In Season 1, Episode 5, "Choose your pain" we see the tardigrade enter survival mode by expelling almost all the water from its body.
Later, we see the it ejected from the USS Discovery into space, where it rehydrates its body and using its relationship with the spores, disappears.
This leads to two questions:
How does the tardigrade rehydrate itself in a vacuum?
What prevented it from using its internal spore drive to escape from the USS Glenn or the USS Discovery whenever it wished?