Thursday, October 10, 2013

Juno: The spacecraft putting sling theory to the test

Juno: The spacecraft putting sling theory to the test
Why a probe passing our planet on its way to Jupiter might end a decades-old mystery, and reveal something completely new about gravity.

When Nasa’s Juno spacecraft arrives at Jupiter three years from now, it will investigate the planet’s origin and evolution by mapping magnetic and gravitational fields. But before it does that, the probe has an opportunity to contribute to a momentous discovery right here in our celestial backyard, and potentially pave the way for the discovery of entirely new physics.

Spacecraft like Juno routinely use flybys of Earth to gain speed and slingshot themselves towards the outer solar system. Occasionally, however, passing spacecraft seem to get an extra boost, picking up more speed than calculations suggest they should. The energy kick is known as the flyby anomaly, and this has happened too many times now to be shrugged off as trivial. Instead, something unidentified is affecting the velocity of spacecraft at their closest approach to our planet.  When Juno swings by Earth, all eyes will be on the spacecraft to see if it can help figure out what is going on.

The most likely explanation is that it is a miscalculation in the tracking software, but there is a tantalizing possibility that navigators are seeing unanticipated physics beyond our present theories of gravity. If so, it would open up a whole new landscape of understanding about the fundamental nature of the universe.
“If we were to establish that the Earth flyby anomaly really resulted from new physics, that would be of major significance,” says Chuck Scott, Juno mission manager at Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

It’s anyone’s guess what any new discovery of this type could yield, but previous breakthroughs in gravitational physics have revolutionized our way of thinking. In the 17th Century the work of Isaac Newton helped trigger the Age of Enlightenment. In the 20th Century, Albert Einstein’s General Relativity led to our discovery of black holes and the big bang. It also made more down-to-Earth applications possible, such as satellite navigation.
However, Scott is cautious about such heady speculation. “Extraordinary claims require extraordinary evidence,” he says. “Most scientists expect that it will turn out to be a software, or some other minor, miscalculation, rather than new physics.” But only by finding the cause of the surge will we know. Which is why researchers will be examining Juno in as much detail as possible to see what’s going on.

Preparations for this flyby began months ago.  NASA scientists are eagerly awaiting the tracking data that will be available, especially by those who helped solve another spacecraft navigational puzzle. The behaviour of NASA’s Pioneer 10 and 11 spacecraft vexed minds for decades, as it looked as if the Sun was exerting a slightly greater pull of gravity than expected from Newton’s theory. After a great deal of international effort and years of work to analyze the tracking data, the explanation was revealed to be a more mundane effect – it was the excess heat bouncing off the back of the spacecraft’s main antenna.

Looking beyond the Juno flyby, Bertolami had proposed a small mission dedicated to studying the anomaly. He envisaged a small independent microsatellite that would constantly orbit the Earth on trajectories that mimic flybys. It would stay in constant touch with ESA’s Galileo satellite navigation system, calculating its position so that any unexpected acceleration could be caught as it happened. That particular proposal seems to have run aground because another proposed ESA spacecraft could do the same job. The Space-Time Explorer and Quantum Equivalence Principle Space Test (STE-Quest) is an ESA candidate mission for launch by 2024. If selected, the mission will explore the force of gravity, but Jorge Paramos, a physicist at Technical University of Lisbon, Portugal, and Gerald Hechenblaikner, Astrium Satellites, Germany, have suggested the spacecraft could also be used to investigate the flyby anomaly, with virtually no change to its original mission and no extra instruments.

Whatever it turns out to be, after decades of head scratching and frustration, there is now a real chance of making progress. All we need is for the anomaly to turn up again on cue. Any time now, hopefully. Why is it important? First of all it will increase our understanding of gravity and other forces in the time space continuum. It may be entirely new physics, which is always exciting. And we may be able to use knowledge of this anomaly to assist us in further space exploration.

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