Comments by "" (@fromagefrizzbizz9377) on "Искаженное восприятие"
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+Tim Webb You're trying to explain to a rocket engine designer how a rocket motor works? Seriously?
[I've designed/built/flown/assisted with rockets/motors up to the 2000 pounds of thrust class, both solids and hybrids.]
Let's keep this brief and simple: I assume you believe that if you took two bowlings balls, and placed a compressed spring between them (not connected to either ball), that the two balls would shoot apart, in both atmosphere and vacuum, when you released the spring, right?
Well, you've just agreed that a rocket motor works in vacuum.
The rocket is one ball, the combustion chamber/pressure is the spring, and the other ball is gazillions of nano-balls called "exhaust gas".
100% of the thrust of a rocket is by accelerating the gas from zero (inside the chamber) to above supersonic speeds in the throat of the nozzle (and bell if it has one). Once the gas has left the bell, it can no longer affect the rocket. Period. If you burn 1000 kg of fuel/oxidizer per second, and manage to accelerate it 1000 metres/second^2 in the nozzle/bell, you get a million newtons of force pushing the rocket up. It's just that simple. If the exhaust gas is heavier, at the same acceleration, you get more thrust.
All air does is reduce the pressure differential between the combustion chamber and the outside. Meaning less acceleration. Meaning less thrust. Rockets in atmosphere produce LESS thrust than in space. Not more.
If rockets worked by pushing on atmosphere, that would mean that if you stood on a skate board, and compared the thrust of throwing a bowling ball to the thrust of throwing a bowling-ball-sized balloon, they'd be the same - and you'd go flying down the road on your skate board at precisely the same speed. Right? Doesn't happen, does it?
You shouldn't accept the babblings of youtube clickbaiters without researching it yourself. Clickbaiters are only interested in your money (sorry, "views"). Not truth.
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+Nine Eleven You cherry pick something to complain about, and conveniently ignore that the explanation and proof were there too.
Mankind has known for a very long time that the air pressure decreases slowly as you rise in altitude. The pressure at 10,000' is lower than that at the earth's surface, but it's still enough for people to breathe without difficulty. At the height of MT. Everest, it's quite a bit lower, and there's not enough pressure to breathe properly unless you're extremely physically fit, and have spent weeks getting your body used to the pressure that low. Yet, still, most people use O2 bottles in order to climb the mountain - pure O2 at that pressure is enough to live on, barely. They don't call the 8000 metre level the "death zone" for nothing. At 40,000', the maximum altitude that commercial airliners fly, it's still lower, so low you cannot survive without a pressurized suit or aircraft cabin being supplied with higher pressure air. As a whole pile of Ryanair passengers found out a week or so ago. Sudden pressurization, and the only chance the passengers had for survival was to dive the aircraft to 10,000 feet before the O2 masks ran out.
It's only logical, and indeed, it could be no other way, that the pressure continues to decline the higher you get until there's virtually no pressure at all - in other words, the vacuum of space.
It's all perfectly predictable by the behaviour of gasses, which we know a hell of a lot about (spent long enough in high school chemistry actually performing the experiments and proving them for myself), and can calculate ahead of time exactly what pressures one would encounter at any altitude. Boyles law. Charles law. And so on.
This has nothing to do with NASA, or anybody else's space program. NASA didn't invent this, it was known centuries before NASA existed, NASA simply uses rocket physics as was already well understood.
Today's little known factoid: NASA didn't invent the physics that governs space flight. Goddard and Oberth and Tsiolkovsky were the ones who developed the equations that determine how rocket engines work. Rocket motors today work in exactly the same way that their equations and experimental models did. Their equations are what NASA uses. In fact, it was Tsiolkovsky who developed the whole notion of multi-stage rockets and various alternatives on how to get to the moon. It was Tsiolkovsky who in the 1890s laid out the mission design that NASA ended up using for Apollo in the 1960s. Not bad for a Russian scientist whose work predates NASA by over 60 years, and who died 20 years before NASA was formed. All NASA does is refine and improve the design of the rockets with new materials and new fuels. The basic science of rocketry and space flight is NOT NASA's. Never was.
There are none so blind than those who will not see.
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+lp d "recoil works because the explosion is happening in an enclosed environment, throw a bullet in the fire and it only explode and goes no where"
There's something you're evidently completely unaware of with firearm cartridges, and similarly with rocket motors:
1) The burn rate of gun powders (as with most rocket fuels) is highly dependent upon the pressure it develops during burning. If it doesn't develop a high pressure, the burn rate is slow and takes quite a while. A cartridge dropped into a fire develops very little pressure before the cartridge pops apart, spilling not yet burned powder into the fire. Which in turn burns very slowly because of lack of pressure. you can prove this yourself by taking a shotgun shell, carefully prying it apart, and spilling the powder onto some tin foil and lighting it with a match. It takes many seconds to burn, and depending on the powder it will seem quite weak. With modern rocket solid propellants, the same thing is true - take a fuel grain out of an Aerotech motor, and light it with a match. Even lighting it isn't altogether easy, and it will sizzle and sputter for a several minutes acting like a weak road flare, compared to the usual few seconds of loud shriek when fitted into a motor.
Which means that uncontained a firearm cartridge has relatively little recoil, but not zero. The bullet will be heavier than the casing. The bullet won't move much because it masses more than the casing does. Looking to see how far the bullet went is pointless, did you bother to look to see where the casing went? I doubt it.
You're forgetting that in a rocket the combustion chamber is entirely enclosed (except for the nozzle, doing much the same duty as a gun barrel). So, yes, recoil is maximized. The only time the combustion chamber isn't enclosed is when the rocket catos. Which is a slang term of us rocket heads for when the rocket motor ruptures.
2) You don't understand that in a firearm cartridge, the mass being thrown is the bullet, but in a rocket the mass being thrown is the gas. The mass of the propellant is far less in a firearm cartridge than in a rocket. For example, in one particular cartridge I'm familiar with, the bullet can weigh 200 grains, but there's only 40-45 grains of propellant (if you exceed that, you may exceed the 40,000-60,000 PSI that the rifle chamber is designed for), which in turn generates (at most) 40-45 grains of gas - and in turn the bullet travels around 2200 feet per second. The payload weighs 5 times as much as the fuel does. So at most, the recoil due to the gas being thrown is 1/5th that of the bullet.
Meanwhile, let's look at a rocket. A particularly big rocket - the Saturn V. Every second the Saturn V consumed 10 tons of fuel+oxidizer, producing 10 tons of gas. The gas coming out the back of the rocket was at a speed of about 4000 feet per second - twice as high as a bullet. This would be like a gun firing a 10 ton truck at speeds of over mach 3. Rather more recoil than 200 grain bullet at mach 1.8, eh?. And _continuously_, not just one sharp jolt.. Think*, if you can, how much recoil a gun firing a 10 ton truck at over mach 3 *every second would generate. That's one freaking hell of a lot of recoil. In fact, it's about 7,500,000 pounds of recoil, *continuously*, not just one sharp jolt. No air resistance required, the recoil from a rocket is enormous, so enormous it easily lifted a rocket that weighed 6,000,000 pounds at lift off.
[I've seen people claiming that there's not much fuel in a rocket. On the contrary, at liftoff the Saturn V weighed 6,000,000 pounds (3000 tons). Without any fuel or oxidizer on board, it weighed about 450,000 pounds (225 tons). More than 90% of the weight of the Saturn V was just fuel and oxidizer. Most model and amateur rockets don't have such high fuel/total mass ratios. But I've worked with a few that were higher.]
There are actually rocket designs based loosely more like a gun. There's the old 1950/60 "Orion" project - a massive concrete and steel plate with a lead-lined compartment for people on top. Underneath, you fired a half kiloton nuclear weapon every second or two. A rough ride to be sure, but with enough mass in the "plate", it would be nothing more than a dull kick in the ass every few seconds. It was cancelled pretty promptly when they started thinking about the fallout it would produce, and there was a test ban on in-air nuclear detonations.
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+thomas Gronek starting multiple postings with different half-baked theories isn't going to do you any good. Rockets moving have nothing to do with pressure, and everything to do with throwing mass. Period. There are rockets that work just fine (in vacuum especially) that don't rely on pressure generation at all. All they do is throw mass one way, and they go the other way. It really is JUST THAT SIMPLE. Not even counter-intuitive.
A rocket would work just as well throwing 10 pounds of lead out the back at, say, mach 3, as it would throwing 10 pounds of any gas out the back at mach 3.
Tsiolkovski rocket equations rulz. Do look him up. That's the basic equation behind ALL rocketry, whether they work by combustion/gas, cold gas, slinghots, cross-bows, Orion nuclear drives, or ion accelerators.
This is the description of the Tsiolkovski rocket equation:
"The Tsiolkovsky rocket equation, classical rocket equation, or ideal rocket equation, describes the motion of vehicles that follow the basic principle of a rocket: a device that can apply acceleration to itself using thrust by expelling part of its mass with high velocity and thereby move due to the conservation of momentum."
Notice it doesn't mention air or pressure anywhere in there?
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+Mr Abelone Youtube doesn't correspond to "intense research". Watching youtube these days on this subject is an exercise in learning bad science from people ignorant of the science or are deliberately out to deceive you - almost always for the express purpose of making money. Infowars has nothing to do with the "truth" (Jones has already admitted as much), Infowars is all about selling T-shirts and vitamin supplements. The conspiracy stories he tells are simply a way of generating free advertising.
Read Tsiolkovski. He developed the rocketry equations that NASA (and everybody else) uses today. In the 1880s thru the 1920s. The most important work was published 60+ years before NASA existed. Try reading "Exploration of Outer Space by Means of Rocket Devices" published in 1903 and its sequel in 1911, where he lays the theoretical ground work for just about everything we've ever done in space - multi-stage rockets, orbits, space stations, escape velocities and so on.
Tsiolkovski never personally built a rocket. He didn't think his ideas would ever be implemented. But in his retirement, he found out he was wrong about that, eg: Goddard, Oberth and so on.
The science of modern rocketry is based on Tsiolkovski's work. Everything else since then is engineering better materials, better propellants and better designs to make better use of Tsiolkovski's science.
And yeah, Tsiolklovski's rocketry equation does show that rockets work in vacuum, and in fact better in vacuum than in atmosphere.
Taking things apart doesn't make one a critical thinker. Understanding how the thing does what it does, and being able to use that knowledge to build something different (and better) makes you a good thinker, "critical" not so much. Unless you're in the mode of taking things apart and proving that the thing can't do what's claimed for it.
if you were a critical thinker, there'd be no doubt in your mind that NASA (and the 50+ other space agencies, and thousands of companies in the field) have accomplished what they say they have.
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+Nicholas Turo-Shields The flattards manage to confuse the issue about newton's third law referring to "rockets", which makes people trying to prove that newton's third law works in a vacuum by experimenting with rockets in vacuum chambers. Which inevitably leads to problems with the flattards claiming that the chamber is filling up with gas. Which it is - not enough to have the effect they claim, but there's no way to make them listen.
The BEST way to do this is as a feasible experiment without the "exhaust gas" whining is with a frictionless (okay, use some wheels) sled with a spring loaded gun throwing something heavy - preferably something that won't shatter the far end of the chamber (eep!). Evacuate the chamber, trigger the "gun", and the wheeled sled moves. Newton's 3rd law. No gas to confuse the issue. A rocket engine is merely a "gun" firing gazillion tiny particles (gas molecules) at very high speed, continuously. Like a gatling gun with gazillions of barrels.
As a by-the-way: the video's referrals to difficulty of igniting the motor is somewhat of a red-herring. Aerotech engines (and I've fired a LOT of them in my day, some far bigger than this one - this is a G77, which is the largest permissible "model" rocket engine size (you have to be certified for anything larger). Aerotechs are notoriously hard to start even under normal amateur launch conditions. It's not at all unusual to spit 2 or 3 igniters without igniting the fuel grain. Aerotech in its infinite wisdom chose a rather poor quality igniter in their motor kits to bring the kit cost down. They're called "copper heads", we called them "crappy heads" for a reason. In Aerotech Gxx motors they're particularly obnoxious because the nozzle is quite narrow, and you need special thin crappyheads (thus yet weaker starts) just to get them shoved up.
Aerotech's principle competitor Cesaroni (I think Cesaroni may own Aerotech now, it's bought up several of the other amateur rocket motor manufacturers like Hypertech) uses a high-grade industrial quality igniter that's used in many other commercial applications where they just have to work the first time. Eg: commercial fireworks. They're about $5-8 apiece, the crappy heads probably cost about 15 cents each to make. They're very energetic and fast - usually making a loud crack when they go off. I don't ever recall ever having an engine start failure with a Cesaroni one.
[At major amateur launches, the Cesaroni dealer does a brisk business selling igniters to aerotech users whose crappyheads didn't work.]
Vacuum makes the igniter's job a little harder staying in the chamber long enough to ignite the fuel grain. The atmosphere provides a bit of resistance to keep the igniter in the chamber longer- the igniter's production of gas is trying to push itself out of the chamber... Crappy heads are much slower and less energetic - in vacuum, it's more likely to push itself out of the chamber before the grain is lit - even with the flimsy loose-fitting plugs they sometimes use. Almost certainly a Cesaroni igniter would have worked first time because of its higher energy and faster ignition. Yeah, they cost more. But they make up for it in reliability - which you MUST HAVE in cluster or multi-stage rockets.
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+Jason Day Project Orion, as you describe, was originally thought up in the 1940s (before NASA), based on preliminary ideas dating back to the late 1800s (at first, ordinary explosives, not nuclear). The Project and designs were sketched out by a scientist at General Atomics and a University professor by 1958. GA was obviously looking for a market for GA products.
NASA (created in 1958) never "had" the project. In 1958/9 NASA was still trying to integrate the Army, Navy and civilian organizations it was made out of into something resembling comprehensibility.
The Orion Project captured some people's imagination, and horrified others. The test ban treaty in 1963 (banning atmospheric nuclear tests) essentially killed it deader than a doornail.
Orion only flew in Niven/Pournelle's novel "Footfall". When faced with a rather obnoxious invading alien race making a mess, setting off a few dozen 1/2 kiloton nuclear weapons in the atmosphere sounded like a better deal.
It's conceivable that when we get out to the outer solar system we might do a few missions with Orion-style rockets. However, Ion rockets, or solar sails are far more efficient, easier to refuel, and, frankly, a lot less messy/likely to have unforseen side-effects.
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+nine Eleven You don't believe in space because you think the air pressure doesn't decrease. But it does. You agree.
Yes, precisely it is the basic science of rocketry. Don't try to lecture me about "rocket sicence" - you are completely ignorant of it. In contrast I'm certified to level 3 high power rocketry, and have designed/built and flown rockets and motors that perform exactly how "rocket science" predicts.
Of course rockets has thrust in vacuum. Conservation of momentum demands it. Newton's 3rd law demands it. "rocket science" proves it. If you had bothered to look at the rocketry equations shown earlier in this thread you'd know it. It's trivial to prove, and has been so over and over. This is not a good video to prove it, but Peter Leane's are.
But rather than look at complex and difficult to perform experiments with rockets that rely on the combustion of fuel and thus give you flatties a thing to whine about because you have the science comprehension of a garden slug, let's go to the basic physics itself:
Take a wheeled cart. Put a heavy spring loaded ball on it with a remote trigger. Put it in a vacuum chamber, and fire it. What happens? No gas confusing the issue. the wheeled cart pushes on the ball, and the ball pushes back. The ball goes one way, the wheeled cart goes the other. Newton's third law at its most basic.
Now turn the "spring loaded gun" into a continuously self-reloading shotgun with super tiny pellets. Continuous thrust. Voila. A rocket.
Yes, a rocket needs something to push off. It's called "reaction mass". It's the gas it pushes out of the chamber. Atmosphere not required.
The Saturn V produced some 10-15 tons of gas per second*, and threw it out the back at speeds up around two miles per *second*. That requires LOTS of force to get 10-15 tons of anything up to 2-3 times the speed of sound. It causes a push forward on the rocket of exactly the same force. Let's say you could push 10-15 tons of gas up to 2 miles per second in a fraction of a second. How much reaction do you think you'd feel? About 7 *million pounds worth. Oh gosh gee, that's more than the Saturn launch stack weighs. No atmosphere needed.
Get back to us when you actually do understand anything about "rocket science" instead of swallowing the BS that scammers and religious nuts spew on yooboob.
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+Paul Barclay "So how to orbital craft slow down when deorbiting?"
Simple:
Orbital craft turn around so their engines are facing forward. The engine's burn slows down the speed of the orbital craft, which means it can no longer maintain orbit. So it falls. They're not called "retrograde burns" for nothing.
[Commercial airliners do something similar when they first touch down. slats come down on the wings behind the engines, which redirect the thrust forwards (instead of turning the aircraft or the engines around, which is a trifle, er, impractical). This is called "thrust reversal". The harrier VTOL jet worked similarly, by redirecting the engine thrust down instead of straight out the back.]
Take a good look at how the shuttle returns to earth: it turns around so that the rocket engines are facing forward, applies a retrograde burn (it only needs to slow down by about 300 mph), and it starts to fall out of orbit. Next, it has to turn around and face forward, and it has a timelimit for this maneuver, because if it's not all the way around when it starts hitting denser atmosphere, it will tumble, break up, burn and crash. Then the rest of the flight is just gliding downwards, shedding speed by keeping the nose up.
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+Thomas Gronek You think pushing tons of combusting fuel (as gas) out the back end is not an action? Why not? Imagine instead, that instead of a few ounces of gas being flung out the back end at several thousand feet per second, you flung that same number of ounces of lead pellets out the back end at the same speed. Same thrust. Newton's third law. Also Tsiolkovski's rocket equation from the 1890s.
[Tsiolkovski is the true father of modern rocketry. Goddard & Oberth were the fathers of liquid fuel rocket engines.]
Rockets aren't particularly difficult to ignite in a vacuum. The reason why this motor was so difficult to start is because he was using the really crappy igniters that come with Aerotech motors (Aerotech calls them "copper heads", we call them "crappy heads"). They're marginal at the best of times even in atmosphere. Been there, got the t-shirt of too many failed Aerotech motor starts. The cool kids use the igniters that come with Cesaroni (and other) motors. The good igniters are what they use with fireworks - where they just HAVE to go without fail within a split second. Aerotech copperheads, in a word, don't*. Have yet to *ever see a Cesaroni fail to start first time.
In point of fact, rockets fired in atmosphere are between 5 and 20 percent less efficient than a rocket fired in vacuum. Why is that you think? Here's why:
- the speed of the exhaust gas depends on the pressure differential between the combustion chamber (typically about 200 PSI in most American-made large liquid fuel rocket engines) and ambient pressure. In short, the exhaust gas has to push the atmosphere out of the way. In air, the total pressure differential is about 200-14.7 or 185.3PSI. In space the differential is a full 200 PSI. So, the exhaust gas comes out about 7% slower in air than it does in space, F=MA, so the thrust is about 7% lower in atmosphere.
*Further*, at the other end of the rocket, the rocket has to push the air out of the way - atmospheric drag. Reducing its overall net thrust even further.
In amateur rocketry calculations (oh believe you me, we do lots of math to predict how fast and high our rockets go, and we get it right) the ONLY influence air has is on the drag induced on the rocket. The diameter of the rocket has more influence on the actual peak altitude than the mass does because of drag. Ironically, because of drag, sometimes you have to add extra weight to a rocket to make it go higher. Yes, it all does make sense once you get into the science of it all.
The basic engine in Space X is always the same. The difference is between first stage and upper stage. The nozzle and thrust bell is different because the first stage is optimized for max thrust in full atmosphere, and the second stage's nozzle/bell is optimized for almost-zero-to-essentially zero atmosphere.
One final point: every single successful orbital launch proves that thrust works in vacuum. Why? Because every single successful orbital launch has required at least two stages. If thrust didn't work in vacuum, the second stage wouldn't do anything. The Saturn V staged at 42 miles up and doing 3000+mph. That's almost (the standard definition of) space, and the pressure is so low as to be almost non-existent. If the second stage didn't work, the rest of the rocket would have made a big hole in the ocean, instead of accelerating even faster. Do remember the top end of the rocket had to reach 17000+ mph. The Saturn V actually had to use 2 1/2 stages to reach orbit.
SSTO (single-stage-to-orbit) is theoretically possible, and it would be desirable if you could keep the costs reasonable (conceptual designs have exotic/nasty/expensive fuels), but it's never been done yet. The earth's gravitational well is the culprit. On the moon, achieving orbit around the moon is something just about any high power amateur rocketry nut can achieve. I helped launch a 200 pound amateur rocket (achieved mach 2.4 and 45,000 feet) which would have done the trick very nicely. You could probably do it with rocket weighing about 20 pounds. No drag to contend with, you just have to reach about 2000-3000mph. Piece of cake without atmosphere.
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+Thomas Gronek "the rocket has nothing to act upon"?
Don't be silly, of course it has something to act upon. The mass of the ejected gas. The action that the Saturn V booster stage had was the equivalent of throwing a 10 ton truck at a velocity of 4000 feet per second every second.
Let's say for sake of argument that you were so strong you could throw a 10 ton truck at 4000 feet per second. You weigh, for sake of argument, 200 pounds. The thing you are throwing outweighs you by a factor of 100. The force you apply to throw the 10 ton truck thataway at 4000 feet per second has an equal and opposite reaction of throwing you the other way at 400,000 feet per second. That's about 80 miles per second, 288000 mph or mach 350. Basic conservation of momentum and Newton's third law - basic physics that every high school student not only should learn, but be forced to prove to themselves in lab experiments. I was. If you weren't, your education was sadly defective.
Obviously this is even more true in vacuum than in atmosphere, because all atmosphere does is slow you down - in fact, you'd be better wearing your asbestos undies because trying to drive yourself through atmosphere at mach 350 is going to get pretty damn hot pretty damn fast.
[The large high power amateur rocket I assisted in launching hit mach 2.7, and was above mach 1 for over a minute. Fried the nose cone paint right off]
Incidentally, 80 miles per second is approximately triple the maximum speed that a solar system originating meteor can hit the earth at. You'd make a rather bigger bang than the Chelyabinsk meteor strike did. You wouldn't just break a million windows (which I seem to recall the Chelyabinsk strike doing), you'd flatten the towns and kill people purely by shock wave. Chelyabinsk's fatalities were caused by poorly constructed buildings collapsing.
The fact that the reaction mass is gas is irrelevant. Whether or not there's atmosphere is irrelevant. The fact that it has mass, and it was accelerated is what gives the rocket thrust. Tsiolkovski's rocketry equation rulz. Look it up. And no, Tsiolkovski was born, raised and worked in Russia, and died about 50 years before NASA existed.
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+Dennis Burbank "dies by literally exploding". Complete abject nonsense.
What does the speed of the space suit have to do with the pressure inside the suit? Well? The answer is *nothing*. No regulation required whatsoever for pressure changes due to changes in speed, because the pressure does not change.
The ISS is pressurized to the same pressure as earth. 14.7 PSI. In order to save weight (don't have to carry around nitrogen) and increase length of time an astronaut can work in a vacuum, the space suits are inflated to 10PSI of pure oxygen in space. That's only a 4.7 PSI difference. Peanuts.
Secondly, since they're breathing pure oxygen and not a oxygen-nitrogen mix, the bends (those bubbles you were so orgasmic about) CANNOT happen, because the blood oxygen is tightly bound to the haemoglobin (the red in the red blood cells) - there's no "simply dissolved" nitrogen to bubble no matter what you did with the pressure.
Thirdly, it's only 4.7 PSI. Let me give you a word of warning: I'm a certified scuba diver, got my certification from a diving organization famous for spending more time on training diving physiology than ANY other.
Going from the ISS into space is the pressure drop equivalent to ascending a mere 8 feet with scuba gear. You don't get the bends from that even if you're breathing O2N2. Which they aren't. Returning to the ISS from space is the equivalent of descending 8 feet. Going down 8' is not a problem.
Fourth: Now, yes, scuba divers are trained to not ascend faster than their air bubbles. But the main reason is not what you think. The main reason is not the bends. The main reason is that if you hold your breath through a drop in pressure by as little as about 4 PSI (equivalent to 7 feet) it is actually possible to rupture your lungs. Which is bad. So scuba divers are trained to breathe normally and not go too fast to essentially eliminate any possibility of blowing out a lung. If they have to ascend without being able to breathe (tank is empty or they've had to drop it), they're trained to breathe out slowly all the way. Which is possible because the air in their lungs is continuously expanding to replace what they're breathing out.
Fifth: And no, moron*, the bends (nitrogen gas bubbles forming in your blood) do not cause you to explode. Even if you become really seriously bent, there is *no external visible evidence of it. You might blow capilliaries in the whites of your eyes, but beyond that, nope. What the bends do is obstruct blood flow. In particular, to the brain. Symptoms range from dizziness, loss of balance, headache, visual impairment and up to seizures, convulsion and death. No explosions, sorry.
Treatment is getting in a hyperbaric chamber under pure oxygen. The nitrogen bubbles redissolve in the blood, and slowly come out in your exhalations and aren't replenished.
People get bent by staying too long at several atmospheres (14.7 PSI each) of pressure for too long (see the US Navy dive tables for numbers that have extremely wide safety margins). With fractional atmosphere pressure differences, it simply isn't a problem at all.
Yes, the astronauts are cautious and move slowly either entering space or leaving it. This is simply a chance to let the astronaut relax and readjust mentally to the changed conditions. The pressure changes are essentially irrelevant.
Let's talk about what the (lack of pressure) in space really means. A soccer or football can be inflated to 14.7PSI and not explode - footballs and soccer balls used to be (and some still are) made out of pig skin. While pig skin is usually a bit tougher than human skin, it's not by much.
A pig's body (or human as well) is not a balloon. It's mostly water, and water does not expand through lack of pressure, so, it's exerting very little pressure out no matter how low the ambient pressure is. Throwing a pig or a human body into vacuum won't explode. The air in their digestive tract or lungs will try to expand. The damage is caused by the fact that there's no air to breathe and hence you asphyxiate. The other effects are far slower.
A minimum spacesuit (ignoring radiation and heat issues) could consist of a tight fitting spandex-like non-porous stretch fabric, you'd merely have to supply a breathing system over your mouth, nose and eyes, and have enough strength (say a strong stretch girdle) around your chest to give your chest muscles and diaphragm a chance to expand and contract. The non-porous stretch fabric prevents your skin from losing moisture and the "girdle" tightness simulates the earth's air pressure so your lungs can work. You want form fitting to avoid annoying air bubble bulges between you and the spandex. That's it.
Oh, and yeah, avoid baked beans.
Then you'd have to add reflective coatings and probably integrated heating and cooling to even out the other things.
It'd be damn difficult to get on and off. So spacesuits are designed as miniature and flexible personal space craft that have their own atmosphere, but are still flexible enough to bend.
The minimum practical spacesuit at the present time is a non-stretchy balloon with reasonable tensile strength. Get inside, fill with air, and voila, you're good to go for a couple hours or until the air in the balloon runs out.
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@UniqueBreakfastTaco "chemical reaction....which is a different reaction than combustion."
Did you get your chemistry degree out of a box of crackerjack?
Did you read somewhere that combustion wasn't a chemical reaction?
Oxygen plus, say, kerosene, is the same reaction whether the Oxygen is LOx in a rocket, or O2 in air and produces the same things. In fact, kero plus LOx burns a lot faster and more powerfully than kero plus atmospheric air, simply because there's a hell of a lot more O2 in a litre of LOx than there is in atmosphere that is only 21% oxygen.
But it is still the same reaction.
Similarly, blackpowder, gun powder, cordite, RDX, AP rocket fuel, AN rocket fuel or any other rocket fuel does not need atmospheric air to work.
Hint: airplanes have air intakes. Rockets do not. Neither do firearms.
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+The Deaner It's perhaps simpler to think of this in terms of how a specific rocket engine is built to figure out whether you can start/stop a given rocket engine, and thus more suited for repeated operation in space or not. This becomes more handy when you think of more exotic motors such as hybrids (eg: solid fuel/gas or liquid oxidizer) or tribrids (which use solids, liquids and gasses at the same time).
If a motor has all of the fuel and the oxidizer inside the combustion chamber[s], that means once you start it, it cannot be turned off until all the fuel is gone, unless you rupture the chamber and spill the combustion pressure. That tends to be kinda rough on the passengers/payload, and almost certainly means that even if you you repaired the rupture, there's no fuel left to restart the engine.
Secondly, if the fuel and oxidizer is all mixed together in the combustion chamber, that means you have little control (if any) over the level of thrust at any given moment. It's either full on, or not running at all. No in-between. The "full on" is defined as how big the surface area of the burn (exposed surface of the fuel grain), how fast the fuel grain regresses once ignited, and how much gas it produces per quantity of fuel. You can define it coarsely in engine design and manufacture, but you can't change it later.
You might think you could build a combustion chamber and hold gas or liquid fuel and oxidizer like a solid. However, gases and liquids move and mix. There you can't design a specific burn surface, potentially the whole mass of fuel is the burn surface simultaneously. So instead of a pre-defined thrust determined by burn area and regression rate, the whole thing goes off at once. Bad.
Controllable motors have a combustion chamber, fuel and oxidizer tanks and some way of moving the fuel/oxidizer from the tanks to the combustion chamber (usually pumps). To start it, turn on the pumps and ignite. To change thrust, change the pump speed. To stop the motor, turn off the pumps.
It's conceivable that you could have a solid rocket that is restartable and throttleable if the fuel/oxidizer was a powder in a tank, and you pumped it to the combustion chamber. This is complicated, very fussy, and very difficult to get right. It's doable in the small scale, but nobody's tried yet in the large scale. Apparently some company is experimenting with something like this now. But since it's complicated/tricky/dangerous nobody else so far has bothered with it. Why would you research pumping solids? Because if you can get it to work, it's more efficient. Getting it to work is the hard part. Why is it hard? Moving large quantities of fine powder very fast is very very difficult. Powder is abrasive, so it eats your plumbing. And there's more.
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+The Deaner I don't think you were mistaken. I seem to recall one myself. The question you must ask yourself - would it make sense to use a solid in a particular case? I sure and hell wouldn't want a solid booster to steer, do soft landings or to dock at a space station, but there are times where dumb simplicity and fire and forget is exactly what you want to do.
For example, staging separation (in atmosphere and in space), isn't necessarily what you think. Most of the time they're small solid rocket motors - the key isn't just to get the connection to come apart, but also to guarantee a safe separation. For example, the staging separation on the Shuttle boosters (if I remember correctly) are essentially "M or N class" rocket motors. Not only must they cut the connection, they have to give a strong sideways boost to the SRBs away from the central core, otherwise, they may whack back into it with catastrophic results. Sticking a liquid-based motor requires computers to control it, you can't control it from the main rocket because you're cutting the connection, so the rocket has to have its own self-contained computer with oodles of sensors. Vastly increasing the chances of it failing to work.
A M class motor is roughly equivalent to a US bazooka or RPG round in total power. In a "short/fast" burn configuration, it could produce thrust well into the thousands of pounds. On the moon, an appropriately configured M-class motor might well be able to put a small payload into lunar orbit, so, they're not a toy. Well past escape velocity on the moons of Mars. The largest amateur motor I've personally seen fired was an O (4-8 times the power of an M), and that was enough to boost a 300-400 pound rocket (just the engine itself weighed over 200 pounds) to 45,000 feet and Mach 2.7.
For example: impactor probes. As long as the thrust is high enough and you're close enough, you really don't care a whole lot about accuracy, you just need the thing to fire, and fire *hard*, after sitting soaking in space for years. Your telemetry can feed you back how fast it was going when it hit, which you then factor into your analysis of what that impact did.
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+rddim Dubstep Just one small word of warning on KN03/sugar rockets - in fact, it's true of most sugar-based rockets. For ideal results (there are several reasons), you want to mix the material up, heat it until it melts, and then cast the fuel into a cylinder. However, particularly with KNO3/sugar, the melting temperature is pretty close to the self-ignition temperature. Which means that if you don't have precise enough control of the temperatures (or spillage/stray sources of ignition) it may just go up in your face. There are other oxidizer/sugar combinations not quite so dangerous, but they're not as easy to get the raw materials, and don't perform as well.
Ammonium perchlorate/fuel, when the fuel is PBAN, other polymerizing rubbers/plastics like HTPB, or epoxies, are inherently much safer, because you can mix/pour/cast the ingredients without having to add any heat. Reasonable quantities of AP-based fuels are rather more difficult to ignite accidentally as well. Which is a good thing. AP isn't exactly easy to get either, but it's worth it. A friend has made AP himself from commonly available chemicals. It's not that hard. But there's a "gotcha step!" in the process that you better get right or bad things happen. If I recall correctly, if you don't wash one of the intermediate stages adequately, for the rest of the process you're dealing with a contact explosive in addition to AP. Ouch, indeed.
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