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#21
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Atomic ramjet for exploring Titan
Pat Flannery wrote: Use a RTG, and you can seal the isotopes in ceramic and just use their heat to drive some sort of power generator. With its high atmospheric density and low gravity, Titan is the place where you could literally float safely down to the ground under a umbrella like in a cartoon, so the wings need not be very big in comparison to the weight they can carry. I just went digging to get some specifics on Titan's atmosphere; pressure is 1.5 times that of Earth, the atmosphere is mainly nitrogen (I thought it would be methane). Maybe airships filled with either hydrogen or helium could also be workable for robotic exploration. Gravity is only .14 g, even less than that of the Moon, so getting something to generate enough lift via wings to keep itself flying in this sort of environment should be a piece of cake. Pat |
#22
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Atomic ramjet for exploring Titan
On Mar 18, 6:23*pm, Pat Flannery wrote:
Martha Adams wrote: I think that's an interesting idea and it sounds doable. *However, is a ramjet really the best vehicle for this? *A slower, propellor driven craft could feature less active and stressed machinery, better for a long life. *And in either case, you'd want to do (in my view) at least three proof-of-principle machines to test out the engineering: where would you fly those machines? We must understand how it flies in a cold dense methane atmosphe First we rent a wind tunnel. Then we put huge air conditioner at the front end of the wind tunnel. Then we put 1,000 cows inside of a building that's air output is fed into the air conditioner's intake. Then we feed the cows nothing but beans and wait for the Wonders Of Biology to begin. For testing the Venus one, we simply reverse the air conditioner's heat exchanger, attach sparklers to the rear end of all the cows, and feed them beans along with rotten eggs - creating a superheated carbon dioxide and monoxide rich atmosphere including exotic sulfur compounds. ;-) Pat JPL has published an engineering model for Titan's atmosphere. A numerical study would be done first using this data gleaned from the best available measurements. http://www.lpl.arizona.edu/~yelle/eprints/Yelle97b.pdf Then, using MEMs based micro-assembly - to build small scale physical models for test. The final version of a nuclear powered Sikorski Cypher like device would have a fan and control set for Earth's atmosphere - and then switch it up for a full scale test - not in a wind tunnel but a big tank |
#23
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Atomic ramjet for exploring Titan
hcobb wrote: Just use a hydrogen balloon and you can stop and sample the surface. The atmospheric turbulence is pretty severe at higher altitudes. Apparently the Huygens probe got quite a wild ride as it parachuted down toward the surface...but conditions near the surface are pretty benign, so if you kept the thing at low altitude it will probably be safe...the flip side is that it may not move around at any great velocity, as winds on the surface were only a few meters per second in velocity where Huygens landed. The big problem with this unpowered approach is that you can't make the thing go where you want it to go, you just have to settle for wherever the winds carry it. Instead of cracking hydrogen from the atmosphere, just make it into a hot-air balloon using a isotopic heat source mounted inside the neck of the balloon to both generate heat for keeping it afloat and simultaneously generating electricity. Touchdowns and liftoffs could then be controlled by simply venting a little of the hot atmosphere from the top of the envelope of the balloon to let it settle to the surface, and then resealing it to ascend. Pat |
#24
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Atomic ramjet for exploring Titan
Pat Flannery wrote:
hcobb wrote: Just use a hydrogen balloon and you can stop and sample the surface. The atmospheric turbulence is pretty severe at higher altitudes. Apparently the Huygens probe got quite a wild ride as it parachuted down toward the surface...but conditions near the surface are pretty benign, so if you kept the thing at low altitude it will probably be safe...the flip side is that it may not move around at any great velocity, as winds on the surface were only a few meters per second in velocity where Huygens landed. The big problem with this unpowered approach is that you can't make the thing go where you want it to go, you just have to settle for wherever the winds carry it. Only partially true. Your maneuverability is limited but you do have some. A hot air balloon pilot doesn't just land where he happens to be when comes time to land. Wind direction will usually vary at different altitudes. So to steer a balloon you go up or down according to which wind you prefer. In the case of a hot air balloon going up or down can be as simple as giving more or less heat. In a hydrogen balloon, you can compress a little bit of the hydrogen or let it expand to control your height. Of course, this maneuverability is nothing like powered flight but you do have some control. Alain Fournier |
#25
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Atomic ramjet for exploring Titan
Alain Fournier wrote:
Only partially true. Your maneuverability is limited but you do have some. A hot air balloon pilot doesn't just land where he happens to be when comes time to land. Wind direction will usually vary at different altitudes. So to steer a balloon you go up or down according to which wind you prefer. In the case of a hot air balloon going up or down can be as simple as giving more or less heat. In a hydrogen balloon, you can compress a little bit of the hydrogen or let it expand to control your height. Of course, this maneuverability is nothing like powered flight but you do have some control. That would have to be autonomous though given the timelags. So, how would such a thing "navigate" - by that I mean know where it was and which way it was going relative to some desired destination? Does Titan have a magnetic field to use as a reference? Occasional signals from something in orbit? rick jones -- I don't interest myself in "why." I think more often in terms of "when," sometimes "where;" always "how much." - Joubert these opinions are mine, all mine; HP might not want them anyway... feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH... |
#26
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Atomic ramjet for exploring Titan
Rick Jones wrote:
That would have to be autonomous though given the timelags. So, how would such a thing "navigate" - by that I mean know where it was and which way it was going relative to some desired destination? Does Titan have a magnetic field to use as a reference? Occasional signals from something in orbit? Or I suppose load the thing with a classic Tomahawk-esque radar terrain map of Titan obtained from an orbiter? rick jones -- oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag these opinions are mine, all mine; HP might not want them anyway... feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH... |
#27
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Atomic ramjet for exploring Titan
Alain Fournier wrote: Only partially true. Your maneuverability is limited but you do have some. A hot air balloon pilot doesn't just land where he happens to be when comes time to land. Wind direction will usually vary at different altitudes. So to steer a balloon you go up or down according to which wind you prefer. In the case of a hot air balloon going up or down can be as simple as giving more or less heat. In a hydrogen balloon, you can compress a little bit of the hydrogen or let it expand to control your height. Of course, this maneuverability is nothing like powered flight but you do have some control. But if you get up too high, that's where you start to run into the turbulent atmospheric conditions on Titan; and one of those is violent vertical wind shear, which could destroy the balloon: http://en.wikipedia.org/wiki/Huygens_probe "Doppler Wind Experiment (DWE) This experiment used an ultra-stable oscillator to improve communication with the probe by giving it a very stable carrier frequency. This instrument was also used to measure the wind speed in Titan's atmosphere by measuring the Doppler shift in the carrier signal. The swinging motion of the probe beneath its parachute due to atmospheric properties may also have been detected. Failure of ground controllers to turn on the receiver in the Cassini orbiter caused the loss of this data. Earth-based radio telescopes were able to reconstruct some of it. Measurements started 150 kilometres above Titan's surface, where Huygens was blown eastwards at more than 400 kilometres per hour, agreeing with earlier measurements of the winds at 200 kilometres altitude, made over the past few years using telescopes. Between 60 and 80 kilometres, Huygens was buffeted by rapidly fluctuating winds, which are thought to be vertical wind shear. At ground level, the Earth-based doppler shift and VLBI measurements show gentle winds of a few metres per second, roughly in line with expectations." Even a wind of a few kilometeres per second may make it impossible for the vehicle to land and stay in one place for long enough to either analyze the soil or take a sample, as the envelope of the balloon will act like a sail and drag the probe around, particularly in the very low gravity and with the dense atmosphere. It might be smarter to have the balloon drop small surface probes as it flies along without landing itself, and have the probes relay signals up to some sort of satellite in Titan orbit for transmission to Earth. The same landing problem would apply to any sort of winged aircraft...you probably get it to land in one piece, but taking off again could be a real problem. Maybe a atomic-powered helicopter is the answer? In that low of gravity with that thick of a atmosphere maybe that could be made to work, and it probably would be heavy enough to stay in one place once landed without the wind blowing it around till it finished its surface examinations and lifted off again. The combo of a thick atmosphere and very low gravity is so odd that it makes it hard to figure out what is possible and impossible in those conditions. You don't know if you want to go with aircraft or submarine type analogies in regards to designs of things. Pat |
#28
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Atomic ramjet for exploring Titan
The only problem with nuclear powered aircraft is that they provided a
clear proof of concept for engines that didn't need oil products to fuel them. http://www.strange-mecha.com/aircraft/APA/APA.html |
#29
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Atomic ramjet for exploring Titan
You'd have both. A payload would aerobrake into orbit around Titan,
using a lifting aerobrake involving multiple passes http://adsabs.harvard.edu/abs/1986STIA...8713820D You would release an orbiter which would circularize its orbit at the apo-apsis of one of the passes, while the lander continued its descent, releasing the nuclear powered drone - which communicates with the orbiting satellite. http://www.youtube.com/watch?v=f1Y3ohmn-OU Of course, a hydrogen filled balloon is also possible in this atmosphere. |
#30
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Atomic ramjet for exploring Titan
Rick Jones wrote: That would have to be autonomous though given the timelags. So, how would such a thing "navigate" - by that I mean know where it was and which way it was going relative to some desired destination? Does Titan have a magnetic field to use as a reference? Occasional signals from something in orbit? You may need some sort of unmanned orbiter around Titan to keep track of where it was. This would also allow it to dump its telemetry into the orbiter which could then relay it to Earth, meaning lower weight and power usage on the balloon probe itself, as it wouldn't need to carry a large transmitter/receiver. Pat |
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