I bought Capsule back when Chris tweeted about it, got to the final stretch, and put it down because I kept running out of fuel. Still felt like I got my money's worth though from what I did play.
Finding out if was on Steam, I got a key off the Humble Store and tried it again. Right away looking at the Steam Achievements clued me into ways to get fuel and air I didn't know were possible. Turns out when you run out of fuel you can jump-start the engine to get a little bit back; something that's hinted at in-game but I didn't realize was possible for the player. I thought that if you ran out of fuel before air you just had to wait to die, which seemed appropriate but got really frustrating on that last stretch.
As for what the environment is, I didn't think it was space or water because the very first base you reach talks about detecting seismic disturbances, erratic movement, and sonic emissions — it's talking about the player's capsule. Then there's the lichens and cycads and immobile arrangements of pylons and crates. I pictured it taking place on solid ground but on a planet with little visibility, or deep underground. Finding out it was made for the Venus Patrol kickstarter makes me think Venus' atmosphere was some of the inspiration.
I'm glad I listened to this episode, it was totally worth revisiting this one.