Spaceflight Insider

NASA’s Juno spacecraft closes in on Jupiter

Artist's depiction of NASA's Juno spacecraft approaching Jupiter. Image Credit: JPL / NASA posted on SpaceFlight Insider

An artist’s depiction of NASA’s Juno spacecraft approaching Jupiter. Image Credit: JPL / NASA

NASA held a media briefing on Thursday, June 16, to discuss the July 4th arrival of the Juno spacecraft at Jupiter. As of Thursday, the solar-powered probe, which is roughly the size of a basketball court, was 18 days and 8.6 million miles (13.8 million kilometers) from Jupiter.The spacecraft’s orbital insertion maneuver will begin with a 35-minute burn of its main engine, which will slow Juno by about 1,200 mph (542 m/s) so it can be captured into a polar orbit around Jupiter. Juno will orbit the gas giant 37 times over 20 months, coming to within 2,900 miles (4,667 km) of its swirling top clouds.

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,” said Kenny Starnes, Juno program manager at Lockheed Martin Space Systems. “But now our greatest challenge lies ahead, as the Jupiter orbit insertion one of the most critical events of the mission. The Jupiter orbit insertion is a [precisely] choreographed dance with the largest planet in our solar system. The spacecraft will arrive at the planet traveling at 130,000 mph (58.1 km/s) 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.”

During its flybys, the spacecraft will use its scientific instruments to probe beneath the clouds to study Jupiter’s auroras and learn more about the planet’s origins, structure, atmosphere, and magnetosphere. Juno‘s investigations will determine how much water is in the gas giant’s atmosphere, which will assist in determining which theory of the planet’s formation is correct, or if new theories are needed.

“At this time last year our New Horizons spacecraft was closing in for humanity’s first close views of Pluto,” said Diane Brown, Juno program executive at NASA Headquarters in Washington. “Now, Juno is poised to go closer to Jupiter than any spacecraft ever before to unlock the mysteries of what lies within.”

Juno’s close approaches during the mission will smash the previous record for Jupiter set in 1974 by NASA’s Pioneer 11 spacecraft of 27,000 miles (43,000 kilometers). Flying this close to Jupiter comes at a considerable risk to the spacecraft.

“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. “[The] 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.”

Graphic showing Juno's mission details as seen on Spaceflight Insider

Graphic showing Juno’s mission details. Image Credit: NASA/JPL-Caltech

Jupiter itself is the source of one of the greatest hazards to the spacecraft. Below the planet’s clouds is a layer of liquid hydrogen under such tremendous pressure that it acts as an electrical conductor. The combination of this metallic hydrogen with Jupiter’s fast rotation creates a powerful, donut-shaped magnetic field that surrounds the planet with electrons, protons, and ions traveling at nearly the speed of light. During its flybys, Juno will encounter 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 at NASA’s Jet Propulsion Laboratory in Pasadena, California. “But, we are ready. We designed an orbit around Jupiter that minimizes exposure to Jupiter’s harsh radiation environment. This orbit allows us to survive long enough to obtain the tantalizing science data that we have traveled so far to get.”

Juno’s polar orbit will resemble a flattened oval. The spacecraft will approach Jupiter over its north pole and then quickly drop to an altitude below the planet’s radiation belts as Juno speeds towards Jupiter’s south pole. Each close flyby is about one Earth day in duration. Then the probe’s orbit will carry it below Jupiter’s south pole and beyond the reach of the planet’s radiation.

Juno is equipped with radiation-hardened electrical wiring and shielding around its many sensors. The spacecraft’s flight computer and the electronics for many of its scientific instruments are inside a specially designed titanium vault. With a weight of nearly 400 pounds (172 kilograms), the vault will reduce exposure to radiation by 800 times of that outside its titanium walls.

While the vault can’t protect the systems forever, Juno‘s unique orbit will allow the radiation dose and the degradation to accumulate slowly, enabling the spacecraft to complete its 20-month scientific mission.

“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, Juno’s Radiation Monitoring Investigation lead. “The constant bombardment will break the atomic bonds in Juno’s electronics.”

Juno launched on August 5 atop a United Launch Alliance (ULA) Atlas V 551 variant booster from Cape Canaveral Air Station’s Space Launch Complex 41 in Florida. The mission is set to conclude in February of 2018, after completing 37 orbits. The spacecraft will then be de-orbited and allowed to burn up in Jupiter’s upper atmosphere in order to avoid any possibility of impact and contamination on one of the Jovian moons.

Video courtesy of NASA/JPL-Caltech


Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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