The thing is we know how to harvest solar energy while in space. Harvesting matter has been proposed with ram scoops but contrary to solar cells, these are just

The thing is we know how to harvest solar energy while in space. Harvesting matter has been proposed with ram scoops but contrary to solar cells, these are just theoretical propositions. Being able to use energy directly instead of propulsion mass would make a lot of travels more sustainable and with potentially lighter vehicles.