There's a massive threat to human space exploration that's on the horizon and it's only becoming more imminent over time.

One of the ultimate threats to humanity is another big space rock or catastrophic event for which we, like the dinosaurs, are not prepared. We’ve done a single experiment to see if we can alter the course of an asteroid through NASA’s Double Asteroid Redirection Test (DART) mission and it was a success--but that asteroid was small, and that may not scale up for a bigger rock.
The second biggest threat, and the one we’re going to address today, is that we may not be able to leave our planet at all...

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