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  Cassini-Huygens at Saturn: Questions, comments (Page 4)

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Author Topic:   Cassini-Huygens at Saturn: Questions, comments
spaceuk
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posted 02-24-2005 01:44 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Blackarrow:
Does anyone know if Cassini has enough fuel left to reduce speed while passing Titan and go into orbit around Titan?
That's a good question.

At launch Cassini had 6,905 lbs propellants (nitrogen tetroxide and monomethylhydrazine) - just love that latter chemical word!

It used just under half that amount of propellant during the 96 minute SOI burn last year. During its orbits of Saturn until 2008 it has 157 trajectory maneouvres to accomplish under the current flight program - some of which include adding the energy derived from the flyby's of Titan.

Because of the difference in orbital inclations it would require a plane change burn - where some considerable amount of propellant would be required. Additional flight plan software would need be developed and uploaded and several TCM's achieved to put Cassini in the right position for a TOI burn.

Would it have such a propellant quantity available left in 2008?

If it did achieve orbit of Titan what additional information could it gather beyond that already being gleaned between now and and its last flyby of Titan in May 2008?

It's a good question though and I'll root a bit deeper for more info.

I've some early Cassini-Huygens material (the craft was based on a Voyager design) and see if there was anything in that where they may have contemplated either orbiting Titan with Cassini or whether a seperate attached probe that would have been released and orbited.

spaceuk
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posted 02-24-2005 03:41 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
There was no particular discussion of Cassini becoming a Titan orbiter in the documentation.

Reading through the material though did highlight some information that is relevant.

Each Titan flyby is primarily aimed at producing the desired spacecraft orbit for other moon flybys rather than optimised for Titan flyby science.

Secondly, low flybys of Titan tend to favour radar imaging and atmospheric science whereas other science experiments favour higher flybys. It mentions, in particular, that the remote sensing packages hich rely on the raection wheels to maintain spacecraft stabilisation. At a low flyby orbit (and by inference an orbit about Titan) would have problems since at low altitudes the the motion of Titan beneath is too fast for the reaction wheels to keep up.

Therefore, any orbital mission about Titan using Cassini, would obviously be comprimised in the results it might achieve.

The main "attractor" on Cassini is, of course, Saturn and any residual propellant would have to be sufficient to overcome that planet's gravitational pull.

Several large burns have already taken place including the Earth, Venus flyby's and the SOI insertion burn and therefore propellant margins must be at about the 2/3rd's used mark - at a guess? Around 2,000 lbs, maybe less, probably left?

Possibility of a Cassini becoming a Titan orbiter? Very very doubtful I would think.

Philip
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posted 02-26-2005 05:57 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Interesting info Phill...

Meanwhile Cassini has made more astonishing photos of Saturn's rings.

spaceuk
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posted 02-26-2005 06:09 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
Philip, I'm still looking at this question in depth - mainly for the fun.

The problem is that detailed engineering data of measurements (propellant, attitude etc) made onboard Cassini are not - as you would expect - in the public domain! If they are - haven't found them!

The closest detail is in press kits, some PI preflight papers and the major burn press releases.

It might be able be 'modelled' (if sufficient accurate data was available) using the "Satellite Toolkit" software?

Toward the end of prime Mission in June 2008 they are going to do a "Titan 180 degree transfer" maneouvre. Not yet been able find out what this is about.

If you look at today's orbit on the "Where Is Cassini Now", it is in a long elongated elliptal orbit almost 90 degrees to Titan orbit looking down onto orbit plots.

I think the largest problem of trying insert into a Titan orbit will be the need for sufficient propellant quantities to undertake the required maneouvres.

A simple Hohmann transfer might be able achieve it by doing a burn to leave the Saturnian orbit,then coast toward Titan and then a burn - with plane change - to enter into a orbit about Titan? But these burns would need considerable propellant quantities which it will not have at end mission?

There may be some other more esoteric trajectory types but don't have enough info to determine that.

It's all good plane trajectory fun.

spaceuk
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posted 02-26-2005 01:34 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
I found the following information which is of direct interest to the question asked.

The total thrust available to Cassini during its many tours of Saturn is only 500 meters per second.

The reason it undertakes the close Titan flybys is that it can change the spacecraft Saturn-relative velocity by many hundreds of meters per second enabling it to do the flybys of several other Saturnian moons.

On average this imparts about 770 meters/second per flyby of Titan.

The small amount of remaining propellant is used to provide for very small trajectory change manoeuvres or to turn it for science experiment pointing requirements and for re-alignment of the antennas with Earth for good communication paths.

There are 45 targeted encounters that will need 135 manoeuvres during the 'prime mission'.

Cassini needs to make a sequence of three small manouvres after each Titan flyby to set its self up again for the next Titan flyby trajectory. These account for about 8 to 11 meters/second for the full sequence.

So, we can probably guess that towards the end of the prime mission in June 2008 there will be very very little propellant left to use.

Blackarrow
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posted 02-28-2005 05:39 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Phill, thanks for the interesting comments. I get the impression that a Cassini orbit is a non-starter. (Given the choice, I would choose extra orbits to provide extra images, preferably the moons which won't get so many visits. I'm particularly keen to see ultra-close-ups of the transition between the light and dark regions on Iapetus.)

DavidH
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posted 03-03-2005 03:19 PM     Click Here to See the Profile for DavidH   Click Here to Email DavidH     Edit/Delete Message   Reply w/Quote
Are there more Huygens images yet to come from on or near the surface of Titan? Initially, it sounded like the one surface picture that was released was just one that was processed quickly, and more were yet to come, but that may have just referred to the descent pictures. Does anyone know?

Philip
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posted 03-04-2005 12:21 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
I guess the Huygens probe is 'silent' nowadays, imagine the extremely cold temperatures it had to endure!

spaceuk
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posted 03-04-2005 06:06 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
I understand that all the Huygens images were downloaded in those few hours that it operated.

These were the images that are displayed as 'raw' images on the UniAZ site.

Because of the orientation of the craft on surface, the camera was pointing in one direction only and several images of the "same scene" therefore appear.

What we may see in the future are cleanedup images but doubt if they will show any further detail beyond what we have already seen.

Astro Bill
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posted 03-04-2005 08:30 AM     Click Here to See the Profile for Astro Bill   Click Here to Email Astro Bill     Edit/Delete Message   Reply w/Quote
I do not know if there are any addditional Huygens photos to come, but the April issue of Astronomy magazine has six pages of Cassini/Huygens photos. Titan is a fascinating place and I am sure that we will return there as soon as we can.

DavidH
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posted 03-04-2005 09:50 AM     Click Here to See the Profile for DavidH   Click Here to Email DavidH     Edit/Delete Message   Reply w/Quote
Thanks for the explanation.

Yeah, I would love to see a return to Titan. Fascinating place.

(Though I certainly wouldn't mind seeing a lander set down on our nearer neighbors, the Jovian moons, first. The space probe image I hope to see before I die: Jupiter-rise from one of its moons. Can you imagine seeing that giant rise into the sky above? Wow.)

Rodina
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posted 03-04-2005 03:15 PM     Click Here to See the Profile for Rodina     Edit/Delete Message   Reply w/Quote
There are no more Huygens images to come off the probe. I don't yet know if ESA has published all the raw images or not.

spaceuk
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posted 03-04-2005 04:26 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
Very good images and a lovely movie sequence of the Cassini-viewed Dione and Rhea "mini eclipse".

spaceuk
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posted 03-05-2005 08:19 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Blackarrow:
Does anyone know if Cassini has enough fuel left to reduce speed while passing Titan and go into orbit around Titan?
Yep, just not enough propellant available.

Not even at this stage in its mission - even if we wanted to.

I still have not yet had time to workout the kinda burn times that would be needed to accomplish this type of Titan orbit scenario.

Just for the fun of it and get a feel for what values of propellants would be needed.

Need to work out how long the burn time would be to accomplish thrusting out of an orbit about Saturn and into an orbit about Titan. Probably need a Hohmann transfer burn out its orbit of Saturn with a plane change burn and orbit insertion burn at Titan.

The biggest problem is trying to find the right maths values in the same measurement units (eg km/sec) for the several calculations needed. Wherever you look the constant values may be given - but in different units ! Hoping get another go at it tomorrow since I found an obscure NASA site with them in.

spaceuk
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posted 04-09-2005 02:40 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
NASA's Cassini spacecraft successfully flew by Saturn's moon Titan at a distance of 2,402 kilometers (1,493 miles) on Thursday, March 31. Cassini's multiple instruments are providing new views of the haze-enshrouded world. Titan's haze was the focus of ultraviolet observations. Titan's transient clouds were also studied during the flyby.

Recently, scientists noticed episodic interferences on the composite infrared spectrometer that were traced back to the time of orbit insertion. A mirror on the spectrometer is showing some signs of jitter. The movement may be associated with the use of the spacecraft reaction wheels, used for spacecraft pointing control. A motor on one of three sensors on the magnetospheric imaging instrument and another motor on the plasma spectrometer are also not working properly. However, a workaround has been identified for the latter. All three instruments continue to function, although with some reduced level of science data collection.

Philip
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posted 05-26-2005 01:02 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Hmm... interesting: Odd spot on Saturn's moon Titan baffles scientists

spaceuk
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posted 06-08-2005 03:46 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
Scientists on the Cassini-Huygens program are saying that they are 99% certain that there is now no liquid methane ocean on Titan. But this new findings means there must be another mechanism behind the methane production.

They have also released an image showing part of Titan with a volcano in the upper right part and what appears to be like a lava flow from it. Further down in the image (lower left) on wider part of this flow this 'lava flow' is where Huygens landed.

Scientists are stressing however, that they are not certain whether it is a volcano or maybe an impact feature in the image. They are also saying they are unsure - at this stage - whether it is a lava flow. But they are looking for any hot spots or volcanic plumes in Cassini data from each fly by it makes.

spaceuk
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posted 07-14-2005 02:40 PM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
Nice recent x-ray image of Saturn's moon Titan showing the "Smile" and Xanadu.

Philip
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posted 07-15-2005 12:03 PM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Great images... pity this month as the planet is located too close to the Sun in the evening to see it through a telescope!

Blackarrow
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posted 07-20-2005 08:22 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Why has there been so little information about the very close flyby (c. 150 miles) of Saturn's moon Enceladus on 14th July? Perhaps not as newsworthy as Deep Impact, but surely worth more coverage? I searched the usual sites in vain for any mention. Of course, raw images are available on the Cassini-Huygens sites, but without commentary. Enceladus is arguably Saturn's most interesting Moon after Titan. It is tiny, only a few hundred miles in diameter, yet extremely active geologically. The surface is apparently being stretched, distorted and torn apart, with cracks and fissures visible down to the limits of resolution. There are areas of heavy cratering adjacent to areas with no craters which must have been totally melted or resurfaced in recent times. If this whets your appetite, look for the raw images. If there are any web-sites interpreting the most recent flyby images, I would appreciate a link.

Geology rocks!

Blackarrow
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posted 07-25-2005 04:53 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
The lack of response to my original post answers my original question.

Carrie
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posted 07-26-2005 07:17 PM     Click Here to See the Profile for Carrie   Click Here to Email Carrie     Edit/Delete Message   Reply w/Quote
If you haven't already noticed, there was a big update to NASA's Cassini site in the last day, with many pics of Enceladus.

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posted 07-29-2005 05:01 PM     Click Here to See the Profile for kymma   Click Here to Email kymma     Edit/Delete Message   Reply w/Quote
Take a look at the latest press release about the Enceladus encounter.

Very Exciting!

Philip
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posted 09-19-2005 05:49 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Take a look at this remarkable NASA-JPL images: Shoreline on Titan?

Scott
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posted 09-19-2005 11:35 AM     Click Here to See the Profile for Scott   Click Here to Email Scott     Edit/Delete Message   Reply w/Quote
Thanks Philip! You always provide the most interesting links and images.

spaceuk
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posted 10-02-2005 04:16 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
I hope you've seen the spectacular images of Hyperion, Tethys and Titan downlinked these last few days?

tegwilym
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posted 10-03-2005 01:41 PM     Click Here to See the Profile for tegwilym   Click Here to Email tegwilym     Edit/Delete Message   Reply w/Quote
Yep!

Blackarrow
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posted 10-03-2005 04:30 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
I remember seeing the Voyager images of Saturn's weird-looking moon Hyperion and wondering how it would look really close up. A quarter of a century later, now I know. And it's even weirder than I expected!

Ben
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posted 10-03-2005 04:59 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
The image of Hyperion is amazing. I keep thinking "there's a moon under those barnacles!"

Philip
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posted 10-04-2005 12:01 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
We're been treated and should be happy to have a spacecraft in orbit around Saturn for the next few years!

Philip
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posted 11-06-2005 08:28 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Features on Titan named.

spaceuk
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posted 12-04-2005 06:41 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
A good techie summary of the results from Huygens descent and landing to Titan surface.

Complete with good images,science charts and images.

Philip
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posted 12-09-2005 10:16 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
Free NATURE webpage with 1-minute animation of the Huygens probe descent onto Titan.

Scott
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posted 12-09-2005 03:15 PM     Click Here to See the Profile for Scott   Click Here to Email Scott     Edit/Delete Message   Reply w/Quote
That's a wonderful movie. Thanks Philip. And thanks Phill for all the exploration links and news you share.

spaceuk
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posted 12-22-2005 06:55 AM     Click Here to See the Profile for spaceuk     Edit/Delete Message   Reply w/Quote
An important flyby of Titan on 26th December by Cassini since it will be in a region of space first explored by Voyager-1 in 1980.

So, any new data collected in that area can be compared to what was collected 25 years ago.

Columbiad1
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posted 03-09-2006 08:58 AM     Click Here to See the Profile for Columbiad1   Click Here to Email Columbiad1     Edit/Delete Message   Reply w/Quote
Is there only one surface photo of Titan? Are there other photos of the surface? Why weren't there more photos taken? Is Huygens still operating sending and receiving data?

Philip
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posted 03-09-2006 11:53 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
There are some nice photos put together from images taken during the descend.

DavidH
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posted 03-09-2006 12:15 PM     Click Here to See the Profile for DavidH   Click Here to Email DavidH     Edit/Delete Message   Reply w/Quote
Water Found?
NASA's Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn's moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

"We realize that this is a radical conclusion - that we may have evidence for liquid water within a body so small and so cold," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colo. "However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms."

SpaceAholic
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posted 05-05-2006 12:26 AM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
This is absolutely the coolest thing I have seen in a long time... is there a high res version of the film (I only can locate what appears to be the small frame Quicktime version).

Robert Pearlman
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posted 05-05-2006 12:52 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
I haven't been able to find a higher resolution of the above movie yet, but coming in a close second on the "cool-o-meter" is this music video (The View from Huygens, 70 mb) which plays the same imagery but with a different perspective and a much larger size.


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