ISEE-3 Reboot: Data, Trajectories, and Engine Burns
As we put out in our project very brief note on Friday, we have successfully contacted the bird! At the time of the contact we had Morehead State University Space Science Center’s 21 meter dish, the 20 meter dish at Bochum Radio Observatory in Germany, and the SETI Allen Array all listening.
This was not without problems. The spacecraft has two transponders, which are oddly enough called transponder A and Transponder B. Transponder B is normally the engineering telemetry transponder and transponder A is the ranging transponder. The final state of the spacecraft before was to have both of the transponders transmitters active and that is what people around the world have been tracking. However, the spacecraft is set up with a lot of redundancy so you can use either transponder A or B to send telemetry or range.
We tried several times to command the spacecraft’s B transponder at 2041.9479 MHz into the mode where it normally sends engineering telemetry, which is our first task. It did not work. We tried several variations of the proper commands and we tried several operational approaches such as scanning across the receive transponder band to make sure that there was not some offset that we did not know about or that the receive frequency had drifted over the years. Nothing worked.
Then we tried the same process on transponder A and BINGO, telemetry! Well not really telemetry itself, but modulation from the output of the telemetry system. The initial command was just to turn engineering telemetry on at 512 bits/second. This was successful. Figure one, generated by Achim Volhardt from AMSAT DL and Bochum, shows the modeled spectrum for a 512 bits/sec telemetry rate, which is what we commanded:
