New Scientist is running an interesting piece [subscription required for full access] on Slava Turyshev (JPL), who plans to investigate the so-called Pioneer Anomaly by re-flying the mission virtually. It’s a fascinating tale for various reasons, not the least of which is how close we came to losing much if not all of the precious Pioneer data. For one thing, 400 reels of magnetic tapes housing information about the trajectories of the two spacecraft had to be saved from years of neglect and transferred to DVD.
And that was just the beginning. When Turyshev visited NASA’s Ames Research Center, his search for project records from the 114 onboard sensors that recorded the Pioneers’ spin rate and other data turned up the floppy disks that mission engineer Larry Kellogg had saved. But Ames managers were close to destroying the disks because of lack of space. Having interceded to save this material, Turyshev then turned to programmer Viktor Toth to write a program to extract 40 gigabytes of data from the old floppies, to be recorded like the tapes onto DVD.
So now we can re-fly the missions, correlating each spacecraft event with tracking data in hopes of finding something that might tell us why Pioneer 10, when last heard from, was off-course by about 400,000 kilometers, and why its sister spacecraft is also not quite where it ought to be. A new challenge for Einsteinian gravity, or an effect created within the spacecraft themselves? Prime candidates for scrutiny are the radioisotope thermoelectric generators (RTGs) that power the Pioneers, and the possibility that their waste heat could raise the temperature of one side of the spacecraft, producing a tiny thrust.
The data should tell us whether we can rule out onboard effects and start contemplating a tweak to current gravitational theories. Such a tweak seems unlikely to Centauri Dreams given the lack of evidence of any such effect on other objects in the outer Solar System, but the investigation is well worth making, and could be further developed in a future space mission. On that score, be aware of Dario Izzo (European Space Agency), whose paper “Options for a nondedicated mission to test the Pioneer anomaly,” written with Andreas Rathke and scheduled to appear in the Journal of Spacecraft and Rockets, is available here.
And get this comment from Izzo on the size of the malfunction (if it exists) aboard the Pioneers: “The leak of a single molecule of gas from the spacecraft will give a momentary acceleration similar in size to the Pioneer anomaly.” That’s not much to work with, but as New Scientist writer Stuart Clark points out, the force acting on the spacecraft is a persistent one, so any malfunction would have to be similarly long-lived. The article is “Have We Got Gravity All Wrong?” in the magazine’s June 3 issue.