We really, really need a second run at Biosphere 2, only this time integrating what the failures of the first run taught us. (Only 25 years ago, with no serious

We really, really need a second run at Biosphere 2, only this time integrating what the failures of the first run taught us. (Only 25 years ago, with no serious follow-up!) The next step would then be something like a Bigelow B330 module in LEO, which is close enough to get the astronauts home from in a hurry if something goes badly wrong. (These steps can be commenced with current tech: Heavy/Starship not required.) Step 3 would be a bigger test hab out beyond the Van Allen belts, preferably a couple of habs revolving around a hub to provide centrifugal "gravity" at Lunar or Martian levels. Goal is to test systems for use on planetary surfaces exposed to cosmic/solar radiation (because outside our atmosphere). Starship is probably mandatory for this phase, because it's a lot more massive and a lot further away. Alternatively: conduct this experiment on the Lunar surface, once astronaut return capability is available (but why waste expensive reaction mass if you can simulate a gravity well?) Without a lot of R&D work under these conditions, a closed-circuit life support system for Mars is a huge safety risk for the astronauts who set it up (and who are too far away to rush home in a hurry if it goes badly). And without closed-loop life support, a Mars "colony" is no more a colony than an Antarctic research station reliant on resupply for everything except air and water.