Sky has created a hard drive that's encrypted based upon her GPS. Yes, it's possible! All you'd have to do is change PGP opensource code to incorporate GPS coordinates into the keypair.
Better yet - incorporate different sets of GPS data for each side of the process: Encrypt at home, but only decrypt when you've reached DizzlyLand.
Since we're messing with space, why not work on time? Incorporate a timeout to ensure JIT location, and poof! Awesomeness.
?? - what if someone spoofs GPS data? Well - there's more to a GPS packet than just coordinates. Zone in on 2-3 additional random data points (perhaps based on specific date/time?), and all-the-harder to replicate.