Well, there’s a quick and easy technical answer: true space is a vacuum and you wouldn’t be able to smell anything whatsoever up there. However, what people likely mean is what it smells like aboard something like the International Space Station (ISS).
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Most astronauts say there are hints of hot metal, burnt meat, burnt cakes, spent gunpowder, and welding of metal”.
Those are some pretty industrial smells, which perhaps shouldn’t come as a surprise given that the ISS is basically a metallic series of tubes full of machinery and equipment.
American astronaut Scott Kelly found that his sense of smell was incredibly important up in space – it helped him to work out when there was too much carbon dioxide in the atmosphere.
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Kelly reported that after some time in space he could “sense the levels with a high degree of accuracy based only on the symptoms I’ve come to know so well: headaches, congestion, burning eyes, irritability. Perhaps the most dangerous symptom is impairment to cognitive function”.