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While the general public may be concerned about safety in space only after an accident or a catastrophe, NASA has ongoing commitments to ensure that vital equipment does not fail on the ground or in flight and to reduce occupational hazards for ground and flight crews.

The fact is, while NASA is moving forward towards its new vision for space exploration in the 21st Century, encompassing a broad range of human and robotic missions, including missions to Moon, Mars and beyond, exposure from the hazards of severe space radiation in deep space long duration missions is ‘the show stopper.’

RAM K. TRIPATHI

That’s the view of Ram K. Tripathi, under whose guidance NASA scientists are developing state-of-the-art radiation protection and shielding technology for space missions. “There is a need to go beyond current technology to the technology of the future”, says Tripathi who is at the NASA Langley Research Center in Hampton, Virginia. “The intensity and strength of cosmic radiation in deep space makes this a ‘must solve’ problem for space missions” he adds.

Tripathi contends that current technology is adequate for single lunar missions but for astronauts in long duration/ deep space human missions, revolutionary shielding materials and concomitant technology need to be developed.

Along with an earlier Indian-American scientist, Gautam Badhwar, Tripathi is a pioneer in this field at NASA. Badhwar had shown that robotic precursor missions to Mars can provide valuable data on the radiation environment to be encountered in future human exploration missions of the red planet and validation of models used for mission design. He set up the NASA Johnson Space Center’s MARIE (Martian Radiation Environment Experiment) instrument on board the 2001 Mars Odyssey spacecraft, which has been collecting and successfully providing data for the Martian radiation environment mapping since 2002.

Both Tripathi and Badhwar were involved in the project ‘IMPROVED SPACECRAFT MATERIALS FOR RADIATION PROTECTION: Shield materials optimization and testing’. They concluded that recent advances in hydrogen storage in graphite nanofibers may have a large impact on radiation safety in future spacecraft design.

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a ‘must solve’ problem for space missions.

First of all, the payload penalty demands a very stringent requirement on the design of the spacecrafts for human deep space missions. Besides, the exploration beyond low Earth orbit (LEO) to enable routine access to more interesting regions of space will require protection from the hazards of the accumulated exposures of space radiation, Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE), and minimizing the production of secondary radiation is a great advantage.

The three primary sources of radiation that spaceflight crews will be exposed to during travel to Mars include: the Earth’s radiation Van Allen’s belt, solar radiation, and galactic cosmic rays. Long term exposure to these rays has been shown to increase the risk of developing certain types of cancer as well as weaken the immune systems of human subjects.

Such radiation damages the DNA of tissues by the formation of hydroxyl and superoxide free radicals that interact with DNA thereby creating single strand and double strand DNA breaks as well as mutations in the DNA.

Tripathi and colleagues are investigating shield optimization for a variety of materials: Aluminum, polyethermide, polysulfone, polyehelene, lithium hydride, liquid methane, hydrogenated nanofiber, liquid hydrogen. Tripathi explains: The reason for the choice of materials is that there is increasing hydrogen content in the materials as we go down the list from Aluminum to liquid hydrogen.

Tripathi has shown that hydrogen is the best shielding material. “We have established that hydrogen is a better shielding material. As a result, the more the hydrogen content the better the material is expected to perform for GCR radiation shielding in space.”

According to Tripathi, “for a single Moon mission the choice of the material is not so important, but for long duration space missions, as for career astronauts, graphite nanofibers and liquid hydrogen out perform other materials.”

PREMKUMAR B. SAGANTI

Another Indian-American scientist involved in analyzing risks to astronauts on the mars surface from galactic cosmic rays is Premkumar B. Saganti of the NASA Center for Applied Radiation Research.

His study shows that “the potential for harmful late effects including cancer, cataracts, neurological disorders, and non-cancer mortality risks, from galactic cosmic rays (GCR) pose a major threat for the human exploration of Mars.”

According to Saganti, “because of their high energies, the GCR are extremely penetrating and cannot be eliminated by practical amounts of shielding.”

Saganti affirms: “The high charge and energy HZE ions portion of the GCR present unique challenges to biological systems such as DNA, cells, and tissue and the risks to humans is highly uncertain at this time.”

He adds: “Another threat in deep space is solar particle events, which could induce acute radiation syndromes including death if the event is large enough and increase the risk of cancer or other late effects. However, shielding offered by the Mars atmosphere and spacecraft structures along with the early warning and detection systems may be effective as mitigation measures.”

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