Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Pseudoscience-is-malarkey on 30/07/2021 00:00:32
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There's a lot of concepts about what would be used for interstellar missions that would take more than a decade of travel. Plutonium-238 dioxide is my guess.
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Plutonium-238 dioxide is my guess.
How would that work?
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Quote from: Pseudoscience-is-malarkey on Today at 00:00:32
Plutonium-238 dioxide is my guess.
How would that work?
A speckle of it fueled New Horizon's nine-year journey.
But you're the physicist...
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Hi.
Could plutonium-238 dioxide fuel be used for interstellar travel?
Possibly. According to Wikipedia there isn't much of it left available. There are plans to fabricate more. I'm only picking data out of a Wikipedia article here.
How would that work?
Thermo-couples to generate electricity from heat sources. Heat source generated by the strong alpha emissions of 238Pu.
https://en.wikipedia.org/wiki/Plutonium-238#Use_in_radioisotope_thermoelectric_generators
This suggests a useful source of electricity but does not indicate how propulsion would be achieved. Speculative possibilities may include gathering a suitable propulsion fluid from space, e.g. interstellar gas, then ionising this and propelling it in an electric field. It doesn't seem to be any more efficient then just harvesting some of the energy from the alpha particles to generate the electric field and then directly propelling the remaining alpha particles out of the ship.
I'm not an expert in this area but propulsion technology would still seem to be the problem, not the long term generation of energy. You may still need to carry propulsion fluids for initial acceleration and then deceleration at your destination.
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You have this too, as a alternative.
https://ntrs.nasa.gov/api/citations/20020023956/downloads/20020023956.pdf
and https://today.tamu.edu/2018/05/11/combining-laser-and-particle-beams-for-interstellar-travel/
but I think it will be unmanned and miniaturized if we ever get it to work.
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unmanned and miniaturized
like a photon, perhaps? And instead of going there to explore the source, we wait for it to come here. Time to invent the telescope - the lazy man's rocket!
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There's a lot of concepts about what would be used for interstellar missions that would take more than a decade of travel. Plutonium-238 dioxide is my guess.
I'm guessing at "No", because it has a half life of about 90 years and I don't think we have any tech on the horizon that would get us to any other star that quickly.
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I liked that one Alan. " The telescope, the lazy mans rocket " :)
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We have those arrays we're building, observing the universe. They will be interesting to watch.
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Could plutonium-238 dioxide fuel be used for interstellar travel?
No.
Pu-238 is better considered a "battery" than a fuel
- A battery that lasts 30 years or so
- And can put out 10 to a few hundred Watts of electricity
- It is used in radioisotope thermoelectric generators, which aren't very efficient (typically 3-7%), and don't produce any usable thrust
- although the Perseverance Mars rover uses this inefficiency as a way to keep the electronics warm at night (combined heat and power)
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
If you want more power (kilowatts), solar cells are more useful in the inner solar system - although the Juno mission to Jupiter (https://www.nasa.gov/mission_pages/juno/launch/Juno_solarpower.html) also uses a very large array of solar cells.
If you want propulsion, the most efficient is probably an ion drive - but for interstellar use, these would MegaWatts of power (current ground-based models have been demonstrated up to 70kW).
- You will probably want a uranium nuclear reactor to power it
- You will quickly run out of reaction mass (typically Xenon)
- You will quickly run out of fuel (typically Uranium)
- And it is hard to find sources of Xenon and Uranium out in interstellar space
https://en.wikipedia.org/wiki/Ion_thruster
To really do interstellar travel, you can't afford to carry all the fuel and power with you - they are too heavy.
- One suggestion is to use magnetic fields to gather hydrogen from space, and fuse it to produce power (perhaps that is what Eternal Student was alluding to?)
See: https://en.wikipedia.org/wiki/Bussard_ramjet
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Hi.
perhaps that is what Eternal Student was alluding to?
Not in any detail or accuracy, just orientating the problem. You've written a good post there evan_au.
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Miniaturised ships:
Un-manned miniaturised space vehicles would seem to be the realistic first interstellar ships, as mentioned by Yor_on.
I also read something recently about un-manned miniaturised telescopes and cameras being launched and directed off in various directions. Which is almost a hybrid of Alancalverd and Yor_on's ideas.
What's the point of sending off telescopes into space instead of waiting on earth the extra minutes for the light to come to you? I mean it's even silly when you realise the radio signal from the camera ship will take just as long to travel. It's partly to get clear of local dust clouds and distortions but also that you if you find something interesting (like an exoplanet) no one minds crashing a miniature camera ship into it to get a good look. There's another interesting possibility if you send a miniature camera fast enough....
Some relativistic astronomy: https://ui.adsabs.harvard.edu/abs/2018ApJ...854..123Z/abstract
Abstract: The “Breakthrough Starshot” aims at sending near-speed-of-light cameras to nearby stellar systems in the future. Due to the relativistic effects, a transrelativistic camera naturally serves as a spectrograph, a lens, and a wide-field camera. .... We suggest that observing celestial objects using a transrelativistic camera may allow one to study the astronomical objects in a special way....
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What's the point of sending off telescopes into space instead of waiting on earth the extra minutes for the light to come to you? I mean it's even silly when you realise the radio signal from the camera ship will take just as long to travel.
Indeed, it is silly if one were to use these probes in this way.
But there is useful information to be gained:
1) The farther we can spread our cameras the more significant the parallax of their combined images. We can use this information to get more precise distances and use that information to more tightly calibrate some of our other measurements.
2) If the camera can get sufficiently close to any object that its resolution is significantly better than any earth-based or solar-system based telescopes could get.
3) If many of them are launched in different directions, based on survival rates we will also get an idea of how dangerous interstellar space is, and possibly sort of map of which regions (trajectories) are more or less dangerous.
4) also, specifically getting off the earth means that we can avoid problems introduced by the atmosphere (improving our resolution, and allowing many more wavelengths to be observed)
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Hi ChiralSPO, I hope you are well.
I especially like ideas (1) and (3).
(2) was mentioned previously but it's a good point.
(4) Is true enough but begs someone to ask - if you just want to get above our atmosphere, why not build telescope ships like Hubble and keep them in orbit.