Spacecraft heading to Jupiter gets a boost from Earth itself

October 10, 2013 by  
Filed under Solar Energy Tips

To reach Jupiter, NASA’s Juno spacecraft will need all the acceleration power that it can get. And it will obtain much of the needed boost, not from a state-of-the art rocket pack or an on-board nuclear reactor, but from the gravity of planet Earth: NASA plans to have the spacecraft fly around Earth on Wednesday, October 9, and pick up a gravitational speed boost, slingshot-style, which will send it flinging Jupiter’s way.

Juno launched back in 2011 aboard an Atlas V rocket and has been following a circuitous route to Jupiter since then. It has flown about 50 million miles, to within the neighborhood of Mars. While Juno has clearly long ago escaped Earth’s gravity, it is slowed down by the gravity of the sun.

The Oct. 9 flyby will bring it back toward Earth and pass within 350 miles of the surface—South Africa will be the point of nearest reach, when the spacecraft flies over it at around 3:21 p.m. EDT. NASA estimates that by the time that Juno has completed its circling of Earth and has resumed its trek toward Jupiter, Earth’s gravity will have boosted the spacecraft’s speed from its current 78,000 miles per hour to a speed of 87,000 miles per hour—an 11.5% difference.

Juno particularly needs the extra boost due to its heft: The robotic vessel weighs 8,000 pounds. Voyagers 1 and 2, by contrast, weighed in at only 1,616 and 1,620 pounds, respectively. The Jupiter-bound probe’s weight owes partially to the three large solar arrays, each of which is the size of a tractor trailer; in addition to a titanium vault that secures Juno’s sensitive electronic equipment from the blasts of radiation, heat, and other abuse that Jupiter’s environs are likely to impose on them.

With its heavy solar array, Juno is the first solar-powered spacecraft to explore the outer reaches of the solar system. And while that may make the spacecraft an impressive landmark in renewable-energy utilization, it also renders it too heavy to propel via traditional rocket boosters. Even a large rocket booster wouldn’t be able to give the spacecraft enough push to get it all the way to its destination, according to Scott Bolton, Juno mission principal investigator.

So instead, Juno’s already-sizable on-board boosters will get an added thrust from Earth’s gravity. Bolton said in a statement that the Earth circling will provide Juno with an initial boost equal to 70% of the propulsion power of the Atlas V rocket that first lifted the spacecraft into orbit two years ago.

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