and typically before falling asleep, these light flashes are thought to originate as an effect of
high-energy particles, abundant in space, interacting with the eye and/or the visual anatomy.
The ALTEA project, active on ISS since August 2006 and currently investigating the ISS-US Lab
radiation environment (ALTEA-DOSI, ALTEA-SHIELD/survey), has also been studying the risks of
possible damage to the brain from particle radiation in space (ALTEA-CNSM). It is proposed that
these interaction effects may go well beyond light flashes and could constitute a new kind of
risk for longer space voyages. One study focus was
on these abnormal visual perceptions and the
impact on retinal and brain visual structures. ALTEA,
with its 6 double detectors covering most of the
astronaut’s head, permits a 3-dimensional
reconstruction of the energy released in the brain by
ionizing particles. In addition, ALTEA monitors the
functional state of the optical pathway in order to
interpret the biophysical mechanisms generating
abnormal perceptions. A survey was conducted in
2003 with 59 astronauts on the perception of light
flashes, or “phosphenes”, during missions. It was
found that 80% of space explorers experience light
flashes at some point (mainly before sleep when the
eyes are night adjusted). As many as 20% of the
respondents thought that light flashes sometimes
disturbed their sleep. Light flashes are
predominantly white, but other colors are
mentioned, in particular yellow (10%). Most light
flashes have an elongated shape, like stripes or
comets, and are associated with a perception of
motion. The motion is left-right or in-out, but never
up-down, and about 8% of light flashes have a “blob”
shape. There is a positive correlation between light
flashes and radiation flux, and the majority of light
flash in space is most likely produced by a direct
interaction of an ion with the retina, although there is indirect indication that light flashes can
result from interaction between particles and brain structures as well.
Solar Particle Events (SPEs) could represent a high radiation hazard for the ISS crew. During
most of the December 2006 SPE, the ALTEA detector collected continuous data inside the U.S.
Lab module. Results indicate that a SPE significantly affects radiation energy levels in the ISS,
producing a substantial increase of low energy radiation rate, which reaches the highest values
in quite short periods. This confirms the need to consider SPEs in those biological processes for
which radiation rate plays an important role. These results provide the first information for
charged radiation risk assessment in space habitats during a SPE.
ISS019E005340 – View of the Anomalous
Long Term Effects in Astronauts Central
Nervous System (ALTEA) experiment and
Silicon Detector Units designed to measure
cosmic radiation passing through the brain.
Photo taken in the U.S. Laboratory/Destiny
during Expedition 19.