To view space play forge on a map (I recommend Valhalla) and set respawn time 3 minutes then infinite ammo on. Kill yourself and make your guy float in the water behind (when you go outside the map) a few times then end it.

Go to the theatre and watch the film. Wait 3 minutes after your spartan or elite dies. Then rewind it.

If done correctly the view should be outside the map. Pause the film otherwise when your guy respawns your view will go back inside the map.

Above you you will see clouds. Move your view up the sky until you are above the clouds.

Keep going up until you see a halo and the sun.

Note: As you go up the sky the sky will turn black to indicate that you in space.

When you see halo and the sun while the sky is completely black your view is in space.
If done correctly you will be viewing outer space. Try looking around when you do it.