Projects: Pioneer Anomaly
Frequently Asked Questions About the Pioneer Anomaly
Never, in 25 years, have we see seen such a response to a letter from The
Planetary Society. Our members responded with overwhelming enthusiasm to the
idea of a new Society project to help solve the Pioneer Anomaly, a mystery
as yet unexplained by the laws of physics. From around the world came letters
and e-mails cheering us on – and asking for more information. To speed
the flow of information, we’ve compiled the questions most often asked,
and here are the answers:
What is the "Pioneer Anomaly"?
The Pioneer 10 and 11 spacecraft are currently headed out of our solar
system. In carefully tracking their 30-year missions, scientists have
found that they have not quite traveled as far as expected. They have
slowed down, every so slightly, compared to what models predict. This variation
from the expected is referred to as the Pioneer Anomaly. Initial analysis
of a portion of the data has not been able to explain this effect from
some spacecraft issue alone. However, much more analysis using the entire
Pioneer data set is required to determine if this is a spacecraft effect
or some "new
physics."
Is the same effect seen with the Voyager spacecraft?
The Pioneers are spin-stabilized spacecraft. The Voyagers are three-axis
stabilized craft that fire thrusters to maintain their orientation in space
or to slew around and point their instruments. Those thruster firings would
introduce uncertainties in the tracking data that would overwhelm any effect
as small as that occurring with Pioneer.
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.
Why does it cost $250,000 to recover the data? This seems like a
lot.
This amount enables us first to save the data from destruction, and then
to support the complex analyses necessary to solve this mystery. We may well
have to bring in more help from other eminent “celestial mechanicians” to
provide fresh perspectives on the anomaly.
Will the data be made publicly available?
Yes. First, the data first must be recovered, validated, documented, and
preliminary analyses must be done. After those tasks are completed (probably
taking months to a year), the data will be made publicly available, including
second-order data products when the raw data is processed by JPL orbit software.
What period of data has been analyzed? What will be analyzed?
The two Pioneer spacecraft returned approximately 30 years of tracking
data that could be used for this analysis. John Anderson and his team have
been able to carefully analyze only 11.5 years worth, from 1987 to 1998.
Our efforts at data recovery will make available nearly the entire 30 years
of data, greatly increasing the possibility of discovering the cause of
the anomaly.
How are things going so far?
Thanks to Planetary Society members, we have already been able to get started
with the Pioneer Anomaly team. With your support, they have successfully
retrieved much of the 30 years of data from the old, “dusty” data
tapes. We have also established a two-phase plan with the team. Phase 1 is
nearly complete: data recovery and validation, which has taken several
months of painstaking, tedious work. Phase 2 will be the intensive data analysis
to search carefully for the source of the anomaly.
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