Juno development, launch, and cruise, Including Earth flyby imaging Oct 9 2013 Options

[Dominik]

@mcaplinger
Wow 4 km per pixel... I wonder what resolution New Horizons had at closest approach.

[elakdawalla]

Mike, given the recent experience with the New Horizons Jupiter flyby, do you think that Junocam will be able to contribute to long-term (by which I mean "the period of time that Junocam is active") monitoring of Io volcanic activity? NH showed that you don't need particularly high-res images to spot active plumes.

--Emily

[mcaplinger]

Mike, given the recent experience with the New Horizons Jupiter flyby...

Comparing Junocam to NH is apples and oranges. Note that LORRI did its imaging from something like 3 million km away and got about 15 km/pix, where Juno will be about 5000 km from the planet at closest approach, where we will get about 4 km/pixel. LORRI is about 150x higher-resolution at a given distance than Junocam, but Juno gets a lot closer to Jupiter than NH did.

As noted before, I don't know what the geometry will be like (we can't be sure until after launch, really), but Junocam is not capable of seeing the satellites with good resolution unless it's quite close to them. At a typical distance of say 500,000 km, Junocam resolution is about 400 km/pix, and Io will be about 9 pixels across.

[vjkane]

My dream shot: Close up of the Great Red spot. This requires that the Red Spot be underneath the orbital track on an orbit in which the remote sensing instruments point at Jupiter. [For most orbits, the remote sensing instruments will not be pointed directly at the cloud deck, and the orbit will be dedicated to fields and particles and gravity measurements.]. Unlikely, but one can dream...

[mcaplinger]

This requires that the Red Spot be underneath the orbital track on an orbit in which the remote sensing instruments point at Jupiter.

The spacecraft is spinning all the time, and Junocam points at the planet once per revolution, so this is not as unlikely as you might think.

[sci44]

It is interesting to read this thread about JunoCam, since a Jupiter mission is long overdue and I think a lot of people would like to see a revisit of the Jovian system with modern imaging systems. Correct me if I am wrong, but Juno is a spin stabilised probe with no gyroscopically controlled scan platform (for weight/power constraints). In that sense, it is more like the scanning photopolarimeter on Pioneer 10/11 than Voyager/Galileo. This very interesting history on Pioneer explains how difficult it was to convert those first extruded images of Jupiter into those famous pictures, and at distant targets it was lacking - it could not image Io's volcanos, for instance.

Even if it is a full framing camera, it must keep a wide frame of view to be able to get sufficient light from the target without motion blur. There are Cassegrain designs where the mirror is moved by an actuator during exposure - maybe that would allow sufficient stability to image Io or the other satellites at the needed magnifications (100x +) - perhaps another agency could contribute such an instrument! Juno is a daring mission, skimming the atmosphere of Jupiter - which I am sure will answer a lot of questions about Jupiter itself - but I am sure there are a lot of people out there who would like to see a replay of Galileo for the icy moons too.
I wonder to what extent the specification is conservative, at 30 orbits (and only 7 for Junocam)? Is this like Phoenix, where we are pretty sure that <-100C is going to crack the electronics, or like MER where +90 days of dust+winter might finish it off, but we are not sure? After the primary mission (in that special radiation-free orbit) I guess we will find out just how well large solar arrays can survive in the Jupiter radiation belts - if it does, it would be a shame if there is not a good imaging telescope there too..

[mcaplinger]

Even if it is a full framing camera, it must keep a wide frame of view to be able to get sufficient light from the target without motion blur...

The field of view has no direct relationship to "sufficient light", this is a function of f/number and exposure time. See the thread http://www.unmannedspaceflight.com/index.php?showtopic=2890 for some insight into how Junocam works.
It's required to have the wide field of view to meet the requirements on Jupiter polar imaging, and as I noted before, it has no requirements to image the satellites at all.

but I am sure there are a lot of people out there who would like to see a replay of Galileo for the icy moons too.

Alas, Juno is not that mission, and I don't think any money is available for enhanced imaging. The Italian IR imaging spectrometer (JIRAM) is the only other imaging system on Juno. http://adsabs.harvard.edu/abs/2007AGUFM.P51A0208A

I wonder to what extent the specification is conservative, at 30 orbits (and only 7 for Junocam)?

I'm not sure if anyone knows how conservative the radiation models are, but the lifetime issues are driven by radiation dose.

[sci44]

The field of view has no direct relationship to "sufficient light", this is a function of f/number and exposure time.

Ok, I should be more accurate, and say "field of view" against "angular scan rate". Presuming a scanning platform rotating with the craft, the more magification you apply, the less time the object is in the field of view - up to the point where you cannot magnify any more - the light will not register with the CCDs. With a scan platform and telescope, you can use an extended exposure to get a picture of distant and/or dim targets. Dont get me wrong - push-broom and photopolarimeter cameras are perfect for orbital missions with reasonably close targets and the right orbital "motion" across the sensors, like MRO/Hirise->Mars - and probably for Juno->Jupiter too - but am I right to assume that major spacecraft manuevers would be needed to image a distant target? Is this complicated by the large solar sails - can Juno slow down its spin rate for such imaging?

Alas, Juno is not that mission, and I don't think any money is available for enhanced imaging. The Italian IR imaging spectrometer (JIRAM) is the only other imaging system on Juno.
I'm not sure if anyone knows how conservative the radiation models are, but the lifetime issues are driven by radiation dose.

Yes I was just wondering if an enhanced imaging system would even be possible - and if so, if another space agency somewhere would like to take it on - otherwise its a long wait for another Jupiter mission (2030+).
As for lifetime - Galileo outlived its specification, so we can hope..

[mcaplinger]

I was just wondering if an enhanced imaging system would even be possible...

At this late date (launch is about 2.5 years from now), I'd say the chances of adding another payload element to Juno are effectively zero.

Note that I neglected the ultraviolet imaging spectrometer in my earlier post. I don't know what the resolutions of either JIRAM or UVS are, but there is public information available if someone wants to make the effort.

I believe imaging is only possible if the target happens to pass through the spin plane +/- half the FOV of the instrument involved. JIRAM has a 1-DOF scan mirror, I think, I don't know how UVS works, and Junocam is mostly insensitive to spin rate owing to our ingenuity in designing it

[Juramike]

While the Junocam will be really cool, one of the main missions for Juno is to try to figure out how Jupiter started and evolved. (link to mission page here)
This might shed light on the origin of our solar system and extend to extrasolar systems.

Here is a recent article in space.com (I tried to link to this a few days ago, but it disappeared from the space.com archives...today it's back) about how Jupiter may have a much bigger core (14-16 Earth masses of rock!) than previously proposed. Previous predictions ranged from a core of 7 Earth masses of rock to no core at all. Juno should help nail down the absolute size of the core, and therefore, whether a rock core was required for the initial accretion.

Which came first: gas or rock?

(Solar system formation discussion that followed moved to another thread, see here - moderator)

[IM4]

Did you know that Juno's pre-launch planning trajectory is available at HORIZONS? (spacecraft ID = -61)
I've created simplest Celestia addon covering time span from 2016-Aug-03 to 2017-Oct-16 (from JOI to atmospheric impact), so you can simulate Jupiter's and Galilean's views for main mission. Download link

PS
I saw some peoples making tables of close approaches for Cassini and Saturnians - a kind of magic with SPICE kernels and routines. Could anyone reproduce that trick for Juno?

[volcanopele]

hehe, you noticed that too. I've been playing with my own for a few weeks in Celestia. I'll post it when I finish my Jupiter system addon (part 2) in a week or so. For mine, I have been using XYZV files (needs the latest Celestia beta).

for those close-approach tables, you really need spice kernel files, but I believe that JPL Horizons also has this capability, but I haven't given a try. Keep in mind that Juno's camera has a very low spatial resolution, as noted above. In other words, fine for looking at Jupiter, but not very good for looking at the satellites. However, it might be interesting to see if decent science might be possible at Io, to look at it in eclipse and look the brightest hotspots. Given the low-priority of the camera though, I doubt the Juno planners would want to sacrifice time near perijove to look at Io.

[mcaplinger]

Keep in mind that Juno's camera is better described as a glorified digital camera, not like the camera systems you find on Cassini, Galileo, or MRO.

I'll try not to be offended by that. Junocam is as much a "real camera" as MARCI on MRO is.

Given the low-priority of the camera though, I doubt the Juno planners would want to sacrifice time near perijove to look at Io.

The imaging would presumably happen near Io closest approach, which is not especially near perijove, since Io's orbit is about 70x higher than Juno's perijove altitude. If there's a good opportunity (and even if there is one for the baseline orbit there's no reason to think the real orbit will have one) I think there's a fairly high chance that it'll be used.

[volcanopele]

I apologize Mike. I edited my post to better state what I wanted to say. I, in no way, meant that Junocam wasn't a "real" camera. More accurately, I meant that Junocam wasn't the same kind of telescopic camera system like ISS, SSI, HiRISE, or CTX. The field of view of the camera and the iFOV are not sufficiently high resolution to do much geologic science.

It is good to hear that JunoCAM could be used to Io science. I love to hear that. However, as you pointed out in earlier posts, the resolution of the camera would likely make it such that observations of Io would need to be acquired within a few hours of perijove, which I would imagine would be a busy time for science on Juno, and because of JunoCAM's spatial resolution, it would be lower priority than Jupiter science during this period.

[mcaplinger]

It is good to hear that JunoCAM could be used to Io science.

Keep in mind that this would rely on a serendipitous and unplannable close approach to Io sometime early in the mission before Junocam (aka JunoCam or JunoCAM) has been toasted by Jovian radiation, and that I have no idea how constrained Junocam operations will be (not sure how many bits the s/c can send down per orbit and what competition will be like for those bits). That said, if there's a good encounter it'd be disappointing to not make use of it. But I just build them, they don't let me push the shutter button, at least not very often.