Juno Flyby of Earth
NASA's Juno spacecraft launched aboard an Atlas V rocket from Cape Canaveral Air Force Station, Fla., Aug. 5, 2011, beginning a five-year journey to Jupiter. But it wasn't charted on a direct path. Before it reaches its destination, Juno will greet the Earth one last time. The spacecraft will perform a flyby Oct. 9, passing within 347 miles of Earth.
The flyby will function as a gravity assist for Juno, with Earth's gravity accelerating the solar-powered spacecraft's velocity by 16,330 miles per hour. NASA launched Juno to an area just past Mars, then two main engine burns executed a year ago maneuvered it back around toward Earth. The purpose of using a gravity assist to get Juno on its way to Jupiter is one of cost.
"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."
Lockheed Martin's Juno team is playing an active and varied role in the mission and is preparing for the flyby.
""While flying Juno is a team effort, the core operations are in Denver," said 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."
NASA's Jet Propulsion Laboratory is providing the critical navigation for the mission and the flyby. In the lead up to the flyby, Gasparrini's team has been active monitoring Juno. "We've been doing final reviews on sequences necessary to conduct the flyby," said Jeff Lewis, spacecraft engineer and Lockheed Martin Space Systems operations lead for Juno. "Most of the commanding is folded into our 28-day background sequence, and most of the sequences started on Sept. 27."
For Lewis and others on the team, a big part of positioning Juno for a successful gravity assist is to ensure the spacecraft steers clear of other objects in its vicinity.
"The day of the Earth flyby, the team will be on hand to monitor things," said Lewis. "We have a couple of possible collision avoidance maneuvers to select from, looking at all the satellites around the Earth. 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," said 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."
On Aug. 12, Juno achieved a milestone by reaching the halfway point on its trek to Jupiter as it had traveled 9.46 astronomical units, equivalent to 879,733,760 miles, at that point. Demonstrating fortuitous timing, the spacecraft is scheduled to reach Jupiter July 4, 2016.
Juno's primary mission is to study Jupiter's atmosphere as a means of better understanding how the planet, and by extension, the solar system originated and evolved. Juno will employ its suite of scientific instruments to peer beneath the planet's dense cloud cover to study the existence of a solid planetary core, map Jupiter's magnetic field, measure water content in the atmosphere and study the planet's auroras.
The spacecraft will orbit Jupiter for about one year, or 33 orbits, operating at times as close as 3,100 miles above the planet's clouds.
According to Gasparrini, the Lockheed Martin Juno team is working collaboratively with other members of the overall Juno program team to ensure mission success. Other team members include NASA, the Jet Propulsion Laboratory, the Southwest Research Institute - including Scott Bolton, Juno's principal investigator - and a number of scientists throughout the world.
As the flyby approaches, Gasparrini and team are locked in and ready.
"The team is 100 percent focused on executing the Earth flyby successfully," said Gasparrini. "We've spent a lot of time looking at possible off-nominal conditions. In the presence of a fault, the spacecraft will stay healthy and will perform as planned."