Identifying effective countermeasures that reduce the risk of biological damage is still a long-term goal for space researchers. These countermeasures are probably not needed for extended duration lunar missions, As far as shielding from GCR, high-energy radiation is very penetrating and the effectiveness of radiation shielding depends on the atomic make-up of the material used. The aluminium walls of the ISS, for example, are believed to produce a net reduction in radiation exposure. In interplanetary space, however, it is believed that thin aluminium shielding would give a net increase in radiation exposure; thicker shielding would be needed to block the secondary radiation. Studies of space radiation shielding should include tissue- or water-equivalent shielding along with the shielding material under study. This observation is readily understood by noting that the average tissue self-shielding of sensitive organs is about 10 cm, and that secondary radiation produced in tissue such as low energy protons, helium, and heavy ions are of high
linear energy transfer (LET) and make significant contributions (>25%) to the overall biological damage from GCR. Studies of aluminium, polyethylene, liquid hydrogen, or other shielding materials should include their combination effects against primary and secondary radiation, plus their ability to limit the secondary radiation produced in tissue. Several strategies are being studied for ameliorating the effects of this radiation hazard for planned human interplanetary spaceflight: • Spacecraft can be constructed out of hydrogen-rich plastics, rather than aluminium. • Mass and material shielding: • Liquid hydrogen, often used as fuel, tends to give relatively good shielding, while producing relatively low levels of secondary radiation. Therefore, the fuel could be placed so as to act as a form of shielding around the crew. However, as fuel is consumed by the craft, the crew's shielding decreases. • Fresh or waste water can contribute to shielding. • Asteroids could serve to provide shielding. • Light active radiation shields based on the charged graphene against gamma rays, where the absorption parameters can be controlled by the negative charge accumulation. • Magnetic deflection of charged radiation particles and/or electrostatic repulsion is a hypothetical alternative to pure conventional mass shielding under investigation. In theory, power requirements for a 5-meter torus drop from an excessive 10
GW for a simple pure electrostatic shield (too discharged by space electrons) to a moderate 10
kilowatts (kW) by using a hybrid design. For passive mass shielding, the required amount could be too heavy to be affordably lifted into space without changes in economics (like hypothetical
non-rocket spacelaunch or usage of extraterrestrial resources) — many hundreds of metric tons for a reasonably-sized crew compartment. For instance, a NASA design study for an ambitious large space station envisioned 4 metric tons per square meter of shielding to drop radiation exposure to 2.5 mSv annually (± a factor of 2 uncertainty), less than the tens of millisieverts or more in some populated
high natural background radiation areas on Earth, but the sheer mass for that level of mitigation was considered practical only because it involved first building a lunar
mass driver to launch material. Since the type of radiation penetrating farthest through thick material shielding, deep in interplanetary space, is GeV positively charged nuclei, a repulsive electrostatic field has been proposed, but this has problems including plasma instabilities and the power needed for an accelerator constantly keeping the charge from being neutralized by deep-space electrons. A more common proposal is magnetic shielding generated by superconductors (or plasma currents). Among the difficulties with this proposal is that, for a compact system, magnetic fields up to 20
tesla could be required around a crewed spacecraft, higher than the several tesla in
MRI machines. Such high fields can produce headaches and migraines in MRI patients, and long-duration exposure to such fields has not been studied. Opposing-electromagnet designs might cancel the field in the crew sections of the spacecraft, but would require more mass. It is also possible to use a combination of a magnetic field with an electrostatic field, with the spacecraft having zero total charge. The hybrid design would theoretically ameliorate the problems, but would be complex and possibly infeasible. This mass can surpass the launch constraints and costs several millions of dollars. On the other hand, active radiation shielding methods is an emerging technology which is still far away in terms of testing and implementation. Even with the simultaneous use of active and passive shielding, wearable protective shielding may be useful, especially in reducing the health effects of SPEs, which generally are composed of particles that have a lower penetrating force than GCR particles. The materials suggested for this type of protective equipment is often polyethylene or other hydrogen rich polymers. Water has also been suggested as a shielding material. The limitation with wearable protective solutions is that they need to be ergonomically compatible with crew needs such as movement inside crew volume. One attempt at creating wearable protection for space radiation was done by the Italian Space Agency, where a garment was proposed that could be filled with recycled water on the signal of incoming SPE. A collaborative effort between the
Israeli Space Agency,
StemRad and
Lockheed Martin was
AstroRad, tested aboard the ISS. The product is designed as an ergonomically suitable protective vest, which can minimize the effective dose by SPE to an extent similar to onboard storm shelters. It also has potential to mildly reduce the effective dose of GCR through extensive use during the mission during such routine activities such as sleeping. This radiation protective garment uses selective shielding methods to protect most radiation-sensitive organs such as BFO, stomach, lungs, and other internal organs, thereby reducing the mass penalty and launch cost.
Drugs and medicine Another line of research is the development of drugs that enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are
retinoids, which are
vitamins with
antioxidant properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.
Transhumanism It has also been suggested that only through substantial improvements and modifications could the human body endure the conditions of space travel. While not constrained by basic laws of nature in the way technical solutions are, this is far beyond current science of medicine.
Timing of missions Due to the potential negative effects of astronaut exposure to cosmic rays, solar activity may play a role in future space travel. Because galactic cosmic ray fluxes within the Solar System are lower during periods of strong solar activity, interplanetary travel during solar maximum should minimize the average dose to astronauts. Although the
Forbush decrease effect during coronal mass ejections can temporarily lower the flux of galactic cosmic rays, the short duration of the effect (1–3 days) and the approximately 1% chance that a CME generates a dangerous solar proton event limits the utility of timing missions to coincide with CMEs.
Orbital selection Radiation dosage from the Earth's radiation belts is typically mitigated by selecting orbits that avoid the belts or pass through them relatively quickly. For example a
low Earth orbit, with low inclination, will generally be below the inner belt. The orbits of the Earth-Moon system
Lagrange points – take them out of the protection of the Earth's
magnetosphere for approximately two-thirds of the time. The orbits of Earth-Sun system Lagrange Points and – are always outside the protection of the Earth's magnetosphere. == Space radiobiology ==