For Questions That Don't Merit Their Own Thread

[kerbiloid]

58 minutes ago, tomf said:

Is there a negative feedback mechanism in the collapse of a cloud of uranium that will result in a steady power output.

They say, the heat production of 238U is ~0.1 W/t, and it's almost  40% of the decay heat in the Earth. So, probably you can take 0.2 W/t to add its products decay.
https://www.virginiauranium.com/uranium-101/
https://physicsworld.com/a/radioactive-decay-accounts-for-half-of-earths-heat/#:~:text=Decay and measure&text=The combined results have allowed,uncertainty of about 8 TW.

(Or you can make a star of radioactive waste instead, then its heat production decreases from 10 kW/t to 1 kW/t after one year.)

https://en.wikipedia.org/wiki/Decay_heat#Spent_fuel

***

And then calculate the Jeans mass

https://en.wikipedia.org/wiki/Jeans_instability

https://en.wikipedia.org/wiki/Number_density

[Gargamel]

11 hours ago, Hyperspace Industries said:

Could you make a hot air balloon which was painted black, or transparent and working like a car in the sun, that heated itself with sunlight? (This might be able to reduce the mass of hot air balloons, allowing more payload.)

Right before the X Prize made space flight the billionaire fashion trend de jeur, round the world balloon flights were all the rage.  IIRC, this was an issue the engineers had to plan for.   More buoyancy during the day, less at night.   
The difference wasn’t enough to launch or not, but it was enough they had to account for it, especially later in the flight when the envelope had leaked a bit of gas and they might have problems clearing some higher peaks. 

11 hours ago, Hyperspace Industries said:

 

11 hours ago, Hyperspace Industries said:

Edited March 25, 2022 by Gargamel
Stupid forum

[ARS]

If I want to break the speed record, which one of these environment that would put the most and the least strain on the vehicle at high speed? (ignoring the difficulty of attaining high speed in that environment, assume we can go as fast as we want)

-sky: flight speed record (vehicle only interact with air)

-ground: land speed record (vehicle interact with air and ground)

-sea surface: sailing speed record (vehicle interact with water and air)

-underwater: submarine speed record (vehicle interact only with water)

Edited March 25, 2022 by ARS

[Hyperspace Industries]

26 minutes ago, ARS said:

If I want to break the speed record, which one of these environment that would put the most and the least strain on the vehicle at high speed? (ignoring the difficulty of attaining high speed in that environment, assume we can go as fast as we want)

-sky: flight speed record (vehicle only interact with air)

-ground: land speed record (vehicle interact with air and ground)

-sea surface: sailing speed record (vehicle interact with water and air)

-underwater: submarine speed record (vehicle interact only with water)

Probably the least would be air, because you only have atmospheric drag, and no ground friction.

Probably the most would be either submarine, with lots of water drag, or land, because sailing ships can use hydrofoils, but on land you either have wheels, which will tear themselves to pieces with centrifugal force, or skids, which will be eaten through like a belt sander eats through a cookie.

[Gargamel]

34 minutes ago, Hyperspace Industries said:

because sailing ships can use hydrofoils,

The latest I've been hearing from the sailing racing circuits is that Engineers are starting to hit 'theoretical' limits of the hydrofoils, for the same reasons you listed for the submarine.  You can only push a hydrofoil through the water before you start exceeding the physical ability of it to not break apart.  They have to be extremely light ( along with the rest of the boat), while still being able to handle the insane forces that are in play with high performance sailing. 

To answer @ARS's question though....   it's kind of a "it depends" answer.   Are we looking to break the ultimate speed record of each medium?   Or are we just looking to find a category of speed record that will get us a plaque to mount on the wall with the least amount of effort?  

If it's the first one, I think land will be your best bet.  Air records are broken by investing a not insignificant percentage of a country's GDP into R&D to go just a little faster.   That alone rules that out.   Same with subsurface, weapon technology has already produced, supposedly, the underwater equivalent of hyper sonic cruise missiles.    Going beyond this will again require serious R&D.    Sailing, because of the various racing circuits out there and independent record breakers that are already pushing the leading edge, it will require a pretty major campaign to mount a serious attempt at an all time best.   Sailing boats are approaching theoretical and weather limits already, and motorized boats are pretty much limited by the surface conditions, much faster than what we have already done usually results in disaster.  Land though, the fastest cars in the world are still basically a group of guys in a garage, with donations for funding, and a decently organized and funded campaign has a shot at setting a record.

If it's the second, then I think it's subsurface.   The other three pretty much all have a "low" barrier to entry, planes just gotta fly, cars gotta roll, boats gotta float, and people want to go fast so they will.   There has been a long history in these three areas for record setting.   Subsurface though, has been primarily a military endeavor, and anything that isn't military really hasn't given a hoot about going fast, it's either deep or shallow with lots of windows.    The military probably looked at manned fast subs, but when they realized those are the equivalent of an underwater Leroy Jenkins, which doesn't bode well for it's occupants life span, they gave up.   So there's probably a very large niche of manned high speed subs that hasn't been fully explored yet.    So if all you really care about is going fast and not drowning, It could be a relatively small campaign to build one that goes fast enough to set a record or two. 

Edited March 25, 2022 by Gargamel

[tomf]

For pretty much any record that you can set out to achieve the difficulty in achieving it is going to be pretty proportional to the coolness of having achieved it + any actual usefulness.

If a record were cool/useful and easy someone would have done it already and pushed the boundary further out.

So by that measure I would expect the submarine record to be easiest simply because it is the least "cool"

Edited March 25, 2022 by tomf
More to say

[Hyperspace Industries]

What are the necessary conditions for energy positive fusion? As in, if you used the best fusion fuel we have, what would you need to do to get it fusing? How strong a magnetic field would you need for magnetic confinement fusion?

Edited March 25, 2022 by Hyperspace Industries

[Terwin]

1 hour ago, Hyperspace Industries said:

What are the necessary conditions for energy positive fusion? As in, if you used the best fusion fuel we have, what would you need to do to get it fusing? How strong a magnetic field would you need for magnetic confinement fusion?

I think the national ignition facility has already reached 'theoretical break-even' where you only look at the energy received and the energy emitted, but as the lasers are no where near 100% efficient, and neither is the energy capture for what is mostly gamma rays, there is still a long way to go for a net energy surplus.

For all we know, it may actually be impossible to produce a cost-effective energy surplus with one (or all) of the methods currently under development for fusion energy

This is a goal that has ben pursued diligently for decades, and while we are pretty good at reliably igniting fusion with some methods(inertial confinement for example), others are still having problems(tokamak, stellarator).

As far as I am aware, if we are working on a discrete fuel pellet, we can ignite it pretty reliably, but it is much harder to break-even with this approach.  While potentially self-sustaining approaches(tokamak or z-pinch for example) have difficulty getting up to ignition temperatures without losing heat(like plasma leaks), or maintaining it once there(fusion by-products escaping with all of their energy, cooling the remaining plasma).

In any case, each design requires different magnetic field strengths.

Lots of links to follow here:

https://en.wikipedia.org/wiki/Fusion_power

[Gargamel]

10 hours ago, ARS said:

If I want to break the speed record, which one of these environment that would put the most and the least strain on the vehicle at high speed? (ignoring the difficulty of attaining high speed in that environment, assume we can go as fast as we want)

Having reread your question, I see I misread it the first time.   I answered "Which medium would be easiest to set a new record".   I still like my answer to that question though.

The question you asked.... It's invalid.   The only real limiting factor in speed records at this point is the resistance caused by the medium.   After some pondering on this question, I think we're just tossing out some fundamental laws of physics.   No air resistance?  Cool, but how do we steer?  No resistance from the ground?  Time to fall through the planet.  No resistance from the water?   Good luck stopping.  

Vehicle strain is caused by the very item you told us to ignore.   The answer is either all or none.   It basically boils down to how big of a rocket motor can we afford to make? 

[DDE]

9 hours ago, Gargamel said:

Having reread your question, I see I misread it the first time.   I answered "Which medium would be easiest to set a new record".   I still like my answer to that question though.

The question you asked.... It's invalid.   The only real limiting factor in speed records at this point is the resistance caused by the medium.   After some pondering on this question, I think we're just tossing out some fundamental laws of physics.   No air resistance?  Cool, but how do we steer?  No resistance from the ground?  Time to fall through the planet.  No resistance from the water?   Good luck stopping.  

Vehicle strain is caused by the very item you told us to ignore.   The answer is either all or none.   It basically boils down to how big of a rocket motor can we afford to make? 

I don't think it becomes a spherical cow in a vacuum - it's worse than that. Max speed would in large part be deiven by power density (governed by cooling, thus largely determined by the density of the medium) and the efficiency of the locomotion system that turns that power into movement. With the exceptions suggested, underwater travel becomes easiest due to the availability of coolant and the ease of converting shaft rotation to forward motion.

Which is, of course, complete nonsense.

Edited March 26, 2022 by DDE

[SunlitZelkova]

Just how big could a rocket built by amateurs with "off the shelf" parts get?

In theory, that is, not so far in real life. Also while ignoring all regulations and safety measures, which IIRC place a limit on model rockets currently.

[JoeSchmuckatelli]

49 minutes ago, SunlitZelkova said:

Just how big could a rocket built by amateurs with "off the shelf" parts get?

In theory, that is, not so far in real life. Also while ignoring all regulations and safety measures, which IIRC place a limit on model rockets currently.

Just how 'off the shelf' does your question require?  Because if you allow 3D printing - then it's just a question of knowledge and money. 

https://youtu.be/cA9HuaQTV_s

 

[steve9728]

On 3/26/2022 at 7:53 PM, SunlitZelkova said:

Just how big could a rocket built by amateurs with "off the shelf" parts get?

In theory, that is, not so far in real life. Also while ignoring all regulations and safety measures, which IIRC place a limit on model rockets currently.

Depends on your budget

[SunlitZelkova]

On 3/26/2022 at 1:49 PM, JoeSchmuckatelli said:

Just how 'off the shelf' does your question require?  Because if you allow 3D printing - then it's just a question of knowledge and money. 

https://youtu.be/cA9HuaQTV_s

 

The question came from narco-submarines. Upon learning about them I was pretty impressed at their technical capabilities (despite being effectively built by amateurs, some cross the Atlantic). Now I wonder about “narco-rockets”.

So basically the types of supplies available in random warehouses in cities and towns of South American countries. Although I suppose cartels could probably acquire a 3D printer if they really wanted to.

But what about propellant?

[steve9728]

1 hour ago, SunlitZelkova said:

The question came from narco-submarines. Upon learning about them I was pretty impressed at their technical capabilities (despite being effectively built by amateurs, some cross the Atlantic). Now I wonder about “narco-rockets”.

So basically the types of supplies available in random warehouses in cities and towns of South American countries. Although I suppose cartels could probably acquire a 3D printer if they really wanted to.

But what about propellant?

Then I think it depends on your budget and also depends on what engine you can got.

UDMH+NTO, the ‘Toxic rocket’, I don't know how the laws and rules about it in the west but it's hard to get it in Asia;

Solid fuel may work and been used in many clips on the Mythsbusters, but it's hard to control. And actually they are high energy explosives;

Liquid oxygen + paraffin, if you can got the engines such as RD-180, then the next problem I think is how you build the rocket. Careful Elon Musk

Liquid oxygen + hydrogen, although the price to making those two things must be more stable than paraffin, more safer than the toxic rocket and more easier to control than the solid fuel. But the associated expenses are not cheap at all: refrigeration equipment, pressurised storage equipment, cryogenic transport equipment and, most importantly, engines.

[JoeSchmuckatelli]

4 hours ago, SunlitZelkova said:

wonder about “narco-rockets

Fun! 

Given the ingenuity of humans in any trade towards overcoming obstacles and narco-subs as one solution... Narco rockets is fair speculation. 

However... (  ;D ) 

The key metric for drug trafficking is to maximize profits while minimizing exposure.  To do that you have to operate just below or at the 'irritant' threshold.  Like a mosquito.  (Once above that threshold the subject stops being irritated and takes active measures to eradicate you). 

A slow sub smuggling drugs is irritating.  But an international missile?  That 'gets on everyone's radar'. Even if the payload isn't explosive - that level of escalation gets a lot of attention. 

I'm fairly critical of 'the war on drugs' for how it was applied domestically and resulted in lopsided, racially biased incarceration in the US... But there were aspects of it that were quite successful.  Examples: JTF - 6 (now JTF North) was manpower intensive but stopped all trafficking and human smuggling for a while and other stuff, like our incursions into Columbia - were from a military and tactical standpoint quite successful - but arguably strategic failures.  Should the cartels decide to 'become interesting' there is nothing to stop military intervention from reducing those capabilities. 

We'd succeed and they would adapt and go back to low tech, low risk successful strategies like those employed currently 

 

[steve9728]

Using submarine to smuggle drug is 'serious international criminal cases'.
Using rocket to throw drug into somewhere, like US, is 'serious national security incidents'.

"Others just want to make lots of money, but you seems really want to end our country!"

[JoeSchmuckatelli]

We already have several "Orion" threads: but I don't want to derail them.

Question:  If someone were to try an Orion launch from the surface... isn't that the equivalent of dumping several EMP blasts on the way up?  So - effectively (and regardless of the pollution) - you destroy your technical infrastructure and economy just to get mass to orbit?

Edited March 28, 2022 by JoeSchmuckatelli

[wumpus]

On 3/25/2022 at 7:30 AM, ARS said:

If I want to break the speed record, which one of these environment that would put the most and the least strain on the vehicle at high speed? (ignoring the difficulty of attaining high speed in that environment, assume we can go as fast as we want)

-sky: flight speed record (vehicle only interact with air)

-ground: land speed record (vehicle interact with air and ground)

-sea surface: sailing speed record (vehicle interact with water and air)

-underwater: submarine speed record (vehicle interact only with water)

Flight speed record.  Look up the X-15 for issues there.  I think atmospheric friction was still the issue, go much faster (like re-entry)  and you get compressive heating.

Ground: limit is the tires.  I think current record holders use steel wheels with no tires.  Also the latest go at the record had to pack up and quit.

Sea surface: the key here is to skim the water, preferably generating lift as a hydrofoil.  That assumes you aren't "cheating" by using ground effect aerodynamics to simply fly "cheaply" just off the water.

Underwater: once you hit cavitation, I'd expect the power needed to scale badly with speed.  There's a reason fast boats use hydrofoils to keep as much of the craft out of water as possible.

Space: I think Far Horizons has the record here.  And not because just Dawn didn't try, but also that Dawn *can't* use her 10k m/s engines for pure speed.   Doing that would take her out of the solar system and her solar panels would stop working with most of the delta-v "in the tank".  A similar craft with an RTG could pull maximum delta-v.

[Gargamel]

1 hour ago, JoeSchmuckatelli said:

We already have several "Orion" threads: but I don't want to derail them.

Question:  If someone were to try an Orion launch from the surface... isn't that the equivalent of dumping several EMP blasts on the way up?  So - effectively (and regardless of the pollution) - you destroy your technical infrastructure and economy just to get mass to orbit?

Where is this recent fascination with ground launching Orion's coming from?   Maybe if the planet is doomed anyways, but let's just orbital launch these things.   They're going to be generational ships, they're going to be huge.   And if they're not generational ships, they're going to be high speed, reusable, interplanetary transports.   They should never need to land anywhere, just dock with the orbital space station. 

Ground launching from a planet means you can only launch them so many times till there isn't any usable surface left. 

[DDE]

8 hours ago, SunlitZelkova said:

The question came from narco-submarines. Upon learning about them I was pretty impressed at their technical capabilities (despite being effectively built by amateurs, some cross the Atlantic). Now I wonder about “narco-rockets”.

So basically the types of supplies available in random warehouses in cities and towns of South American countries. Although I suppose cartels could probably acquire a 3D printer if they really wanted to.

But what about propellant?

Hm. Small packages with soft-landing capability, IRBM range? In terms of tech and size this sounds like North Korea from a few years back. They generally spent a lot of time scaling up the basic design of the SCUD with its nitric acid oxidizer.

[JoeSchmuckatelli]

20 minutes ago, Gargamel said:

Where is this recent fascination with ground launching Orion's coming from?   Maybe if the planet is doomed anyways, but let's just orbital launch these things.   They're going to be generational ships, they're going to be huge.   And if they're not generational ships, they're going to be high speed, reusable, interplanetary transports.   They should never need to land anywhere, just dock with the orbital space station. 

Ground launching from a planet means you can only launch them so many times till there isn't any usable surface left. 

Sci-Fi application: as I mentioned in the other thread, I first stumbled upon the idea through reading Niven/Pournelle's Footfall, where it was an act of utter desperation to 'not lose' the war (that was almost assuredly already lost).  Then with some handwavium about 'hard-wired universal surrender by rolling on one's back' the good guys stomped an elephant-thingy on the chest and won the day.

...

I looked into Orion back then, (concurrent with some non-proliferation studies in college) and became wholly dissatisfied with it as a concept.  Basically completely forgot about it for decades.  Only since KSP2 looks to be including it has it been a fascination on this board (and b/c SpaceSciFi is apparently writing about it) and so, thus, it keeps popping up.  I don't want to discourage him - and worry that at times I have come off as overly critical - but that doesn't change my opinion of the thing.  It's nuts.

Edited March 28, 2022 by JoeSchmuckatelli

[SunlitZelkova]

7 hours ago, JoeSchmuckatelli said:

We already have several "Orion" threads: but I don't want to derail them.

Question:  If someone were to try an Orion launch from the surface... isn't that the equivalent of dumping several EMP blasts on the way up?  So - effectively (and regardless of the pollution) - you destroy your technical infrastructure and economy just to get mass to orbit?

I don’t think that was taken into account. But they would launch from a remote area anyways (obviously with no populated areas down range) which would likely reduce the impact.

Keep in mind though that the Orion was designed in an age when kids stood on their feet in the front seats of cars and “dilution is the solution to pollution” (read: dumping in the ocean) was considered to be a thing. So we shouldn’t have high safety expectations anyways.

[razark]

6 hours ago, Gargamel said:

Where is this recent fascination with ground launching Orion's coming from?

When I first heard of the concept years ago, I always assumed it was clearly to be built in orbit.  It wasn't until I read stuff on this forum that I ever even considered ground launch for Orion.

And I can't wrap my head around why anyone would ever do such a thing.  I would have sworn we learned enough to not do something so damned stupid after years of above-ground nuclear tests.

[SunlitZelkova]

2 hours ago, razark said:

When I first heard of the concept years ago, I always assumed it was clearly to be built in orbit.  It wasn't until I read stuff on this forum that I ever even considered ground launch for Orion.

And I can't wrap my head around why anyone would ever do such a thing.  I would have sworn we learned enough to not do something so damned stupid after years of above-ground nuclear tests.

It was conceived before we agreed upon above ground nuclear tests being bad.