What to expect from JunoCam at Jupiter

Juno will go in to orbit at Jupiter on July 5 (July 4 in North and South American time zones), and it's carrying a camera that's going to take really awesome photos of Jupiter. But you're going to have to be patient. We won't be able to see spectacular views of Jupiter's belts and zones from Jupiter orbit until the very end of August, and it'll be November before we'll see automated release of high-resolution raw images. Want to know what to expect from JunoCam, when, and where to find it? This post is for you.

A brief JunoCam primer: The Juno spacecraft did not need a camera to accomplish its science goals. But everyone recognized that it would be a crime to send a spacecraft to Jupiter and not include a camera. Thus NASA procured JunoCam from Malin Space Science Systems for public outreach purposes. The head of the JunoCam team is Candy Hansen, of the Planetary Science Institute. JunoCam is a very small instrument; its electronics are based on the small boxes developed for Curiosity's science cameras. Its camera head looks very similar to Curiosity's MARDI, but JunoCam is much heavier because it has additional shielding to protect it from Jupiter's radiation environment. Its wide (58-degree) field of view is selected to allow it to take in all of Jupiter's globe when Juno is flying close over the Jovian poles at about an hour before and an hour after its closest approach on every science orbit. It's mounted to the side of Juno, which continuously spins at 2 rotations per minute. It can take images in RGB color or through an infrared filter sensitive to the presence of methane, which will highlight Jupiter cloud features. To take images, JunoCam uses the rotation of the spacecraft to sweep its view along, building up image swaths. To get super technical, it's a pushframe camera that uses time-delay integration to build up adequate signal despite the low light levels and rapidly rotating spacecraft. For the gory details, you can read this open-access paper describing it.

Key JunoCam Jupiter imaging points:

• Everything described in this post is planned imaging. Plans could change due to a variety of unforeseen circumstances. 
• During approach and early orbits, JunoCam will take hundreds of sequential image frames that can be assembled into three different movies: the "Approach Movie", the "Marble Movie", and the "One-Orbit Movie." More details on these movies below. During the science mission (which begins on November 9), Juno will acquire data less frequently: 5 to 20 images on each 14-day orbit, mostly around perijove.
• JunoCam's wide field of view means that most of the time, its photos of Jupiter will be quite small. It can achieve higher resolution than most amateur astrophotos only when it is within roughly a million kilometers of the planet. (As a general rule of thumb, divide 210 by the range to Jupiter in millions of kilometers and you'll get Jupiter's apparent diameter to JunoCam, in pixels.)
• No high-resolution Jupiter photos will be taken during Jupiter orbit insertion on July 5. JunoCam and all the science instruments will be turned off from 5 days before Jupiter arrival until 2 days after Jupiter arrival. Jupiter arrival is also called Perijove 0.
• Juno's orbit is highly elliptical, so it spends almost all of its time much farther than a million kilometers from Jupiter. During the science mission, it will only get moderately high-resolution photos of Jupiter within a two-day period around each perijove.
• Truly detailed photos -- ones in which Jupiter appears bigger than the full JunoCam field of view, and in which Juno can see more detail than Cassini did during its one Jupiter flyby -- are only possible within a two-hour period around each perijove.
• The next time after Perijove 0 that Juno will be within a million kilometers of Jupiter is on August 27, beginning about 12 hours before Perijove 1. All the science instruments will operate through Perijove 1. August 27 should be a fantastic day for JunoCam!
• JunoCam photos received on Earth will not be automatically posted to the mission website until some time after Perijove 1 and possibly as late as Perijove 3. That is to say, automated raw image release is planned to begin some time in September or October. Other images will be released before that, but not all of them, and after some delay. Once automated image release does begin, all of the images that Juno has taken will be made available to the public.
• Because Juno has to do a large rocket maneuver on Perijove 2 (October 20), JunoCam will be turned off for the 48 hours around Perijove 2, and therefore JunoCam will take no high-resolution images from JunoCam between its departure from Perijove 1 and its approach to Perijove 3.
• So the first time we will see high-resolution images automatically released to the JunoCam website will be after Perijove 3, which happens on November 2.
• Keep in mind that, like all deep-space missions, Juno doesn't transmit all its data in real time. Image data will trickle to Earth hours to days after it's acquired.
• When the Juno mission does begin automated release of raw images, you will be able to find them here.
• After images from Perijove 3 become available (after November 2), the public can start participating in online voting to select targets for JunoCam imaging for Perijove 4 (which will happen on November 16). Because it's a public outreach instrument, the JunoCam team has committed to allowing the public to choose where most of its highest-resolution Jupiter images will be targeted.
• You can already participate in online discussion about features visible on Jupiter on the JunoCam website, thanks to the wonderful efforts of amateur astrophotographers taking photos of Jupiter for the Juno mission.

Here's a photo that JunoCam took during the Earth flyby on October 9, 2013, to whet your appetite for the quality of images that we will eventually get from JunoCam, come August.

Here's a diagram of Juno's Jupiter trajectory. Following are a few more detailed notes on what the JunoCam team has planned.

Approach Movie (acquisition dates: June 12-29, 2016)

As I write this, Juno is now in the Jupiter Approach phase of its mission. As Juno closes from 16 million kilometers away from Jupiter on June 12 to 5 million kilometers away from Jupiter on June 29, JunoCam will capture color photos covering one entire spacecraft rotation at a rate of 2 to 4 times per hour. During this time, Jupiter will grow from about 13 to about 40 pixels in diameter, but Juno will be seeing it at half-full phase. The wide field of view will encompass the orbits of all of Jupiter's moons out to Callisto, so the main attraction of this movie will be the fun of watching Jupiter's large moons orbiting the planet. The movie is planned to cover 17 days, which one complete Callisto orbit (2.4 Ganymede orbits, 4.8 Europa orbits, and 9.6 Io orbits).

This is a lot of data; even one day's worth of data is more than JunoCam can store in its buffer. All the data will have to be relayed to Earth more than once a day in order to keep making room for new images. If there are any interruptions in data receipt (if, for instance, there is bad weather or an equipment failure at a Deep Space Network station), some frames from the movie may be lost and won't be able to be retransmitted. The Juno team plans to wait for the complete downlink of all of the Approach Movie frames before releasing the images, so don't bother to start looking for it until the day of orbit insertion.

Marble Movie (acquisition dates: July 11-August 26 and August 28-September 23 and September 30-October 18)

Each of Juno's first two elliptical loops around the planet will take 53.5 days to complete. For most of that time, JunoCam will be acquiring about 5 full-color images per hour, watching Jupiter spin from a distance. The planet will appear less than 50 pixels across for the great majority of that time. The movie will run from July 11 to October 18 with two interruptions. The first interruption happens around August 27, during Perijove 1. (JunoCam will be acquiring images then, but not ones timed to continue the movie.) The second interruption happens from September 23 to 30, when Jupiter will be passing through solar conjunction. When spacecraft pass through solar conjunction, controllers on Earth can't reliably communicate with them, so spacecraft are usually put into a lower-activity state to minimize the risk that they'll need intervention from Earth during that period. So JunoCam won't acquire data during conjunction. That period happens to coincide with Juno's apojove on September 23, so Jupiter would appear at its smallest then, anyway. The Marble Movie will end shortly before Perijove 2 (which is on October 19). The Marble Movie will provide the JunoCam team with up-to-date maps of Jupiter. During conjunction, Jupiter is too close to the Sun in the sky for Earth-based astronomers to photograph it, so JunoCam's images will be the only information we can get on Jupiter's atmospheric dynamics throughout this period

Here is how Jupiter's apparent size will vary throughout the Marble Movie. These numbers are for the whole Jupiter disk, but Jupiter will only appear half-full to Juno.

• July 11: 47 pixels
• July 18: 31 pixels
• July 25: 27 pixels
• August 1: 26 pixels
• August 8: 27 pixels
• August 15: 32 pixels
• August 22: 48 pixels
• August 26: >100 pixels
• August 28:
• September 4: 41 pixels
• September 11: 30 pixels
• September 18: 27 pixels
• September 25: 26 pixels (conjunction overlaps with apojove)
• October 2: 28 pixels
• October 9: 34 pixels
• October 16: 61 pixels

Perijove 1 (August 26-28)

Because all the science instruments must be turned off for Perijove 0, Perijove 1 will be the first opportunity that they have to operate close to Jupiter. The scientists won't find out how well their instruments work up close to Jupiter until Perijove 1, so this is a really important day for the mission. JunoCam will be commanded to take a wide variety of different types of observations in order to test out its capabilities and different operational modes. It will get polar images of Jupiter with the globe just filling the frame and then do lots of closer imaging of Jupiter, which should show cool cloud features. The orbital path takes Juno close to the terminator -- the boundary between day and night on Jupiter -- so it's possible that tall clouds that poke up vertically might cast shadows that JunoCam could see. JunoCam will try to image the rings, and will also attempt to photograph Ganymede from a distance near 500,000 kilometers. Perijove 1 will be the first time that JunoCam will be able to acquire images more detailed than we can get from Earth.

One-Orbit Movie (October 21-November 2, including Perijove 3)

On Perijove 2 (October 19), Juno will conduct a large Period Reduction Maneuver, a rocket burn that will shorten its elliptical path around Jupiter to one that takes only 14 days to complete. A few days after this maneuver, there will be one final, much smaller rocket burn to clean up any mismatch between Juno's actual and desired science orbits. Once that final burn is safely out of the way, JunoCam will be clear to turn on and take regular photos of Jupiter for its third and final movie. It will acquire frames for this movie through Apojove 2 and Perijove 3, so the "One-Orbit Movie" will be the first movie that will include regular frames during Juno's closest approach to Jupiter. You might also hear the JunoCam team referring to this as the "Zoom Movie," because JunoCam will appear to zoom all the way in to Jupiter, with the planet more than filling the field of view. The JunoCam team may also perform a few more experiments with different kinds of imaging near close approach, the way they did on Perijove 1, but these will be fit among movie frames.

Public-directed targeted imaging (November 3, 2016 until the radiation death of JunoCam or the end of the last science orbit, February 14, 2018)

The images that Juno captures during Perijove 3, combined with images taken by amateur astrophotographers from Earth, will be combined to make a map of Jupiter. Anybody who registers on the JunoCam website can select, discuss, and vote for which spots on this map of Jupiter they would like JunoCam to take images of during the next perijove.  Voting for Perijove 4 targets will open on Friday, November 4, and close on Wednesday, November 9. From then on, public voting for JunoCam targets will open every other Friday and close every other Wednesday. Based on the ranking of targets, engineers at Malin Space Science Systems will generate commands for JunoCam to take images covering those targets. (In some cases, two or more targets that are very close to each other might be able to be covered by a single JunoCam image.) Once those commands are written, they are run through a program that estimates the data volume of the resulting images. The final commands will include everything JunoCam can acquire within whatever its data volume limit is for each perijove. The actual number of images that JunoCam will get on each perijove pass depends on their compression ratio -- the more detail there is in an image, the less it can be compressed. There will probably be between 5 and 20 targeted JunoCam images per perijove pass.

Since it's not a science instrument, JunoCam wasn't required to be heavily shielded enough to guarantee its survival throughout the prime science mission. It is shielded, but the Jupiter radiation environment is a nasty one, and JunoCam will suffer radiation damage over time. It was designed to withstand 8 Jupiter orbits, which roughly coincides with the end of 2016. Still, it's more likely to be a slow death (a steady increase in noise) than a sudden failure. We'll probably see degradation of the quality of JunoCam images in 2017, but hopefully the camera will hold up well enough to continue to operate for many more science orbits and voting rounds before Jupiter finally kills the camera. If we're lucky, JunoCam will survive until February 21, 2018, when Juno will plunge into Jupiter, on Perijove 37.

Here's a table of major events to look forward to on the Juno mission.

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