NASA’s Juno spacecraft soared directly over Jupiter’s south pole when JunoCam acquired this image on Feb. 2, 2017, from an altitude of about 62,800 miles (101,000 kilometers) above the cloud tops. This image was processed by citizen scientist John Landino. This enhanced color version highlights the bright high clouds and numerous meandering oval storms.

Credits: NASA/JPL-Caltech/SwRI/MSSS/John Landino

JunoCam raw images

NASA’s Juno mission to Jupiter, which has been in orbit around the gas giant since July 4, 2016, will remain in its current 53-day orbit for the remainder of the mission. This will allow Juno to accomplish its science goals, while avoiding the risk of a previously-planned engine firing that would have reduced the spacecraft’s orbital period to 14 days.

“Juno is healthy, its science instruments are fully operational, and the data and images we’ve received are nothing short of amazing,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “The decision to forego the burn is the right thing to do – preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Juno has successfully orbited Jupiter four times since arriving at the giant planet, with the most recent orbit completed on Feb. 2. Its next close flyby of Jupiter will be March 27.

The orbital period does not affect the quality of the science collected by Juno on each flyby, since the altitude over Jupiter will be the same at the time of closest approach. In fact, the longer orbit provides new opportunities that allow further exploration of the far reaches of space dominated by Jupiter’s magnetic field, increasing the value of Juno’s research.

During each orbit, Juno soars low over Jupiter’s cloud tops – as close as about 2,600 miles (4,100 kilometers). During these flybys, Juno probes beneath the obscuring cloud cover and studies Jupiter’s auroras to learn more about the planet's origins, structure, atmosphere and magnetosphere.

The original Juno flight plan envisioned the spacecraft looping around Jupiter twice in 53-day orbits, then reducing its orbital period to 14 days for the remainder of the mission. However, two helium check valves that are part of the plumbing for the spacecraft’s main engine did not operate as expected when the propulsion system was pressurized in October. Telemetry from the spacecraft indicated that it took several minutes for the valves to open, while it took only a few seconds during past main engine firings.

“During a thorough review, we looked at multiple scenarios that would place Juno in a shorter-period orbit, but there was concern that another main engine burn could result in a less-than-desirable orbit,” said Rick Nybakken, Juno project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “The bottom line is a burn represented a risk to completion of Juno’s science objectives.”

Juno’s larger 53-day orbit allows for “bonus science” that wasn’t part of the original mission design. Juno will further explore the far reaches of the Jovian magnetosphere – the region of space dominated by Jupiter’s magnetic field – including the far magnetotail, the southern magnetosphere, and the magnetospheric boundary region called the magnetopause. Understanding magnetospheres and how they interact with the solar wind are key science goals of NASA’s Heliophysics Science Division.

"Another key advantage of the longer orbit is that Juno will spend less time within the strong radiation belts on each orbit,” said Scott Bolton, Juno principal investigator from Southwest Research Institute in San Antonio. “This is significant because radiation has been the main life-limiting factor for Juno.”

Juno will continue to operate within the current budget plan through July 2018, for a total of 12 science orbits. The team can then propose to extend the mission during the next science review cycle. The review process evaluates proposed mission extensions on the merit and value of previous and anticipated science returns. 

The Juno science team continues to analyze returns from previous flybys. Revelations include that Jupiter's magnetic fields and aurora are bigger and more powerful than originally thought and that the belts and zones that give the gas giant’s cloud top its distinctive look extend deep into the planet’s interior. Peer-reviewed papers with more in-depth science results from Juno’s first three flybys are expected to be published within the next few months. In addition, the mission's JunoCam – the first interplanetary outreach camera – is now being guided with assistance from the public. People can participate by voting on which features on Jupiter should be imaged during each flyby.

“Juno is providing spectacular results, and we are rewriting our ideas of how giant planets work,” said Bolton. “The science will be just as spectacular as with our original plan.”

JPL manages the Juno mission for NASA. The mission’s principal investigator is Scott Bolton at Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, for the Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is managed for NASA by Caltech in Pasadena, California. 

Quelle: NASA

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Update: 21.02.2017

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NASA made the decision to leave the Juno spacecraft, currently orbiting Jupiter, in its current orbit that cycles around the gas giant every 53 days.  The choice hinges on worries surrounding Juno's main engine, which displayed some out-of-the-ordinary readings as the team was preparing to shorten the probe's orbit.

“Juno is healthy, its science instruments are fully operational, and the data and images we’ve received are nothing short of amazing,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “The decision to forego the burn is the right thing to do – preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Juno's original mission plan entailed arriving and Jupiter and performing two 53-day orbits.  Then it would fire its main engine and reduce its orbit to 14 days, making more close passes of Jupiter.  Those "science passes" are where most of the work gets done, but as the probe was preparing to shorten its orbit, the team found anomalous readings from the engine.

 

"We wanted to take a really good look at that," said Keith Robinson, Juno's mission manager at the Marshall Space Flight Center in Huntsville, Alabama.  "We've got a very valuable asset doing very well."

For the past few months, Juno's mission team at the Jet Propulsion Laboratory in California has been working with Robinson and other NASA staff have been looking at the options and weighing the risks and benefits associated with leaving Juno in its current orbit or firing the main engine.

"We do a piece of it here with the resources we have available and then it all goes into a decision made by the Planetary Science Division at headquarters," Robinson said.

The final decision came on February 17, when NASA HQ decided that firing the engine would be too risky.  Juno will remain in its 53 day orbit through the remainder of its mission.

“During a thorough review, we looked at multiple scenarios that would place Juno in a shorter-period orbit, but there was concern that another main engine burn could result in a less-than-desirable orbit,” said Rick Nybakken, Juno project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “The bottom line is a burn represented a risk to completion of Juno’s science objectives.”

 

But it's not all bad news.  The current orbit avoids the majority of Jupiter's radiation belts, which are an object of concern among the mission team because the strong radiation could fry the onboard electronics.  

"Another key advantage of the longer orbit is that Juno will spend less time within the strong radiation belts on each orbit,” said Scott Bolton, Juno principal investigator from Southwest Research Institute in San Antonio. “This is significant because radiation has been the main life-limiting factor for Juno.”

There's also an opportunity for some "bonus science."  While Juno will still be able to do most of its mission, it will do it slower because of the lower frequency of close passes.  But from its current orbit, Juno has a better view of Jupiter's magneosphere, which creates the gas giant's strong magnetic fields. 

Quelle: SPACE ALABAMA

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Update: 16.03.2017

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What Should NASA's Jupiter Probe Photograph? Cast Your Vote!

Starting today (March 15), citizen scientists can help decide what the Juno spacecraft will photograph during its next flyby of Jupiter.

On board Juno is an instrument called JunoCam that has already snapped some truly amazing images of the swirling surface of Jupiter's cloudy atmosphere. The raw images from JunoCam are uploaded to the project website, and citizen scientists can download and process those images as they see fit. The processed images have ranged from scientific to artistic. 

The JunoCam project is primarily an outreach effort, aimed at letting members of the public participate in multiple aspects of a space exploration mission. In addition to having access to the raw images, members of the public can make suggestions about what JunoCam should photograph during the close flybys. Other members can then vote on those suggestions, and the JunoCam team selects the final targets based on those votes. The current voting period starts today (March 15) and ends on March 20. 

 

Juno is currently on a 53-day orbit of Jupiter; its next close approach will take place on March 27. No other probe in history has ever come this close to the Jovian giant. The spacecraft must orbit Jupiter in a very elongated loop that allows the probe to slip in between the planet and a belt of intense radiationthat surrounds it. Orbiting inside that radiation belt would quickly destroy the spacecraft and the electronics on board. 

Because of this deliberate orbital path, Juno only spends a matter of hours in close proximity to Jupiter. In addition, the spacecraft is rotating, so JunoCam can only take pictures when its "eye" is facing the planet. (The instrument has no moving parts.) JunoCam also has a limited amount of data storage — another restriction on the number of images it can capture during a given flyby. 

"We take the highest-vote recipient, schedule that and calculate the data volume the image will require," Candy Hansen, a Juno co-investigator and head of the JunoCam team, told Space.com. "Then we move to the next-highest vote getter in the list, schedule that one and continue scheduling images until we run out of data volume."

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