Juno (spacecraft)

Juno is a NASA New Frontiers mission currently orbiting the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011, and arrived on July 4, 2016. The spacecraft is in a polar orbit to study Jupiter's composition, gravity field, magnetic field, and polar magnetosphere. Juno will also search for clues about how the planet formed, including whether it has a rocky core, the amount of water present within the deep atmosphere, mass distribution, and its deep winds, which can reach speeds of 618 kilometers per hour (384 mph).

Juno is the second spacecraft to orbit Jupiter, following the Galileo probe, which orbited from 1995 to 2003.

The Juno spacecraft is powered by solar arrays, commonly used by satellites orbiting Earth and working in the inner Solar System, whereas radioisotope thermoelectric generators are commonly used for missions to the outer Solar System and beyond. For Juno, however, three solar array wings, the largest ever deployed on a planetary probe, play an integral role in stabilizing the spacecraft and generating power.[8]

The spacecraft's name comes from Greco-Roman mythology. "The god Jupiter drew a veil of clouds around himself to hide his mischief, but his wife, the goddess Juno, was able to peer through the clouds and see Jupiter's true nature." The mission had previously been referred to by the backronym JUpiter Near-polar Orbiter in a list of NASA acronyms.

Overview

Juno's interplanetary trajectory; tick marks at 30-day intervals.

Juno spacecraft trajectory animation

Juno completed a five-year cruise to Jupiter, arriving on July 4, 2016. The spacecraft traveled over a total distance of roughly 2.8 billion kilometers (18.7 AU; 1.74 billion miles) to reach Jupiter.[11] The spacecraft will orbit Jupiter 37 times over the course of 20 months. Juno's trajectory used a gravity assist speed boost from Earth, accomplished through an Earth flyby in October 2013, two years after its launch on August 5, 2011.[13] On July 5, 2016, the spacecraft performed an orbit insertion burn to slow it enough to allow capture. It will make two 53-day orbits before performing another burn on October 19 that will bring it into a 14-day polar orbit.

Once in the 14-day orbit, infrared and microwave instruments will begin to measure the thermal radiation emanating from deep within Jupiter's atmosphere. These observations will complement previous studies of its composition by assessing the abundance and distribution of water, and therefore oxygen. This data will provide insight into Jupiter's origins. Juno will also investigate the convection that drives general circulation patterns in Jupiter's atmosphere. Other instruments aboard Juno will gather data about its gravitational field and polar magnetosphere. The Juno mission is set to conclude in February 2018, after completing 37 orbits of Jupiter, when the probe will be de-orbited to burn up in Jupiter's outer atmosphere, so as to avoid any possibility of impact and biological contamination of one of its moons.

Flight trajectory

Launch

Juno was launched atop the Atlas V at Cape Canaveral Air Force Station, Florida. The Atlas V (AV-029) used a Russian-designed and built RD-180 main engine, powered by kerosene and liquid oxygen. At ignition it underwent checkout 3.8 seconds prior to the ignition of five strap-on solid rocket boosters (SRBs). Following SRB burnout, approximately 1 minute 33 seconds into the flight, two of the spent boosters fell away from the vehicle, followed 1.5 seconds later by the remaining three. When heating levels had dropped below predetermined limits, the payload fairing that protected Juno during transit through the thickest part of the atmosphere separated, about 3 minutes 24 seconds into the flight. The Atlas V main engine cut off 4 minutes 26 seconds after liftoff. Sixteen seconds later, the Centaur second stage ignited and burned for approximately 6 minutes, putting the satellite into an initial parking orbit.[15] The vehicle coasted for approximately 30 minutes, and then the Centaur was re-ignited for a second firing of 9 minutes, placing the spacecraft on an Earth escape trajectory in a heliocentric orbit.

Prior to separation, the Centaur stage used onboard reaction engines to spin Juno up to 1.4 RPM. About 54 minutes after launch, the spacecraft separated from the Centaur and began to extend its solar panels. Following the full deployment and locking of the solar panels, Juno s batteries began to recharge. Deployment of the solar panels reduced Juno's spin rate by two-thirds. The probe is spun to ensure stability during the voyage and so that all instruments on the probe are able to observe Jupiter.

The voyage to Jupiter has taken five years, which included an Earth flyby on October 10, 2013. On August 12 in 2013, Juno had traveled half of its journey to Jupiter. As it reached the Jovian system, Juno had traveled approximately 19 AU

Cost

Juno was originally proposed at a cost of approximately US$700 million (fiscal year 2003) for a launch in June 2009. NASA budgetary restrictions resulted in postponement until August 2011, and a launch on board an Atlas V rocket in the 551 configuration. As of June 2011, the mission was projected to cost $1.1 billion over its life.[34][dated info]

Scientific objectives

Jupiter imaged using the VISIR instrument on the VLT. These observations will inform the work to be undertaken by Juno.[35]

The Juno spacecraft's suite of science instruments will:[36]

• Determine the ratio of oxygen to hydrogen, effectively measuring the abundance of water in Jupiter, which will help distinguish among prevailing theories linking Jupiter's formation to the Solar System.

• Obtain a better estimate of Jupiter's core mass, which will also help distinguish among prevailing theories linking Jupiter's formation to the Solar System.

• Precisely map Jupiter's gravitational field to assess the distribution of mass in Jupiter's interior, including properties of its structure and dynamics.

• Precisely map Jupiter's magnetic field to assess the origin and structure of the field and how deep in Jupiter the magnetic field is created. This experiment will also help scientists understand the fundamental physics of dynamo theory.

• Map the variation in atmospheric composition, temperature, structure, cloud opacity and dynamics to pressures far greater than 100 bars (10 MPa; 1450 pound/sq inch) at all latitudes.

• Characterize and explore the three-dimensional structure of Jupiter's polar magnetosphere and its auroras.[37]

• Measure the orbital frame-dragging, known also as Lense–Thirring precession caused by the angular momentum of Jupiter,[38][39] and possibly a new test of general relativity effects connected with the Jovian rotation.

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