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Neptune Orbiter, Another proposed mission
chris
post Dec 5 2005, 03:07 PM
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QUOTE (Toma B @ Dec 5 2005, 01:27 PM)
Question:
Will methane explode without oxygen?
NO IT WILL NOT !!!
...there's not much oxygen on Triton isn't it?
About Nitrogen...
How long would rocket engine work when verry close to surface...2-3 seconds perhaps?
Without any atmospheric presure there might be some sublimation but I'm sure nothing exiting....

*


Toma,

I wasn't talking about combustion. The explosion I am postulating would be purely mechanical, driven by gas pressure. Imagine if the exhaust warmed some water ice with pockets of nitrogen gas in it.

Secondly, remember the geysers on triton - small in temperature lead to some pretty dramatic effects - from Wikipedia:

"It is thought that the surface of Triton probably consists of a semi-transparent layer of frozen nitrogen, which creates a kind of greenhouse effect, heating the frozen material beneath it until it breaks the surface in an eruption. A temperature increase of just 4 K above the ambient surface temperature of 38 K could drive eruptions to the heights observed."

(That height being 8Km!)

Chris

Edit: added Wikipedia info
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JRehling
post Dec 5 2005, 04:23 PM
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QUOTE (Toma B @ Dec 5 2005, 12:34 AM)
Mars atmosphere is 143 times less efficient in aerobraking then atmosphere of Earth is...
Triton atmosphere is 467 times worst then Mars... sad.gif
So it would take gazillon passes through it to slow down significantly... sad.gif
*


The proposal is certainly complicated, but your calculations are not relevant. Aerobraking would not take place at the surface, but high up, and Triton would have a high scale height. Whereas aerobraking at Earth would involve a short skip through the upper atmosphere, aerobraking at Triton would involve about 1000 km through gas not that much less dense than at Triton's surface.

Of course, if you want a source of gas to really slow down through, Neptune is right next door. The problem is, if aerocapture is used on the way in, the resulting orbit would probably be one that would make it very difficult to later pass through Neptune's atmosphere again -- unless a low peri-neptune were maintained throughout the mission.

A more feasible combo mission might be an orbiter/Triton lander duo. One heatshield for braking in Neptune's atmosphere would be utilized. The craft would be stacked as follows:

Heatshield
Triton lander
Neptune orbiter

On arrival, the stack would aerocapture into a Neptune orbit with peri-neptune very near the cloudtops. The orbit would be highly eccentric, and intersect Triton's, allowing several flybys to perform initial reconnaisance and landing site selection. Then, on one apo-neptune, the orbiter's thruster would point the stack onto a path into Neptune's atmosphere. Then the orbiter would separate, leaving the heatshield on the lander. The lander would decelerate through Neptune's atmosphere, and emerge on an "orbit" that would just barely make it to Triton at apo-Neptune, at a low velocity relative to Triton. Then a ballute system might be able to bring the lander down. The orbiter would continue on indefinitely.

Seems inordinately difficult. Also, I don't see a Triton lander being part of the next mission to that part of the solar system. I'd bet on a Neptune entry probe first.
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Toma B
post Dec 6 2005, 08:48 AM
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QUOTE (chris @ Dec 5 2005, 06:07 PM)
I wasn't talking about combustion. The explosion I am postulating would be purely mechanical, driven by gas pressure. Imagine if the exhaust warmed some water ice with pockets of nitrogen gas in it.
*


All right Chris...maybe you are right...I'm no expert in Triton's surface nor atmosphere...

But I do know this:
It's not like we are going to land 10 ton "lander-rover", using some surplus Saturn-5 rocket engines that burn ferociously for 10,15 seconds near surface so that they can melt some nitrogen ice andtherefore cause violent sublimation...
It's more like small lander 100-200 kg with small engines working at low power near the surface for 2-3 seconds...so if there would be some melting/sublimation it would not be verry hazardous to the unfortunate lander in question...

BTW it's not like they are really planing any Neptune/Triton mission so it's not so big deal... sad.gif


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chris
post Dec 6 2005, 10:41 AM
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QUOTE (Toma B @ Dec 6 2005, 08:48 AM)
All right Chris...maybe you are right...I'm no expert in Triton's surface nor atmosphere...


Me neither - my expertise comes straight from Google smile.gif
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ermar
post Dec 10 2005, 02:23 AM
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As a long-time lurker, sorry for spamming links, but I couldn't help but notice:

http://news.bbc.co.uk/2/hi/science/nature/4515752.stm

Of course, if such a mission were ever to fly, they'd likely ditch the probes/landers... (not that I am advocating that, but how many times have mission add-ons been sacrificed before the bottom line?)
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Guest_BruceMoomaw_*
post Dec 10 2005, 06:42 AM
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They definitely won't fly the nuclear-propelled version. Not only would it be gigantically expensive -- Project Prometheus, O'Keefe's brain child (if that's the word for it), has now been cancelled -- but it would actually take considerably longer to reach Neptune than the tremendously cheaper alternative version of this mission, which will reach Neptune with a Jupiter gravity-assist and/or solar-powered ion engines, and then brake into orbit around Neptune with aerocapture. JPL has worked out the design for that one in great detail already, and I think it likely to fly some time before 2030 -- although it will still cost $2 billion or more. (Its main rival for an expensive Solar System launch in the 2020s seems to be a large Europa lander.) At a minimum, it would carry two Neptune entry probes (unless NASA has already taken them to Uranus or Neptune on a cheaper flyby mission) -- but a Triton lander is definitely an optional accessory for it, depending on funds.
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Toma B
post Dec 10 2005, 06:56 AM
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QUOTE (ermar @ Dec 10 2005, 05:23 AM)
As a long-time lurker, sorry for spamming links, but I couldn't help but notice:
http://news.bbc.co.uk/2/hi/science/nature/4515752.stm
Of course, if such a mission were ever to fly, they'd likely ditch the probes/landers... (not that I am advocating that, but how many times have mission add-ons been sacrificed before the bottom line?)
*

Welcome ermar! Nice catch!
I particularly like this part:
QUOTE
"The probe would have a mass of about 500kg - 65% of that is a propulsion system to slow you down so you don't crash," he explained.
"There is a very thin atmosphere on Triton but there's not enough for parachutes to slow you down. You've got a lot of engineering overhead just to deliver the science package."

So if my calculation is right lander would have "dry" mass of 175kg - That's like Spirit or Opportunity...Maybe they should think about attaching some wheels on it... smile.gif
Seriously I don't believe that thing is ever going to fly...
BTW BruceMoomaw is there any way you could post link to that JPL Neptune project...?


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The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.
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My "Astrophotos" gallery on flickr...
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Guest_BruceMoomaw_*
post Dec 10 2005, 08:46 AM
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Sure: http://www.lpi.usra.edu/opag/jun_05_meetin...eptune_API1.pdf

http://trs-new.jpl.nasa.gov/dspace/bitstre...5/1/98-0675.pdf

Regarding the possible addition of a Triton lander:
http://www.aas.org/publications/baas/v37n3/dps2005/504.htm

There's also a description of a Triton lander design that could work for this mission in
http://solarsystem.nasa.gov/multimedia/dow...inal_011205.pdf (pg. 22-36).
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tedstryk
post Dec 10 2005, 01:29 PM
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QUOTE (BruceMoomaw @ Dec 10 2005, 08:46 AM)
There's also a description of a Triton lander design that could work for this mission in
http://solarsystem.nasa.gov/multimedia/dow...inal_011205.pdf  (pg. 22-36).
*


I noticed they used my combined HST view of Neptune and Triton in that pdf.


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Guest_AlexBlackwell_*
post Jul 17 2006, 07:51 PM
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I apologize for reviving a dead thread; however, Frank Morring Jr., reporting from the Farnborough 2006 Air Show, has an interesting article ("Improving Solar Cell Efficiency Enables NASA's Solar-Powered Jupiter Probe") in the July 17, 2006, issue of Aviation Week & Space Technology.

While the bulk of the article relates to the Juno New Frontiers-class mission, there is an interesting passage relating to a Neptune orbiter concept:

QUOTE
While Juno will be pushing the state of the art for deep-space use of solar power, scientists have analyzed the use of sunlight to power spacecraft at planets even more distant from the Sun. NASA has studied a Neptune orbiter that would use inflatable structures to deploy the ultra-large solar arrays that would be needed there and concentrators to focus the dim sunlight on the collectors (AW&ST Dec. 13, 2004, p. 56).

[Paul] Stella [principal engineer for space power systems at JPL] is skeptical. Even without considering the inflatable structures that would be needed to hold the solar concentrators and underlying cells, there would be difficult problems to overcome with the power-generating system itself. NASA flew a solar concentrator based on Fresnel lenses on its Deep Space-1 technology testbed, which he says "worked very well." But array pointing is more critical with concentrators than with conventional planar solar arrays, and the concentrator aperture will be "about the same size" as a planar array, even if the number of cells beneath it is reduced. Ultimately, it becomes a question of whether an array large enough can be built and delivered.

"Those are pretty advanced studies," Stella says. "A solar cell at Neptune will probably generate some power, but . . . the amount of power is going to be dropped down by literally hundreds, close to a thousand, and that makes for a very big solar array. The question is, if you need 30 watts at Neptune, which is a small amount, how many thousands and tens of thousands of watts do you have to build on Earth? Our biggest communications satellites are probably on the order of 20 kw., and that's lot of solar array, very complex, and again we might need even more than that. We're getting into uncharted territory."

Engineers at JPL also are working on boosting solar-cell efficiency by increasing the number of junctions, with promising results. But there is a limit to how much sunlight can be converted to electricity.

"I would think that numbers approaching 50% are probably at least analytically feasible," says Stella. "We've done some work here. We looked at going from three junction cells to four to five to six to seven. And there's a point of diminishing returns . . . . I think we ended up probably in the order of 50%, and that doesn't mean you're going to get there."
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Rob Pinnegar
post Jul 18 2006, 03:36 PM
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QUOTE (AlexBlackwell @ Jul 17 2006, 01:51 PM) *
I apologize for reviving a dead thread... <<snip>>

Yeah, but a thread like this is by its very nature of the type that can be expected to go dormant for long periods. After all, it isn't as if we're hearing Neptune Orbiter news every day.
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JRehling
post Jul 18 2006, 03:38 PM
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I would think that at some point the weight of the solar panels would be prohibitive.

I guess another concept for a Neptune orbiter would be to have solar panels spend 90%+ of a highly elliptical orbit charging batteries, with periapsis spent using that battery power to run instruments and transmit data home. In principle, there's almost no limit to how high the apoapsis is -- and such an orbit would also require less propellant. If the Neptune encounters are far apart in time, that would increase operations costs, but there'd be a lot of savings in engineering.
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Chmee
post Jul 18 2006, 03:47 PM
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QUOTE (JRehling @ Jul 18 2006, 11:38 AM) *
I would think that at some point the weight of the solar panels would be prohibitive.

I guess another concept for a Neptune orbiter would be to have solar panels spend 90%+ of a highly elliptical orbit charging batteries, with periapsis spent using that battery power to run instruments and transmit data home. In principle, there's almost no limit to how high the apoapsis is -- and such an orbit would also require less propellant. If the Neptune encounters are far apart in time, that would increase operations costs, but there'd be a lot of savings in engineering.


By why even consider a solar array when RTG's are a proven, safe, and stable power source for deep space missions? It seems such large, heavy, and complex solar arrays are solution for a problem that does not exist.
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Guest_AlexBlackwell_*
post Jul 18 2006, 04:42 PM
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QUOTE (Chmee @ Jul 18 2006, 05:47 AM) *
By why even consider a solar array when RTG's are a proven, safe, and stable power source for deep space missions? It seems such large, heavy, and complex solar arrays are solution for a problem that does not exist.

It depends on one's definition of "problem." Non-nuclear power sources are politically and programmatically more palatable, even if in some cases such solutions are more difficult to implement from an operational/engineering standpoint.
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ljk4-1
post Jul 18 2006, 05:34 PM
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I wonder if a very large solar sail could be designed not just for getting a
probe to Neptune but also to serve as a solar collector/reflector?

Would it be less heavy than any currently conceivable solar panel for such a
mission?

This could solve the nuclear "problem" - though I personally have no issues
with nuclear power as the energy source for craft in deep space. Or on this
planet, for that matter.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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