After almost five years and 1.7 billion miles (2.7 billion km), NASA’s Juno spacecraft successfully entered the orbit around the biggest planetary inhabitant in our Solar System during a 35-minute main engine burn. Confirmation that the engine burn had completed was received Monday, July 4, at 8:53 p.m. PDT (11:53 p.m. EDT, 3:53 a.m. UTC/July 5).
Juno arrives at Jupiter. Image credit: NASA / JPL.
The burn of Juno’s 645-Newton Leros-1b main engine is called Jupiter orbit insertion, or as Juno mission managers refer to it, ‘JOI.’
The burn began on time at 8:18 p.m. PDT (11:18 p.m. EDT, 3:18 a.m. UTC/July 5), decreasing Juno’s velocity by 1,212 mph (542 m per second) and allowing the spacecraft to be captured in orbit around Jupiter.
Soon after JOI was completed, Juno turned so that the Sun’s rays could once again reach the 18,698 individual solar cells that give the spacecraft its energy.
“Juno worked perfectly, which is always nice when you’re driving a vehicle with 1.7 billion miles on the odometer,” said Juno project manager Dr. Rick Nybakken, from NASA’s Jet Propulsion Laboratory.
“JOI was a big step and the most challenging remaining in our mission plan, but there are others that have to occur before we can give the science team the mission they are looking for.”
“Independence Day always is something to celebrate, but today we can add to America’s birthday another reason to cheer – Juno is at Jupiter,” added Dr. Charlie Bolden, NASA administrator.
“And what is more American than a NASA mission going boldly where no spacecraft has gone before? With Juno, we will investigate the unknowns of Jupiter’s massive radiation belts to delve deep into not only the planet’s interior, but into how Jupiter was born and how our entire Solar System evolved.”
“This is the one time I don’t mind being stuck in a windowless room on the night of the 4th of July. The mission team did great. The spacecraft did great. We are looking great. It’s a great day,” said Juno principal investigator Dr. Scott Bolton, from Southwest Research Institute.
Over the next few months, Juno team will perform final testing on the spacecraft’s subsystems, final calibration of science instruments and some science collection.
“Our official science collection phase begins in October, but we’ve figured out a way to collect data a lot earlier than that,” Dr. Bolton said.
“Which when you’re talking about the single biggest planetary body in the Solar System is a really good thing. There is a lot to see and do here.”
Juno launched aboard an Atlas V551 rocket from Cape Canaveral, Florida, on August 5, 2011.
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.
The spacecraft’s main body is approximately 11.5 feet (3.5 m) high and 11.5 feet (3.5 m) in diameter, with a launch mass of 7,992 pounds (3,625 kg).
Juno’s hexagonal two-deck structure uses composite panel and clip construction for decks, central cylinder and gusset panels. Polar mounted off-center spherical tanks provide spinning spacecraft designs with high stability.
For weight savings and redundancy, the spacecraft uses a dual- mode propulsion subsystem, with a bi-propellant main engine and mono-propellant reaction control system thrusters.
The Leros-1b main engine is a 645-Newton bi-propellant thruster using hydrazine-nitrogen tetroxide. Its engine bell is enclosed in a micrometeoroid shield that opens for engine burns. The engine is fixed to the spacecraft body firing aft and is used for major maneuvers and flushing burns.
The 12 reaction control system thrusters are mounted on four rocket engine modules. They allow translation and rotation around three axes. They also are used for most trajectory correction maneuvers.
Juno’s Electrical Power Subsystem manages the spacecraft power bus and distribution of power to payloads, propulsion, heaters and avionics. The power distribution and drive unit monitors and manages the spacecraft power bus, manages the available solar array power to meet the spacecraft load and battery state of charge, and provides controlled power distribution.
Power generation is provided by three solar arrays consisting of 11 solar panels and one MAG boom. Two 55 amp-hour lithium-ion batteries provide power when Juno is off-sun or in eclipse, and are tolerant of the Jupiter radiation environment.
The Juno spacecraft carries a payload of 29 sensors, which feed data to nine onboard instruments.
Eight of these instruments (MAG, MWR, Gravity Science, Waves, JEDI, JADE, UVS, JIRAM) are considered the science payload.
One instrument, JunoCam, is aboard to generate images for education and public outreach.
The Juno mission investment is $1.13 billion in total. This cost includes spacecraft development, science instruments, launch services, mission operations, science data processing and relay support for 78 months.
Juno’s primary goal is to improve our understanding of Jupiter’s formation and evolution. The spacecraft will investigate the planet’s origins, interior structure, deep atmosphere and magnetosphere.
Juno’s study of Jupiter will help us to understand the history of our own Solar System and provide new insight into how planetary systems form and develop in our galaxy and beyond.
During its mission of exploration, Juno will circle the Jovian world on a path that passes over the poles. Because polar orbits are best for mapping and monitoring a planet, many satellites that study Earth follow a similar path. Until now, this type of orbit has not been tried at Jupiter, so Juno will be the first to get a detailed look at the planet’s poles.
Juno will circle the gas giant 37 times, soaring low over the planet’s cloud tops — as close as about 2,600 miles (4,100 km). If Jupiter were the size of a basketball, the equivalent distance would be only one-third of an inch (about 0.8 cm). During these flybys, Juno will probe beneath the obscuring cloud cover of Jupiter.
Juno’s close orbit also enables it to avoid the most intense region of Jupiter’s harmful radiation, which is concentrated in a belt around the planet’s equator. In this region, tiny particles – ions and electrons – zip around at nearly light speed. Even though they’re small, they pack quite the punch, and they can damage a spacecraft’s electronics.
Even with this special orbit, over about a year, the amount of radiation that’s expected to bombard Juno is the equivalent of more than 100 million dental X-rays. This extreme dose of radiation is destructive to electronics and is the main limiting factor for the length of the mission.
To help the spacecraft cope with this hostile environment, Juno’s most sensitive electronics are housed within a titanium vault. Inside the vault, Juno’s hardware will be exposed to radiation about 800 times less intense than outside.
After about a year in orbit, Juno’s mission will be complete and it will be commanded to dive into Jupiter’s atmosphere, where it will burn up like a meteor. This protects Jupiter’s potentially habitable moons from any threat of contamination by hardy microbes that might stow away from Earth.
