I’ve periodically reported on the status of the International Sun-Earth Explorer (ISEE-3), a spacecraft that was launched in 1978 to study Earth’s magnetosphere and repurposed in 1983 to study two comets. Renamed the International Cometary Explorer (ICE), it has been in a heliocentric orbit since then, traveling just slightly faster than Earth. It’s finally catching up to us from behind, and will return to Earth in August. It’s still functioning, broadcasting a carrier signal that the Deep Space Network successfully detected in 2008. Twelve of its 13 instruments were working when we last checked on its condition, sometime prior to 1999.
Which is great. Except for one thing. We can no longer communicate with this spacecraft:
How could this happen? Well, the fact that ISEE-3 is still broadcasting a carrier signal was actually an error; it should have been shut down. If they had planned for it to still be functioning at this point, they would have maintained the capability to communicate with it. I don’t comprehend the intricacies of deep-space communications well enough to understand the obstacles here, and I don’t question their conclusion, but that doesn’t make me any less sad.
So ISEE-3 will pass by us, ready to talk with us, but in the 30 years since it departed Earth we’ve lost the ability to speak its language. I wonder if ham radio operators will be able to pick up its carrier signal — it’s meaningless, I guess, but it feels like an honorable thing to do, a kind of salute to the venerable ship as it passes by.
Thanks to Cary Corse @vialde for the tip!