NASA's Juno spacecraft completed its third close flyby of planet Jupiter on Sunday, Dec. 11, at 12:04 p.m. EST..
At the time of closest approach (called perijove), Juno was about 4,150 km above the gas giant’s roiling cloud tops and traveling at a speed of about 57.8 km/s relative to the planet.
Seven instruments and the spacecraft’s JunoCam were operating during the flyby to collect data that is now being returned to Earth. Mission managers decided not to collect data with the Jovian Infrared Auroral Mapper (JIRAM) instrument during this flyby, to allow the team to complete an update to the spacecraft software that processes JIRAM’s science data. A software patch allowing JIRAM’s operation is expected to be available prior to the next perijove pass on Feb. 2, 2017.
Juno is currently in a 53-day orbit, and its next close flyby of Jupiter will occur on Feb. 2, 2017.
Here is an image taken by the JunoCam imager on Dec 11, which highlights the seventh of eight pearls on Jupiter; the “pearls” are massive counterclockwise rotating storms that appear as white ovals in the gas giant's southern hemisphere.
Juno’s History
After its arrival at Jupiter on July 4, 2016, Juno was planned to complete two 53 day orbits and then transfer to a 14-day orbit for the next 17 months after its second flyby (perijove 2) on Oct 19. The team intended to precede the flyby with a period reduction maneuver (PRM) - a main engine burn designed to reduce the spacecraft’s orbital period from 53 days to 14. This would increase the frequency of Jupiter flybys, allowing the science team to collect data more rapidly.
But as they were pressurizing the system in preparation for the burn in October, the team noticed an anomaly in an engine valve system and decided to postpone the PRM. Telemetry indicated that two helium check valves, that are part of the fuel pressurization system of the spacecraft's main engine, did not operate as expected during a command sequence that was initiated by ground control. The valves should have opened in a few seconds, but it took several minutes.
The team then proposed turning perijove 2 into a science pass: they would turn on the science instruments and collect data as they flew past Jupiter. That plan had to be abandoned on October 18 when the spacecraft unexpectedly went into safe mode 13 hours before its closest approach. The spacecraft apparently detected an unexpected condition, rebooted, turned off all unnecessary subsystems—which included the science instruments—and then pointed at the Sun to link up communications with Earth.
The system was successfully recovered and brought out of safe mode a week later on Oct 24. In preparation for the December flyby, Juno executed an orbital trim maneuver using its smaller thrusters. The burn, which lasted just over 31 minutes, changed Juno’s orbital velocity by about 2.6 meters per second and consumed about 3.6 kg of propellant.
Juno Status
On Sunday, Dec 11, Juno made a successful third flyby (perijove 3), all but one instrument faithfully executing their missions.
The main engine burn is not planned at this time; NASA engineers are still evaluating if and when they will perform the orbit maneuver. The spacecraft is otherwise healthy and performing its mission. NASA engineers are wary of adding unnecessary risk to the mission, so they are moving forward carefully.
Until the orbit maneuver is done, Juno will be able to collect essentially the same science in a 53-day orbit as it would in the planned 14-day orbit. The mission can continue using the 53-day orbit until the end of the mission. The only significant issue lies several years ahead: if the spacecraft is still in the 53-day orbit by mid-2019, it will end up in Jupiter’s shadow for an eclipse of roughly six hours. As the first solar-powered spacecraft to operate around an outer planet, this lack of sunlight could be a concern.
Juno Spacecraft and Mission
The Juno spacecraft was launched on Aug. 5, 2011, from Cape Canaveral, Florida, and arrived at Jupiter on July 4, 2016.
During its mission of exploration, Juno will soar low over the planet's cloud tops -- as close as about 4,100 km. During these 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.
Juno will be the second spacecraft to orbit Jupiter, following the nuclear powered Galileo orbiter which orbited from 1995–2003. Other spacecraft have visited Jupiter to get gravity assisted sling shots en route to outer planets.
Unlike all earlier spacecraft to the outer planets, that have used radioisotope thermoelectric generators, Juno is powered only by solar arrays. The Juno spacecraft uses three solar panels with a combined mass of 340 kg; each panel is 2.7 by 8.9 meters long, the biggest on any NASA deep-space probe. About 486 W is generated by the panels while in orbit around Jupiter; the power will decline to 420 W over time as radiation degrades the cells.
Juno’s main computer is based on the radiation hardened RAD750 flight processor with 256 megabytes of flash memory and 128 megabytes of DRAM local memory.
In addition to special radiation-hardened electrical wiring and shielding to protects its sensors, Juno carries a first-of-its-kind 1-centimeter-thick 180 kg titanium vault, to protect the spacecraft's flight computer and the electronic hearts of many of its science instruments.T
Juno’s orbits are designed to fly around the harshest regions of Jupiter’s monstrous radiation belts. The magnetosphere of Jupiter is the cavity created in the solar wind by the planet's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System. Scientists believe that the combination of 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. This is far more intense than the radiation experienced by earth orbiting satellites.
There are 67 known moons of Jupiter. The most massive of the moons are the four Galilean moons, which were independently discovered in 1610 by Galileo Galilei and Simon Marius — Io, Europa, Ganymede, and Callisto.
Jupiter (and Juno) is currently at a distance of 864 million km from Earth; it take a signal 48 minutes to travel from Juno to Earth and vice-versa.
Juno's name comes from Greek and Roman mythology. The 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 — NASA.
The mission had previously been referred to by the backronym JUpiter Near-polar Orbiter.
In mythology, Juno is an ancient Roman goddess, the protector and special counselor of the state. She is a daughter of Saturn and sister (but also the wife (go figure)) of the chief god Jupiter and the mother of Mars and Vulcan. Juno also looked after the women of Rome.
Here is a video from NASA on Juno -
End of Mission
Juno’s end of mission is planned for Feb 2018 with a controlled de-orbit and disintegrate into Jupiter's atmosphere. During the mission, the spacecraft will be exposed to high levels of radiation from Jupiter's magnetosphere, which may cause future failure of certain instruments and risk collision with Jupiter's moons. The controlled deorbit will eliminate space debris and risks of contamination in accordance with NASA's Planetary Protection Guidelines.
The mission period will probably get extended if Juno stays in its 53-day orbit much longer.
Mission Extension to Europa
There are proposals being studied to extend Juno’s mission to explore Europa. The extension would modify Juno’s orbit around Jupiter such that it would provide close flybys over Europa. A final extension would put Juno in a circular orbit around Europa itself. All this would require the main engine to be operational.
A Few Mission Videos
As can be seen from the first video, after traveling for two years, Juno returned to pass by Earth in October 2013. It used Earth's gravity to help propel itself toward the Jovian system in a maneuver called gravitational slingshot. The spacecraft received a boost in speed of more than 14,000 km/h. Earth a lost a tiny bit of its orbital speed around the Sun, nothing to lose sleep over.
NASA News
To no one’s surprise, NASA has been named the “Best Place to Work” among large agencies in the federal government for an impressive fifth year in a row. The annual results of this survey of federal workers is published by the Partnership for Public Service. It ranks nearly 400 federal organizations by overall employee satisfaction and commitment, and also evaluates key workplace focus areas, such as innovation, training and development, leadership and diversity. blogs.nasa.gov/…
Concluding Remarks
It is important we make sure that Congress provides adequate funds for space and science research and not let needless tax cuts for the super-rich bulldoze away our future. Let’s stay abreast of budget fights and write to our Congress person.
Also, let’s make sure that our fellow citizens, especially our children, understand and work with science, instead of faith based mumbo-jumbo peddled by the right. Science will set our minds free.
References
- NASA Juno website — www.nasa.gov/…
- NASA JPL Juno mission website — www.jpl.nasa.gov/…
- Juno wiki — en.wikipedia.org/…
- Jupiter wiki — en.wikipedia.org/...
- NASA to Hold Media Call on Evidence of Surprising Activity on Europa — www.dailykos.com/...
Notes
My other SciTech diaries are listed at www.dailykos.com/...