For Questions That Don't Merit Their Own Thread

[p1t1o]

@ChrisSpace

For the cryogenic question: naturally, there are a lot of unknowns, but I have a couple of datapoints.

First, going very close to absolute zero will probably be very destructive due to exotic phase changes and other alterations of material structure.

Currently, in most contexts, freezing a higher vertibrate is fatal (ignoring for the moment examples of reptiles with anti-freeze compounds in their blood etc.)

However, in BioTech contexts, bacteria are routinely stored at -80C and can be reanimated without issue.

But even at -80 there is plenty of atomic motion, and because biological systems are complex down to the atomic level, there is damage accumulated (that canot be healed as those systems are frozen) so there is a time limit that is imposed by entropy, thermodynamics and biological organsims simply being complex on the atomic level.

Ergo, any biological system, no matter how alien the biochemistry, would suffer the same consequences.

 

So, IMO, it might be possible, with technological advances, to cryogenically suspend a higher organism and successfully revive, but over time, thermodynamics and entropy will degrade even a very cold body.

I would not expect any frozen biological entity to remain viable over cosmically relevant periods of time, no matter the chemistry or cryo tech.

Of course, if the biochemistry is OVER THE TOP ESOTERIC,  such as liquid nitrogen as a fluid solvent and cryogenically stable alloy solid components, or exotic physics controlling molecular motion and phase at near-absolute zero temperatures, then all bets are off.

 

tl;dr - I think in almost any scenario, if you find frozen aliens after 2-4million years, they are almost guaranteed to be dead. Unless their molecular make-up is being actively repaired/reconstructed, but then you're not really frozen.

If the aliens were NOT frozen, but were merely unconcious but tended by machines, I think that would be more likely to be made survivable over the long term, as damage to the body can be healed naturally and machinery can be made arbitrarily reliable and self-repairing (at least more so than a corpse can at 10K).

Edited September 22, 2017 by p1t1o

[DDE]

On ‎22‎.‎09‎.‎2017 at 11:25 AM, shynung said:

Is it possible to alleviate their boredom by altering their perception of time so that, to their minds, 1000 seconds felt like 1 second?

Likely not without compromising their ability to take care of themselves, similar to how people with no sense of pain keep injuring themselves until they die of sepsis.

[0111narwhalz]

What are the scaling laws for rocket nozzles? Particularly, to which variable to they scale? Only sensible candidates I can think of are ṁ, F, or maybe F_p.

[Steel]

8 hours ago, 0111narwhalz said:

What are the scaling laws for rocket nozzles? Particularly, to which variable to they scale? Only sensible candidates I can think of are ṁ, F, or maybe F_p.

You'll have to define your variables to stop everyone guessing. I'm assuming mass flow rate, thrust and something to do with pressure?

Edited September 27, 2017 by Steel

[0111narwhalz]

Just now, Steel said:

You'll have to define your variables to stop everyone guessing. I'm assuming mass flow rate, thrust and something to do with pressure?

Apologies. Mass flow rate (ṁ), thrust (F), and thrust power (F_p).

[Steel]

Thanks! Rocket nozzles aren't quite that simple unfortunately. 

Generally you can get most of the potential thrust from a short nozzle with a well designed bell contour, however increasing the length can also improve your thrust slightly. The size of this increase is dependent on how good the nozzle is, so generally you'll see a larger effect for simple nozzle (i.e conical) than for more complex ones.

However, the biggest thing that changes with nozzle length is ISP, since a longer nozzle has a larger exit area, thus a larger throat-to-exit area ratio and thus a faster exhaust velocity.

Mass flow rate is fixed for any given combination of chamber pressure, throat area and outside pressure, so the nozzle has no effect.

 

Basically, it scales with exhaust velocity, which is related to thrust and ISP. It also differs depending on the design of the nozzle, but that's another story.

Edited September 27, 2017 by Steel

[0111narwhalz]

1 hour ago, Steel said:

Basically, it scales with exhaust velocity, which is related to thrust and ISP. It also differs depending on the design of the nozzle, but that's another story

My question was more related to scaling of the "size" of a rocket nozzle. That is, when you use a larger rocket for more thrust power (which itself scales quadratically with respect to ehaust velocity and linearly with respect to each of thrust and mass flow rate), how do the dimensions (and thus mass) scale? Is it polynomial? If so, what is its degree?

[Steel]

3 minutes ago, 0111narwhalz said:

My question was more related to scaling of the "size" of a rocket nozzle. That is, when you use a larger rocket for more thrust power (which itself scales quadratically with respect to ehaust velocity and linearly with respect to each of thrust and mass flow rate), how do the dimensions (and thus mass) scale? Is it polynomial? If so, what is its degree?

Are we talking about the nozzle specifically or about the general dimensions of the rocket as a whole (one chamber size, throat area, e.t.c)

[0111narwhalz]

Just now, Steel said:

Are we talking about the nozzle specifically or about the general dimensions of the rocket as a whole (one chamber size, throat area, e.t.c)

I enquire only of the nozzle which converts pressure to velocity. That is to say, nothing before the throat. Throat size may change to create changes in mass flow rate, but I already know how those two variables relate.

In particular, I ask of the scaling of the overall "scale" (that is, length and radius without much change in shape) and of thickness.

[Steel]

So, basically for any engine you will have a target area ratio (area of the throat Vs area of the nozzle exit) which will be decided based on how much ISP you require and how heavy can allow the nozzle to be. The area ratio then determines the length and radius of the nozzle, since the exit radius is related to the length.

[0111narwhalz]

23 minutes ago, Steel said:

So, basically for any engine you will have a target area ratio (area of the throat Vs area of the nozzle exit) which will be decided based on how much ISP you require and how heavy can allow the nozzle to be. The area ratio then determines the length and radius of the nozzle, since the exit radius is related to the length.

So nozzle scale is linear with mass flow rate?

How about thickness?

[Steel]

6 minutes ago, 0111narwhalz said:

So nozzle scale is linear with mass flow rate?

Roughly, but there are a lot of other factors that go into it, so a linear scale will not always be true. For example, the Merlin 1D vacuum nozzle is the same size as the entire standard Merlin 1D engine and nozzle put together, but the M1D and M1DVac have almost identical mass flow rates.

6 minutes ago, 0111narwhalz said:

How about thickness?

Thickness is down to aerodynamics and cooling requirements. So an ablatively cooled vacuum nozzle will be very thin, while a regeneratively cooled sea level nozzle will be much appreciated thicker

Edited September 27, 2017 by Steel

[Grand Ship Builder]

Basically, longer nozzle = better vacuum performance, and shorter nozzle = better atmosphere performance.

[WinkAllKerb'']

why some river are full of mercure ? why some people have to swim in them ? is it unhealthy ? badum tshhh ...

Edited September 27, 2017 by WinkAllKerb''

[Green Baron]

Mercury in rivers results most often from illegal / criminal discharge of industrial waste (e. g. from coal mining, coal burning, others ?) in rivers. People swim in it because they either don't know, don't care or have no choice.

Mercury is extremely toxic and a severe health risk for wild life as well as humans.

http://www.who.int/mediacentre/factsheets/fs361/en/

 

[WinkAllKerb'']

i met one of thoose no choice guy 20 25 years ago because the way you cross people road in life is random, anyway, i always keep him and it's pal somewhere in my mind, weird life amongst others, thks for the explain

Edited September 27, 2017 by WinkAllKerb''
pidgin typo

[Terwin]

11 hours ago, Steel said:

So, basically for any engine you will have a target area ratio (area of the throat Vs area of the nozzle exit) which will be decided based on how much ISP you require and how heavy can allow the nozzle to be. The area ratio then determines the length and radius of the nozzle, since the exit radius is related to the length.

If you still have margin on the max temp and pressure for your combustion chamber, is there any reason not to narrow the throat instead?  

Seems like a lower mass approach than increasing the size of the nozzle.

Could a super-strong alloy allow very high ISP from a small nozzle due to a tiny throat?

[Steel]

3 minutes ago, Terwin said:

If you still have margin on the max temp and pressure for your combustion chamber, is there any reason not to narrow the throat instead?  

Seems like a lower mass approach than increasing the size of the nozzle.

Could a super-strong alloy allow very high ISP from a small nozzle due to a tiny throat?

Reducing the throat area reduces mass flow rate and thus thrust.

Edited September 27, 2017 by Steel

[Terwin]

4 minutes ago, Steel said:

Reducing the throat area reduces mass flow rate and thus thrust.

Would it be plausible to try and increase the pressure in the combustion chamber to compensate for the smaller throat, or would the proposed super-alloy need to have implausible properties to allow strengthening the combustion chamber sufficiently without paying the same(or higher) mass penalty you would get from a longer nozzle?

[Steel]

20 minutes ago, Terwin said:

Would it be plausible to try and increase the pressure in the combustion chamber to compensate for the smaller throat, or would the proposed super-alloy need to have implausible properties to allow strengthening the combustion chamber sufficiently without paying the same(or higher) mass penalty you would get from a longer nozzle?

You could try, but as you say, you start running into material problems because increasing chamber pressure usually necessitates an increase in temperature too. My guess would be that any mass savings in the nozzle would be at the very least cancelled out by the increase in mass of the chamber, if not exceeded by it.

Edited September 27, 2017 by Steel

[K^2]

On 9/27/2017 at 12:42 PM, Steel said:

Reducing the throat area reduces mass flow rate and thus thrust.

That's really not how hydrodynamics of a nozzle works. Reducing the throat actually speeds up the flow, keeping mass flow rate constant. This will go on until you hit the critical speed (AKA speed of sound) and only at that point you'll start actually reducing the flow rate. But it also happens to be the point where you can start expanding the nozzle to get more energy out of the fluid.

As the result, the cross-section of the nozzle is not designed for a specific flow rate. It's the other way around. The cross-section of the throat is completely determined by the diameter of the combustion chamber, chamber pressure, and chamber temperature. If you want more flow, you have to either increase temperature or size of the combustion chamber, and resulting throttle diameter is something you just compute from a formula at that point.

[Steel]

3 hours ago, K^2 said:

That's really not how hydrodynamics of a nozzle works. Reducing the throat actually speeds up the flow, keeping mass flow rate constant. This will go on until you hit the critical speed (AKA speed of sound) and only at that point you'll start actually reducing the flow rate. But it also happens to be the point where you can start expanding the nozzle to get more energy out of the fluid.

As the result, the cross-section of the nozzle is not designed for a specific flow rate. It's the other way around. The cross-section of the throat is completely determined by the diameter of the combustion chamber, chamber pressure, and chamber temperature. If you want more flow, you have to either increase temperature or size of the combustion chamber, and resulting throttle diameter is something you just compute from a formula at that point.

My point was that, keeping all the rest of it the same (i.e exit area, chamber size e.t.c) reducing the size of the throat of an engine would decrease mass flow rate.

[K^2]

On 9/29/2017 at 9:08 AM, Steel said:

My point was that, keeping all the rest of it the same (i.e exit area, chamber size e.t.c) reducing the size of the throat of an engine would decrease mass flow rate.

No, that's not true as a general statement. A sub-critical flow will speed up to compensate, resulting in almost exactly the same mass flow rate. That's the whole point of having a throat in the nozzle in the first place. Only once you've reached the critical speed does reducing throat size further will start reducing the mass flow rate.

[Steel]

38 minutes ago, K^2 said:

No, that's not true as a general statement. A sub-critical flow will speed up to compensate, resulting in almost exactly the same mass flow rate. That's the whole point of having a throat in the nozzle in the first place. Only once you've reached the critical speed does reducing throat size further will start reducing the mass flow rate.

Yeah fair point. So assuming the engine was designed by a sane person in the first place such that it is sonic in the throat region, reducing the throat area will decrease mass flow rate.

[WinkAllKerb'']

can we start a freud the proud, jung the mystic thread arround here and discuss about random there sparse their view are  ? psycho is that even a neuro thing ?

Edited October 7, 2017 by WinkAllKerb''