For Questions That Don't Merit Their Own Thread

[Grand Ship Builder]

2 hours ago, Racescort666 said:

I get your point though, a thread for random science facts or something?

Great idea.

 

[JucheJuiceMan]

Would it be possie to use Long March 3A to send a single person on the moon and back?

Could Hwasong-14 if used as SLV place a few dozen or even 100 kilogram satelite in orbit?

[TheDestroyer111]

On 10/28/2017 at 12:48 AM, JucheJuiceMan said:

Would it be possie to use Long March 3A to send a single person on the moon and back?

If 2 metric tons are enough for you to make a manned spacecraft, yes. And if you mean ORBITING the moon, and especially LANDING on it, this would also have to include some fuel.

Could Hwasong-14 if used as SLV place a few dozen or even 100 kilogram satelite in orbit?

Only Kim knows that.

 

[JucheJuiceMan]

2 hours ago, TheDestroyer111 said:

Could Hwasong-14 if used as SLV place a few dozen or even 100 kilogram satelite in orbit?

Only Kim knows that.

I hoped someone who has all necesary mods to have decently accurate simulation could answer that, saw on Youtube uploaded Unha-3 and Hwasong-12.

Oh well.

[Steel]

2 hours ago, JucheJuiceMan said:

I hoped someone who has all necesary mods to have decently accurate simulation could answer that, saw on Youtube uploaded Unha-3 and Hwasong-12.

Oh well.

So little is known about its design that it's very difficult even to guess. 

Edited October 29, 2017 by Steel

[monophonic]

Can you really negate the gyroscopic effect by placing an identical wheel that rotates in the other direction next to the original wheel?

(Yes, I started wondering this reading the bicycle stability thing in the random facts thread.)

[magnemoe]

2 hours ago, monophonic said:

Can you really negate the gyroscopic effect by placing an identical wheel that rotates in the other direction next to the original wheel?

(Yes, I started wondering this reading the bicycle stability thing in the random facts thread.)

Two gyros rotating opposite of each other will not negate each other, the gyro stability will actually increase. 

[monophonic]

14 hours ago, magnemoe said:

Two gyros rotating opposite of each other will not negate each other, the gyro stability will actually increase. 

That's what I thought, but did not feel adequate to talk against quoted scientists without backup. Thanks!

[p1t1o]

Is there such a thing as a "free" quark?

If yes, is there anything especially noteworthy about them? Any properties worth mentioning?

If no, why not?

 

[Steel]

39 minutes ago, p1t1o said:

Is there such a thing as a "free" quark?

If yes, is there anything especially noteworthy about them? Any properties worth mentioning?

If no, why not?

 

Not at any temperature below a few trillion Kelvin, because of something called "colour confinement".

Basically, because of the interesting (read very complex) way quarks interact, when you try to pull them apart it is more energetically favourable to form a new quark-antiquark pair than for a free quark to exist.

Edited November 7, 2017 by Steel

[shynung]

How small can a functional nuclear power generator be built, in order to use them as a vehicle's power source? We know that nuclear-powered ships and submarines exist, but can we scale the reactors down even more, while keeping a usable power-to-weight ratio?

[ARS]

Actually, there's indeed a vehicle powered by a small nuclear reactor. Back then during atomic age, the Americans are so obsessed with atomic power that they start putting atomic in anything, even commercially irradiated drinking water. One of the proposed idea during that time is a nuclear powered car, which, in theory could be used for a very long time without refueling. The Ford company designed a prototype car called Ford Nucleon (Google it to see how it looks), a car powered by a nuclear reactor. However, the project was cancelled after it's evident that incident involving cars are far more common than incident involving ships and subs, and any traffic collision/ accident involving nuclear powered cars, even a small damage could mean a mini Chernobyl disaster to the surrounding area when there's a containment breach on the reactor. And that's not even counting those drivers who tend to drive their cars recklessly, meaning every police chase is potentially creating nuclear fallout if there's a crash. Seeing the hazard of having multiple mobile nuclear reactors running around operated by civillians offset it's benefit, the project was scrapped, and any small sized nuclear power source is relegated to power devices that'll be left unattended for a very long time or very far from civilization such as far-off autonomous lighthouse or space probes

Edited November 8, 2017 by ARS

[James Kerman]

I had read about this car but needed to see it to fully appreciate how ugly it is:

[DerekL1963]

3 hours ago, ARS said:

Actually, there's indeed a vehicle powered by a small nuclear reactor. Back then during atomic age, the Americans are so obsessed with atomic power that they start putting atomic in anything, even commercially irradiated drinking water. One of the proposed idea during that time is a nuclear powered car, which, in theory could be used for a very long time without refueling. The Ford company designed a prototype car called Ford Nucleon (Google it to see how it looks), a car powered by a nuclear reactor.

It was never built, and the reactor "design" never advanced beyond the most basic assumptions and bar napkin calculations.

The smallest operational (mobile) power plant that I'm aware of would be NR-1's...   And that looks to be about sixty feet long and twelve feet in diameter.

[wumpus]

7 hours ago, DerekL1963 said:

It was never built, and the reactor "design" never advanced beyond the most basic assumptions and bar napkin calculations.

The smallest operational (mobile) power plant that I'm aware of would be NR-1's...   And that looks to be about sixty feet long and twelve feet in diameter.

RTGs aren't so constrained by space, but unless you can get the thing even somewhat critical (at which point it is a reactor and not an RTG) you can't expect much power at all (unlikely enough to  power a rover, they prefer solar power even on Mars).

[sevenperforce]

14 hours ago, DerekL1963 said:

It was never built, and the reactor "design" never advanced beyond the most basic assumptions and bar napkin calculations.

The smallest operational (mobile) power plant that I'm aware of would be NR-1's...   And that looks to be about sixty feet long and twelve feet in diameter.

The various fission reactors built for satellites and spacecraft were much smaller. 

https://en.wikipedia.org/wiki/Nuclear_power_in_space#Fission_systems

[peadar1987]

The critical mass isn't a hard physical property, you can modify it by things like geometry, moderators and neutron reflectors. The critical mass of a sphere of Californium-242 is just 2.7kg and has a diameter of 7cm. The mass could be further reduced by adding reflectors and a moderator, so you could probably get a "reactor" that would fit in a suitcase (while spraying out some extremely hard radiation)

[DerekL1963]

3 hours ago, peadar1987 said:

The critical mass isn't a hard physical property,

No, critical mass isn't a hard physical property.   But critical mass isn't the topic of discussion here - a self sustaining chain reaction with power extraction (a reactor, not a "reactor") is the topic of discussion.  And it's the power handling and extraction machinery that dominate the design.
 

19 hours ago, sevenperforce said:

The various fission reactors built for satellites and spacecraft were much smaller. 

Though the heat was generated by criticality rather than spontaneous decay, those reactors were really just fancy RTG's - and they weren't self mobile as specified by the OP.  (Not that there's any particular reason they can't be...)
 

[Racescort666]

1 hour ago, DerekL1963 said:

Though the heat was generated by criticality rather than spontaneous decay, those reactors were really just fancy RTG's - and they weren't self mobile as specified by the OP.  (Not that there's any particular reason they can't be...)

I think maybe the better question is: what is the power requirement when you cross over from an RTG (decay or criticality) to something like a closed cycle gas turbine (brayton cycle) power generator. RTGs still require a temperature differential and I'd imagine that the thermodynamic efficiency is better than the conversion efficiency of RTGs.

[shynung]

For some context, the small fission reactor (or oversized RTG) is meant to power a manned rover, something like NASA Space Exploration Vehicle.

[sevenperforce]

22 hours ago, DerekL1963 said:

Though the heat was generated by criticality rather than spontaneous decay, those reactors were really just fancy RTG's - and they weren't self mobile as specified by the OP.  (Not that there's any particular reason they can't be...)

Well, the defining difference between an RTG and a nuclear fission reactor is whether the heat comes from steady-state decay or from induced criticality. The SAFE-400 nuclear fission reactor used uranium-nitride fuel with rhenium neutron moderator rods and could be turned off and on at will. Rather than the thermocouple used by most RTGs, it used a helium-xenon closed gas coolant loop via Brayton cycle. Nothing about that is "fancy RTG".

SAFE-400 was about 2 feet tall and about 1 foot in diameter. Of course, it massed half a tonne.

SNAP-10A, launched into space by the US in 1965, used thermocouples for the electrical energy conversion, but the nuclear reactor itself was a uranium-zirconium-hydride core with beryllium neutron reflectors for criticality control. I'd argue this is still a fission reactor even though it used thermocouples instead of a coolant loop.

On 11/9/2017 at 9:39 AM, peadar1987 said:

The critical mass isn't a hard physical property, you can modify it by things like geometry, moderators and neutron reflectors. The critical mass of a sphere of Californium-242 is just 2.7kg and has a diameter of 7cm. The mass could be further reduced by adding reflectors and a moderator, so you could probably get a "reactor" that would fit in a suitcase (while spraying out some extremely hard radiation)

I've formerly speculated that a very very small nuke could be built by using neutron poison rods to keep a critical mass subcritical until detonation.

EDIT: SNAP-2 was built to be paired with a liquid-mercury Rankine cycle power loop and it was nearly as small as SAFE-400.

Edited November 10, 2017 by sevenperforce

[Grand Ship Builder]

What safety measures are taken when securing a Falcon 9 booster on a drone ship? While highly unlikely, what would the recovery crew do if the booster started wobbling around, about to fall?

[Steel]

42 minutes ago, Grand Ship Builder said:

What safety measures are taken when securing a Falcon 9 booster on a drone ship? While highly unlikely, what would the recovery crew do if the booster started wobbling around, about to fall?

Well there aren't any crew... so not a lot

[p1t1o]

3 hours ago, sevenperforce said:

I've formerly speculated that a very very small nuke could be built by using neutron poison rods to keep a critical mass subcritical until detonation.

I had a look at your diagrams over on XKCD. I think that there is a fizzle problem,  the device is only confined at the ends, the weapon will expand radially until it is no longer critical, this of course happens in every weapon, but without significant radial confinement I suspect it will disrupt itself too quickly to release much energy. In other words, your design would be much more efficient if there were an extention of the confinement, but this would add radius and essentially defeat the object.

Compare to the Little Boy device. This was "assembled" explosively, but confinement was due to the tensile strength inertia* of the casing. The casing was very thick and very heavy and produced an inefficient device. I feel like the thickness of casing needed to make your device detonate with a decent efficiency would defeat all gains in reducing radius by making it a cylinder.

However, I think it is likely that you were thinking along the right lines, there was a revolution in US warhead design that vastly reduced the radius of fission devices, called the "Swan device" it was an oval-shaped primary, that had a compression system that used clever timing to achieve spherical compression.

It is worth noting that the Swan configuration, intended to produce a minimum-diameter device, was usually used entirely without a reflector/tamper/strong casing, as doing so - even though less fissiles would be required, increased the diameter. Ergo, swan devices used rather more fissiles than would otherwise be required, in order to achieve lower radius.

Very modern warhead are said to have [details are obviously not available] an actual pit that is oval, or "prolate", using again clever timing and construction to compress, forming a sphere at the right moment.

Making a subcritical oval is essentially similar to your subcritical rod design in terms of reducing the radius of your subcritical component. In fact it can be seen as your rod device but with the compression system covering laterally as well, as described above.

So the rod idea itself is totally solid.

As for using neutron poisons, i dont see why this approach wouldnt work, but I dont see why it is necessary when geometry is already controlling the criticality. You risk poisoning the reaction itself, increasing the proability of a fizzle or even a dud, especially since a mature compression system has to have full coverage (or your plutonium will be squirted out the same gap as your poison, spoiling the criticality).

 

 

*at the temperatures and pressures involved, chemical-bond tensile strength is meaningless and it is the inertial mass of material which provides the brief resistance to outwards expansion. This is true whether you are considering a Little Boy-like device or the inwardly collapsing tamper of a spherical implosion device, it is even true down in the chemical-energy realm and applies to things like shaped charges and kinetic penetrators. The energies at which chemical bonds become trivial is suprisingly low, in a scientific context.

Edited November 10, 2017 by p1t1o
inertial confinement

[DerekL1963]

7 hours ago, sevenperforce said:

I've formerly speculated that a very very small nuke could be built by using neutron poison rods to keep a critical mass subcritical until detonation.

Not using that design, no.   With so little compression, essentially zero confinement or tamping, and already being so close to criticality...  it'll blow apart and fizzle.  (Even making the assumption that the 'control rods' will be ejected rather than being captured.)  Nor will the pressures rise to anywhere near that needed to trip the core over into fusion (since they'll be barely more than you can generate with just high explosives).