Pioneer Anomaly: What Is It?
July 18, 2012

Pioneer Anomaly: What Is It?

Lee Rannals for - Your Universe Online

NASA's Pioneer 10 and 11 spacecraft have apparently slowed down due to heat pushing back on the spacecraft, according to new findings.

The effect, known as "Pioneer Anomaly," takes place when heat emanates from electrical current flowing through instruments and the thermoelectric power supply.

"The effect is something like when you're driving a car and the photons from your headlights are pushing you backward," Slava Turyshev, lead author of the paper published in the journal Physical Review Letters, said in a prepared statement. "It is very subtle."

Pioneer 10 and 11 have been on an outward trajectory from our sun ever since they were launched in 1972 and 1973.  Navigators in the 1980s saw a deceleration on the two spacecraft as they were approaching Saturn. They dismissed the effect of dribbles of leftover propellant still in the fuel lines after controllers cut off the propellant.

By 1998, the spacecraft kept traveling on their journey, and were over 8 billion miles away from the sun, when a group of scientists realized there was a deceleration of about 300 inches per day.

The scientists, led by John Anderson of NASA's Jet Propulsion Laboratory, raised the possibility that this deceleration could be some new type of physics that contradicted Einstein's general theory of relativity.

Turyshev decided to start gathering records stored all over the country and analyze the data to see if he could figure out the source of the deceleration back in 2004. He and colleagues were contemplating a deep space physics mission to investigate the anomaly, and he wanted to be sure there was one before asking NASA for a spacecraft.

The team went searching for Doppler data and telemetry data from the Pioneer spacecraft, which was still being stored on punch cards. The team was able to copy digitized files from the computer of JPL navigators who have helped steer the Pioneer spacecraft, and also found over a dozen boxes of magnetic tapes stored under a staircase.

Turyshev collected over 43 gigabytes of data, and managed to save a vintage tape machine that was about to be discarded so he could play the magnetic tapes.

Eventually, the team determined what was happening to Pioneer wasn't happening to other spacecraft, mostly because of the way the spacecraft was built. The Voyager spacecraft are less sensitive to the effect seen on Pioneer, because their thrusters align them along three axes, whereas the Pioneer spacecraft rely on spinning to stay stable.

The team calculated the heat put out by the electrical subsystems and the decay of plutonium in the Pioneer power sources, which matched the anomalous acceleration seen on both Pioneers.

"The story is finding its conclusion because it turns out that standard physics prevail," Turyshev said. "While of course it would've been exciting to discover a new kind of physics, we did solve a mystery."

The Pioneer spacecraft are no longer communicating with Earth, with Pioneer 10's last signal being received in January 2003, and Pioneer 11's last signal sending off in November 1995.