B Discussing Juno/JunoCam Mission and Jupiter Data

[lpetrich]

Some pages on spacecraft navigation:

The Navigators: How We Fly Spacecraft Around the Solar System - Universe Today
How do space probes navigate large distances with such accuracy and how do the mission controllers know when they've reached their target? - Scientific American
Basics of Space Flight Section II. Space Flight Projects
Spacecraft Navigation

There are several sorts of data that spacecraft navigators use.

• Pictures of the spacecraft . That's mainly useful in low Earth orbit. It gives the spacecraft 's direction relative to the stars from the observation site.
• Radio ranging. A round trip of a signal gives the spacecraft 's distance.
• Radio range rate. Doppler shift of the signal frequency gives the spacecraft 's radial velocity.
• Radio ranging with receivers in different positions, like on different continents. The relative arrival times and radial velocities can be combined to find the spacecraft 's direction.
• Optical navigation. The spacecraft takes an overexposed picture of a nearby celestial body, the overexposure being for seeing stars in nearby directions. This gives the body's direction, and if the body was resolved, its distance.

They then compare their data with their calculated positions and velocities for the spacecraft , and improve their calculations with it.

For doing the calculations, they typically do numerical integration, though analytic approximations are often good starting points. Approximations like the Newtonian two-body problem. For going from the Earth to Mars, one starts with geocentric calculations, then switches to heliocentric calculations for most of the trip, then switches to areocentric calculations at Mars.

They have to take into account not only celestial bodies' gravity, but also the pressure of sunlight and the solar wind. But they have gotten very good at that, and they also maintain very precise ephemerides, tables of the celestial bodies' positions. One can use spacecraft navigation data as inputs for those also.

 

[lpetrich]

One can get not only planets' masses with spacecraft , but also planets' departures from sphericity. Planets' equatorial bulges pull on spacecraft , and this causes their orbits to precess. How much precession gives how much material is in the bulge, and that in turn gives clues as to the planets' internal structures. One can get more fine-grained gravity data in this way, data that revealed the presence of mass concentrations or "mascons" in the Moon.

However, such gravity data is essentially 2D and not 3D, so it has limits.

A planet's gravitational field can be given by a multipole expansion, where one finds the expansion's coefficients. One then finds those coefficient values from how the planet fields affect spacecraft orbits.

V = - \frac{GM}{r} \left( 1 - \sum_{l=2}^\infty J_l \left( \frac{R}{r} \right)^l P_l(\hat r \cdot n) \right)

for mass M, equatorial radius R, spin-axis direction n, and Legendre polynomials P. There are additional terms with variation in the azimuthal coordinate.

One of the purposes of the Juno mission is to try to get improved values of Jupiter's gravity's multipole coefficients. These values can then be compared to the results of internal-structure calculations.

 

[1oldman2]

Awesome posts ! Thanks.

 

[1oldman2]

The first raw images have been released, If anyone is planning on using the processing aspect of Junocam this might be good practice. they can be downloaded at. https://www.missionjuno.swri.edu/media-gallery/jupiter-approach

 

[dragoneyes001]

like the first pic from juno just one question being out in space without any light wouldn't the star field be super visible in the background?

 

[OmCheeto]

like the first pic from juno just one question being out in space without any light wouldn't the star field be super visible in the background?

From my experience of the Dawn mission photographing Ceres, my guess is no.
The only time I remember seeing stars was from a composite image.

Good question though.
I asked the same thing last year about Ceres, and got the following response:

June 4, 2015
Marc Rayman, director and chief engineer for NASA's Dawn mission; "... For the approach phase images, we used two different camera integration times (what most people call exposure times). One value was chosen to ensure Ceres was correctly exposed and the other was chosen to bring out the background stars. The images alternate, so we interpolate to get Ceres' location relative to stars. ..."​

[ref: PF]

Ah ha! Just found the explanation of the image I was referring to.

But, I'm afraid I'm not much of an astronomer, so I don't quite understand how "apparent magnitude" works.
Does Jupiter get brighter as you get closer?

Anyways, here's a list of the "apparent magnitude" of Jupiter and the 4 brightest stars:

Jupiter at brightest: -2.7
Sirius: -1.46
Canopus: -0.72
Rigil Kentaurus: -0.27
Arcturus: -0.04​

My guess is, that Sirius would probably show up, if the camera were pointed in the right direction.

 

[dragoneyes001]

From my experience of the Dawn mission photographing Ceres, my guess is no.
The only time I remember seeing stars was from a composite image.

Good question though.
I asked the same thing last year about Ceres, and got the following response:

June 4, 2015
Marc Rayman, director and chief engineer for NASA's Dawn mission; "... For the approach phase images, we used two different camera integration times (what most people call exposure times). One value was chosen to ensure Ceres was correctly exposed and the other was chosen to bring out the background stars. The images alternate, so we interpolate to get Ceres' location relative to stars. ..."​

[ref: PF]

Ah ha! Just found the explanation of the image I was referring to.

But, I'm afraid I'm not much of an astronomer, so I don't quite understand how "apparent magnitude" works.
Does Jupiter get brighter as you get closer?

Anyways, here's a list of the "apparent magnitude" of Jupiter and the 4 brightest stars:

Jupiter at brightest: -2.7
Sirius: -1.46
Canopus: -0.72
Rigil Kentaurus: -0.27
Arcturus: -0.04​

My guess is, that Sirius would probably show up, if the camera were pointed in the right direction.

thanks

 

[1oldman2]

From my experience of the Dawn mission photographing Ceres, my guess is no.
The only time I remember seeing stars was from a composite image.

Hi Om, Marc pretty well described what's going on in the paragraph quoted from your link,
"Ceres is the bright spot in the center of the image. Because the dwarf
planet is much brighter than the stars in the background, the camera team
selected a long exposure time to make the stars visible. The long exposure
made Ceres appear overexposed, and exaggerated its size; this was
corrected by superimposing a shorter exposure of the dwarf planet in the
center of the image."
The brightness of background objects (stars etc. is relative to the object being targeted as far as "brightness", kind of like how Occator glowed so brightly in the earliest images. It's also why in the feed from the ISS no stars are visible.

 

[D H]

But, I'm afraid I'm not much of an astronomer, so I don't quite understand how "apparent magnitude" works.
Does Jupiter get brighter as you get closer?

Yes, it does. That's the reason for using apparent magnitude as opposed to absolute magnitude. Absolute magnitude does not change with distance. Apparent magnitude does change with distance, in an inverse square manner.

 

[1oldman2]

Finally ! Juno's about to go inbound for a practice run with the science payload operating,
http://www.nasa.gov/feature/jpl/five-years-post-launch-juno-is-at-a-turning-point
Juno's science instruments were turned off during orbit insertion, to simplify spacecraft
operations during that critical maneuver. In contrast, all the instruments will be collecting data
during the Aug. 27 pass, which serves as a trial run before the mission gets to work collecting
the precious data it came for.

 

[Clever Penguin]

Finally ! Juno's about to go inbound for a practice run with the science payload operating,
http://www.nasa.gov/feature/jpl/five-years-post-launch-juno-is-at-a-turning-point
Juno's science instruments were turned off during orbit insertion, to simplify spacecraft
operations during that critical maneuver. In contrast, all the instruments will be collecting data
during the Aug. 27 pass, which serves as a trial run before the mission gets to work collecting
the precious data it came for.

I can't wait. I hope it takes the scenic route...

 

[1oldman2]

I hope it takes the scenic route...

The route is guaranteed "scenic" (and the science is going to be super)... just a thought, super science sounds like something on a McDonald's menu, probably not the dollar menu either.

 

[enorbet]

Oh yes the Science does indeed promise to be super-sized. Juno will hit ~260,000 kph (yes, 4 zeroes) fastest unmanned human made object ever and already there is apparently some evidence supporting the hypothesis that "some sort of sonic event" from the insane turbulence below (think mega thunder!) as a contributing factor to higher than accounted for temps in upper atmosphere.

Someone said they would be disappointed if Juno didn't gather moon data but I am pleased this is a very singularly focused mission. Lots of answers and new questions about how our Solar System and others with gas giants, formed. Just terribly exciting stuff!

 

[1oldman2]

New imaging data dump from juno here.
https://www.missionjuno.swri.edu/junocam/processing?id=40
https://www.missionjuno.swri.edu/junocam/processing

Every year there is a period of time that Jupiter is too close to the sun for earth-based astronomers to
observe. This year that time co-incides with Juno’s initial large orbits of Jupiter. Ordinarily we would not
take images with JunoCam during this time however in the absence of our amateur ground-based
support we are collecting RGB images 4 times per hour. We call this the "marble movie" because Jupiter
is so small in the image. We have enough resolution to see if something major happens, like the
disappearance of the Great Red Spot, or the fading of the South Equatorial Belt. We are also imaging
Jupiter through our methane filter.

 

[1oldman2]

Closest pass to Jupiter during the entire mission coming up, It seems likely a portion of the data will be useful modeling the formation and life of exo-planets such as Proxima B, as well as solar system dynamics in general.
From, http://www.nasa.gov/feature/jpl/nasas-juno-to-soar-closest-to-jupiter-this-saturday

This Saturday at 5:51 a.m. PDT, (8:51 a.m. EDT, 12:51 UTC) NASA's Juno spacecraft will get
closer to the cloud tops of Jupiter than at any other time during its prime mission. At the
moment of closest approach, Juno will be about 2,500 miles (4,200 kilometers) above Jupiter's
swirling clouds and traveling at 130,000 mph (208,000 kilometers per hour) with respect to the
planet. There are 35 more close flybys of Jupiter scheduled during its prime mission (scheduled
to end in February of 2018). The Aug. 27 flyby will be the first time Juno will have its entire suite
of science instruments activated and looking at the giant planet as the spacecraft zooms past.

While the science data from the pass should be downlinked to Earth within days, interpretation
and first results are not expected for some time.

"No other spacecraft has ever orbited Jupiter this closely, or over the poles in this fashion," said
Steve Levin, Juno project scientist from NASA's Jet Propulsion Laboratory in Pasadena,
California. "This is our first opportunity and there are bound to be surprises. We need to take
our time to make sure our conclusions are correct."

Not only will Juno's suite of eight science instruments be on, the spacecraft 's visible light imager
-- JunoCam will also be snapping some closeups. A handful of JunoCam images, including the
highest resolution imagery of the Jovian atmosphere and the first glimpse of Jupiter's north and
south poles, are expected to be released during the later part of next week.

This dual view of Jupiter was taken on August 23, when NASA's Juno
spacecraft was 2.8 million miles (4.4 million kilometers) from the gas giant
planet on the inbound leg of its initial 53.5-day capture orbit.

 

[1oldman2]

http://www.nasa.gov/feature/jpl/nasas-juno-successfully-completes-jupiter-flyby

From, http://www.planetary.org/blogs/emily-lakdawalla/2016/08271754-junos-first-jupiter-close.html
NASA announced this afternoon that Juno passed through its first perijove since entering orbit successfully, with science
instruments operating all the way. This is a huge relief, given all the unknowns about the effects of Jupiter's nasty
radiation environment on its brand-new orbiter.

NASA's Juno mission successfully executed its first of 36 orbital flybys of Jupiter today. The time of closest
approach with the gas-giant world was 6:44 a.m. PDT (9:44 a.m. EDT, 13:44 UTC) when Juno passed about 2,600
miles (4,200 kilometers) above Jupiter's swirling clouds. At the time, Juno was traveling at 130,000 mph (208,000
kilometers per hour) with respect to the planet. This flyby was the closest Juno will get to Jupiter during its primemission.

While results from the spacecraft 's suite of instruments will be released down the road, a handful of images from
Juno's visible light imager -- JunoCam -- are expected to be released the next couple of weeks. Those images will
include the highest-resolution views of the Jovian atmosphere and the first glimpse of Jupiter's north and south
poles.

 

[enorbet]

Thanks 1oldman2. Nice update. I wonder what all the secrecy is about?

 

[collinsmark]

Thanks 1oldman2. Nice update. I wonder what all the secrecy is about?

It's not so much about secrecy as it is about transmission time.

Imagine you are standing next to someone: you can tell them your thoughts pretty quickly; but the Juno probe is not right next to us, so that situation doesn't quite apply. Now imagine that the person to whom you are talking to is a block away. You could shout really loudly, but there are limits to how loud you can shout.

There is another approach: you could shout slowly. The listener can then integrate over time. Assuming all the noise around the listener is random, it allows your shout to rise above the noise around the listener if your shouting is slow enough.

Beyond that, if you add some redundancy to your shouts, adding repetition/redundancy in a pre-agreed upon manner ("repeating" things in an a priori fashion), it allows the listener to detect and correct communication errors that might happen during the transmission.

Simply put, in a power limited system (such as a probe far from Earth), communication takes a while.

 

[1oldman2]

At the time of Juno's capture orbit (7/5/16) the distance was 48 light minutes. There is processing time involved and of course important discoveries will likely have an embargo placed on them while the review/publication process takes place. As you can see the image I posted (taken at a distance of 703,000 km) was processed and released quickly, the good stuff, from as close as 4,200 km will be released within a couple of weeks. once the science mission gets fully established ( early November) the data should be released without the delay (at least within days rather than weeks). According to JPL this pass was intended as a trial phase to check out instrumentation. Patience, there's plenty of "good stuff" to come.

 

[enorbet]

Thanks guys but I was only commenting on remarks made in the linked planetary.org blog that made a comparison to similar flights and concluding "secrecy" specific to Juno. The site has been generally reputable so I wonder about that writer as well as the conclusion.

Also having studied this shot for some time I am very prepared with patience as I'm sure enough focused data will be retrieved for at least 5 years of study.

 

[1oldman2]

Thanks guys but I was only commenting on remarks made in the linked planetary.org blog that made a comparison to similar flights and concluding "secrecy" specific to Juno. The site has been generally reputable so I wonder about that writer as well as the conclusion.

I caught the gist of your comment in regards to the "secrecy" and the site mentioned does have very good coverage of the mission.
"I don't know what other images have been planned, because the mission has inexplicably chosen not to share
information with the public about those plans. This is really weird, because Cassini and New Horizons were both very
open about their plans for imaging with their science cameras. Juno's JunoCam is an instrument intended specifically for
public outreach, and yet they're keeping information about it close to the vest. Apart from the types of imaging mentioned
in the press release, there has been discussion of attempting 3D imaging of clouds by taking images closely spaced in
time as the spacecraft passes from north to south. There was also an opportunity to image Ganymede yesterday. We'll
have to wait and see!"
Any way one looks at it this mission has great potential and I can't wait to see it evolve.

 

[collinsmark]

Regarding the communication link, and for a bit more explanation as to why it can take a while, here's something from the wiki:

"Due to telecommunications constraints, Juno will only be able to return about 40 megabytes of camera data during each 11-day orbital period. This photography downlink average data rate of less than 337 bit/s will limit the number of images that are captured and transmitted during each orbit to somewhere between 10 and 100 depending on the compression level used."​

(link: https://en.wikipedia.org/wiki/Juno_( spacecraft )#Telecommunications)

which references this source:

http://planetary.org/blogs/emily-lakdawalla/2011/3133.html

 

[1oldman2]

Regarding the communication link, and for a bit more explanation as to why it can take a while,

Interesting reading! thanks for posting that info, I'm curious about how much data (imaging) will make it back to Earth, considering the Hi-Def nature of the cam the downlink seems like one heck of a bottleneck.

 

[enorbet]

40MB? In eleven days? Wow! How did I miss that? That is such a terrible constraint and I didn't even realize it existed these days. Thank you for the links. I can't help but wonder why such important exploration, particularly now when understanding planetary weather can be so... so... urgent! how NASA got such a "back seat". I suppose Crisis Management still rules most people. Foresight requires actual critical, abstract thinking. ; )

 

[glappkaeft]

While JunoCam is not entirely without a scientific mission it was designed to be a education/outreach tool and thus has low priority for the scarce bandwidth. Originally Juno would not have a camera at all.

https://www.missionjuno.swri.edu/pub/e/downloads/JunoCam_Junos_Outreach_Camera.pdf

 

[1oldman2]

https://www.missionjuno.swri.edu/pub/e/downloads/JunoCam_Junos_Outreach_Camera.pdf

Great link! thanks.

 

[rollete]

Can't wait for the pics. Waiting for Pluto's high resolution imagery was hard but worthwhile.

 

[Clever Penguin]

What's new from the Juno mission?

 

[1oldman2]

What's new from the Juno mission?

Just waiting on data release, should be something soon.

 

[rootone]

Orbit insertion and the first of the planned close fly-bys worked perfectly and was largely an exercise in calibrating instruments.
There will be have been useful data collected as well, although it'll take a while for all of it to be downloaded.
36 orbits are planned in total, ending in early 2018.
That could be extended as is frequently the case with probes that successfully complete their primary mission and are still functional..
https://www.nasa.gov/feature/jpl/nasas-juno-successfully-completes-jupiter-flyby