Washington, DC-June 1 – The National Space Society (NSS) congratulates Elon Musk and the entire SpaceX team on the Dragon spacecraft’s historic mission to the International Space Station (ISS) and its safe return to Earth yesterday.
“The mission was truly spectacular and marks a watershed moment in space history – proving that the commercial sector can successfully service the ISS,” said NSS Executive Director Paul E. Damphousse. “We were especially fortunate to celebrate the Dragon’s grappling at ISS on Friday morning with NASA Administrator Charles F. Bolden, Jr., who was at that very moment addressing an audience of nearly one thousand at NSS’s recent International Space Development Conference (ISDC).”
ISDC, the National Space Society’s annual conference, wrapped up in Washington, DC earlier this week. Administrator Bolden was delivering the opening keynote speech just as Dragon approached and then berthed at the ISS.
The safe return of Dragon and the advancement of commercial cargo and crew programs mark true milestones on the path to enabling a space-faring civilization. NASA’s efforts to advance space technology will also have a significant impact: technologies such as cryogenic propellant storage and transfer (CPST), solar electric propulsion (SEP), and advanced robotics are “mission-multipliers,” and are but a few examples being advanced by NASA’s Office of the Chief Technologist. These efforts will help to enable robust space operations while providing dramatic reductions in overall costs.
The National Space Society recognizes that there is still much to be done, and maintains that strong leadership in government will be critical going forward. In this context, NSS calls on the Senate to fully fund the commercial crew development program and space technology lines of the NASA budget as proposed in the President’s budget request earlier this year, removing the proposed cuts made by the House in May. While NSS acknowledges the difficult budgetary parameters under which Congress must work, we strongly encourage both the Senate and the House to accede to the President’s FY2013 budget request for both commercial crew and space technology during conference later this year.
“The successful conclusion of SpaceX’s COTS-2/3 missions has demonstrated that the commercial sector is now ready to move forward with increased responsibility for servicing ISS, including the development of crew transport capability,” Damphousse said. “If funded and executed correctly, the commercial crew program will end our sole reliance on foreign providers and bring that capability – and the jobs associated with it – back home. We should be preserving funding for these commercial and space technology programs – which are producing tangible successes today, and will continue to do so in the near-term and beyond – rather than shifting it to already well-funded programs that may be years away from providing results.”
About the National Space Society: NSS is an independent, educational, grassroots, non-profit organization dedicated to the creation of a spacefaring civilization. Founded when the National Space Institute and the L5 Society merged in 1987, NSS is widely acknowledged as the preeminent citizen’s voice on space. NSS has over 10,000 members and supporters, and over 50 chapters in the United States and around the world. The society publishes Ad Astra magazine, an award-winning periodical chronicling the most important developments in space. To learn more, visit www.nss.org.
The Augustine Commission identified Galactic Cosmic Radiation, or Galactic Cosmic Rays (GCR), as one of the high priority technical challenges facing the Deep Space program.
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.
- Compilation of Spacecraft Shielding papers by Simon G. Shepherd at the Dartmouth Thayer School of Engineering.
- Scientific American article on Shielding Space Travelers.
- 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
- Regolith shielding limits GCR and SPE exposure effectively
- Its shielding capabilities against GCR can be better than conventional Al structures as in the ISS