June 16, 2016 – On July 4, NASA will fly a solar-powered spacecraft built by Lockheed Martin Space Systems within 2,900 miles (4,667 kilometers) of the cloud tops of our solar system’s largest planet.
As of Thursday, Juno is 18 days and 8.6 million miles (13.8 million kilometers) from Jupiter. On the evening of July 4, Juno will fire its main engine for 35 minutes, placing it into a polar orbit around the gas giant.
“Over the past five years, the Juno spacecraft has been great to operate and we’ve had very few issues during its long journey to Jupiter. But now our greatest challenge lies ahead, as the Jupiter orbit insertion is one of the most critical events of the mission,” said Kenny Starnes, Juno program manager at Lockheed Martin Space Systems. “The Jupiter orbit insertion is a precise choreographed dance with the largest planet in our solar system. The spacecraft will arrive at the planet traveling at 130,000 mph and with perfect timing, in perfect sequence, the computer has to fire the main engine for 35 minutes all by itself, with no interaction from our controllers back at Earth. If this doesn’t happen just right, there’s no second chance.”
Juno’s name comes from Greek and Roman mythology. The mythical god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife — the goddess Juno — was able to peer through the clouds and reveal Jupiter’s true nature.
During the flybys, Juno will probe beneath the obscuring cloud cover of Jupiter and study its auroras to learn more about the planet’s origins, structure, atmosphere and magnetosphere.
A series of 37 planned close approaches during the mission will eclipse the previous record for Jupiter set in 1974 by NASA’s Pioneer 11 spacecraft of 27,000 miles (43,000 kilometers). Getting this close to Jupiter does not come without a price — one that will be paid each time Juno’s orbit carries it toward the swirling tumult of orange, white, red and brown clouds that cover the gas giant.
“We are not looking for trouble, we are looking for data,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “Problem is, at Jupiter, looking for the kind of data Juno is looking for, you have to go in the kind of neighborhoods where you could find trouble pretty quick.”
The source of potential trouble can be found inside Jupiter itself. Well below the Jovian cloud tops is a layer of hydrogen under such incredible pressure it acts as an electrical conductor. Scientists believe that the combination of this metallic hydrogen along with Jupiter’s fast rotation — one day on Jupiter is only 10 hours long — generates a powerful magnetic field that surrounds the planet with electrons, protons and ions traveling at nearly the speed of light. The endgame for any spacecraft that enters this doughnut-shaped field of high-energy particles is an encounter with the harshest radiation environment in the solar system.
“Over the life of the mission, Juno will be exposed to the equivalent of over 100 million dental X-rays,” said Rick Nybakken, Juno’s project manager from NASA’s Jet Propulsion Laboratory in Pasadena, California.
Juno’s orbit resembles a flattened oval. Its design is courtesy of the mission’s navigators, who came up with a trajectory that approaches Jupiter over its north pole and quickly drops to an altitude below the planet’s radiation belts as Juno races toward Jupiter’s south pole.
“Juno will have a designed orbit to minimize its time in the radiation belt around Jupiter,” said Guy Beutelschies, Director, Interplanetary Missions, Lockheed Martin. “The data that we want to take will be at the closest point of its orbit.”
Each close flyby of the planet is about one Earth day in duration. Then Juno’s orbit will carry the spacecraft below its south pole and away from Jupiter, well beyond the reach of harmful radiation.
While Juno is replete with special radiation-hardened electrical wiring and shielding surrounding its myriad of sensors, the highest profile piece of armor Juno carries is a first-of-its-kind vault, containing the spacecraft’s flight computer and the electronic hearts of many of its science instruments.
“Sensitive electronics on the Juno spacecraft are inside a vault made of titanium,” said Beutelschies. “This presented a complex engineering challenge because we’ve never designed one of these. There are computers in there, which tend to get hot, so we had to develop a system that would keep them cool inside the vault.”
Without the vault, Juno’s electronic brain would more than likely fry before the end of the very first flyby of the planet. Titanium was a good choice of material for radiation tolerance, but the vault still weighs in at almost 400 pounds (172 kilograms) and will reduce radiation by 800 times, but will not block it completely. The quantity and energy of the high-energy particles is just too much. However, Juno’s special orbit allows the radiation dose and the degradation to accumulate slowly, allowing Juno to do a remarkable amount of science for 20 months.
“Over the course of the mission, the highest-energy electrons will penetrate the vault, creating a spray of secondary photons and particles,” said Heidi Becker of JPL, Juno’s Radiation Monitoring Investigation lead. “The constant bombardment will break the atomic bonds in Juno’s electronics.”
The Juno spacecraft launched on a United Launch Alliance Atlas V rocket on August 5, 2011 from Cape Canaveral, Florida.
Lockheed Martin designed and built the Juno spacecraft for NASA’s Jet Propulsion Laboratory and is also providing spacecraft day-to-day flight operations from its Denver Mission Support Area.
JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate. The California Institute of Technology in Pasadena manages JPL for NASA.