Projects: Pioneer Anomaly
Technical Information
Until just recently, only about 11 years of the more than 30 years of Pioneer Doppler data (velocity data derived from the Doppler shift of the received frequency of the Pioneer signal) had been analyzed, and the Pioneer anomaly remained. The Planetary Society stepped in and funded the effort to recover and validate these precious data. We have recovered large parts of the 30-year histories of the two spacecraft, and the data are now being collected, arranged, validated, and written to modern media.
Here we present at-a-glance technical information about the spacecraft and the data recovery.
Pioneer Anomaly Data Recovery Facts
| Facts (6/1/2006) |
Pioneer 10 |
Pioneer 11 |
| Escape velocity, i.e. will it leave solar system? |
Yes |
Yes |
| Current distance from Sun |
>90AU |
>71 AU |
| Launch Date |
March 2, 1972 |
April 5, 1973 |
| Last communication |
April 27, 2002 |
October 1, 1990 |
| Planets encountered |
Jupiter |
Jupiter, Saturn |
| Stabilization |
Spin* |
Spin* |
| Amount of Doppler data analyzed before current data "rescue" |
1987-1998
20,055 data pts. |
1987-1990
19,198 data pts. |
| Doppler data available to analyze after data “rescue” |
1973-2002
~95,000 data pts. |
1974-1994
~65,000 data pts. |
| Size of Doppler data files after data “rescue” |
20 GB |
15 GB |
| Master Data Records (i.e. telemetry or spacecraft housekeeping information including temperatures, voltages, etc.) recovered from the NASA Ames Research Center, Moffet Field, CA |
20 GB |
~20 GB |
| Pioneer Project Documents (designs, calibrations, descriptors, plans,
etc.) recovered |
1966 -- 2003 |
1996 -- 1990 |
*Spin stabilization allowed precise measure of the accelerations down to about 10-10 m/s2, whereas Voyager's 3 axis-stabilization (using propulsion to maintain orientation) only allowed a sensitivity about 50 times worse (not good enough to measure the Pioneer Anomaly). This difference in the way the spacecraft are stabilized actually is one of the reasons the Pioneer data are so important and unique. Most current spacecraft are three-axis stabilized, not spin stabilized.
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How big is the acceleration?
The anomalous acceleration of the Pioneer spacecraft
directed towards the Sun (i.e., slowing the spacecraft as it leaves the solar
system) is a
= (8.74 +/- 1.33) x 10-10 m/s2. This is one ten-billionth
the acceleration you feel due to gravity on the surface of the Earth.
Explanations of the Pioneer Anomaly that have been ruled out include:
* Solar radiation, solar wind, or effects of solar corona
* Kuiper Belt object gravity
* Dust
* Lorentz Force
* DSN: phase stability, location, or clocks
* Effects of Earth atmosphere on radio signal
Explanations still under study include:
* Thermal effects of RTGs and/or spacecraft bus (e.g., thermal radiation pushing
preferentially in one direction)
* Gas leakage (although considered unlikely because would have to exist in
both spacecraft
* Dark Matter
* Dark Energy
* A New Physics
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