I believe the idea was to get IR spectra, at wavelengths unavailable from the ground, to give some information on the composition of the exoplanet's atmosphere. That's much more difficult than just detecting the transit, and I think this was actually done as a proof of concept.

No, that was never in the plan. To simplify operations and planning in the Solstice mission, the project has switched to dedicating each periapsis to one scientific discipline (Saturn, rings, icy satellites or magnetosphere/plasma.) There are some exceptions, and Titan science is handled differently (lots of encounters, all dedicated to Titan, but those aren't in the periapsis periods.) But the exceptions are pretty carefully selected. Rev 146 is a Saturn periapsis and looking at Telesto isn't one of those exceptions.

We'll have to wait for the Mishap Investigation Board's report, but this isn't my understanding from the press conference. They completely replaced one part of the fairing separation system. The pressure to kick it open was from compressed nitrogen for the Glory launch, as opposed to a hot gas source for OCO. But the whole separation system is more complicated than that, and I didn't hear anything about changes to other parts of the system.

I think that's what Mark Showalter said when they based the original hazard assessment on his Voyager-based E ring model...

Just for reference, there are only six more dust hazard periods which will require pointing the high gain antenna to ram. Those are all Janus-Epimetheus ring crossings in 2015-2017, and all about 10-15 minutes long, plus turn time. (This doesn't include the final orbits inside the D ring; analysis and plans for that are still pending.) All the other hazard periods just require closing the main engine cover. Also, although there was some early talk about it, Cassini has never turned to keep instrument optics out of the ram direction. There was lots of analysis and testing on mirror samples before they decided this would be ok. (Part of the reason for all the testing and analysis was to impact those turns would have had on science: If "turn optics out of the ram direction when the spacecraft is in the E ring" were a rule, imaging during the inbound leg of an Enceladus encounter would have been forbidden.)

That's pretty much true, but maybe I can say this more clearly. On perijove for the MWR orbits, with Jupiter in the spin plane (spin axis perpendicular to orbital plane), the JunoCam or JIRAM having a chance to see a satellite are pretty small. They would have be crossing Juno's orbital plane at the time. That's also (more or less) true of the gravity orbits at the beginning of the mission. At first, the orbital plane is almost perpendicular to the Earth line (polar orbit, periapsis close to dusk local time.) But over the course of the mission, the orbital plane precesses and perijove moves towards noon. I think it moves about a degree to two per orbit, and it's at 30 or 40 closer to noon by the end of the mission. So, when Juno is 20 R_J from Jupiter, it will also be about 10 R_J behind Jupiter (as seen from Earth or the Sun.) The remote sensing fields of view would be scanning out a plane perpendicular to the Earth line and 10 R_J behind Jupiter. As Juno moves goes through periapsis, that plane would move sunward, get just a hair sunward of Jupiter itself at periapsis, and then move back again. That could greatly increase the odds of catching a satellite.

I think it's a moot point: JunoCam and JIRAM were really designed for atmospheric science, not satellite geology, so I'm not sure if this is more than a theoretical exercise. I think they could do it, but the results might be unimpressive.



I don't think that's quite true. UVS (and WAVES, since radio astronomy might be called remote sensing) is designed to operate for the whole mission. The others are designed to accomplish all of their official goals in the first half of the mission. Because of that, they could designed to survive a lower radiation dose. But that just means no one is officially promising they will survive to the second half of the mission. They could. (For example, Galileo survived a far higher radiation does than it was designed for.) I strongly suspect the project will keep operating them for as long as they last; if they get lucky, that could be through the whole mission.



Towards the end of the MWR/nadir pointed perijove periods (orbit 10 or so, I think), there is a significant difference, and the power off the solar arrays is down. But that's what batteries are for. I think these perijoves were one of the things that determined the battery capacity.

JunoCam and Juno don't do any pointing as such. The spin axis will point either at Earth or perpendicular to the orbital plane (so nadir on Jupiter is in the spin plane.) JunoCam just takes images at a commanded time and a commanded spin phase. So I don't think they can do anything like a skeet shoot. But it also means the smear from the relative velocity is less of a problem than you might think. It's designed to image from a platform spinning at 2 rpm. That's 12 deg. per second. At periapsis, the clouds are 4300 km away and the spacecraft is moving at about 50 km/s. That's about 0.7 deg. per second of smear, not much compared to the smear from spacecraft spin the instrument's built to deal with.

The odds are much better than that: Juno is a spinning spacecraft. Every 30 seconds, JunoCam's field of view will scan out the entire plane perpendicular to the spin axis. It could image anything in that plane. Over the course of a periapsis, that plane slides over most of the inner jovian system. Depending on the orientation of the orbit and the location of the satellites, I'd guess there is about a 50% chance to image any given satellite on a given periapsis. They just need to put in commands to image at the right time and spin phase.

That does not, however, say what the range to the satellite will be. It could be quite distant. In fact, the range to the Galilean satellites is always large on purpose. The observations of Jupiter call for a pretty well-controlled orbit. For example, each periapsis is 192 deg. of longitude from the last (to give an even sampling grid for the magnetic field/internal core measurement.) To do that without using too much fuel, the orbit was designed to avoid the Galilean satellites: Even a distant (e.g. 100,000 km) encounter would perturb the orbit and require additional corrections.



That's true of the mission's science goals, but I'm not sure about JunoCam. It is on the spacecraft for public outreach and education. It isn't tied to the formal mission science requirements. It does get the best view and range of Jupiter, I think its filters reflect that, and I suspect most of the images will be of Jupiter. But if satellite images support JunoCam's outreach and education goals, I'd think they would be taken.

Strictly speaking. a skeet shoot isn't automatically labor intensive. This is one of several sorts of observations where the Cassini project has to make a hard choice. Doing a skeet shoot without adding too much work would add wear on the reaction wheels (which is a bad idea, if we want the mission to continue until the end of the Solstice mission in 2017.) Finding a way to do a skeet shoot without adding wear on the reaction wheels is possible, but it would take quite a bit of labor on the part of the spacecraft team, and the extended mission work force can't really support that.

If you mean cloud and storm imaging, I'm pretty sure there is going to be quite a bit of that in the visible and IR. If you mean night-side images of lightning flashes, I don't think that will be possible. During the perijove phase of the orbit, the spacecraft is over the day side. I'm fairly sure JunoCam and JIRAM can't point off nadir at all. I do think we'll get whistler data from Waves. That's caused by lighting and has been used as a measure of overall activity (as well as the source latitude.)

I'd have to check the latitude, but it's possible. There have been night side images taken to look for lightning. My guess is that any influx of ring particles could not be seen. There is (or should be) D ring particles entering the atmosphere, but those are primarily < 0.1 mm (see Hedman et al., 2007.) They definitely wouldn't produce enough of a flash to be seen. In addition, lightning has been observed, but only at equinox (where the ring shine went to zero) and I think those were estimated to be very large events by terrestrial standards. If you take that as a standard for just-detectable flashes, I doubt Cassini could see a meteor.

(By the way, in the earlier post, I did drop a zero. It should be a 470 m^2/kg, not 4700, sail to hover a kilometer over the rings.)

Cassini empties the recorders every few days, and almost never retransmits data. Retransmission is a planned, automatically-play-back-twice practice that's reserved for Titan and icy satellite encounters. You're probably seeing the difference between data the DSN sends to JPL immediately, and the "bested" data. There is some level of error correcting that the DSN can do, to recover packets corrupted in transmission, which they can't do on the fly. That is usually available a few days after the bits hit the ground. The really ratty data is probably from downlinks where the conditions were so bad that no amount of reprocessing and error correction can help.

I don't think they had any choice about it. At the time of the encounter, Pluto will have a moderately high, southern declination (something like 10 deg, if memory serves.) They definitely wanted to get to Pluto before it was too far from the Sun, and Pluto is in a Kozai resonance, so its declination and distance from the Sun are highly correlated. A side effect of this, by the way, is that some New Horizons and Cassini scientists may end up arguing with each other about the use of the Canberra 70-m DSN station, since it is by far the best for a spacecraft in the southern sky. Since there is an overlap in the science teams, some scientists will get to argue with themselves about this.

And depending on what you mean by an image. If electron flux as a function of direction counts as an image, CAPS sees the "shadow" of the high gain antenna all the time. RPWS and CIRS can "hear" the reaction wheels. In one way or another, it is almost impossible to build a spacecraft which can't observe itself.

Interesting idea. I don't think I've heard Forward's solar sail idea applied to hovering over the rings. But if I did the numbers correctly, you need 4700 square meters of sail per kilogram of spacecraft mass in order to hover 1 km above the A ring. (If anyone cares, that scales with the height over the ring plane divided by the cube of the distance from Saturn.)

Galileo was on a very different orbit. It spent almost no time in the worst parts of the radiation belts. Between orbital insertion and about a year or so into extended mission, Galileo never went inside the orbit of Europa. Juno will be spending a much larger fraction of its time in the high flux parts of Jupiter's magnetosphere. The orbit is designed to avoid that, at first, but the orbit precesses over the course of a year. I think the total, unshielded dose for Juno is estimates at three or four times what they think Galileo was exposed to.

The red tag is on one of the reaction control thruster towers. They probably want the nozzles covered during shipping and handling.

It isn't a bad camera, and if you don't have a wavelength bias, Juno has an very nice imaging UV spectrometer.

Actually, that's another reason the Helene images very interesting. Helene is a trojan moon of Dione. It turns out the three-body interaction makes Helene's orbit a sensitive measure of the Dione:Saturn mass ratio. I suspect someone can turn an off-center image of Helene into an improved determination of Dione's mass.