>>281493508
The joke is about Ekiben (Station [Eki] bento) becoming Ekiben (Slime/Jelly [Eki] bento) because they're in space.
And well, real astronauts do eat that stuff (fully dehydrated food they just fill with the ever-recycling water). Even jelly food is a thing. There's this brand of e-sports ramen, for instance.