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.

Synopsis

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.

More on the Falcon 9/Dragon Test Flight

* The Falcon 9 rocket performed nearly flawlessly. The roll attitude was solid through the entire flight. The first stage sep was without impingement.

* The Dragon capsule entered orbit 301×288 on a targeted 300km circular.

* The capsule thrusters were tested on maneuvers similar to what is required for ISS docking.

* 4 Cubesats were successfully released into orbit.

* After separation from Dragon, the Falcon 2nd stage was fired again and placed in an orbit with an 11,000km apogee.

* The capsule re-entry burns were spot on.

* All three parachutes deployed perfectly.

* The capsule came down so close to the recovery ship that they have a good photo of it under the parachutes.

* It was being recovered within 35 minutes of the opening of the drogue chute.

* The heat shield barely got warm. We have now been told that this craft has a heat shield that can handle a free return from the Luna or Mars, i.e. it can be used as an interplanetary vehicle.

* Plans are for the next generation to do powered landings on a helipad sized landing pad.

* The volume and capabilities of Dragon meet or exceed those of the not yet ready for test Orion capsule.

* Today’s mission was so stunningly successful that SpaceX wants to move directly to an ISS flight on the next test. NASA is thinking about it

Historic Day for Commercial Space Flight

Today, SpaceX became the first commercial company in history to re-enter a spacecraft from low-Earth orbit.

SpaceX launched its Dragon spacecraft into low-Earth orbit atop a Falcon 9 rocket at 10:43 AM EST from the Air Force Station at Cape Canaveral.

The Dragon spacecraft orbited the Earth at speeds greater than 17,000 miles per hour, reentered the Earth’s atmosphere, and landed in the Pacific Ocean shortly after 2:00 PM EST.

This marks the first time a commercial company has successfully recovered a spacecraft reentering from low-Earth orbit. It is a feat performed by only six nations or government agencies: the United States, Russia, China, Japan, India, and the European Space Agency.

It is also the first flight under NASA’s COTS program to develop commercial supply services to the International Space Station. After the Space Shuttle retires, SpaceX will fly at least 12 missions to carry cargo to and from the International Space Station as part of the Commercial Resupply Services contract for NASA. The Falcon 9 rocket and Dragon spacecraft were designed to one day carry astronauts; both the COTS and CRS missions will yield valuable flight experience toward this goal.

View the press kit: http://www.spacex.com/downloads/cots1-20101206.pdf

Spaceport America Runway Dedication

SpaceShipTwo
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