For Questions That Don't Merit Their Own Thread

[KG3]

  Something you seem to hear during interviews of people who witnessed above ground nuclear tests is something like "It was so bright I could see the bones of my hands".  Does anybody know if this is actually a thing?  I'm assuming that these are people who had covered their faces with their hands during the first seconds after detonation.  Could the light have been that bright without their flesh bursting into flames?  Maybe they were seeing an optical illusion of some kind?  Could there have been enough x-rays emitted that they could be seen by the human retina?  Maybe something caused the calcium in their bones to momentarily fluoresce.   Or maybe one person just said it as an exaggeration and others repeated it just because it sounded cool.

[Niccolo]

15 hours ago, KG3 said:

  Something you seem to hear during interviews of people who witnessed above ground nuclear tests is something like "It was so bright I could see the bones of my hands".  Does anybody know if this is actually a thing?  I'm assuming that these are people who had covered their faces with their hands during the first seconds after detonation.  Could the light have been that bright without their flesh bursting into flames?  Maybe they were seeing an optical illusion of some kind?  Could there have been enough x-rays emitted that they could be seen by the human retina?  Maybe something caused the calcium in their bones to momentarily fluoresce.   Or maybe one person just said it as an exaggeration and others repeated it just because it sounded cool.

There's a lot of questions there, so I'll tackle them one by one.

• Could the light have been that bright without their flesh bursting into flames? 

It could have, yes. One thing you need to remember is that, above all else, above its destructive force, its massive radioactive fallout and its thunderous, literally earth-shaking roar, is that a nuclear explosion is really, really bright. So bright that one of the smallest tests, Trinity, burned a hole through the photographic film. The light from Trinity was seen three hundred and seventy-five kilometres away (about 280 miles). This was light so bright that it turned the air around the explosion opaque for a few moments.

Depending on your distance from the explosion, it is fully possible to be close enough for your eyes to be overwhelmed by the light, but you are otherwise (mostly) okay in the short-term. First-degree burns would be common at the inner limits of this range, appearing as really bad sunburn. 

• Could there have been enough x-rays emitted that they could be seen by the human retina? 

No. The compounds in our eyes that enable our vision don't react to X-Ray spectrum photons in a way that our brains interpret as a light signal. The viewers might have experienced phosphenes, but those generally aren't discrete and are instead flashes.

• Maybe something caused the calcium in their bones to momentarily fluoresce.  

Although I may be wrong on this, I'm fairly sure that bone fluoresces in blues and/or greens, which would be absorbed by the flesh in the way. If the bones were fluorescing brightly enough that that was why we could see them, then your hand would probably be on fire. 

However, bones are very, very opaque - even moreso than flesh and skin. So what is instead possibly happening is pretty much the same thing as if you hold a torch under your thumb and switch it on. The light shines through the flesh and blood, but not through bone. Finger-bones are too thin to show up that way though, since the light just diffracts around them entirely and hides them from view. So a torch won't show your finger bones.

A penlight under your palm won't shine through your hand since the meat is too thick, but enough light (such as the light from a nuclear blast) may well. Even better would be the bones in your forearm. Those are big, and so have a decent chance of casting a shadow compared to the (relatively) less opaque flesh.

• Or maybe one person just said it as an exaggeration and others repeated it just because it sounded cool.

Distinctly possible. There's a lot of hearsay and anecdotal evidence, but as you said it may have started as an exaggeration. Who knows?

I for one do not want to find out the truth firsthand.

 

Edited December 9, 2017 by Niccolo

[Grand Ship Builder]

Can sound use light as a medium?

[Green Baron]

42 minutes ago, Grand Ship Builder said:

Can sound use light as a medium?

Not naturally. Needs transformation. Like in a CD-player e.g.

[0111narwhalz]

19 hours ago, Grand Ship Builder said:

Can sound use light as a medium?

Light doesn't interact with other light. (Except in edge cases where you get an obscene amount of light together, like a kugelblitz.) Light in a vacuum also always travels at exactly c. Together, these factors make it pretty much impossible to create the compression waves that make up sound. Unless you're using some kind of incredibly precise thing that translates the red/blueshift of a warm speaker cone's blackbody radiation into sound, but that's not really sound in the conventional sense.

[Spaced Out]

Okay so which is more efficient one continuous burn to orbit or a circularisation burn? Also answer this too. How do you calculate the efficiency of a trajectory?

Edited December 11, 2017 by Spaced Out

[Niccolo]

6 hours ago, Spaced Out said:

Okay so which is more efficient one continuous burn to orbit or a circularisation burn?

Assuming perfect conditions for both options, then the single continuous burn will be more efficient than a two-stage burn of elevate followed by accelerate. Going to space requires two steps: First, get high enough (elevate) to be outside the atmosphere. Second, go sideways fast enough that you stay out of the atmosphere (accelerate). These are basically vertical and horizontal vectors (Yes, math has entered the game). A gravity turn involves your rocket tipping over, such that a portion of the thrust goes towards acceleration instead of elevation.

A theoretically 'perfect' launch involves you burning such that you are burning all the way to your apoapsis with a perfect, continuous gravity turn such that as you hit your target apoapsis, your rocket is perfectly horizontal and thus putting all further momentum straight into acceleration. Drawn out, the perfect launch has a hyperbolic trajectory with a horizontal asymptote at your target altitude.

A single continuous burn (without your nose dipping below the horizon) means that your gravity turn is dead perfect, and that your tipping rocket has smoothly transitioned from elevating to accelerating with an absolute minimum of wasted energy. Basically your rocket's path has minimally deviated from the perfect path.

In contrast, a two-stage burn (even with a gravity turn) means that your rocket's trajectory reached the target height too early, and so your path deviated from that of perfect. An imperfect trajectory requires additional energy to essentially "bend" it into shape so that it will (in the future) intersect again with the perfect path.

[DDE]

On 11/23/2017 at 7:23 AM, shynung said:

Going all the way on that idea: just dump some chlorine trifluoride in their general direction. It'll eat through most materials, and thoroughly corrode what is left behind.

That’s overkill. But I am trying to slap a similar design to a fictional bomber jet. Basically, I don’t think anything will be left out of a sizeable target area after a ton of ClF5 is dropped inside ordinary, napalm-style tanks.

On 11/22/2017 at 2:57 PM, Racescort666 said:

Defeating the tracking system is usually the best way I’d say. That’s basically how most aircraft countermeasures work. 

It’s definitely the most popular way of dealing with UAVs and UCAVs.

[wumpus]

9 hours ago, Niccolo said:

In contrast, a two-stage burn (even with a gravity turn) means that your rocket's trajectory reached the target height too early, and so your path deviated from that of perfect. An imperfect trajectory requires additional energy to essentially "bend" it into shape so that it will (in the future) intersect again with the perfect path.

Note that on planets with an atmosphere, you wind up optimizing for a lot of variables.  An ideal path should only burn along prograde, any used to turn the rocket are considered "cosine losses" (your loss is proportional to the cosine of the angle between your thrust vector and prograde).  I'd call what you are asking for "hypotenuse losses".  An ideal burn would calculate the vertical delta-v and horizontal delta-v, add them up in right angles and then burn along the hypotenuse.  Of course in worlds with an atmosphere, you want to minimize aero losses so you start by heading straight up.

Presumably NASA computers work out the amount of aero loss and "hypotenuse" loss and work out a trajectory that minimizes both (actually I'm sure they do a single burn to minimize the thrust needed from the second stage).

[StrandedonEarth]

On 2017-12-09 at 5:50 AM, Grand Ship Builder said:

Can sound use light as a medium?

As a medium, no. As a carrier, yes; sound is already carried on radio waves. To carry sound on visible light would just need a different mechanism to modulate and receive it. 

Edit: actually, I believe stellar and/or neutron star quakes have been detected by their effect on the starlight. Sound is a vibration, and quakes are vibrations, basically infrasound. 

Edited December 11, 2017 by StrandedonEarth

[KG3]

Are there any gasses that are denser than liquids so that if up together in a container the gas would bubble to the bottom?  I'm not too concerned if the two can't actually exist in the same place at the same time because of temperature differences or because they wouldn't play nice together chemically.  Like maybe Uranium hexafluoride put in liquid Hydrogen or Tungsten vapor mixed in liquid Helium or some such thing. 

It's just that there are so many solids that float on liquids why not a liquid that floats on a gas?  I've been wondering about this for a while now.    

[sevenperforce]

2 hours ago, KG3 said:

Are there any gasses that are denser than liquids so that if up together in a container the gas would bubble to the bottom?  I'm not too concerned if the two can't actually exist in the same place at the same time because of temperature differences or because they wouldn't play nice together chemically.  Like maybe Uranium hexafluoride put in liquid Hydrogen or Tungsten vapor mixed in liquid Helium or some such thing. 

It's just that there are so many solids that float on liquids why not a liquid that floats on a gas?  I've been wondering about this for a while now.    

The least dense known liquid is some methyl-butene group hydrocarbon, at 650 g/L. The densest possible gas would be uranium hexachloride at 19.5 g/L. So, no.

If you used an incompressible liquid and put the whole affair under pressure, there's a chance you could get the gas to be denser than the liquid. But probably not.

[monophonic]

Obligatory Cody's Lab video:

 

[shynung]

Is it possible to build a hybrid fission-fusion reactor design? If so, how would it perform against standard fission reactor designs?

[DerekL1963]

5 hours ago, shynung said:

Is it possible to build a hybrid fission-fusion reactor design? If so, how would it perform against standard fission reactor designs?

I can't even figure out what such a thing would look like...  the materials that fizz don't fuze, and vice versa.  So I'd say, it's not possible to build a hybrid reactor of that nature.  (And no, Teller-Ulam isn't a reactor and doesn't count.)

[shynung]

1 hour ago, DerekL1963 said:

I can't even figure out what such a thing would look like...  the materials that fizz don't fuze, and vice versa.  So I'd say, it's not possible to build a hybrid reactor of that nature.  (And no, Teller-Ulam isn't a reactor and doesn't count.)

I'm thinking of a gas-core fission reactor (think nuclear lightbulb) with the fusion fuel snuck into the fuel loop.

[DerekL1963]

6 hours ago, shynung said:

I'm thinking of a gas-core fission reactor (think nuclear lightbulb) with the fusion fuel snuck into the fuel loop.

Oh, that's an easy answer - all you'll accomplish is diluting your fission fuel.  The pressures/temperatures inside such a reactor aren't anywhere near fusion territory.

[USB4]

Is an atmospheric motor carrying its own oxidizer verging on kerbin jet efficiency possible? Essentially a weebly without needing oxygen in the atmosphere.

[shynung]

58 minutes ago, USB4 said:

Is an atmospheric motor carrying its own oxidizer verging on kerbin jet efficiency possible? Essentially a weebly without needing oxygen in the atmosphere.

It is, it's called an air-augmented rocket. Still uses internally-stored fuel and oxidizer, but takes extra propellant from the surrounding atmosphere. It won't approach turbojet levels of efficiency, but pretty close to LH2-fed nuclear thermal rocket.

 

[USB4]

2 hours ago, shynung said:

It is, it's called an air-augmented rocket. Still uses internally-stored fuel and oxidizer, but takes extra propellant from the surrounding atmosphere. It won't approach turbojet levels of efficiency, but pretty close to LH2-fed nuclear thermal rocket.

That basically works like Dyson hair dryers/the same principle as syphoning right?

 

Anyhow I was really hoping more for something that could function for longer/more efficiently similar to the vtol engines  here 

 

I was considering just basically making the basically same thing but more geared towards forward flight for flying on planets like eve, but id prefer to make it at least somewhat scientifically based so its not cheaty or magical.

[Terwin]

3 hours ago, USB4 said:

I was considering just basically making the basically same thing but more geared towards forward flight for flying on planets like eve, but id prefer to make it at least somewhat scientifically based so its not cheaty or magical.

For eve, you could always try the reverse approach:

If the explodium sea is actually a combustible fuel, there must be plenty of it in the atmosphere, so you could just bring your own oxidizer.

 

[Rus-Evo]

I have a question.  Why isnt more effort made to recover service modules (thinking specifically SpaceX)?  Do they intend Dragon service modules to always be expendable?

To attempt to answer my own question, is the extra heat shielding neccessary to stop a greater mass so much heavier that it affects cargo ability too much?

[Canopus]

15 minutes ago, Rus-Evo said:

I have a question.  Why isnt more effort made to recover service modules (thinking specifically SpaceX)?  Do they intend Dragon service modules to always be expendable?

To attempt to answer my own question, is the extra heat shielding neccessary to stop a greater mass so much heavier that it affects cargo ability too much?

The dragon basically doesn‘t have a service module. Behind the Capsule is nothing much more than a hollow tube with solar arrays. All thrusters are on the reentry capsule. The same will be true for the dragon 2 so there is little to recover.

[Rus-Evo]

13 hours ago, Canopus said:

The dragon basically doesn‘t have a service module. Behind the Capsule is nothing much more than a hollow tube with solar arrays. All thrusters are on the reentry capsule. The same will be true for the dragon 2 so there is little to recover.

Oh interesting!! My assumption was that it held oxygen tanks, life support and fuel.  Is Boeings capsule the same?

[Canopus]

11 minutes ago, Rus-Evo said:

Oh interesting!! My assumption was that it held oxygen tanks, life support and fuel.  Is Boeings capsule the same?

No i think the CST-100 has the traditional design with life support and propulsion in the service module.

Edited December 17, 2017 by Canopus