I was recently introduced to Death in Space.

Things that I like about it:

• it’s a simple system
• it’s got cool lore (the universe is dying, aberrations are infiltrating the local solar system, all ships and technology is scavenged)
• it’s got some overlapping mechanics with 5e, which makes introducing it simple (advantage, d20 checks, etc)
• it’s got some nice rules for ship combat, space walks, etc
• combat turns are basically just go next if you have something, then the enemies do their thing, and players coordinate on whatever works best for them

My fiancé was running it, but lost the time to continue running it. I might take over with my own group soon.