I wasn't keeping track but I just completed my 500th RisingStar mission. How do I know? I was awarded a free pack! Here's the message you get:
That's awesome because I certainly wasn't expecting any packs to come my way. Here's what I got when I opened it:
Stig looks like a good addition with more skill than fans. The RS vulture adds a bit of luck and another Buster to add to the collection. Looking at the achievements page:
The next free pack will come at the 1000th mission and then 1000 mission intervals subsequently. It will take a couple of months to reach that so not any time soon.