A common effect of radiation exposure that is reported by astronauts is the perception of light flashes. The actual mechanism of these light flashes is not understood. Earlier studies on the Mir space station suggest that both heavy nuclei and protons trigger abnormal CNS responses. (Casolino et al, 2003). A Visual Stimulator tests the astronaut's overall visual system, including dark adaptation stimuli to monitor visual status. While not manned, the ALTEA hardware provides a continuous measure of the cosmic radiation in the ISS U.S. Laboratory, Destiny. The neurophysiological effects of cosmic radiation in long term space travel have never been explored with the depth of the ALTEA experiment. Data collected will help quantify risks to astronauts on future long-duration space missions and propose optimized countermeasures.
While not being worn by the crewmember, the hardware will continue to measure the radiation environment in the US Lab.
In addition to measuring the radiation exposure on a crewmember's head, the Anomalous Long Term Effects in Astronauts' Central Nervous System (ALTEA) hardware can also provide an assessment of the radiation environment in the ISS. Since June 1st 2009, a new analysis technique has been employed by researchers to make use of the 3-dimensional capability of the ALTEA space radiation detector to measure both the direction of radiation particle flow and its linear energy transfer (LET) rate inside the Space Station.
The radiation field in low-Earth orbit (LEO) is a combination of galactic cosmic rays (GCR), trapped ions (in the South Atlantic Anomaly, SAA) and radiation due to solar events. It penetrates the International Space Station (ISS) through the vessel hull as well as through the uneven shielding due to the many racks, experimental devices, etc. on the walls. Results from this study further confirms that the radiation environment inside the Space Station is directional and the energy of ionizing particles is affected by the amount of shielding these particles encountered on their path. High-LET particles show a minimum along the longitudinal axis (most shielded) and a maximum perpendicular to the cylindrical hull of the ISS. However, the sum of the energy from light ions and the fragments produced by heavier ions appears to be independent of direction, and the average radiation dose rate measured by ALTEA is similar to those previously measured by the Tissue Equivalent Proportional Counter (TEPC) and the Columbia Resin #39 (CR-39) detectors. Researchers are planning to move the ALTEA unit to another ISS site for more survey.
Detailed measurement of the angular components and total energy of space radiation is relevant in helping scientists to design radiation experiments and interpret results by providing information about the different quality of radiation impinging on the same spot from different directions. Recent calculations show that space radiation may exceed recommended risk levels for long voyages outside the protection of the Earth?s magnetic shield and atmosphere, and the major goal of space radiation research is to enable the human exploration of space within acceptable radiation risks. This requires a detailed characterization of the space environment in which the astronauts are living and are expected to live (Di Fino et al., 2011).