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.

New Coalition for Space Exploration PSA Video

The Coalition for Space Exploration, of which the National Space Society is a member, has produced another in its series of short public service announcement videos intended to provide some answers to the question “Why spend money on space when we have so many problems here on Earth?”

The new video is called “Think Outside the Circle” and can be viewed on the NSS website by clicking on the image below.

Think Outside the Box

NSS Competitions for 2010 -2011


For all of you space enthusiasts out there, listen to this podcast by National Space Society member Lynne Zielinski as she discusses contests for students. Lynne teaches at Glenbrook North High School in Northbrook Illinois, and the podcast provides details on competitions sponsored by the National Space Society.

1. NASA/NSS Space Settlement Student Design Contest (for grades 6-12)

NASA Ames Research Center in conjunction with the National Space Society sponsors an annual space settlement design contest for 6-12th grade students. Each spring students send their designs for homes in space for judging by NASA engineers and scientists. The contest has inspired thousands of students and helped hundreds of teachers bring the excitement of space settlement to the youth of America and the world.

2. International Space Settlement Design Competition (for high school)

This contest puts high school students in the shoes of aerospace industry engineers designing a city in space that will be a home for over 10,000 people. Student engineers demonstrate creativity, technical competence, management skills, space environment knowledge, teamwork, and presentation techniques to conquer the problems inherent in siting and designing a Space Settlement (aka Space Colony).

3. Pete Conrad Spirit of Innovation Awards (for high school)

The Spirit of Innovation Awards program challenges teams of high school students to create innovative products using science, technology, and entrepreneurship to solve 21st century, real-world problems. Eligible students may compete on teams in any of three Challenge Categories.

4. Jim Baen Memorial Writing Contest (any age)

Since its early days, science fiction has played a unique role in human civilization. It removes the limits of what “is” and shows us a boundless vista of what “might be.” Its fearless heroes, spectacular technologies and wondrous futures have inspired many people to make science, technology and space flight a real part of their lives and in doing so, have often transformed these fictions into reality. The National Space Society and Baen Books applaud the role that science fiction plays in advancing real science and have teamed up to sponsor this short fiction contest in memory of Jim Baen.

Spaceport America Runway Dedication

White Knight Two flyover of Spaceport America Terminal carrying SpaceShipTwo
Image Credit: Barbara David

The two mile runway at Spaceport America in New Mexico was dedicated Friday, 22 October 2010. One of the highlights of the celebration was the flyover and landing of Virgin Galactic‘s White Knight Two carrying the rocket plane Space Ship Two, named Enterprise by Virgin Galactic.

Governor Bill Richardson of New Mexico, for whom the runway (spaceway) was officially named during the ceremony, commented that:

“We are celebrating the world’s first spaceway at the world’s first purpose-built, commercial spaceport. New Mexico is not only helping to launch the commercial spaceflight industry, but we are launching new jobs and opportunities for the people of southern New Mexico. Today marks a significant milestone on our historic and exciting journey.”

Sir Richard Branson and approximately 30 of more than 380 Virgin Galactic future astronauts attended the event. Two of the future passengers in attendance were Sonja Rohde from Germany and Perveen Crawford of Hong Kong. Both have already paid the full $200,000 price for their flight into space. “It’s like Christmas, you want to go, you can’t wait. It was always a childhood dream to go to space,” Rohde said. Crawford noted that “It’s a bargain compared to the Russians,” referring to the roughly $35 million past space tourists have paid to ride aboard the Soyuz to the International Space Station.

Approach to Spaceport America
White Knight Two carrying Space Ship Two on Approach to Spaceport America
Image Credit: Virgin Galactic

Virgin Galactic – First Free Flight

VSS Free Flight
Virgin Galactic’s SpaceShipTwo Enterprise during its first free flight
Image Credit: Virgin Galactic

Commercial spaceflight took another step forward this past Sunday, 10 October 2010.

Virgin Galactic’s SpaceShipTwo, named Enterprise, was dropped from its mother ship at 45,000 feet and successfully completed maneuvers and landing at the test facilities in the Mojave Desert. Enterprise is designed to carry two pilots and six passengers to an altitude of over 100 kilometers.

Sir Richard Branson, founder of Virgin Group, who was present during the first successful flight, commented that “This was one of the most exciting days in the whole history of Virgin.

The flight was designed to test the release mechanics from the mother ship and then verify the handling and stall characteristics as well as the lift to drag ratio. A complete set of landing maneuvers were executed at a high altitude, and the ship then made its final descent and landing.

Scaled Composites pilot, Pete Siebold, said “The VSS Enterprise was a real joy to fly, especially when one considers the fact that the vehicle has been designed not only to be a Mach 3.5 spaceship capable of going into space but also one of the worlds highest altitude gliders.”

Virgin Galactic will continue testing the new rocket ship during the coming year, and expects to fly its first commercial passengers within 18 months.

George Whitesides, former Executive Director of the National Space Society and current CEO of Virgin Galactic, was also present at the historic flight. Whitesides said, “To see the world’s first manned commercial spaceship landing on a runway is a sight I always dreamed I would behold. Now, our challenge going forward will be to complete our experimental program, obtain our FAA license and safely bring the system into service at Spaceport America, New Mexico.”

First Crewed Flight

First Crewed Flight of VSS Enterprise on 15 July 2010
Image Credit: Virgin Galactic

The Wilkinson Microwave Anisotropy Probe

Completed Microwave Map of the Universe
Image Credit: NASA

Scientists announced this week that the mission of the Wilkinson Microwave Anisotropy Probe (WMAP) has been completed. The last set of observations were downloaded on 20 August 2010, and researchers are compiling the final results. The satellite was placed in a permanent parking orbit around the sun on 8 September 2010.

WMAP was launched on 30 June 2001 and placed into an orbit around SEL-2, the second Sun-Earth Lagrange point. SEL-2 lies 1,500,000 kilometers beyond the Earth on a line from the Sun to the Earth. WMAP was the first spacecraft to occupy this location. SEL-2 is extremely cold, shaded from the Sun’s activity by the Earth’s shadow and ideal as an astronomical location in space. In 2009, the Herschel Space Observatory and Planck space observatory took up residence at SEL-2. They will be joined in 2014 or 2015 by the James Webb Space Telescope.

First detected in 1964, the cosmic microwave background (CMB) radiation (television “snow” – before cable), is the remnants of the extremely hot radiation from the big-bang, now cooled to almost absolute zero after 13.73 billions years of the expansion of the universe. It is a pattern frozen in place when the cosmos was only 380,000 years old.

WMAP COBE was the successor to NASA’s Cosmic Background Explorer (COBE), which was launched on 18 November 1989 and produced the first map of the microwave radiation. Note the great increase in resolution between the COBE map at the right, and the WMAP result above.

The Planck observatory is currently making high resolution measurements of both the total intensity and polarization of the primordial CMB anisotropies that were first observed by COBE and WMAP.

The observations made by WMAP are the most accurate to date and have allowed scientists to rule out several “inflation” models about what happened in the first trillionths of a second during the birth of the cosmos, while supplying support for several other models:

  • The age of the universe is 13.73 billion years old to within 1% (0.12 billion years)
  • Ordinary matter (atoms) makes up only 4.6% of the universe (to within 0.1%)
  • Dark matter (not made up of atoms) makes up 23.3% (to within 1.3%)
  • Dark energy makes up 72.1% of the universe (to within 1.5%)

Dark energy is the force driving the galaxies in the universe apart at an ever increasing rate. At some point in the future, inhabitants of the Milky Way will not be able to see any other objects in the sky. These entities will conclude that they are at the center of the universe, and will have no information about the big bang and the creation of the cosmos as we know it today.