This might come as the biggest surprise to be on the list. After all, space exploration is expensive and difficult. But there are very few out there who are actually working on how to change humanity from being a Single Point of Failure System. If we are serious about longtermism and truly decreasing x-risk, this might be one of the most crucial achievements needed. Any x-risk is most likely greatly reduced by this, even perhaps AGI*. The sooner this process begins, the greater the reduction in risk, since this will be a very slow process.
Seems not everyone agrees with you that this is hard. See also the paper if video is not your thing.