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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

#131

Post by pault »

nickserv wrote: post #47
sandworm101 wrote: post #33

Earlier quoted context omitted.

No. >> The Pentagon is aware of a Russian test of a nuclear-powered cruise missile but the system is still under development and had crashed in the Arctic in 2017.[17][18][19] A RAND Corporation researcher specializing in Russia said "My guess is they're not bluffing, that they've flight-tested this thing. But that's incredible." https://en.wikipedia.org/wiki/Nuclear-powered_aircraft#Russi... https://en.wikipedia.org…

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.

Does that mean a nuclear powered cruise missile could stay airborne until mechanical failure? That would make future warfare... interesting.

Re: NASA plans to launch a spacecraft to Titan

#132

Post by gene-h »

martinald wrote: post #92
T-hawk wrote: post #63

Earlier quoted context omitted.

From a scientific standpoint, there's really no value in downlinking video as opposed to still images. It costs several multiples worth of scarce downlink bandwidth, for a tiny gain in what there is to see of the same rocks at slightly different angles. Same reason we didn't have New Horizons at Pluto or the various Mars rovers do any video.

Why is bandwidth so scare still? Satellites in geosynchronous orbit on earth can do terabit/sec of total capacity now. Obviously latency is going to be extremely high, but I can't really understand why data rates are still so low?

Spacecraft transmit power and antenna size is limited. This means the amount of power that arrives at earth is rather low because microwaves spread out quite a bit with distance. The other issue is that NASA only has so many big radio dishes in the deep space network[0] to gather this small amount of power and extract a signal. Technology has improved, but in order to get much higher bandwidth we'd need bigger dishes. We also need at least three around the globe to get continuous coverage. Although perhaps by the time this mission lands we could have multi-kilometer aperture receivers on the ground or in space. Laser communication could allow for much higher bandwidth, because lasers have a shorter wavelength they don't spread out as much with distance. However, laser space communication is in its infancy and would not work well on Titan due to the smog.

[0]https://en.wikipedia.org/wiki/NASA_Deep_Space_Network

Re: NASA plans to launch a spacecraft to Titan

#133

Post by garmaine »

martinald wrote: post #92
T-hawk wrote: post #63

Earlier quoted context omitted.

From a scientific standpoint, there's really no value in downlinking video as opposed to still images. It costs several multiples worth of scarce downlink bandwidth, for a tiny gain in what there is to see of the same rocks at slightly different angles. Same reason we didn't have New Horizons at Pluto or the various Mars rovers do any video.

Why is bandwidth so scare still? Satellites in geosynchronous orbit on earth can do terabit/sec of total capacity now. Obviously latency is going to be extremely high, but I can't really understand why data rates are still so low?

I don’t think you realize just how far away the outer solar system is.

Re: NASA plans to launch a spacecraft to Titan

#134

Post by garmaine »

martinald wrote: post #123
zild3d wrote: post #109

Earlier quoted context omitted.

Inverse square law. For the same transmit power, your received signal strength diminishes with the square of the distance That received signal strength is what determines channel capacity (C) which is the upper limit on the bit rate you can get. see Friis and Shannon's channel capacity [0] https://en.wikipedia.org/wiki/Friis_transmission_equation [1] https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...

Yes, I get that. But it seems that performance has barely improved since the 1970s despite the massive gains in telecommunication efficiencies since then. Or is the SNR so poor that even 1970s era technology was able to be close to the limit?

These are physical restrictions, not technological.

Re: NASA plans to launch a spacecraft to Titan

#135

Post by samstave »

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…

Why arent we just mass launching probes to all the planets?

Serious question: Why is it not OK to have a standard sensor array on every planet in the solar system?

Re: NASA plans to launch a spacecraft to Titan

#136

Post by [deleted] »

ajmurmann wrote: post #52
cwkoss wrote: post #17

Earlier quoted context omitted.

In addition to lack of solar energy, I wonder if nuclear power source is necessary to keep batteries or other electronics warm enough to function properly. Conversely, on Titan, we won't need to worry about heat sinks as everything is kept at ~94K in a bath of liquid and frozen methane. Perhaps in a few hundred years AWS's most popular region for intensive compute will be under Titan's methane sea. High spin up cost,…

Hah, I was always intrigued by the idea of placing solar cells on the bright side of Mercury and servers on the dark side. I wonder what other good options might exist in the solar system.

[deleted]

Re: NASA plans to launch a spacecraft to Titan

#137

Post by rags2riches »

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…

The oldest preserved share of any company is from 1288. It's since been merged, but it's still around.

https://en.wikipedia.org/wiki/Stora_Enso#History_of_Stora

Re: NASA plans to launch a spacecraft to Titan

#138

Post by AmericanChopper »

bdamm wrote: post #124
swebs wrote: post #121

Earlier quoted context omitted.

There will be at least an hour delay. Saturn is pretty far

10 seconds of video from Titan would change the world. It's shame we don't have this from Mars already. So it would take a few weeks to transmit - we got time. Now figuring out which 10 seconds to select and send to earth... that'll be interesting. An on-board cache of x GB data storage, with key frames taken every 30 minutes, would probably be able to select some pretty compelling 10 second segments.

What about the world would be different after getting a 10 second video from Titan?

Re: NASA plans to launch a spacecraft to Titan

#139

Post by krapp »

samstave wrote: post #135
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…

Why arent we just mass launching probes to all the planets? Serious question: Why is it not OK to have a standard sensor array on every planet in the solar system?

> Why arent we just mass launching probes to all the planets?

Because we don't live in a fictional sci-fi universe where launching things into space doesn't cost a ridiculous amount of money, time and effort, and can't only be done at certain times from certain locations in order to get the orbits right, or where years of effort and millions of dollars (or whatever currency) don't also go into building the things to be launched into space. The world has better things to spend its money on.

>Why is it not OK to have a standard sensor array on every planet in the solar system?

What is a "standard sensor array?" We've already sent a lot of probes to a lot of places[0] around the solar system. But read the rest of this thread - it's a lot more complicated than it seems. Also, remember how hostile and difficult the solar system can be. Jovian planets don't even have a solid surface to be "on," for instance, and Venus has a pressure of 90 atmospheres and it rains sulfuric acid.

[0]https://en.wikipedia.org/wiki/List_of_landings_on_extraterre...

Re: NASA plans to launch a spacecraft to Titan

#140

Post by Rebelgecko »

dev_tty01 wrote: post #130
p1mrx wrote: post #28

Earlier quoted context omitted.

Will this be the first-ever instance of nuclear-powered flight?

NASA has been using nuclear powered probes for 50 years. It is called a redioisotope thermoelectric generator (RTG). https://www.space.com/13709-plutonium-shortage-nasa-planetar... Unfortunately, there is a shortage of plutonium-238 to run these RTGs (see above story). I guess that will get resolved somehow. The current Mars Curiosity rover is powered by an RTG. Since this is the first flying (post-landing of course)…

DOE has restarted Pu238 production. They're only making about a pound a year but they're still scaling up
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