The cause? It's not exactly clear just yet, but Reboot project team suspects the probe's pipes aren't the problem -- ISEE-3 may have instead run out of the Nitrogen needed to help operate the propulsion system. To hear project leader Keith Cowing tell the tale, there was likely just left in the pipes for that first spin, making the maneuver nothing more than an incredibly promising tease. Cowing and the rest of the crew ultimately hoped to nudge the ISEE-3 back into position and resume its original mission: measuring how the solar wind interacts with the Earth's own magnetic field. That's starting to look impossible, though, and after the probe flies by the moon in August it might be time to bid it one final farewell. While certainly a bummer, the situation isn't completely without its upsides. Our species will have one more wandering spacefarer to commemorate us after we've gone, another metallic paean to a people who could never quench its thirst for understanding.