Oh, I forgot to reply to a few things!
1. We're going to Monongahela NF in West Virginia.
2. Interested_Observer, I'm not sure which you one this thread you meant, but I at least have a K-3, not a K-5. I didn't even know the K-5 did intervals! Something else to look into
3. I also didn't know it had a mirror lock-- if anyone knows how to do that, please let me know, too!
4. I've also got the preview screen turned off to save all the extra power I can for shooting.
5. Well, I tried a test on the burst mode last night, and it got over 118 before the already-low-from-other-tests battery died, so I'm recharging and going to try again. If it works and I can get a cloudless night before this weekend for tests, we may have found a good workaround, since intervals is just being so difficult. I wonder if Pentax keeps up with any of these things, because it would be so appreciated by so many people if they would get their software straightened out. Most cameras I've seen don't come with built-in intervalometers, and require either hacking or something external. It would be a great selling point for them with astrophotographers.