I started watching Space Brothers, it's free on Crunchyroll. I didn't expect it to be so silly, but that isn't necessarily a bad thing. I think there's too much exposition though. For brothers, they look too dissimilar. Mutta actually looks Asian, but Hibito looks white. That and the use of Engrish, especially in America, breaks the suspension of disbelief. My complaints aren't major and the story does a good job of making me like Mutta.
The story's conflict takes place in a much less science fiction world than Planetes, for comparison. No futuristic technology has been shown so far.