JUNO Returns to Earth Wednesday for Critical Gravitational Slingshot to Jupiter

An artist's concept of JUNO's approach to Earth for an October 9 gravity-assist maneuver.  Image Credit: NASA/JPL-Caltech

An artist’s concept of JUNO’s approach to Earth for an Oct. 9 gravity-assist maneuver. Image Credit: NASA/JPL-Caltech

On Aug. 5, 2011, United Launch Alliance sent NASA’s JUNO spacecraft on a five-year trip to visit our Solar System’s largest planet—Jupiter. Problem is, Jupiter is so far, and the 8,000-pound solar-powered JUNO is so heavy, that the Atlas-V rocket used to launch the spacecraft only provided half the energy needed to make the trip within a reasonable amount of time. In order to make up for this, NASA sent the spacecraft out beyond Mars like a boomerang, and this Wednesday, Oct. 9, JUNO will return to Earth for the other half of that energy needed to reach Jupiter in what can best be described as a slingshot maneuver.

This gravity-assist will take advantage of the Earth’s natural pull on the spacecraft as it approaches, which in turn means JUNO is accelerating rapidly as it “falls” back to Earth at 23 miles per second. On Wednesday, the spacecraft will fly within 350 miles of the Earth’s surface, cruising over the southeastern coast of South Africa and flying with the movement of our planet to slingshot for one final major push toward Jupiter—a maneuver which will boost JUNO’s velocity by over 16,000 mph. JUNO will eventually reach a velocity of about 93,000 mph, fast enough to reach Jupiter by summer 2016.

The launch of NASA's JUNO to Jupiter atop an Atlas-V rocket August 5, 2011.  Photo Credit: Mike Killian / www.MikeKillianPhotography.com

The launch of NASA’s JUNO to Jupiter atop an Atlas-V rocket on Aug. 5, 2011. Photo Credit: Mike Killian / www.MikeKillianPhotography.com

“Even with a big rocket we couldn’t get enough speed to get to Jupiter, so we launched and got out all the way to about the asteroid belt, and then the sun kind of pulls us back in because we’re not going fast enough to reach Jupiter and get away from the sun completely,” said Dr. Scott Bolton, Space Science Director at the Southwest Research Institute and JUNO principal investigator. “So we use what’s called a gravity assist, we come back toward the Earth and fly by the Earth, and we actually gain momentum. We get that speed given to us and that allows us to reach Jupiter.”

JUNO’s approach to Earth on Oct. 9 will also serve another purpose: to show mankind a view of the Earth and Moon we have never seen before.

“We’ll be coming from the sunlit side, we’re coming from deep space, so JUNO’s going to get a perspective that has never been seen by humans,” said Bolton. “Earth from far away, with the moon, Earth spinning on its axis, we’re going to make a movie so we can all see what we look like from that deep space perspective. Sort of what we look like if you were on Mars, or Jupiter.”

Although Jupiter is the most visited planet in our Solar System, only one spacecraft in history was actually dedicated to exploring the giant planet, which by itself is larger than all the other planets in the Solar System combined. That spacecraft, Galileo, spent eight years exploring Jupiter and its many moons before NASA ended the mission by sending the spacecraft into a suicidal dive through Jupiter’s atmosphere at 30 miles per second, which protected the moons around Jupiter from contamination.

Now, over 10 years later, JUNO is returning to pick up where Galileo left off, looking for answers about Jupiter’s origins, which in turn will help scientists understand the processes that formed all of the planets—including Earth.

“The prime objective of JUNO is to go after some of the most fundamental questions about our solar system, to learn about how Jupiter formed, how it evolved, what really happened early in the solar system that eventually led to all of us,” said Bolton. “We know that it’s very similar to the sun, it’s almost all hydrogen and helium just like the sun is, but it has a smidgen more of what cosmologists call heavy elements. Those are everything heavier than helium – carbon, nitrogen, sulfur, we don’t know how that happened, but we know it’s important because the stuff that Jupiter has a little more of than the sun is what we are made out of. Jupiter is like a time capsule, whatever happened after the sun is recorded in Jupiter, and because of its giant gravity field its been able to hold on to that material.”

Video Credit: NASAJuno

JUNO is already more than halfway through its 2-billion-mile journey to Jupiter, in terms of distance traveled, but the $1.1 billion mission still has over 2.5 years of travel time to go before arriving at Jupiter in July 2016. Upon arrival, JUNO will burn its engine and place itself into an 11-day polar orbit, using eight science instruments to study the planet’s atmosphere, gravity and magnetic fields, polar magnetosphere, and composition in unprecedented detail. Thirty-three orbits are planned over the course of one Earth year to help JUNO answer questions about whether or not Jupiter has a rocky core, how much water may be present in the planet’s atmosphere, and how its mass is distributed. JUNO will also study the winds in Jupiter’s atmosphere, which put Category 5 hurricanes and F5 tornadoes on Earth to shame.

But first, before any science can be performed, JUNO has to reach Jupiter, and Wednesday’s Earth flyby will provide the final push needed to reach the colossal planet—the mission up to this point has been in preparation for the Earth flyby. JUNO mission operations are exempt from the current government shutdown (97 percent of NASA’s workforce is furloughed until further notice), and the space craft is reported to be in excellent health and is operating nominally.

“The team is looking forward, preparing for the day we enter orbit around the most massive planet in our solar system,” said Bolton.  “Jupiter was likely the first planet to form, and by learning more about the earliest steps in the history of the solar system, we learn about our history too.”

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