IEEE Spectrum December, 2012 - 62

from the spacecraft model,
we found that the two values
matched within 20 percent.
Once uncertainties are taken
into account, there is no statistically significant difference. Three decades after its
discovery, we can now say
there is no exotic cause for
the Pioneer anomaly: The
puzzling deceleration was
produced by the asymmetric
radiation of waste heat created onboard the spacecraft.
Fo r s o m e, t h i s m i g ht
s e e m l i ke a d i s ap p o i nti ng conclusion to such a
long-standing mystery, but
accounting for the anomaly
actually cements Pioneer 10
and 11's place in history. These spacecraft accomplished something that isn't
likely to be repeated anytime soon: They
completed a high-precision validation of
Einstein's theory of how gravity works,
out to tw ice the distance between
Pluto and the sun. No other spacecraft
launched since could have been used for
such a test (or would show such a subtle anomaly); later spacecraft were too

BoxeD Set: the data collected
by navigators on the trajectories
of pioneer 10 and 11 were stored
on magnetic tapes. A number
ultimately wound up in cardboard
boxes that were found in stacks
beneath a staircase at NAsA's Jet
propulsion Laboratory.
photo: SLAvA g. tuRyShev

reliant on thrusters, weren't tracked
continuously, or just didn't travel far
enough. Pioneer 10 and 11 remain our
most precisely navigated deep-space
probes to date and will probably hold
that distinction for many years to come.
These spacecraft also underscore
the value of data preservation. In the
early days of the Pioneer missions, scientists and engineers often viewed the

medium as more valuable
than the data it contained.
Many considered raw data
to be worthless once "useful"
scientific and technical information had been extracted.
Nowadays data storage may
be cheap, but we're still in
danger of suf fering from
shortsightedness when it
comes to data custodianship.
Every experiment needs a clear plan in
place to ensure that a record of the original observations is still available and
readable, even decades into the future.
It may very well be the only way we'll
resolve the next confounding mystery. o
post your comments online at http://
spectrum.ieee.org/pioneer1212

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2012