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NASA plans to launch a spacecraft to Titan

theatlantic.com

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Re: NASA plans to launch a spacecraft to Titan

#141

Post by newsoul2019 »

cookingrobot wrote: post #77
AnIdiotOnTheNet wrote: post #57

Earlier quoted context omitted.

Mercury's whisper thin atmosphere won't be much use for cooling anything, though possibly the surface would be. However, the real problem is that Mercury isn't actually tidally locked anyway.

In certain regions on Mercury the temperature stays within 1 degree of room temperature less than a meter underground. http://einstein-schrodinger.com/Mercury_temperature.pdf It’s actually relatively habitable. http://einstein-schrodinger.com/mercury_colony.html

> In fact, if we delay until the distant future, or even 50 years or so, such an effort probably will become impossible. This is because us humans will consume the Earth's non-renewable energy and mineral resources almost completely within the next 50-100 years, severely reducing our discretionary income for costly activities such as space travel.

I wonder when that was written...

Re: NASA plans to launch a spacecraft to Titan

#142

Post by thatcherc »

Sharlin wrote: post #62
nickserv wrote: post #47

Earlier quoted context omitted.

This case is different though, using the fission reaction to generate electricity which in turn powers the electric motors among other things. The nuclear powered missiles use the fission reaction to heat incoming air similar to how a jet engine works.

No fission reaction, just radioactive decay in Dragonfly's case. It will use an RTG (radioisotope thermoelectric generator) not unlike Curiosity and most missions to the outer planets to date.

Just a note - radioactive decay is is fission, since it involves a nucleus splitting apart.

Re: NASA plans to launch a spacecraft to Titan

#143

Post by bduerst »

rzimmerman wrote: post #4

A flying drone is a really solid idea for a Titan lander for a couple reasons: * The surface atmosphere density is higher than Earth's (1.5 atm) * Gravitational force is much lower (0.15g) * We don't know a lot about the surface composition or topography, so wheels and motors represent a challenge * Visibility may be poor, making visual navigation tricky (though that's also a problem for a flying vehicle I suppose) I…

Probably a dumb question, but how does the nuclear source work? Nuclear powerplants work by heating steam to turn a turbine. This drone won't have heavy water reservoirs so how does it convert the fission heat into electricity? Stirling engine?

Re: NASA plans to launch a spacecraft to Titan

#144

Post by elihu »

Sharlin wrote: post #62
nickserv wrote: post #47

Earlier quoted context omitted.

This case is different though, using the fission reaction to generate electricity which in turn powers the electric motors among other things. The nuclear powered missiles use the fission reaction to heat incoming air similar to how a jet engine works.

No fission reaction, just radioactive decay in Dragonfly's case. It will use an RTG (radioisotope thermoelectric generator) not unlike Curiosity and most missions to the outer planets to date.

RTGs are heavy; I suppose this means that it'll park itself for a long time to charge its batteries and then do a quick flight and repeat. Which sounds like it could work pretty well for this use case.

On the other hand, a hot-air balloon kept aloft by excess heat from radioactive metal might be a more attractive option if we were selecting proposals based on awesomeness.

Re: NASA plans to launch a spacecraft to Titan

#145

Post by gao8a »

eindiran wrote: post #64
magnamerc wrote: post #44

Earlier quoted context omitted.

I find it kind of funny that you think AWS will still be around in a hundred years.

This paper company was founded 771 AD: https://www.shinise.ne.jp/j_kyoto/voices/vol/48/48-d.html It's not even the longest-lived company in the world. This construction company was founded in 578 AD and continuously operated until 2006 when it was bought by a larger company: https://en.wikipedia.org/wiki/Kong%C5%8D_Gumi 100 years ago was only 1919 -- here are some random companies from 1919 that I found on Wikipedia…

Heck, IBM is 100+ lol

Re: NASA plans to launch a spacecraft to Titan

#147

Post by Gibbon1 »

bduerst wrote: post #143
rzimmerman wrote: post #4

A flying drone is a really solid idea for a Titan lander for a couple reasons: * The surface atmosphere density is higher than Earth's (1.5 atm) * Gravitational force is much lower (0.15g) * We don't know a lot about the surface composition or topography, so wheels and motors represent a challenge * Visibility may be poor, making visual navigation tricky (though that's also a problem for a flying vehicle I suppose) I…

Probably a dumb question, but how does the nuclear source work? Nuclear powerplants work by heating steam to turn a turbine. This drone won't have heavy water reservoirs so how does it convert the fission heat into electricity? Stirling engine?

Most nuclear power sources for space stuff works by Peltier effect. See Radioisotope thermoelectric generator.

radio-isotope decay -> heat -> Peltier stack -> electricity.

Advantages: no moving parts, no vibration, infinitesimal mass change, exceedingly reliable. 'Small'

Disadvantage: Efficiency kinda crummy at ~5%. Slowly loses output as fuel decays and the Peltier stack degrades.

Re: NASA plans to launch a spacecraft to Titan

#148

Post by petascale »

bduerst wrote: post #143
rzimmerman wrote: post #4

A flying drone is a really solid idea for a Titan lander for a couple reasons: * The surface atmosphere density is higher than Earth's (1.5 atm) * Gravitational force is much lower (0.15g) * We don't know a lot about the surface composition or topography, so wheels and motors represent a challenge * Visibility may be poor, making visual navigation tricky (though that's also a problem for a flying vehicle I suppose) I…

Probably a dumb question, but how does the nuclear source work? Nuclear powerplants work by heating steam to turn a turbine. This drone won't have heavy water reservoirs so how does it convert the fission heat into electricity? Stirling engine?

Probably an RTG [1], it's what NASA normally uses. It's thermoelectric [2]: Heat (in this case from radioactive decay) is converted directly into electricity without moving parts.

[1] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

[2] https://en.wikipedia.org/wiki/Thermoelectric_effect#Seebeck_...

Re: NASA plans to launch a spacecraft to Titan

#149

Post by ekianjo »

bduerst wrote: post #143
rzimmerman wrote: post #4

A flying drone is a really solid idea for a Titan lander for a couple reasons: * The surface atmosphere density is higher than Earth's (1.5 atm) * Gravitational force is much lower (0.15g) * We don't know a lot about the surface composition or topography, so wheels and motors represent a challenge * Visibility may be poor, making visual navigation tricky (though that's also a problem for a flying vehicle I suppose) I…

Probably a dumb question, but how does the nuclear source work? Nuclear powerplants work by heating steam to turn a turbine. This drone won't have heavy water reservoirs so how does it convert the fission heat into electricity? Stirling engine?

Just like nuclear sources work on sattelites. You produce heat with fission or nuclear degradation and then thermoelectric conversion.

Re: NASA plans to launch a spacecraft to Titan

#150

Post by apo »

dmurray wrote: post #53
apo wrote: post #13

> Scientists suspect that Titan might even have water—real, actual H2O—lurking beneath its surface. Not just a little, but a lot of water: > The density of Titan is consistent with a body that is about 60% rock and 40% water. > ... > Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, a small amount of ejecta remains as liquid water within the crater. It m…

> The density of Titan is consistent with a body that is about 60% rock and 40% water. That's extremely misleading. First, rocks have different densities. Sandstone weighs 2g/cc, basalt weighs 3g/cc, so a density "consistent with" 50% basalt, 50% water would be equally consistent with 100% sandstone, not to mention the possibilities of rocks with drastically different densities such as pumice or iron. Secondly, we ar…

> That's extremely misleading.

You're right - I should have said: "potentially a lot of water."

Sandstone (silicon oxides) seems unlikely given the reducing nature of the atmosphere. I'm no expert, but when liquid hydrocarbons rain down, there's not a lot of free oxygen on the surface at least. Ditto for basalt, which is about 40-50% silicon oxide. Still there could have been some process by which the interior sequestered most of the planet's oxygen, leaving what remained on the surface as water.

In contrast, liquid hydrocarbons seem plausible given the stuff rains down from the atmosphere and its density (methane ~0.5 g/mL, -162 C).

Titan's orbit provides some evidence consistent with a body that's more dense at the surface than at the core. One explanation is large amounts of subsurface liquid, but there are others:

https://www.popsci.com/science/article/2011-04/titan-could-h...

There's been some discussion about the apparent massive block of ice in Titan's surface, so the idea that Titan's putative subsurface ocean could contain water isn't too wild a speculation:

https://www.space.com/titan-saturn-moon-weird-ice-formation....

A subsurface ocean composed of water and liquid hydrocarbons would be consistent with everything I've been able to find so far.

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