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SAFER is an updated version of the Manned Maneuvering Unit (MMU), which was regularly used by Space Shuttle crews to help salvage satellites in the 1980s, until Challenger’s loss led to tighter safety rules.Īstronauts do lose accessories, if not themselves: in 2008 a toolbox drifted away, but fortunately posed no collision risk. “I think it’s because you see nothing touching the bottom of your feet – and Earth is 400km away.”īut the nightmare of drifting away from the ISS is unrealistic – spacewalkers stay tethered at all times and are equipped with a ‘jetpack of last resort’ called the Simplified Aid for EVA Rescue (SAFER). “During a spacewalk, you might suddenly realise you’re gripping tightly to a handhold for no conscious reason,” recalls Smith. Drifting awayĪstronaut Mark Lee tests the Simplified Aid for EVA Rescue (SAFER). Galactic cosmic rays are more hazardous still, because these high-energy particles cannot practically be deflected today – astronauts headed to Mars should expect every cell nucleus in their bodies to be struck during the trip. Radiation from solar flares monitored between Apollo missions was strong enough to have incapacitated or killed moonwalkers. More serious risks come once you leave Earth behind. Most radiation of both types is deflected by Earth’s magnetic field, which is fortunate for ISS crews as artificial shielding options are limited.Įven so, parts of the ‘dormitory’ modules are lined with polyethylene plastic, a more effective radiation shield than metal, which is prone to triggering harmful secondary particle showers. Space radiation comes from two sources: energetic particles from the Sun, peaking at times of high solar activity, and galactic cosmic rays – atomic nuclei shot across the Universe by ancient cosmic explosions. Spacewalkers briefly experience higher exposures, as measured by crew dosimeters and a mannequin containing actual bones that was temporarily placed outside the ISS. ISS astronauts are officially classed as radiation workers: a single day on board could expose them to up to one millisievert, roughly four months’ worth of typical UK background radiation. The study explores how cells repair DNA damaged by space radiation. NASA astronaut Jessica Meir prepares DNA samples for sequencing for the Genes in Space-6 experiment, 26 December 2019.