I'm chuckling at that one, I'll pass it on to my friends in space systems.
When I worked at surveillance systems, my forte was low sideband noise pll's, and high intercept compressive receivers.
The job at space systems was kind've unique, the master clock was in one satellites, the other satellites had synchronizable clocks (I.E. you could move the frequency say...30 or 40 Hz) The problem was... that input was a digital code, instead of a sinusoid, thus, we scrapped the conventional PLL. We thought we'd try a sampling technique, but that would only work if the code repeated itself. The code appeared to be pseudo random, the project failed.
If you can figure out how to phase lock a pseudo random code, you can go to work for Lockheed.