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.