There's already the Blockstream Satellite, which perpetually broadcasts the blockchain to most of the world from space. It's not Mars or Venus but it's getting there, and it helps reduce the network's dependency on internet access.
Indeed this is a very promising development on the crypto-industry but I believe this technology is not applicable or not viable to most ordinary users at least not at the moment. This is simply because we have better alternatives of syncing the Bitcoin blockchain particularly the Internet and its ever growing infrastructure had already produced a widespread internet coverage around the world. Also, advances in cellular and wireless technology had helped enabled remote areas to have internet connectivity, so I think it is redundant as of now.
Moreover, I also think ordinary people or even merchants will find it less interesting to use because I understand they will eventually have purchase satellite dish receivers to use the system and this might be costly and may prove harder to operate and maintain. However, if we are considering the possibility of any catastrophic event that may happen, then I guess there is no sense in keeping the nodes alive if humanity will ever cease to exists.
