I always shoot in RAW and highest jpg too.
My only regret is that I didn't start shooting RAW from the start when I first started in astro.
Shooting in both modes (if you can) gives you the most flexibility.
I can quickly view/download all my shots in jpg and go back and select the RAWs I want to work on.
Do yourself a favour, shoot in both.
If you don't have enough experience working in RAW then use your jpgs but at least you'll have the RAW file if one day you want to go back and re-edit once you acquire the knowhow.
Memory is cheap now, LOL a 4gb CF Sandisk is around $100, even cheaper if you shop around, this is huge storage.
When I got my 300D, a 256mb CF was considered large !
