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Heard talk about He3 on the Moon and launching a fusion rocket. Is this all just a mashup of Sci-fi ideas?

Fission fragment rockets are much more realistic at the moment. And very cool.

yes, but that was lifting a much larger mass, and it was fighting air pressure in front of the rocket, and it throttled back part way through to avoid too much friction

Hmm. Maybe, this isn't such a crazy idea, if... Bear with me. The tube slopes upward and ends at a high altitude where the air poses little frictional resistance, say 10km. There is a cover over the top end preventing the thin air entering. At ground level, it is also sealed by a door, and large...

You mention "radial velocity" - so, did the video mean to say "radial momentum"? In a simple system of one star and one planet, would they have equal radial momentum around their shared centre of mass?

To enable the fission fragments to escape, yet allowing a critical mass, there could be multiple small sub-cores each with its own magnetic coils, which exchange neutrons to achieve criticality as a group. The obvious place for control rods is then between the sub-cores.

In that reactivity link I found a mention of submarine reactors that use a high proportion of U235. Wikipedia states: "many designs use highly enriched uranium but incorporate burnable neutron poison in the fuel rods. This allows the reactor to be constructed with an excess of fissionable...

The NASA study quoted above uses a dusty plasma, and has two designs, one with a critical mass of Pu, and one with U238. In both, the moderator reflects back neutrons to achieve criticality. With no moderator, the mass of fuel would need to be greater, but I don't think it would need to be...

No, I'm not writing Sci Fi, I'm just being curious. I'm not an undergraduate student, although I was, years ago. Maybe a course would be a good idea, but I don't have time. I'm sorry if my questions appear random.

Thanks for the replies everyone. Yes, controlling the reaction is basically what I'm asking about. Since the dusty plasma can be controlled by electromagnetic fields which can be rapidly altered, perhaps it could be compressed to the point of criticality, then very quickly expanded again before...

a dusty plasma design : https://www.nasa.gov/pdf/718391main_Werka_2011_PhI_FFRE.pdf has nuclear fuel held in place by electromagnetic fields. It uses a very massive moderator around the fuel to slow and reflect neutrons back to the fuel, to enable continued fission. But, there is one kind of...

I suspect that Janus is right - by that time living in "ships" or habitats will be considered preferable to life on a planet, and they will make long trips between Kuiper belt objects to gather resources. In that scenario, a generation ship is not so far from what is already common.

Ball park probability - between 0 and 1. There are so many unknowns. I can only conclude that living in space is a lot harder than we think. And don't forget that many of the worlds that could harbour life have stronger and deeper gravitaional fields, as well as thicker and deeper atmospheres...

Don't be disheartened. I think we will gradually colonise outward in the Solar System, using forms of nuclear energy as we move further away from the Sun. Then the objects of the Kuiper belt and the Oort cloud will entice us out further. One day, some pioneers will realize they are halfway to...

Could we launch a set of relay probes at the same time, spaced out over the distance, to relay the signal? Since the power required is the square of the distance, doing it in two hops halves your total power needs. Ten hops cuts it by 90%. They would need to be nuclear isotope powered. The...

I see where I'm going wrong here - I meant a minimal infrastructure, just enough to provide fuel, or maybe some other mass-heavy components? For example, a car-sized ice mining robot and a distillation machine, and solar panels, and some small maintenance and operation robots controlled from...

But does it? Recently they found evidence of water ice on the Moon. That could be made into fuel.

Former 'Mars czar' in a Phys.org interview: Read more at: https://phys.org/news/2018-08-mars-czar-latest-news-red.html#jCp But would it? Surely the Moon is a perfect launchpad for Mars, a testbed, and a supply base? Going from Earth direct is a truly huge task. From an established Lunar...

So, if you add heat, the temperature goes down? If heat is lost, it goes up? How does that work in, say, a planet + moon system?

But, what about within the event horizon of a black hole? No radiation escapes from there...

I'm just thinking of reasons why you might want a wind turbine. btw, the real reason is that a 2-blade has one blade in slower air nearer the ground, hence vibration. With three blades, smoother torque.

Yes, unless there are some jobs that robots find really hard. Probably, if the infrastructure grows to a certain size, there will be. I mean, not that it wouldn't matter, but that it would be trivial compared to the billions we are talking about now. It would be an everyday expense.

Yes, unless you are trying to make an electric generator on Mars.

I was looking at NASA saying they might not have enough funds to put humans on Mars by 2040. OK, zoom forward maybe 200 years and the cost might be, maybe, just buy a ticket. Or people might already be working there; they will be paid to go there. So, here's the question. What is the least cost...

There are non-GM microbes that can do the job. Apparently used commonly in Europe and the US in industrial cheese making.

Although, if someone wanted to genetically engineer a poisonous strawberry, for example, that would be entirely possible, given the required skill and lab setup. At least with traditional foods (including old varieties produced by selective breeding) we have the assurance that comes from...

IMHO, the real danger of GMO foods is not from directly eating them, but the effect that GM might have on the world ecosystem if modifications escape the farm and thrive in the wild. Think about how introduced species have damaged ecosystems across the world, almost every continent has it's...

Important to note, I think, that light does not choose that particular path from the start. It emanates in all directions, and you simply see the light that ends up at your eye. The light you see, because it headed off in the direction that gets it to your eye, is also the light that gets to...

If I can measure the air coming out, it covers the first points. That is, if it comes out with less methane, it doesn't much matter what is going on inside. I can't blow concentrated methane into the soil, I'm trying to reduce atmospheric methane, and I don't think I can reasonably concentrate...

From photovoltaics, like in the article in the link. As I understand it the Bussard Ramjet has not yet been built. But this thruster has, although it's not yet flown. I'm just thinking about a next-step innovation. Perhaps, without the need to carry reaction mass for the return trip, a Mars...

I wasn't thinking about nuclear. The craft in the article uses solar. Solar can still work further out - the panels need to be bigger. They could collect power during the high phase of the orbit, it gets stored, then fold up the panels, dip into the atmosphere, run the pump on a little battery...

Ah, yes, but if you look at the article, they have dealt with that already. The atmosphere is extremely thin, and the panels are on the sides of the craft. It's essentially orbiting in space, with just a little drag from a very tenuous gas.

Sorry to be vague. I mean reaction mass.

Methanotrophs already exist in most soils. If we expose them to more methane, will they eat more? A solar powered fan blowing air down a tube that ran along under soil, with lots of small holes along its length - would that reduce the methane in the air? As a second part to the question, does...

Yes, you. :smile:

Yes, but the thrust motor, AFAIK, collects the molecules into a chamber as a low density gas as part of the process. At this point, some could be pumped off into a pressure vessel. The thrust values are low, but if the orbit was a high elliptical one, there would be time to rebuild velocity and...

https://phys.org/news/2018-03-world-first-air-breathing-electric-thruster.html If it dipped into the atmosphere temporarily on an elliptical orbit, could the air gathered be stored for a long flight? Then maybe get more fuel from another planet's atmosphere or moon for the return trip?

To answer the original question of the topic - how about Brownian Motion? A good optical microscope should be able to show it, in a little smoke trapped in a transparent container. Other evidence might come from crystals, with a little reasoning. And to add weight to the reasoning, perhaps a...

- as they head in the opposite direction!

Thanks, nice article in the link. Yes, a power cable running out to two panel sites makes more sense. I think a vehicle can be built that can handle 30% grade, and initially it's much less mass than a long cable. How about, thinking about a minimum mass solution, a steerable mirror on the rim...

Exactly. I think that we should concentrate on building large, comfortable free-flying space stations (perhaps with spinning to create artificial gravity) and build and sustain them with robot mining, so they have freely available resources. Then we can head off to Mars in comfort and safety...

Very little power from a panel in Earthshine. The albedo of the Earth is 0.37 (de Pater and Lissauer), and the Earth receives 1000W/m^2 from the Sun and appears as a disc covering 3 degrees seen from Moon. So, ballpark less than 1 Watt per square metre. The mast would have to at least 100m high...

Check out the Star Tram :http://www.startram.com Is this the kind of thing you mean?

It may be that nuclear power is getting compact and light enough to be realistic in the early stages of development. But there is still the problem that it needs huge radiators. Or - the type of isotope based power used in probes, but they have quite low power output. For the first, smaller...

I get what you mean, people will move to where life is easiest. I think on the Moon that will be the poles. It's close to known important resources - volatiles. It has near-constant light without the need for nuclear plant and lightbulbs. It has the capacity to keep things constantly cold or...

Sure, but that is a long way ahead in time. Both poles will likely be explored and mined by that time, I guess. The OP is about considering which pole to focus on first, in the near term.

But, with constant power at the poles, sensitive equipment can be heated continuously.

Well it is a bit of a problem. Without constant power all the equipment has to go down to cryogenic temperatures at night. Why run into these issues if you don't have to? And why not keep running constantly?

I think the highly abrasive nature of the Lunar dust would prohibit the use of tyres. Look at how the Mars rover's wheels were worn through, and Mars dust is thought to be less abrasive than Lunar. I expect there will need to be extremely hard, thick coatings on the wheels. Tungsten carbide or...

I just noticed in the previous link: https://phys.org/news/2018-01-lava-tube-skylights-north-pole.html "if ice is present inside the lava tubes – which is not yet known—it could be in the form of massive ice formations as often occur in cold lava tubes on Earth – instead of mixed-in within...