https://arxiv.org/abs/2102.06824 https://arxiv.org/abs/2102.06824 for an unpaywalled version of the paper. I (kind of) understand their argument, but am unclear

https://arxiv.org/abs/2102.06824 https://arxiv.org/abs/2102.06824 for an unpaywalled version of the paper. I (kind of) understand their argument, but am unclear on how the physical shell is supposed to be filled with energy, eg is one supposed to just get inside and hook it up to the terminals of a battery or other power generator? Also slightly unsure about their insistence on propellant as a means of locomotion, as opposed to hanging out a sail and riding solar winds toward the nearest gravitational slingshot.