One day separates us from the moment Juno achieves orbit insertion.
JOI (Jupiter Orbit Insertion) is the final approach phase in which Juno’s main engine starts to burn to reduce its velocity to establish the required orbit.
The Juno spacecraft launched aboard an Atlas V551 rocket from Cape Canaveral, Florida, on August 5, 2011.
Juno’s trajectory to Jupiter consisted of multiple phases over 5 years and one and a half orbits around the sun.
The first phase was a transition from the Launch Phase occurred 3 days after launch and lasted 63 days. During this phase, the spacecraft ran instrument checkouts and antenna deployment and a trajectory correction maneuver.
On Aug. 30, 2012 and Sept. 14, 2012 and beyond Mars’s orbit, Juno performed deep space maneuvers using its main engine. The spacecraft performed instrument checkouts again.
The phase lasted 1.6 years.
After both maneuvers during phase 2, Juno was falling back towards Earth for a gravity assist. The phase lasted for around 5.3 months
Closest approach to Earth occurred on Oct. 9, 2013, at an altitude of 310 miles (500km). It boosted Juno’s velocity by 16,330 mph (about 7.3 kilometers per second), placing the spacecraft on its final trajectory for Jupiter.
This phase is the last part of the space journey to Jupiter. Lasted for 26 months (2 years) from Earth flyby to 6 months before JOI.
Approach phase to Jupiter lasted for the final 6 months of the cruise phase. Here Juno started observing Jupiter and performed checkouts to prepare for JOI.
JOI (Jupiter Orbit Insertion)
The Jupiter Orbit Insertion Phase begins 4 days before the start of the orbit insertion maneuver and ends about 2.5 hours after the start of the insertion maneuver. The burn (insertion maneuver) occurs at the spacecraft’s closest approach to Jupiter and slows it enough to be captured by the giant planet’s gravity into a 53.5-day orbit. If the Jupiter Orbit Insertion burn fails to insert the spacecraft into orbit around Jupiter, there will be no science mission.
The burn occurred on July 5th, 2016 at 0238 UTC and lasted for 35 minutes.
In a Table
Capture Orbit Phase
After the 35 minute burn at Jupiter’s closest approach, Juno will be placed on a 53.5 day orbit that will last for two orbits. During this phase, instruments will be checked, science observations, calibrations and prepare the team to acquire Jupiter science data during the first planned science orbit (Orbit 4).
The Period Reduction Maneuver phase. Juno transitions from a 53.5-day orbit to only 14 days. Much like the previous burn, this will only be for 22 minutes. This burn happens after the second 53.5-day orbit (Orbit 2).
This video animation for the 14-day orbit.
From the end of Orbit 2, Science orbits start from orbit 4 to orbit 36.
Jupiter orbits are highly elliptical polar orbits. For the science to be accurate, Juno has to get closer to Jupiter than any previous missions. Flying over the polar from north to south will reduce Juno’s exposure to radiation allowing it to get as close as 2,600 miles (4,200km) and as far out as 4,900 miles (7,900 km). As Juno exits over the south pole, its orbit carries it far beyond even the orbit of the Jovian moon Callisto.
Juno’s elliptical orbit around Jupiter has another benefit. It allows the spacecraft’s three massive solar panels to be constantly bathed in sunlight. This is important because the amount of sunlight that reaches Jupiter is only 1/25th that which reaches Earth.
This is the final orbit of the mission that is necessary in order to make sure it does not drift away toward Europa and contaminate it with possible bacteria on the spacecraft from Earth. Europa has never been touched and we need it to stay that way for the 2022 exploration mission by ESA.
By orbit 36, a deorbit burn will be executed, placing the spacecraft on a trajectory that will reset its point of closest approach to the planet to an altitude that is below the cloud tops on February 20. 2018. Juno is not designed to operate inside an atmosphere and will burn up.
Fun Fact: Juno is the wife of Jupiter in Roman mythology.
The spacecraft carries three LEGO figures of Galileo, Juno , and Jupiter. They are currently in orbit.
Gelileo, Juno, Jupiter