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A few days ago, I was reading the wikipedia entry for the International Cometary Explorer (ICE) / International Sun-Earth Explorer 3 (ISEE-3) satellite, that was launched August 12, 1978. Down near the bottom of the page it states:

On February 4, 2014, the Goddard Space Flight Center announced that the Deep Space Network equipment necessary to transmit signals to the spacecraft had been decommissioned in 1999, and that replacing it was not economically feasible

Does anyone know what equipment it was that was decommissioned leaving us unable to contact the spacecraft? Also on that note what would it take to contact ICE/ISEE-3 or any spacecraft at a distance of ~1AU? Would it be possible to contact ICE/ISEE-3 on a 10-meter dish? 5-meter dish?

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The obstacle is sending commands to the spacecraft. We can receive its signals and interpret them, but sending commands to adjust ISEE's orbit would be difficult.

There's some information on the unmannedspaceflight forum:

...This report ... indicates that ICEE-3 was never designed to use the DSN for communications and a special filter had to be added to the Block V masers at DSS-14 and DSS-63 in the mid-80s to communicate with it. According to this report the maser was replaced at DSS-14 (Goldstone) in 2010 but the one at DSS-63 (Madrid) isn't going to be until this November, but S-band uplink isn't supported at Madrid because of frequency conflicts.

To summarize, ICE commands need to be sent on a frequency not normally used by the DSN. In order to send on this frequency, a filter needs to be added to the antenna to prevent the powerful broadcast from frying the incredibly sensitive receivers that are connected to the same antenna. This is not a matter of soldering a few components onto a breadboard. These are waveguides tuned to the filter frequency and able to withstand the power of the transmitter (20 kW?).

There is another factor that would have influenced NASA's decision not to pursue communication with ISEE: DSN availability. ISEE does not have any recording equipment; any measurements it takes must be transmitted immediately or they're lost. That means NASA would have to allocate a DSN antenna to the ISEE mission full-time, displacing several more recent missions. Normally DSN time is allocated in blocks of ~8 hours, so one antenna can serve several missions.

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A private group, with some cooperation from NASA is making progress on recovering the spacecraft. Using a slightly re-tuned cellphone transmitter and the Arecibo observatory dish, they have been able to command the spacecraft to do things and get the correct responses using only 400W. A major challenge has been finding and interpreting documentation on the spacecraft and its supporting ground systems.

On 18-Jun-2014, they are paying NASA's DSN to provide an updated, precise trajectory for the spacecraft. On 21-Jun, they plan to fire thrusters to increase it's spin rate to specification. Around the end of the month, they expect to adjust the trajectory to put it back in an earth orbit (probably at the earth-sun L1 point).

For long-term retrieval of information, they have enlisted support from Morhead State University, Radio Amateurs in Germany, and others. Additional radio and radio-astronomy amateurs have picked up the signal with small dishes. So, no, DSN is NOT required to listen to the spacecraft at this time. Nor will it be when its placed in a new orbit.

Follow along at http://spacecollege.org/isee3/, where you can find a lot of the gory details, and additional references.

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