We have now confirmed that both ISEE-3 transponders - A & B - are in coherent ranging mode. We have a very strong confirmation (correct number of commands accepted) that transponder A is in coherent ranging mode and we have reasonably strong confirmation that transponder B is also in coherent ranging mode. We are now set up and ready to go for our first ranging session with DSN on 18 June. Our first session will use DSS-24, a 34 meter dish with 20kW transmitter located at Goldstone in California.
If this ranging session with DSN is successful then we will proceed with plans to briefly fire two of the spacecraft's thrusters on 21 June so as to spin it up from 19.16 rpm to the mission specification of 19.75 +/- 0.2 rpm.
Our spin-up target is 19.733 rpm, which is an increase of 0.573 rpm from the currently observed 19.16 rpm. This burn would utilize spin-up thrusters A and B (see image above - larger view) at a 22.5 degree pulse-width. There would be 11 pulses, taking 34 seconds to complete, with a total fuel usage of 0.0418 pounds.
This optimal spin rate is required in order to properly fire the axial thrusters during the much longer trajectory correction maneuver (TCM) we need to perform to adjust the spacecraft's course. That TCM burn is now scheudled to happen between 30 June and 2 July.