We have before us several months devoted almost exclusively to study Titan. Does anybody know how many and which flybys will be dedicated for radar imaging ?

Almost exclusively to Titan is a huge exaggeration. There's lots of other stuff going on including all these Enceladus flybys you've been seeing and studies of the rings and Saturn's atmosphere for instance. Equinox will be an interesting time for these things.
From a slide I've seen there are 13 flybys in the XM that use RADAR. Not sure what mode it will be in though for each of those, so don't know which ones are SAR.

Brief note about extended extended mission planning:

Hmmm interesting Steve...
I wonder what the proposals were to "mitigate the shortfall" of available power?

I know very little about the power requirements for instruments on board, so am guessing here, but what can you not do without?

Thrusters/reaction wheels, computers, communications and heaters

I suppose it must come down to a decision over which science instruments are considered 'most important' and which draw the most power - a very difficult call, which will change on each orbit according to target importance/flyby distance.

I'm guessing that fields and particles experiments don't draw a lot of power, so perhaps mission planners may consider doing without the WAC, MIMI or UVIS for interesting encounters in a putative XXM?

Incidentally, I suppose that XXM planning is now at a fairly advanced stage, as we're a little over a year and a half from the end of the XM

As an addition to XXM musings, I notice that it has been at least posited that Cassini could continue actively gathering science at Saturn until the Northern summer solstice in 2017 (see Carolyn Porco's comments in 'Sector 6' on the Ciclops website here )
She points out that this would be nearly half a Saturnian year since orbit insertion.

Budgetary considerations aside, I was under the impression that propellant usage would allow another year or two at most of science operations after the extended mission finishes in 2010.

Obviously science activities would be severely curtailed with respect to the prime and extended missions, but non-targeted encounters would presumably still come about on occasion, with perhaps a handful of choice very close targeted flybys possible (Rings/Enceladus?) before EOM.

Many many 'if's' and not a few 'but's', but here's hoping.....

I've been told that the prime mission was a bit propellant hungry because they wanted to cram so many things in to the first four years. The extended mission is a little less propellant hungry, but still has lots of targeted flybys. If they're willing to wait a long time between targeted flybys, emphasize long-term monitoring of atmosphere, rings, and magnetosphere over icy sats -- and it'd help if they could plan for a many year chunk of XXM rather than just two years at a time -- they could be quite conservative with propellant, make it last a long time.

--Emily

That is always a tough one. One side of me wants to be as fuel efficient as possible. However, I would hate to play it ultraconservative and then have it pull an MGS-style vanishing act.

I imagine the arguments go a lot like the ones about Opportunity's next goal. Opportunity wouldn't be driving to Endeavour -- a goal it may never reach -- unless there was compelling science to be done on the way. The question is whether there's a stronger case to be made for more targeted flybys and a shorter extended mission, or a long "journey" of many orbits without targeted flybys. The latter will win only if the science being done on the journey is compelling enough to compete with the science that could be done with more targeted flybys.

--Emily

For me the main target is long term lake and weather monitoring of Titan. That's the place where decade-scale changes can be expected and where the available instruments can study an entire active system from surface to exosphere evolving through the seasons. Many close flybys may not be necessary for this, though a few well-spaced ones would be nice, especially for rotation studies.

I suppose most people fall into two camps:

1) Keep a sentinel out at Saturn that is serviceable and able to return data for as long as possible (though at a much less intense pace than the earlier segments of the mission), observing seasonal changes and with occasional Titan flybys to constrain atmospheric properties for future missions, or further Enceladus study.

Cons:
Possible failure of the spacecraft in the longer term before all goals are achieved
Greater cost

Pros:
More numerous non-targeted flybys of other places of interest
Seasonal changes on Saturn and Titan may produce some surprises.
The unknown - What price some images of a Schumacher-Levy type event impacting the rings or atmosphere in the longer timescale?

2) Design a spectacular and daring final two-year segment to the mission

Cons:
Missing out on seasonal changes
When she's gone, she's gone

Pros:
Cheaper

The ability to conduct some seat-of-the-pants investigations with a spacecraft that is already paid-for, and which you won't get the opportunity to do again.
This might include a highly-inclined trajectory with periapsis interior to the D ring (as has been suggested) with very close study of magnetosphere, Saturn's upper atmosphere and rings.
Or remain close to the plane of the rings and skim a few kilometres above them in the final couple of orbits, perhaps with the possibility of fields and particles instruments directly sampling the 'spoke' material and ISS obtaining some very high-resolution images of the ring constituents themselves.

Perhaps we should institute a UMSF poll.....

I think that's the key argument right there. (lower risk AND cheaper)

Well a Solstice Mission has already been talked about, so some on the team must already be inclining to the long option. It might cost more in the long run, but it might actually cost less per year which I'm sure would be welcomed in the current budget squeeze.

I would go with keeping Cassini going as long as possible, with occasional flybys using the lowest energy trajectories possible.
Taking "Guest Analysts" post earlier in this thread as a basis, in 2006 Cassini used 40 kg biprop (480kg down to 440kg) and 11 kg mono (104kg down to 93 kg) during a very active tour year. Assuming monoprop to be the limiting factor, if using 27g/day mono for "tour" mode, thats 10 kg year = 9 more years usage (from end 2006). If you are prepared to reduce towards "cruise" mode usage for long periods (6g/day) thats about 2kg/year = 45 more years usage. Of course the limit would then be the RTGs, batteries, gyros and other instrument life - but taking Voyager as an indication of what may be possible, we *could* have 20-30 years more use out of Cassini before its "death plunge", with sufficient biprop left for occasional major maneuvers & targetted flybys. Again, thats all just based assuming those original figures are right.
It would also be really useful to still have Cassini to hand if there is a future mission to Titan, a decade or more hence.

The largish amount of remaining biprop on board is intriguing - I wonder how much would be needed for orbital insertion into Titan, together with an aerobrake procedure? I know this idea was mooted/dismissed a long time back, but it would be interesting to know what the figures are. Would a high orbit around Titan be considered "bio-safe" and stable long term?

"Lower risk" because you are killing the craft before it has time to die itself.
Cheaper because you are killing the craft relatively quickly and ending ongoing costs.

I think the key argument is which mission will gain the more valuable information. Given the long life of various satellites and probes recently, I think its reasonable to think Cassini can last until the fuel runs out. I do recall some concern about gyros, and maybe that is a legitimate concern for and "untimely" end.

I haven't done the math, but I would guess that it might be tricky. I would venture to guess that Titan's atmosphere probably fills a decent portion of the volume of Titan's gravitational sphere of influence. Orbit around Titan would have to have an altitude of several hundred km of course, but how high can you get without Saturn's gravity plucking you from orbit?

Plugging in the numbers into the approximation from the Wikipedia page (caveat emptor), Titan's Hill radius is ~55,000 km.

Ttan's atmosphere is extended. Cassini's flybys had to be raised from the early mission plans to over 1000 km to reduce aerodynamic heating at the flyby speeds. It's a little less dense over the poles, so the polar flybys go in near the original planned 950 km.

The TSSM3 pdf from the November OPAG meeting mentions Titan orbit altitudes. For aerobraking, periapsis is ~600 km (dual purpose of direct atmospheric sampling for the mass spectrometer). Circular orbit is ~1500 km to avoid having to burn propellant to maintain altitude.

Just a small correction, AFAIK it wasn't aerodynamic heating that was the problem, it's that the atmosphere appeared to be exerting more torque on the spacecraft than their models predicted, which creates a problem for planning the spacecraft's attitude during the flyby.

--Emily

A few asides from the peanut gallery...for the iceball-obsessed crowd, myself included, I think we've gotten a virtually miraculous tour and XM. I'd like to see another reasonably close pass at Hyperion from a different perspective, a couple more close views of Dione's cliffs, preferably in low sun, and as many visits to the various rocks as are possible. Another Iapetus encounter is probably out of the question. Gapfill imaging of the north polar regions of each world would be nice wherever possible as well. In the XM, we have high-resolution coverage of the poorly imaged leading hemisphere of Enceladus, the fractured side of Dione, Rhea again, and Herschel on Mimas to look foreward to already, not to mention the Helene flyby and a few decent nontargeted encounters. A few more SAR swipes at Titan would give us 50% coverage in the long term, and maybe complete IR coverage of the emerging northern hemisphere. I'm inclined to support the long option, with the primary focus on atmosphere and rings, especially in light of the ugly financial picture. It would be cool to see those ring-shadows spread again, and watch the south turn blue.

I never did reply to this because I really don't know, although it is important to remember that without a scan platform good chunks of the instruments aren't necessarily being used at times. Fly-bys now will change pointing several times, but if you're assuming that (for example) the imaging instruments are off for an entire fly-by, you probably get much simpler mission planning as well as lower power consumption. I don't know if you could do it without reaction wheels. Fields and particles, I guess.

Stumbled across this kodak moment using the solar system simulator
Click to view attachment

Completely new design of Cassini-Huygens site.
http://saturn.jpl.nasa.gov/
I liked the old.

Looks like the ESPN site. Can I get the basketball scores on the Cassini page now?

Seriouserly, I fondly recall the way the Cassini page looked during the long flight to the Saturn system. The status reports gave me comfort, and made me feel very close to the mission itself. IMO there's not much need to go for the "wow" factor with a splashy front page -- there's plenty of "wow" in the images themselves to attract people to the amazing scientific achievements of the Cassini mission.

I like it. The stuff I regularly look at is still easy to find, and the stuff I didn't know about is now there as well. The old site was a navigational mess.

I liked the current number of moons counter they used to have on the Cassini site . That was a good way of keeping up with the scores.

For me the new site takes ages to start. The raw image thumbnails have a bizarre horizontal stretch. Worst of all searching the raw images is so slow as to be completely impractical. When I eventually got page 2 of 'Titan' 'Newest' to open just now I fiound myself looking at an image from February. I seem to recall we've had more that 10 images of Titan since then.

Call me when it's fixed.

How about emailing the Cassini web team to report your problems?

The new site is horribly slow. All of that Flash stuff on the main page with lots images etc. takes ages to load (several minutes). Hopefully this is just a temporary problem.

However, I like its new look.

Yeah. I was half joking. I'm sure they've got people on the case. I thought I'd wait and see how it settles in after a few days, also try logging in from a couple of other terminals, see if others here are having similar trouble etc.. But If I still can't search the raws properly I will certaily contact them direct.

FWIW - speed wise - it's as good for me now as it was before. Several minutes is certainly not right.

Maybe everyone is rushing to check if the site is really that slow, thus making it slow .

I can't get any of the selected raw images to open up. When I click on a (distorted) thumbnail, it goes to a generic page, after a multi-second load.

I'm really, really hoping that this all gets sorted out quickly.

[Lucky for me, I'd downloaded the T46 Raws as few days ago, no way do I have the patience to do it now.]

As I said before, if you're having technical issues - email them in. FWIW - The raw page is as fast as it was before for me. The thumbs are a bit distorted in a slight 4:3 sized window, but that doesn't matter.

Doug

Looks ok to me in Firefox 3. It is a little slow but not much.

Then it screwed up on this page......

http://saturn.jpl.nasa.gov/photos/imagedet...fm?imageId=3329

"an
e-mail sent to Cassini.Edu@jpl.nasa.gov.

The "Millenn"

seems some fine tuning is needed.

I have bad timing when it rolls between 3 lead stories with images, captions and "Read More". Might as well have my eyes closed, hehe.

I'm having more luck at home with Firefox than with Internet Explorer at work, but even so the raw images don't seem to come up in correct chronological order all the time.

The old site had a link on the right hand side that went to a page with what I thought of as CPOD (Cassini Picture Of the Day). IIRC, the link was named "Latest Images" or something to that effect. I did not find the equivalent page on the new site.

Just to let you know the Cassini realtime simulation at http://www.dmuller.net/cassini finally includes trajectory data and some fixes to make it load faster.

On that note, if anybody has a standard solution (like an exe file) of converting NAIF SPICE kernel files into (x,y,z,t) coordinates, pleeeease let me know :-)

Thanks, Daniel, what a great resource.

Thanks to a very kind soul who provided a very easy solution (easy = I can handle it!) I can now load SPICE kernels into the realtime simulations, greatly enhancing the accuracy of the trajectory of some missions. First update applied to Dawn. Go Celestia!


You're welcome! Glad that it is of use.

With the drawing-to-a-close of the first mission extension, and to express appreciation of Cassini-Huygens so far, I thought I'd put together a brief round-up of the achievements so far of this remarkable mission.

Distance travelled: around 5.5 billion kilometres
Time in flight: ~13 years
Orbits of Saturn: 133
Titan flybys: 71
Enceladus targeted flybys: 11
Images taken: around 200,000

Major discoveries/confirmations:

Standing bodies of liquid methane/ethane on Titan
Active cryovolcanism on Enceladus, and a big hint towards subsurface oceans
6 new moons
Multiple new rings/ring arcs
Rings/ring arcs around Rhea
Organic materials in the Enceladan plumes, hydrocarbons on Hyperion

Images/movies obtained of:

Saturn's north and south poles
Surface of Titan at ground level
Specular reflection from Ontario Lacus on Titan (the first time time has been observed anywhere except earth)
Saturnian lightning and aurorae
Numerous occultations and mutual events between the moons and rings
21 icy moons at better than 100,000km range
Of which 15 at better than 25,000km range
Of which 5 at better than 5,000km range

Other achievements:

Doppler tracking gravity measurements at Enceladus
Multiple radio ring occultations
Radar mapping of around 40% of Titan
Light-curve analysis of many of the tiny outer moons to attempt to discern rotation rates
Infrared analyses of Enceladus' polar vents, a well as the other icy moons

I was trying to think of the most stunning image returned so far, and am torn between three:

Enceladus' plumes rising into the sunlight from beyond the terminator
Close-up of Iapetus' mountains
Saturn from the very high orbital inclination with it's shadow cutting across the rings


The spacecraft is apparently in fine fettle, and we have another 7 years of the solstice mission to look forward to, including more of the same, and those proximal orbits towards mission end - can't wait!

Jase

Good list.

One question: The rings or ring arcs around Rhea haven't been confirmed yet, have they? AFAIK, we have some inference from magnetometer readings & those odd crater chains on the surface, but that's it.

Yeah, the Rhea flyby in (IIRC) March hasn't had any F&P data released yet. If there is something wonderful forthcoming that would be great.


I didn't know about the outies light curve studies. Interesting to see if any oddments turn up. BTW, I can't think of any way light curve data would yield orientation of spin axis, but I would be happy to be wrong. I suppose colorimetry data on the outies would be asking too much too . . .

Yes, perhaps me being a bit over-eager Nick!

The literature seems a little contradictory in some respects - when reading the reports, you get the impression that a set of rings or arcs is the only explanation for the data, but they can't be definitively confirmed without visual evidence.

Three instruments detected dust directly, and the magnetometer readings point strongly towards something present, as the pattern of fluctuations in the readings was mirrored on either side of Rhea (analogous to the discovery of Uranus' rings when they occulted a background star as seen from Earth). Then there is, as you say, the equatorial band of dark markings on the moon.

Visual observations during the close flyby failed to turn up anything, so if there are rings or arcs, then they're likely larger constituents, and probably with low albedo (that omnipresent dark stuff in the saturn system again)

Perhaps it would be better for now to put this in the "strongly circumstantial, but not confirmed" pot then....

Jase

I would include sublimation/albedo/temperature feedback on Iapetus as a major discovery. Also there have been many more big discoveries on Titan besides the lakes, such as convective storms that produce precipitation, river valley networks, complex organic chemistry and the equatorial dune seas.

Very detailed update of the Cassini trajectory information over at Emily's blog Thanks Emily!

Encounter distances for the remainder of the mission change a little, with some minuses and some pluses.

For example, Telesto's encounter distance in May 2012 rises from 2,868km to 10,989km and Helene in June 2011 rises from 1,807km to 6,982km

But Rhea's closest encounter distance in January 2011 drops from 201km to 76km, and Dione's closest approach in December next year drops from 199km to 99km.

As Emily says, lots of geek fun to be had here perusing the detail

Jase

Awsome Cassini has turned out to be so much bigger than ever expected back in 1997.