Someone previously said they would have used a PIC 12F629, and I would too. This is an 8-pin device (like the 555) and has an internal oscillator with an accuracy of +-4% over -40C to +125C which is good enough for biochemistry, so to speak. And not much worse than most capacitor based circuits... You can also get new 6-pin devices, but I never used them yet.
I'm not quite sure how the circuit in the original article worked, as it had no capacitors or resistors (perhaps the DHS hacked the site). But a PIC12F629 based solution would not have needed any additional components either
The PIC does have disadvantages - it has a slightly higher power consumption than the low-power 555, and it leads to feature creep - I would have wired in a button and a time delay so that the kite didn't start taking pictures for 10 seconds after it was launched (or 20 seconds if you press the button twice quickly, or not at all (cancel) if you press and hold it for 5 seconds...). But perhaps most of all it costs £50 for a cheap programmer and I think this would put off people who were less interested in the electronics side of things.