Yes, I am going into a little more detail then lunar, but not much;
As you know the "Astral Plane" is a plane were your spirit travels. There are uncountable emounts of planes.
Your question " Is it possible to preform spells in the Astral Plane?"
Yes it is, this is because the "Astral Plane" is made from anything and everything. Sense your spirit is separated from your body, your spell progress will work more efficiantly. Meaning less worry about backfires. This is because in the "Astral Plane" you can do anything.
Our physical bodies can only do so much with the energies without almost harming ourselves or going beyond the physical power.
Backfires are usually caused with lack of knowing what you are doing, getting distracted during your spell. Your imagination changes into a different scene (meaning you start thinking about something else.). Spells are very tempramental your need to be dedicated and well prepared. That is why most people spend months trial and erroring their spells before officailly using them.