Solving NASA's great gravity mystery

'A major event'
“The Pioneer spacecraft conducted the largest ever gravitational experiment that humanity attempted to test Newton’s Law, and it failed,” Turyshev told SPACE.com. “If we will identify an anomaly due to conventional physics thermal mechanism or propulsion or a combination there off, that’s a major event.”

Finding a physical source will not only prove Newton right, but also allow engineers to cancel out the Pioneer Anomaly on future spacecraft to make them more stable, added Turyshev, who said that he is striving to remain unbiased to the anomaly’s cause.

Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources — known as radioisotope thermal generators (RTGs) — could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.

Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL.

“We’re really encouraged by the preliminary results and we think we’re going down the right track,” Kinsella said during the Monday discussion.

Edward Belbruno, a former JPL researcher and gravitational trajectory expert at Princeton University who also served the panel but is unconnected with the anomaly research, said that another possible explanation for the Pioneer Anomaly rests in the mass of the Milky Way galaxy, which — when taken to account — yielded the exact acceleration change for Pioneer 10 as that observed. While he found that the technique did not yield a specific direction for the acceleration, it may shed some insight into the anomaly and warrants further study, Belbruno added.

Recovered data
During their first Pioneer Anomaly analysis, researchers relied on data that spanned about 11.5 years of Pioneer 10’s mission, though they only had about four years worth for Pioneer 11.

After an exhaustive search sponsored by the Planetary Society, Turyshev and his team recovered complete telemetry data sets for both Pioneer probes, as well as about 30 years of data for Pioneer 10 and a 20-year set for Pioneer 11.

Much of the data sat inert, recorded on about 400 magnetic tapes in deep storage at JPL. Altogether, it included almost 40 Gigabytes of Pioneer 10 and 11 mission data, or about the equivalent of a half hour of high-definition television (HDTV) programming from your local cable TV provider.

Transferring the data from 9-track magnetic tapes to a modern digital format, and screening it to reduce artifacts and other corrupted material, has proven time-consuming for Pioneer Anomaly researchers. But Turyshev remains confident that once the information is ready for analysis, the anomaly shed new secrets.

He is also keeping a close watch on NASA’s New Horizons probe, which may one day show signs of the anomaly as it heads out beyond Pluto’s orbit after 2015, but only if the mystery force is found to be an actual effect.

“We are truly in a unique situation now with the recovery of the new data assets,” Turyshev said. “Once this data set is analyzed, let’s talk then.”

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