From the ISEE-3 Returns Facebook page: Communication involves speaking, listening and understanding what we hear. One of the main technical challenges the ISEE-3/ICE project has faced is determining whether we can speak, listen, and understand the spacecraft and whether the spacecraft can do the same for us. Several months of digging through old technical documents has led a group of NASA engineers to believe they will indeed be able to understand the stream of data coming from the spacecraft.
NASA's Deep Space Network (DSN) can listen to the spacecraft, a test in 2008 proved that it was possible to pick up the transmitter carrier signal, but can we speak to the spacecraft? Can we tell the spacecraft to turn back on its thrusters and science instruments after decades of silence and perform the intricate ballet needed to send it back to where it can again monitor the Sun? The answer to that question appears to be no.
The transmitters of the Deep Space Network, the hardware to send signals out to the fleet of NASA spacecraft in deep space, no longer includes the equipment needed to talk to ISEE-3. These old-fashioned transmitters were removed in 1999. Could new transmitters be built? Yes, but it would be at a price no one is willing to spend. And we need to use the DSN because no other network of antennas in the US has the sensitivity to detect and transmit signals to the spacecraft at such a distance.
This effort has always been risky with a low probability of success and a near-zero budget. It is thanks to a small and dedicated group of scientists and engineers that we were able to get as far as we have. Thank you all very much.