yeah it bugs me that AIAA charges so much (even when they don't hold the copyright the expect you to pay them for photocopies). The best I can do is to recommend a nearby university library... often computers in the library can download these papers.... I got one paper this way... and I'd attach it, but it's too big (1.7 MB)

Of course I want to concentrate on Titan and Enceladus.....

BUT..................AHHHHHHHHhh... but even the Dead Tell Tales.... (and no, I do not watch CSI). Something very interesting happened(s) at Iapetus that affected the outer reaches of the Saturn system at least inwards to Titan. And the Jupiter system has taught us that "old" surfaces can hide young interiors.... look at the hints of oceans under Caliisto's battered exterior... a moon that is not even completely differentiated. And Ganymede, cratered as he is, has a significant magnetic field and is completey differentiated.

Do not just write off what stories Iapetus has to tell.... I am always reminded of Poul Anderson's ditcum that every body is a " world" with a unique history and it's own personality.

Another reason I want to see us return to the Moon... that "dead" world will teach how to really respect the dead. And live under very harsh conditions.

Craig

True. Pretty much destroys my assertion, in fact.

There are small craters with bright rims but dark floors that show us that the dark stuff was emplaced after those craters were formed, and this pretty much tells us that the dark stuff happened in the last fraction of Iapetus's history. I should have reviewed this before posting.

I think there's a pretty good chance of that.

They can take a stab wound and determine where the assailant was relative to the victim. Or a bloodstain and determine the geometry of a gory deed.

The interaction between topography and the dark-light pattern is going to tell us a lot we don't know already.

We already know a lot, and it seems to thwart a lot of simple models. Particularly, the Snowman craters give us some trouble. But we've mainly seen the eastern border of Cassini Regio. The September flyby will give us a great look at the western border. That alone will tell us if CR was emplaced from east to west, west to east, or from inside out. Or none of the above, also a real possibillity.

I'm reminded of the pre-Apollo situation with three theories about the origin of the Moon. It turned out that a combination of two of them best explained the data. Maybe Cassini Regio had a single catastrophic event as its origin, but it has had a continuing evolution since then.

Callisto may offer a useful analogue in terms of the interaction of dark surface with brighter, more volatile ice. Iapetus must be a little more complex than that, but that may partly explain things.

That's one interpretation. Another interpretation of the craters with bright rims and dark floors is that the entire crater was once all dark, but mass wasting has exposed brighter materials in the rims.

I tend to agree, though, that the dark stuff probably was emplaced over top of the craters, and happened pretty much after all of the visible craters were formed.

-the other Doug

Iapetus is so battered that extra-high resolution will have rather little information to yield on global geology, at least directly, but global coverage is needed at good resolution and sun angles just to see the global geology well.

Where resolution higher than Cassini can provide (except for perhaps one tiny spot) is infrared spectral mapping for composition. Looking at steep crater walls and other topographic features to see the intimate mixing and distribution of ices and the darker materials will give a better understanding of their stratigraphic relations and transport processes and thus the geologic history of the albedo patterns and ice migrations.

Cassini won't be able to do much of that, unfortunately, even on it's fall flyby.

The basic problem so far has been the lack of encounters in mid-range distances - as far as I remember
one in 120.000 km, 600.000 km and 800.000 km - to poor to allow a satisfiable resolved mapping.
Due to CASSINI's orbit unfortunately only the saturn facing hemisphere could be observed so far.
Not comparable to all other saturnian moons - even the Phoebe encounter showed more...
Septembers close outbound encounter will improve this situation a lot for sure, but still enough regions will only be bad imaged - for instance the northern polar regions (Voyager images being still the best) or the Snowman with its dark terrains.
Hopefully an extension of the extended mission will give us the opportunity to visit Iapetus once more in an outbound passage over this regions not exactly so close as this fall.
If feasible an elongated orbit with its apoapsis outside of Iapetus' course - and eventually a bit tilted - would be favorable.
So Iapetus could be passed several times in say a few 10.000 to 100.000 kilometres showing different longitudes under changing illumination conditions.
But this is certainly at first a propellant question I guess...

Bye.

Have more details of the extended tour been made public yet?

At the moment, I'm particularly interested in what will happen around the solar ring plane crossing in August 2009. What sort of inclination will Cassini have at this point? Are there any specific opportunities to see the shadows of satellites stretching across the rings? (I realise the latter doesn't necessarily require knowledge of the tour.)

john_s mentioned the RPX in his glog entry, but without much detail of what Cassini will be up to.

I wonder whether there will be interesting deductions to be made from the thermal properties of the ring particles as the sunlit and dark sides of the rings swap places -- we will presumably be able to look at both sides more-or-less simultaneously for the first time.

during the equinox period the inclination profile is something like:

~45 deg up to DOY 205
~35 deg DOY 205 to DOY 221
~21 deg DOY 221 to ~DOY 237
~12 deg from DOY 237

the process for deciding what observations Cassini will make during extended mission has only just begun. At the moment preparations are being made for the division of the extended mission into periods of time and allocating those periods to TWTs (Target Working Teams) and OSTs (Orbiter Science Teams). The process is called "segmentation" and the periods of time "segments". Segmentation will be completed by sometime this summer.

The TWTs and OSTs will then decide what observations will be carried out in their segments in a process called "integration", which can obviously only start after segmentation has been completed.
Integration may take a year or so to complete, I expect the extended mission will be intergrated from the beginning forwards as its possible that the XM might actually begin (July 2008) before integration has been completed.

Right now Cassini science team members will have a good idea of the type of observations they want to make and when they can make them but simply won't know until a segment has been integrated the exact observations and times. Its worth mentioning that there will be far more requests for observation time than there is time in the XM and only a fraction of requests will actually get allocated time and be included in the SOP(Science Operations Plan -- I think) during integration.

The TWTs and OSTs are made up of people from the Cassini science teams, any science team member who is interested in that TWT/OSTs general area of responsibility can participate, supported by Science Planning Engineers from the Cassini Project at JPL. This means that it is the Cassini scientists themselves who decide what science Cassini will perform, of course there are various safety constraints and engineering requirements where the Cassini Project at JPL decides but by and large its the scientists themselves who determine what Cassini does.

I'm less interested in the shadows of the moons upon the rings as I am in the shadows of the rings upon themselves. I expect that will be quite a sight.

Good point. Something you can notice on a brick wall when the sun is almost coplanar with it: The first/last shadows become incredibly stretched out as 1/sin(0) goes to infinity and the shadow becomes a kind of infinitely powerful form of magnification of the wall's topography. The right image at the right time could provide what is essentially the highest magnification "image" in the history of space exploration (well, not counting ones taken within 1 km [cm] of the object in question).

It should at the very least give us a good idea of the thickness and vertical density profile of the F Ring, and perhaps some of the other rings too.

I checked my calculated numbers of propellant remaining posted in this thread against some numbers given in this document from March 28th 2006 (page 3).

For March 28th 2006 I calculate a spacecraft mass of 2.706 kg, the document gives 2.710 kg. DSM, SOI and PRM used 2.086 kg calculated vs. 2.083 kg given. So I conclude my calculations are pretty much correct.

Based on this we have right now a spacecraft mass of 2.649 kg including 433 kg biprop and 91 kg monoprop. This translates into a biprop delta v capability of about 529 m/s.

Analyst

PS: The propellant remaining number given in the above document (422 kg) seems to be wrong.

Impresssive piece of analysis! You chose your handle well. :-)

One thing that confused me at first: in America a mass of "2.649 kg" would just be 2649 grams -- not much at all! Confused me for a bit, until I realized what was happening.

Question (for everyone): Is this business of swapping comma and decimal point a US/Europe thing, or an English/non-English thing? That is, for the speed of light (for example), who writes 299.792,458 km/s vs. 299,792.458 km/sec?

--Greg

It's country specific. South Africa uses "," for decimal position and "." as a thousands separator. The Irish and British definitely use "." and "," in the same way as the US. The French use a space for thousands separation and the Swiss use an apostrophe. It gets even more different if you move outside of the western hemisphere - you cannot assume that number grouping always happens in threes for example (Japan and China group numbers using a space as a "10 thousands" separator and a "." as a decimal).

Quite mad.

And don't even get me started on what and American and a Briton think constitutes a billion... *sigh*...

-the other Doug

How many Carl Sagans does it take to screw in a light bulb?

BILLIONS AND BILLIONS!

<you may shoot me now.>

Considering the number of minds Sagan has turned
on to the cosmos, maybe it should be:

How many lightbulbs can Carl Sagan screw in?
Billions and billions.

For those of you who want to "play" with the ephemeris of the extended mission, the official data for the extended tour is now delivered to the NAIF ftp site (for SPICE kernels).

hehe:

Click to view attachmentClick to view attachmentClick to view attachment
Click to view attachmentClick to view attachment

if people can play around with these spice kernel files, the file you are looking for is 070620AP_SCPSE_08102_10191.bsp

Looks like a double header for Enceladus in 2010 from VP's Celestia images. Should fill in details nicely in leading hemisphere.

Hey - where did you get that Titan map??

Those graphics are from a few months ago when I was testing out Celestia and spice files. The Titan map I used here is our released Titan map:

http://photojournal.jpl.nasa.gov/catalog/PIA08346

Does anybody know if the extended mission has been 'ratified' as yet by NASA?

Also, a thought occurs: If the extended mission does go ahead, might there be any advantage in retargeting some instrument pointing for the last few months of the primary mission??

An example: We now know that Cassini is due to come within 500km of Dione in July 2010. This presumably will yield some very good science, and with that in mind, perhaps some observations of Dione between now and July next year (say in the 50,000 - 100,000km range) could be sacrificed in favour of other targets at that time?? i.e. ignore Dione at that time as we know we're getting closer later, and point the instruments elsewhere.

I don't pick on Dione for any particular reason (it could be mid-range shots of Mimas, or Tethys, or the rings) This principle would be especially apposite for instrument pointing at or around periapsis where there are a lot of tempting targets.

Obviously Cassini's trajectory remains the same, and there might be a tiny bonus in terms of usage of the precious hydrazine.

I understand the constraints on time, forward planning, and uploading of information to the spacecraft, but with around a year to affect any changes perhaps the last couple of revolutions could be made 'more useful' in this way?


Jase

This has multiple answers....

First ... All of the time in the PM has already been planned and is "on the shelf" but small observation tweaks and shifts are being made as they move closer to uplink....but all changes get made in the AfterMarket process which goes on nearly 200 days before Uplink.


Next... Various groups are already busy with science planning for the first revs of the XM. ( In fact most of the high priority science for all of the XM has already been laid out long ago ) The schedule for XM Science Planning is very tight and begins at a royally fast pace begining right around Sept 1 2007.


Not only has the XM been approved but the XM Science planning and Timeline Integration is moving along at high speed

partly related:

http://www.spaceref.com/news/viewpr.html?pid=23130

"Alan Stern, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, will host a media teleconference at 1 p.m. EDT, Wednesday, Aug. 1. Stern will discuss plans for NASA's Cassini mission to make an unusually close encounter with Saturn's geyser-moon Enceladus and provide project updates for a variety of science flight programs. Planetary and astrophysics program developments also will be discussed"

Thanks guys - 200 days in advance is quite some forward-planning.
Hat's off once again to the whole Cassini team for this magnificent achievement.
Roll-on the extended-extended mission......

Does anyone have precise information on the Titan surface coverage by SAR during the extended mission?

What other mission proposals had been there (PF6h9 sounds complex)?

Is there any useful visualization of the orbits which can be used to tell the people what is going on?

I am giving planetarium lectures in a larger city and would be interested in these details.

Thanks a lot in advance!

Harkeppler

We've moved on from PF6h9 (which was renamed XM0). I think the iterations on this got as far as XM10 before the emergence of the "official delivery of 2-year extended mission trajectory" which is called XM070620. The SPICE kernel of this XM reference trajectory is publically available from the NAIF anonymous FTP site (naif.jpl.nasa.gov:/pub/naif/CASSINI/kernels/spk) and is called 070620AP_SCPSE_08102_10191.bsp for those of you who might be interested in generating your own visualisations.

Hi,
as Solar System Viewer isn't capable of simulating views of the extented mission so far,
is anybody here able to create some views of Iapetus of the following nontargeted encounters with Celestia or another simulation?

2009 07 05 05:00:00 - 2,089,800 km
(low phase, sub-saturn hemisphere, eastern Cassini regio, Snowman craters)

2009 09 11 19:47:00 - 1,161,000 km
(high-phase leading hemisphere, extreme eastern Cassini Regio, western snowman crater)

2009 12 01 15:07:00 - 1,377,900 km
(moderate phase (~100 deg.) , southern leading hemisphere, extreme eastern Cassini Regio, western Snowman crater,western Terra Incognita)

2010 02 21 10:00:00 - 1,469,800 km
(moderate phase (~50 deg.), southern sub-saturn hemisphere, view of eastern Cassini Regio, Snowman craters, Terra Incognita)

2010 05 08 16:30:00 - 1,234,800 km
(high phase (~110 deg.), southern leading hemisphere, crescent view of extreme eastern Cassini Regio and western Terra Incognita)

THX & Bye.

I found a nifty little presentation from the May 2007 Cassini Plasma Spectrometer Team Meeeting, about the extended mission, available at:

caps.space.swri.edu/caps/teamMeetings/teamMeetings.shtml (then click on "Meeting #34", then "extended mission")

The presentation is biased towards particles and fields observations, but still lots of interesting bits of info. A
particularly useful part said "an 'extended, extended' mission should be possible", stating that the prime mission will end with 342.3 m/sec delta-V remaining (95% confidence level) and the PF6H9/XM-9 extended mission is predicted to use 216 m/sec delta-V. However, it went on to say that the reaction wheels may ultimately detemine how much longer Cassini will function (one of four wheels is off due to "bearing cage oscillation", and three wheels are needed for normal operations).

Some cool details on Enceladus encounters I hadn't read before, too. Fifteen pages total, well worth downloading.

Clarification: click on "Minutes from CAPS Team Meeting #34", then "Extended Mission"

There you go

Cassini's a big spacecraft. Would flying it into the dark material on Iapetus be a good end of mission scenario? Could the impact flash be observed from Earth based telescopes?

I'm gonna go with: no.
SMART-1 was barely detected and it was in our backyard, Iapetus is waaaaaaay out there...

Yeah, you're right, the numbers don't look at all good for observability. Maybe it would be worth doing to leave a fresh crater for a future spacecraft to the Saturn system to investigate.

A 'Deep Impact' style end of the mission has been raised in another forum, and the suggestion is making it's way up through the appropriate hierarchy.

The goal would be a fresh crater of known age for a future mission to observe, and to perhaps establish a rate for the accumulation of the CR 'crud'.

A bad idea in my opinion. Iapetus is difficult to reach and the delta-v penalty is significant so if you reach it for a second time you want to observe it, not crash into it. If Cassini has to be destroyed by crashing it into something, crashing it into something easy to reach (and preferably uninteresting) is a better idea I think.

Sure would be nice if they could go for a super close-up look at the rings. IIRC Carolyn Porco mentioned something about that way back when (but more along the lines of "sure would be nice" than a plan).

Obviously, if Cassini were to be placed in an orbit that passed through the rings, the most likely outcome is total destruction of the craft. But if the orbit were perpendicular to the rings (so as to give the shortest travel time), and passed through a known low-density area, isn't there some non-insignificant chance that it might actually survive the passage? Aren't the rings ridiculously narrow, so that if you don't happen to hit a boulder the first time, you might actually be through in a matter of seconds -- maybe sandblasted, but still perhaps in one piece?

Going perpendicular, you'd be through the main part of the rings in a fraction of a second. As to whether there are areas between ringlets that are clear enough of material to give a fighting chance of survival, I'm not sure anyone really knows. Perhaps in the Cassini or Encke divisions. I doubt in the B ring.

I'm not sure from your question whether you are worried or hopeful. One pass survived would certainly send back some very unique data. As to any worry that it might continue to live, don't. If it somehow managed to survive one ring passage, it will just keep coming back on subsequent orbits. Eventually... SPLAT.

I am noting the amazing amount of interest in the current Iapetus encounter, and point out we have not had a Titan or Enceledus encounter generate this kind of interest in a long time.


Therefore:

Be it resolved, the primary goal of the extended, extended mission:

Iapetus

I must choose my words more carefully then! It was definitely a hopeful thought. Though I imagine a spacecraft might be better designed than Cassini to maximize the chances of a successful passage.

Paraphrasing from Silent Running: Cassini ain't built for shooting the rapids!

I've always imagined it would be spectacular to go thru the wake of Atlas or Pan.

And I would like to point out, Iapetus still has additional wonders for us to explore!

The 'tiger scratches' (around 30 degrees south, and 355 degrees around) are quite fascinating and I strongly suspect they are also a unique feature we have not encountered (on this scale) elswhere.
Conveniently south of the 'tiger scratches' is also a candidate crater for a large grazing impactor. A possible source for the ring materials.

Dynamically that would be a challenge - because Iapetus is so far out there
the orbits are long, so you get far fewer flybys total.

A lot of the interest in Iapetus is simply because it has only this close flyby -
if there are X interesting things about a body (argue amongst yourselves about
how much X is for Titan vs Europa vs Callisto vs Iapetus etc.) and you
discover some fraction f of the remaining mysteries on the Nth flyby
then
first flyby gives you fX, second gives you (1-f)fX, third gives you (1-f)^2fX findings
etc. After 35 flybys, the incremental value of each indeed goes down. If f is very
small, the rate of novel findings declines only slowly

If the observation/operations are well-understood (as I'd argue is mostly the case
for optical/spectral study of Iapetus etc) then f is large - say 0.3 or something
So this first Iapetus flyby has tons of excitement

Enceladus and Titan had more total surprises and exploited more novel
instrumentation like Radar and INMS which took a while to figure out, and figuring
out how to best acquire VIMS and ISS data through the atmosphere also took some
trial and error) maybe f is smaller, 0.05 or less? (Recall many instruments are
recording seasonal or local time variability, radar sees only 1% of the surface at
a time, etc.)

Sooooo, I agree another flyby or two of Iapetus (particularly to get gravity to understand
its internal structure) would be nice, but the question is how many Titans and Enceladi
to you sacrifice to get them? (And as I've argued above, the answer depends how many
Titans you have under your belt already..) I bet after two or 3 more Iapetus flybys, it
would get pretty uninteresting, whereas Titan's mysteries will endure..

then of course these idealistic arguments have to be modulated by what a dynamically
feasible orbital tour can do (delta-V, flyby geometries, making sure the flyby doesnt happen
in eclipse, or during solar conjunction or something..), and then there is ring science, and
Saturn science, and magnetospheric science to fold in....

p.s. don't underestimate Dione

Do tell! Does it have anything to do with interesting magnetometer readings?

i agree with ralph's assessment, including the comment about Dione. Dione is probably number 3 in terms of geologic and other complexities, behind Titan and Enchaladas. volcanic smooth plains, extensive graben networks and possible outgassing (all these are being worked on....). it is, or was, a dynamic moon indeed!
paul

Enchaladas?

I've always been in favor of ending the mission with a final Titan series ramping up the orbit so much that Cassini gets catapulted out of the Saturian system. This would preserve the spacecraft as a future museum piece. Either the last couple of orbits or the final escape could be aimed for a last swing past Iapetus.

In my daydreams, I see a final inbound of Cassini passing close by the fully lit trailing hemisphere of Iapetus, with the Snowman in all it's glory, on the way to the last ever Titan pass. Then Cassini is hurled sunward, where the last propellant is used to establish a halo orbit at Saturn's L1, where it continues to observe the planet till the day the reaction wheels give out.