Juno slingshot – Spacecraft zips past Earth en route to Jupiter

by Chris Gebhardt and Chris Bergin

NASA’s Juno spacecraft performed a close gravity assist flyby of the Earth on Wednesday, aiding its five-year journey to Jupiter. Earth’s gravity accelerating assist for the solar-powered spacecraft will result in increasing its velocity by 16,330 miles per hour, en route to studying Jupiter’s atmosphere as a means of better understanding how the planet, and by extension, the solar system originated and evolved.

Juno Mission:

Riding atop the second most powerful configuration for the Atlas V rocket, the Juno mission lifted off at 12:25 EDT on 5 August 2011 – after a 51 minute delay for a technical issue and a boat in the launch restriction zone.

Since launch, Juno has traveled approximately 221 million miles and has achieved a velocity of 55,800 miles per hour relative to the sun.

A41Named after the Roman goddess of marriage and the wife of the god Jupiter, the Juno mission is the second mission in NASA’s New Frontiers program – the first being the New Horizons probe currently on its way to an encounter with Pluto and its moons in July 2015.

The spacecraft made its first of three Mars orbit crossings on December 13 in anticipation for its August 2016 arrival at Jupiter after a five year trek through the inner and outer solar system.

However, before it reaches its destination, Juno had to greet the Earth one last time, performing a flyby, passing within 347 miles of Earth.

The flyby functions as a gravity assist for Juno, with Earth’s gravity accelerating the solar-powered spacecraft’s velocity by 16,330 miles per hour. The purpose of using a gravity assist to get Juno on its way to Jupiter is one of cost.

Z3“A direct mission to Jupiter would have required about 50 percent more fuel than we loaded,” said Tim Gasparrini, Juno program manager for Lockheed Martin Space Systems. “Had we not chosen to do the flyby, the mission would have required a bigger launch vehicle, a larger spacecraft and would have been more expensive.”

While NASA’s Jet Propulsion Laboratory has the role of providing the critical navigation for the mission and the flyby, Lockheed Martin’s Juno team is also playing an active and varied role.

“While flying Juno is a team effort, the core operations are in Denver,” added Gasparrini. “We are responsible for systems engineering, subsystem performance and execution of the commanding that goes to the Juno spacecraft. During the flyby, the team will be monitoring the spacecraft because gravity is doing all the work.”

In preparation, most of the commanding was folded into a 28-day background sequence, and most of the sequences began on September 27.

One major challenge related to ensuring Juno found a clear path, given its trajectory involved passing well inside the orbit of Geostationary (GEO) satellites.

“We have a couple of possible collision avoidance maneuvers to select from, looking at all the satellites around the Earth,” added Jeff Lewis, spacecraft engineer and Lockheed Martin Space Systems operations lead for Juno ahead of the flyby. “We are passing inside the orbits of geostationary spacecraft.”

Catching a velocity boost isn’t the only value in the effort. The operation also will permit officials to test Juno’s instruments and observe the spacecraft’s flight handling.

“We’ll exercise the science instruments, since Juno’s instruments will be operating in a magnetospheric environment for the first time,” added Lewis. “The Earth’s magnetic field will allow a number of the instruments to be tested. We’re also using the flyby of the moon as an opportunity to gauge how the spacecraft operates.

“Since Juno is a spinning spacecraft, we need to sense the right time to take data as the Moon, or Jupiter, passes through the instruments’ fields of view.”

Once it arrives at Jupiter, Juno will enter a zenocentric orbit of the gas giant for a primary scientific mission that is scheduled to last 14 months and allow the spacecraft to study Jupiter from a polar orbit.

A61To accomplish this, the Lockheed Martin-built spacecraft will carry nine instruments to Jupiter to study electric currents flowing along field lines in the planet’s magnetic field, ultraviolet and electromagnetic emissions of the energetic particles in Jupiter’s aurora, heat being emanated from the planet, the structure of Jupiter’s atmosphere, the magnetosphere’s structure in the planet’s polar regions, and the energy and distribution of particles and the polar regions of Jupiter’s magnetosphere.

In all, Juno will be the ninth spacecraft to visit the planet Jupiter, the first being the pioneer 10 spacecraft which flew through the Jovian system in December 1973.

Juno will be the first spacecraft to be placed into orbit around Jupiter since the Galileo mission which lasted from December 8, 1995 to September 21, 2003.

The connection between Juno to its predecessor Galileo is somewhat ironic to space fans. The Juno mission was in fact the first NASA mission to be launched after the fly out of the Space Shuttle Program.

The final flight of the shuttle program flown by orbiter Atlantis landed just 15 days before Juno’s launch. The previous Jovian orbiter mission of Galileo was launched by the very same Space Shuttle – Atlantis – in 1989.

(Images via JPL)

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