Not a Teacher.
In my opinion there is no difference. They mean something with close relation to the stars. It is like Pit, Gehenna or Inferno, three different words relating to one and the same thing - Hell. So I think you can say astronauts lost in an astral solitude, astronauts lost in a stellar solitude or astronauts lost in a sidereal solitude which would mean one and the same thing - the poor devils are lost somewhere in cosmos, universe or space.
But it is true the word astral may be used also in different connection; for example an astral body.
Student or Learner