Habitat

    • Regolith shielding limits GCR and SPE exposure effectively
    • Its shielding capabilities against GCR can be better than conventional Al structures as in the ISS

See also the recent article in New Scientist about radiation hazards. A tip of the hat to ParabolicArc.

From Olduvai Gorge to the Sea of Tranquility


By far the two most remarkable photographs of the twentieth century are the ones shown above. For they encapsulate the whole evolutionary and cultural history of humanity and its possible destiny.

In 1978, paleontogist Mary Leaky and her team discovered the earliest hominid footprints (dated to be three and a half million years old) preserved in the volcanic ash at Laetoli, forty-five kilometers south of Olduvai Gorge in Tanzania. They belong to one of our proto human ancestors – Australopithecus afarensis. The picture above shows one of these fossil footprints next to the boot print left by Neil Armstrong in the volcanic soil of Mare Tranquilitatis (the Sea of Tranquility).

It is very symbolic of the giant evolutionary leap forward we have taken as a species. From Olduvai Gorge to the Sea of Tranquility, we humans have traveled very far.

Exploration has always been vital to the survival of our species and an integral component of our evolutional heritage and survival imperative. The lure and call of distant lands and new horizons is rooted in our very genes.

The descendents of Australopithecus afarensis – Homo Erectus eventually migrated out of Africa some two million years ago and were to disperse throughout the old World. This was the first of four major waves of human migration from Africa culminating in the last major migration some sixty thousand years ago of fully modern humans (Homo sapiens, sapiens).

Since April 2005 through the efforts of Dr. Spencer Welles and the National Geographic Society’s Genographic Project we have begun to map out the migratory story of the human Diaspora out of Africa out onto a wider global stage. This evolutionary step and the migrations that preceded it were vital to humanity’s long term survival in the face of the vicissitudes of a changing global climate.

Eventually the descendents of this last major migration would spread out from the Old Worlds of Europe and Asia into the New Worlds of the Americas and Australia.

It was during this phase of the human story that we became a planetary species. Eventually we discovered agriculture, built the first cities, developed culture and writing and became the pioneers of a totally new domain of evolution.

We are the pioneers of a whole new form of evolution which is distinctly non-biological. This new realm of evolution is Cultural Evolution. It is this new dominion of evolution that has made us the most dominant life form on this planet and has set us on a trajectory that will one day take us out amongst the stars.

In this epoch of human history we face many dangers both old and new. The past has shown us that many species have been wiped off the evolutionary stage because of catastrophic climatic shifts, super-volcanism and asteroidal bombardment. Our species is no different. Some seventy-five thousand years ago our species barely survived a long volcanic winter triggered by the supereruption of Lake Toba on the island of Sumatra in Indonesia. And, at least one ancient culture – the Clovis people of North America, may have met their demise as a result of the celestial equivalent of a 9/11 event. Some thirteen thousand years ago a comet exploded over North America, wiping out the mega fauna of that continent, and the people who hunted them, off the face of the Earth.

Today we still face the threats of climate change (both natural and anthropogenic), resource depletion and the products of our own technological folly: environmental degradation, resource depletion, total nuclear warfare, and biological terrorism. Our intelligence and the fact that we were disperse globally helped ensure our survival as a species.

Yet, our species is curious, brave and shows much promise. We are graced with a towering intellect that stands poised on its next evolutionary leap that may one day take us beyond the Sea of Tranquility and ensure our long term survival.

Neil Armstrong’s one small step for [a] man was the culmination of the greatest scientific, technological and cultural advance in human history. It was indeed a giant leap for mankind. It proved, beyond any question of doubt, that humankind had taken the first evolutionary stride in becoming a multi-planetary species. The time has now come to venture further out on this vast new ocean of space and to chart humanity’s Diaspora out amongst the stars.

We must return to the Moon, this time to stay. We must learn to utilize the vast untapped energy and mineral treasures of the Moon and the Near Earth Asteroids. We must eventually settle the entire solar system from the planet Mars and out to the edge of the solar system. One day our species will continue its migration out into the Milky Way Galaxy. But, this is very far from being our assured manifest destiny. The choice is entirely ours to make. Humans have labeled their species “Homo sapiens, sapiens” – wise, wise man. The time has now come to use our double measure of wisdom to climb out of planetary cradle and take our evolutionary destiny into our own hands and transform ourselves from Homo sapiens, into Homo Stellaris and find our home among the stars.

Only then can we ensure the long term survival and immortality of humanity.

World Moon Bounce Day Celebrates 40th anniversary of Apollo 11 Moon Landing

World Moon Bounce Day will be June 27 in Australia and June 26 in the U.S., Echoes of Apollo (EOA), an international space education organization, in cooperation with the National Space Society, will announce Tuesday. Participants worldwide will celebrate the 40th anniversary of the 1969 Apollo 11 moon landing by bouncing radio voice transmissions off the moon, known as “moon bounce.”

Moon Bounce DayIn collaboration with schools, amateur radio organizations, and cultural groups, people from around the world will communicate with one another via the moon using more than 13 dish antennas, including the 150-ft.-diameter Stanford Research Institute radio dish in Palo Alto, California; the 70-ft. dish at Morehead State University at Space Science Center in Kentucky; the 25-meter Dwingeloo Radio Telescope dish in Dwingeloo Holland; and the 90-ft. dish of the University of Tasmania, Hobart, Tasmania.

These antennas will bounce transmissions off the moon, to be received by dish antennas in other countries. Station operators and their guests will experience the thrill of hearing their own voice or that of others talking via the moon, with a delay of about 2.5 seconds. (The June 27 date is based on optimal alignment of the Moon and Earth for participating dish locations.)

“World Moon Bounce Day is part of Echoes of Apollo, a four-year global party that will re-educate new generations about the Apollo missions and in particular, the Apollo 11 mission,” said Sydney-based Robert Brand, the International Events Manager for EOA. In 1969 at age 17, Brand wired up NASA communications equipment in Sydney that relayed the data from the moon via the Parkes and Honeysuckle Creek radio telescopes, including video and data from the Lunar Module and Command Module.

World’s biggest space party

Echoes of Apollo, billed as “the world’s biggest space party,” was formed in 2008 by people involved in or interested in the Apollo moon missions. It is the first stage of a four-year-long effort to re-focus attention on the moon, the Apollo missions of 40 years ago, and a possible future return to the moon. The group will further the spirit of exploration of space and the advancement of science, recognize space as a way to connect the people of Earth, and show how the knowledge of space can be used to solve the problems of the planet.

“For three months (June to August 2009), we will be celebrating space exploration around the world with an incredible diversity of events, fun, and learning in honor of the 40th anniversary of Apollo 11’s mission to the moon,” said California-based EOA coordinator Patrick Barthelow, AA6EG. This may be the last time that those involved in the original Apollo 11 mission can take part in a public celebration. It will bring people together after 40 years, and help focus attention on the future of space exploration.”

Resources: Rare video footage of Apollo 11, photos, a review of moon-bounce (EME, Earth-Moon-Earth) communications, and a profile of “The Dish,” an award-winning 2000 film starring Sam Neill.