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Posted by: ustrax Mar 12 2007, 03:22 PM

I thought about a new thread since there are possibilities of an http://spaceurope.blogspot.com/2007/03/fly-me-to-moons-athena-coustenis-and.html.

The idea is to know what would people like to see on a mission like that, nature of probes, instruments, experiments...you name it!

Posted by: Juramike Mar 15 2007, 08:39 PM

In order to deliver a box into Titan orbit or onto it's surface/lower atmosphere, could you perform two aerobraking/aerocapture maneuvers? (This was proposed by Zvezdichko for Jupiter orbit in the Jupiter forum and seems interesting for Titan) A potential scheme is shown below.

Advantages might be to be able to launch directly and often from Earth orbit (a la New Horizons) or with a gravity assist from Jupiter (in which case timing becomes key).

Risk of hitting material in the ring plane would be minimized since the probe would be passing in the atmosphere in this area. Ring material would not in a stable orbit at this low altitude.

Another advantage would be that minimal thrust would be needed for orbital insertion (either Saturn or Titan), one would use the atmospheres of both for slowing the box down. (The atmospheres should be pretty well-studied from analysis of Cassini data)



(Please forgive my obvious naivite with orbital mechanics and Powerpoint drawings)

-Mike

Posted by: JRehling Mar 15 2007, 08:57 PM

I like it -- but the potential for bending the path around Saturn by the needed amount seems wishful. It seems to me that without a lot of chemical engine use, the intersect point with Saturn would be at very high latitudes and bounce it back out while still at high latitudes. In essence, the path needs to bend 270 degrees from cruise to Titan entry, and I'm not sure that the specified plan would do that. A lot of propellant would be required in any case. This situation would be eased if things stayed more in the ring plane so that an arbitrarily lower "bend" would be required.

Posted by: Juramike Mar 15 2007, 08:59 PM

Maybe a sample return mission from Titan is reasonably doable after all.

Getting a package to Titan's surface has been done (Huygens landed and survived)
Getting a package off Titan's surface may be a bit trickier, but Titan has the bonus of liquid fuel in the form of Methan/ethane. We would only need to supply the oxidizer (oxygen).

I picture an atmospheric balloon with multiple sample containers. It sets down, scoops stuff into a container. Proceeds to the next location, scoops more in, etc.. It finally drifts over to a methane/ethane lake, fills up the propellant tanks for the escape package. Floats up to maximum altitude and the escape package (which has the oxygen tank) ignites, separates and goes back to Earth on a long slow trajectory.

Even after the escape package separates, the balloon could still maintain a smaller instrument package for surface imaging, MS analysis, and other meteorological analysis for a long duration stay in the Titan atmosphere.


Even a small amount of non-volatile material from the Titanian surface delivered to Earth would speak infitine volumes about Titan surface chemistry and the potential for life.

-Mike

Posted by: mchan Mar 16 2007, 04:30 AM

At this point we don't know what the exact constituents of the "lakes" are or even 100% certain that the "lakes" contain liquid. Good knowledge of this from precursor missions would be required before designing a sample return mission around the use of in-situ fuel. E.g., can the fuel be used as-is or would some separation / refining be required? One might be able to burn some crude oil pumped directly from the ground in an automobile engine, but refined gasoline or diesel would be better.

Regarding the dual aerobrake, the Titan aerobrake is not required to be on the 1st outbound leg after the Saturn aerobrake. Recall Cassini's trajectory and Huygen's deploy after the SOI burn. The delayed Huygens deploy was because of the link receiver problem, but the point is that there is flexibility to schedule / delay critical orbit maneuvers to make more efficient use of trajectory correction fuel.

Posted by: Greg Hullender Mar 16 2007, 04:01 PM

Sadly, this isn't much of a win. When you burn methane or ethane in oxygen, 2/3 of the mass comes from the oxygen.

--Greg

Posted by: Edward Schmitz Mar 16 2007, 04:42 PM

she talks of acetylene icebergs - but acetylene sinks in methane...

my links didn't work...

Posted by: JRehling Mar 16 2007, 04:47 PM

I guess the problem is assuaged by the fact that a nuclear power source could extract oxygen from ice, if H2O is within grabbing distance. That may not be a trivial assumption or engineering feat. And it leaves the problem that this rocket ultimately has to escape not just Titan but Saturn.

Posted by: centsworth_II Mar 16 2007, 05:16 PM

Maybe acetylene polymers with voids?

Posted by: Edward Schmitz Mar 16 2007, 06:35 PM

Escaping Saturn is easy with Titan's help. Getting to another assist after Saturn might be difficult. It could always get a second boost from Saturn - 29 years later!

Actually, now that I think about it, I'll bet it could do a short loop (free of Saturn) and intercept it (saturn) several months later. This should be able to get it to Jupiter, which of course could launch it toward the inner solar system.

Yes, if it could escape titan, it should only need mid-course-correction fuel after that.

ed

Posted by: Rob Pinnegar Mar 16 2007, 07:13 PM

Nice idea, but the problem is that it would re-encounter Saturn at more or less the same relative velocity with which it departed. In a vacuum, what goes up comes down the same way.

Perhaps there's some way to make this work, but if there is, it'd have to be pretty convoluted. A VEEGA-type trajectory might be technically feasible for the outer planets, but it'd be a long wait, even for one loop.

Posted by: Edward Schmitz Mar 16 2007, 10:36 PM

If Saturn was in deep space (not in orbit around the sun), the second encounter would not be possible. It would have already achieved escape velocity. They would forever continue to move apart.

This theoretical probe would be flung into a solar orbit. This orbit would be highly unstabile and heavily influenced by Saturn. By the time it made it's second encounter, it would have a significantly different geometry than during the escape.

After escape, the probe would briefly get out ahead of Saturn in a higher orbit. Saturn would then approach the probe from below and behind. As Saturn's pull slowed the probe down, it would fall lower until it swooped past Saturn on the inside of it's orbit. This would have a stalling effect on the probes motion. It would fall inward toward the sun. I believe this could be pretty dramatic.

I'm not sure I'm describing it well but I can picture it.

ed

Posted by: Juramike Mar 16 2007, 11:01 PM

Dear Ed,

Are you talking about a second Saturn encounter after escape from Titan surface, or before landing on Titan's surface (outbound to Titan vs. inbound to get to Titan)?

Sincerely,
-Mike

Posted by: Edward Schmitz Mar 20 2007, 04:28 PM

We were discusing escape of a probe from the saturn system with the intent of returning to earth.

I was talking about using saturn for a gravity assist after the probe had left saturn. I would like to creat a simulation but it will take some time...

ed

Posted by: Greg Hullender Mar 20 2007, 04:50 PM

You only have to reach the Sun-Saturn L1 point; from there, you have a free transfer to the Sun-Jupiter L2 point. That takes “a few decades” according to Shane Ross.

http://pr.caltech.edu/periodicals/EandS/articles/LXV4/exit.html

It's a free transfer from Sun-Jupiter L2 to L1, and then about as far as Mars, but from there you're on your own; the free transfer from Mars to Earth is about 10,000 years, so burning some fuel would seem in order.

--Greg

Posted by: ustrax Mar 21 2007, 04:16 PM

Greg, the implications of this are incredible!
It's like we've been swimming against the current so far...
Off topic question, will an object free from Earth's gravitacional attraction, head to some particular direction?
Will it end its journey in the Sun?

Posted by: PhilCo126 Mar 14 2009, 12:33 PM

Today's Sky at Night: The Fountains of Enceladus
Saturn's mysterious moon Enceladus has startled astronomers with its amazing ice geysers, which spew out material into space. Sir Patrick Moore talks to the scientists who are trying to unlock the secrets of this tiny world.

Posted by: lyford Mar 30 2009, 03:12 AM

Kind of a silly aside, but the built in Mac spell check came up with this:

Apparently, there are those who prefer this pronunciation!

Posted by: Shaka Mar 30 2009, 06:06 AM

...of course, in Mac spell. But the more compelling question is: Should it be "en-sel-a-dus" or "en-kel-a-dus"?

(This should drive a wedge in the anglo-american alliance!)

Posted by: stevesliva Mar 30 2009, 03:26 PM

sel. With the second syllable accented, it seems. I personally always read it with the third syllable accented, but that's because I spanishize all unfamiliar words.