So, as some of you know, I work for the Ion and Neutral Mass Spectrometer (INMS) team for the Cassini/Huygens mission. It turns out that I'll be heading to the Jet Propulsion Laboratory (JPL) in Pasadena, CA for the Saturn Orbit Insertion (SOI) event. (pardon the acronyms: they fly fast and loose around NASA).

I figured that ya'll might have some questions about Cassini/Huygens operations, science, planning, SOI itself or whatever. I will do my best to answer them, and I'll try to use this location to post what I hear during the SOI event and anything else of interest. This evening, I'll try to put up our own schedule, if anyone is interested in it -- the rough times when I'll be looking at data and such.

For the SOI period itself I'll probably be at the friends and family shindig at Pasadena City College’s Sexson Auditorium. That means I won't be able to post much during that time period (I doubt I'll have access to a computer then). Anyone else from the board going to be in the area? NASA TV will be carrying the event: see ToSeek's post about the schedule for more information.

The next morning, when data is coming down, I will try to get a few status messages in and I'll also try to post a summary of the event.

Finally, for reference, the public Cassini portal can be found here:

http://saturn.jpl.nasa.gov/index.cfm

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Hi, I have been reading the weekly e-mail newsletters for years, now, keeping up with even the mundane reaction-wheel unloads, and mid-criuse program high-water-mark clear operations, etc.

Everything seems to be looking great!

In none of the updates, or websites, or articles I have read, does it mention any photos taken during the SOI (from any attitude). Are there going to be any photos taken during SOI from whatever attitude the cameras happen to be aligned? (I realize that priority to whatever makes SOI successful is given to attitude, and no priority is given to science/imaging attitude during SOI.)

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Yup. All latest checkouts are clear. So far, so good!

Sort of; there will be pictures after the SOI burn (as well as our instrument's first real data!), but not before or during. The quiet period is in effect, so no instruments can do anything at all. It's more than just science not getting priority, it gets nothing! Rather extreme safety margin, I agree, but one always wants to minimize the chance of error or crossed commands for these things. Plus, for the ascending ring-plane crossing, we'll be moving so fast the images would be just a blurr!

I'll see if I can get a little more information about when the post-SOI imaging happens, but I won't be able to post exact time or pointing data. Some of that is best left as a surprise anyway!

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Heya!

What will Cassini be doing, insofar as detecting thunderstorm activity on Saturn? Will it try to take pictures of lightning on its night side, as Galileo did at Jupiter?

And is there any possibility of lightning on Titan?

Thanks, and good luck!!

Yes! There are going to be lightning searches by both the imaging teams and radio science (looking for whistlers and other lightning signatures). I don't think there are any in the first couple orbits, but there are definitely several on the list.

There are also auroral searches by the imaging and Magnetospheric and Plasma Science (MAPS) teams (that includes us), which should prove interesting. Did you ever see the Hubble images of Saturn's aurora? Neat stuff! Similar observations were made by Hubble, Galileo and Chandra of Jupiter's aurora, though the aurora on Jupiter are much more powerful than Saturn has.

That's a very good question. Unfortunately, the answer really depends on who you ask, just like the subject of methane rain (there are still a few holdouts on that one). I think the chances are pretty small, but non-zero. Our team's first good look at Titan comes in late October, and that should give us a decent grasp of the atmospheric profile, which is needed to pin down how lightning would work on Titan. We'll probably have to wait for Huygens for a good answer though, since it will be going all the way down.

Patience! :wink:

Thanks. At this point, all I can do is hope: our commands are up there and frozen, so it's just a matter of waiting. I'm not particularly worried though. Mostly just tired and eager to see some data!

For tlbs101:

I looked over the observation list for SOI, and you'll be happy to note that there are several ring observations shortly after the main engine burn. There are no specific observations that I can find during the descending ring plane crossing but the imagers will be running during that period. Remember though, we'll be moving so fast, things will rather smeary. But very soon after that, there is another large set of ring images.

In summary: expect some very detailed rings images for the SOI period.

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

parejkoj writes:

Cool!! =D>

There is something I'm wondering about. I'm wondering if thunderstorm activity on Saturn is more severe than on Jupiter. I'm wondering about this due to the greater temperature difference on Saturn that must be causing those 1,000 mph winds. There were also those huge explosions of white cloud spotted along the equator; I'm wondering if those are massive thunderstorm complexes. Jupiter's thunderstorms are the most severe thunderstorms in the solar system that we know of. It's my main focus of interest on the Cassini mission. I've always had a fascination for violent weather, particularly violent weather on other planets.

What's your take on this?



Edited to add: I'm tryng to see if I can get a copy of a show called PLANET STORM, that appeared on the Discovery Channel. VERY cool. 8)

Link here on alien thunderstorms:

http://www.channel4.com/science/micr...rm/alien2.html

Nuts, I forgot-a question on Saturn's winds...

I read somewhere that the wind speeds on Saturn have dropped from 1,000 mph to around 600 mph. Is this true, and if so, could this be due to a seasonal change? If not, any speculation what may be causing this change in wind speed?

Question about the recently released pictures of Titan that were on the Cassini site. The dark markings that we see, has it been determined that they are on the surface or clouds?

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I think that this is the surface feature dubbed the "lying H" that was seen by ESO's VLT in Chile (and earlier in Keck images): http://www.astrobio.net/news/print.php?sid=927
(Notice that the caption of first graphic on the right has the image descriptions reversed: the top image shows the surface.)

Here is a graphic showing the region of Titan that will be imaged during the July 2 flyby. http://solarsystem.dlr.de/PG/cassini.../titan_t00.JPG . It includes the area of the "lying H" feature, although that doesn't show as a continuous feature in this Hubble image-based version ( and which also doesn't show the bright surface feature at 15 deg long. and 45 deg S ). Hopefully they will release some images on Saturday. Surface resolution may be a few km/pixel.

Titan was well placed last week and more images with resolutions in the 35-40 km/pixel range evidently were acquired. Some may be released prior to SOI.

wheee! So much for having time to properly answer questions. I'll see if I can grab a copy of this page and work on them, and a few from other threads on the flight over. I'll post when I get a chance.

Sorry about that!

But everything is still fine for SOI. They should be starting the 24 hour DSN coverage shortly. Here we go!

Briefly:
Extreme weather certainly is cool, but not one of my specialities. However, I'll be meeting with some folks tonight for whom it is! I'll see if I can remember to ask about your Saturn weather questions.

The bright features in the image are almost certainly on the surface. The band those images were taken in cut through the smog quite well. But the spectral bands that can see through Titan's atmosphere tend to be absorbed by ours. Makes ground-based observation hard. I'll try to dig up the Keck movies from Caltech. You can see some surface features move, one of which was imaged this time around.

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Forgive me for asking, but could you please explain that in relation to the information here. From information on that page we learn that a 1.2 second exposure cause significant overexposure when imaging the rings. From studying the Cassini trajectory during the SOI, we learn that even though the spacecraft certainly moves fast during the SOI/ring plane crossings, the view from it does not change significantly during 1.2 seconds or less. And so, I do not understand why images taken of the rings will be "rather smeary". Please explain?

Since parejkoj is going to be pretty busy the next few days, perhaps we can help him out a bit here.

From the linked page So the rings were intentionally overexposed as part of post-imaging processing. This doesn't mean the images themselves were overexposed.

From the linked page At 19.2 million kilometers and approaching Saturn essentially head-on, the angular effects of points on the objects as a function of how far their images move on the CCD is minimal at 1.2 seconds.

Conversely during the SOI two of the above factors will have significantly changed. A third will come into effect.

1. The spacecraft will be no more than 19980 kilometers from Saturn's cloud tops and also very close to the top (north side) of the rings. Even if the approach were still head on, there would enough angular change/time during a 1.2 second exposure to affect the resolution of the image.

2. The spacecraft instead is going by the planet in a path normal to Saturn's radius, which means the effects of the probe's speed no longer cause just an angular change to the image, but a translational one, too, as a function of velocity and distance.

3. Cassini's cameras are fixed; there's no scan/pan platform. So the above translational effects can't be compensated for, except for the attitude controls, which will not happen during the SOI/ring passage.

Imagine being in a car going 60 MPH and trying to take a 1.2 second exposure of someone standing next to the highway, without being able to "pan" the camera. The image of the person in the photo will be blurry, even the hula hoop around their waist. :wink:

Even though the cameras may be turned back on after the SOI, the main antenna will still leading the way, so there's no guarantee the cameras will be pointed the correct way for ring photos.

Once the second F-G gap passage is completed, then the spacecraft will be able to position itself for whatever photos are desired, and will be at a far enough distance and low enough velocity to allow for "smear-free" photos.

I need to get some additional numerical on ring distances, shutter speeds, etc. More later.

8)


[edit/typo]

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While I'm doing some math on orbital info, here's an excellent site with lots of detailed information on the SOI. Thank you, The Planetary Society! =D>

BTW, if my preliminary math is right, when Cassini is only a couple 1000 kilometers north of the outer edge of the A ring it will be travelling at approx. 120,000 KM per hour (~75,000 MPH). Now look at films of the Earth from the shuttle at 250 miles going only 17,000 MPH, notice the rapid movement, then do the ratios. In both cases, it would take a short exposure time (1/500th sec) or controlled panning to eliminate the effect of the apparent motion on the image.

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Per the TPS site:

So each event will have already happened 84 minutes earlier when we find out about it here on Earth.

Relatively.

8)

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Mak, after posting I re-read the article and saw it. That's why my post has vanished... ;-)

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In response to the questions about Titan's atmosphere, and the recent Cassini images, ya'll might want to check these out.

http://www.gps.caltech.edu/~antonin/titan/

They were displayed at the Cassini PSG (Project Science Group) meeting in fall 2002. They had a movie of showing the rotation of that bright feature, which should correspond to the bright one that was found in the ISS images. The stellar occultation is also pretty neat, since they got two stars for the price of one! Notice the refracted double-image of the stars as they pass behind Titan... nifty!

There are dozens of occultations over the course of the mission, of Titan and many other moons -- and the rings!. You can expect even niftier movies like that in the future.

Thanks for handling the ring plane imaging question, Mak. You summed it up nicely. The ascending ring plane crossing happens at about 70,000 km/h, and we're going through the rings. The descending crossing happens at about 110,000 km/h! That is far to fast to get good images, even if we weren't in a safe pointing. However, I was just looking at an orientation video, and there are some interesting ring scans going on between the main engine burn and the descending crossing.

Things are going to be interesting tonight!

(I haven't forgot the weather question, just didn't get a chance to ask people. I'll definitely do so tonight, though.)

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Titan's weather vane

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