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

International SunSat Design Competition

SunSat Design is an international competition intended to accelerate the design, manufacture, launch and operation of the next-generation satellites that will collect energy in space and deliver it to earth as electricity.

Registration Deadline:  January 10, 1011

Design Submission Deadline:  April 4, 2011

Winners will be announced at the National Space Society’s International Space Development Conference in Huntsville in May.

This Design Project will generate visualizations to aid in the design, manufacture, launch and operation of the new types of satellites that will collect sun’s rays in space and deliver them to earth as a clean and renewable source of energy. These visualizations will also inform the public debate about the way forward for development and implementation of universal access to space-based solar power.

Winning designs will be high-impact digital art, supported by credible science, engineering and business plans, that best promote media understanding and public acceptance of a path forward in using space satellites to deliver energy on-demand to any and all places on earth.

The SunSat Competition is an initiative of The Online Journal of Space Communication in partnership with The Society of Satellite Professionals International, the National Space Society, and the Ohio University GRID Lab.

For more information and registration, go to http://sunsat.gridlab.ohio.edu.

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

The Garden on The International Space Station

The latest crop harvested from the Garden on the International Space Station is Mizuna lettuce. The lettuce was returned to Earth for scientific research, aboard the Discovery shuttle in April 2010.

The greenhouse, first sent up in 2002, has been used for 20 plant growth experiments so far. Now, a second unit has been added, and the lettuce crop was the first experiment to test different conditions side by side.

For many years, the experiments have sought to confirm Earth side results which show that minimizing water usage and salt accumulation would lead to healthier crops. During this experiment, two different root growth mediums were used. One was the traditional root pack used on all the previous tests. The second was the new and improved root pack, with slow release fertilizer. The hypothesis was that the slow release would help reduce salt intake.

Science is sometimes best when things go wrong.

Mizuna Lettuce
Mizuna Lettuce On ISS
Image Credit: NASA

For some reason, the sensor controlling the watering in the first (traditional) module failed. This resulted in “over-watering” the plants. The results were surprising, but microgravity has held many surprises for scientists. First, the seeds that got “too much” water sprouted quicker and developed leaves twice as fast as the second (improved) module. The second surprise was that the plants grown in the slow release fertilizer in the second module had more salt accumulation than the plants in the first module.

The results suggest that plants in space need a larger volume of water and a faster rate of fertilizer than they do under normal gravity. Shane Topham, an engineer with Space Dynamics Laboratory at Utah State University in Logan, said that “the conservative water level we have been using for all our previous experiments may be below optimal for plant growth in microgravity”.

Overall, the garden experiments have four objectives:

  • Can the crops grown in space be consumed safely
  • What microorganisms grow on the plants, and how do you prevent or minimize microorganisms in the modules prior to launch
  • How do you clean and sanitize the crops after they are harvested
  • What conditions optimize the production of crops in microgravity

One additional objective of the experiments is to measure the non-nutritional benefits (stress relief, etc.) that crew members experience working with plants in space. Growing and tending to the crops provides comfort and relaxation to the crew. On a long voyage, this activity may contribute to the success of the mission.

Lada Module
A view of the Russian BIO-5 Rasteniya-2/Lada-2 (Plants-2)
plant growth experiment located in the Zvezda Service Module
on the International Space Station (ISS).
Image Credit: NASA

Sprouts
A close up view of sprouts on the Russian Lada-2 experiment.
Image Credit: NASA

Peas
A view of peas growing in the Russian Lada-2 plant growth experiment.
Image Credit: NASA

Bloom
A close up view of a bloom on the Russian Lada-2 plant growth experiment.
Image Credit: NASA