Pioneer 10 distance from Sun: 77.86 AU
Speed relative to the Sun: 12.24 km/sec (27,380 mph)
Distance from Earth: 11.81 billion kilometers (7.34 billion miles)
Round-trip Light Time: 21 hours 52 minutes
The Geiger Tube Telescope instrument (James Van Allen, P.I.) data have been analyzed. Van Allen reports that the successful DSS63 reception total of 2 hours of clean data from the GTT instrument from the 28 April and 19 May tracks. The cosmic ray intensity has continued to decrease since 6 August 2000 and is now 77 percent of its maximum value in late 1998-early 1999. Hence, Pioneer 10 at ~78 AU is still under the delayed influence of solar activity and has not yet reached the cosmic ray modulation boundary of the heliosphere.
At GMT 17:27:30, Saturday, 4/28/01, the signal from Pioneer 10 was received at station 63 in Madrid, the first time since August 5/6 of last year. So it appears that Pioneer 10 has life, albeit in another mode - i.e., only in a two-way coherent mode. We have been listening for the Pioneer 10 signal in a one way downlink non-coherent transmission mode since last summer with no success. We therefore conclude that in order [for Pioneer 10] to talk to us, we need to talk to it. This means from now on, we need two-way round-trip light time (RTLT) passes to allow the Deep Space Network (DSN) to send up a strong stable signal to lock up with a coherent downlink signal. After our last attempted pointing maneuver in July of last year, the operations center lost the capability to command the spacecraft. Our command capability has now been reestablished. We can now repoint the spacecraft towards Earth when that becomes necessary.
Larry Lasher, Pioneer Project Manager