Biggles<font color=#AAFFAA>The Man Without a Face</font>
[quote]Originally posted by samuelk:
[b]I have a degree in mechanical engineering. If it's one thing I was taught, it's how to think freely. Just because I'm educated in a certain area doesn't mean my thought process is restricted.[/b][/quote]
I'd just like to point out that Sam is entirely correct about what an engineering degree taught him. I have a degree in computer systems engineering, and if there is one thing I learnt from my 4 years there (and will further learn over the next 3 or 4 years there) it was how to think freely and flexibly to solve any problem.
------------------
[url="http://www.minbari.co.uk/log12.2263/"]Never eat anything bigger than your own head.[/url]
"Nonono...Is not [i]Great[/i] Machine. Is...[i]Not[/i]-so-Great Machine. It make good snow cone though." - Zathras
any training is in essence 'a way of thinking', a learned pattern, even given the human minds ability to think laterally and to think in very flexible ways...you can fall unknowingly into a mode of thought which blinkers you to possibility...
I pride myself on being onw of the most lateral thinkers out there... and yet.... I catch myself regularly resorting to routine, to 'tried and tested' methods without even thinking... never actually asking myself why on Earth I'm doing a specific task the way I am.
qualifications, experience, knowledge... all have handmaidens... cynsism, resentment of the new, jadedness. it happens to all of us to a degree, the important part is to recognise it and do our best to mitigate it and not get lost in 'when I was a boy' stories and 'whipper-snapper' bashing.
stop taking it personally, I'm as much having a go at myself as at anyone else.
excuse me Sam... was I referring to you when I asked if you had qualifications ?? I was referring to Davids post...
as far as concrete goes...ok sure... by the sounds of it its impractical, I can think of counters to some of your arguement but... its getting us precisely nowhere so I'm not going to continue in this vein.
I still think theres plenty of miles though.. in disposable re-entry shells, perhaps when mining stuff on the moon... we crudely smelt/process/refine ores and use them in re-entry shells, then.. collect them for final processing when they land.... precisely where of course is a big issue...
oh yeah... if you've shed your big heavy shell after the re-entry heat is gone.... 'wot me worry' about inertia... the actual re-entry vehicle can be much lighter/less robust
if we go up in stages... why the hell cant we come down in stages ??
[This message has been edited by shadow boxer (edited 02-05-2003).]
[quote]Originally posted by shadow boxer:
[B]any training is in essence 'a way of thinking', a learned pattern, even given the human minds ability to think laterally and to think in very flexible ways...you can fall unknowingly into a mode of thought which blinkers you to possibility...[/quote]
You're really stuck on this idea of structured education teaching closed-mindedness, aren't you?
College gave me the factual knowledge to think effectively. My experience in and outside of college working with various materials (concrete, steel, wood, etc.) gave me the knowledge to know that many of the things you suggest just aren't practical. It has nothing to do with narrow-minded thinking.
[quote]I pride myself on being onw of the most lateral thinkers out there... and yet.... I catch myself regularly resorting to routine, to 'tried and tested' methods without even thinking... never actually asking myself why on Earth I'm doing a specific task the way I am.[/quote]
It's easy to get caught up in one particular method. But one of the things I learned in college was how to effectively "brainstorm" a problem. Works wonders for coming up with new ideas.
[quote]qualifications, experience, knowledge... all have handmaidens...[/quote]
Yes, and so do ignorance and lack of experience and knowlage. If I had my choice, I'd go with knowing more than knowing less in this case.
[quote]cynsism, resentment of the new, jadedness. it happens to all of us to a degree, the important part is to recognise it and do our best to mitigate it and not get lost in 'when I was a boy' stories and 'whipper-snapper' bashing.[/quote]
But it's also important to recognize when someone is telling you your idea isn't practical because they may know a little more than you do about the subject (or may have experience to back it up).
[quote]stop taking it personally, I'm as much having a go at myself as at anyone else.[/quote]
As for me, I'm not taking anything personally. But I do find it amusing that you can't keep from insulting people or resorting to a condescending attitude (as if YOU know how to think and reason better than anyone else) and spewing out quaint little metaphors to teach the rest of us about life.
Skip the zen mysticism and just talk.
[quote]excuse me Sam... was I referring to you when I asked if you had qualifications ?? I was referring to Davids post...[/quote]
WHO you were referring to doesn't reall matter. I was talking about the fact that you continue to condemn qualifications, knowledge and experience even [i]after[/i] asking someone to back up his ideas with his qualifications, knowledge and experience (namely "concrete studies").
[quote]as far as concrete goes...ok sure... by the sounds of it its impractical, I can think of counters to some of your arguement but... its getting us precisely nowhere so I'm not going to continue in this vein.
I still think theres plenty of miles though.. in disposable re-entry shells, perhaps when mining stuff on the moon... we crudely smelt/process/refine ores and use them in re-entry shells, then.. collect them for final processing when they land.... precisely where of course is a big issue...
[/quote]
Disposable reentry shells are one thing. Disposable [i]concrete[/i] reentry shells are another.
But by all means, list your counter arguments...this is a discussion, after all.
[quote]oh yeah... if you've shed your big heavy shell after the re-entry heat is gone.... 'wot me worry' about inertia... the actual re-entry vehicle can be much lighter/less robust
if we go up in stages... why the hell cant we come down in stages ??[/quote]
Because when you reenter the atmosphere, you're at the whim of more forces than just gravity; you're also affected by air turbulence.
There are a few reasons why shedding parts of a craft on reentry is more dangerous than shedding parts of a craft on ascent:
1. When you shed part of a craft, it's weight aerodynamics change drastically. During seconds or milliseconds in which that weight is removed it only takes a small error to cause catastrophy. For the sake of simplicity, let's say your heatshield is designed to split in half and separate from the craft. If, during reentry, one side of the heat shield separates ONLY MILLISECONDS before the other half, the center of gravity of the craft will shift unexpectedly and it could start to tumble. Even worse, what happens if one of the explosive bolts (or whatever mechanism you use to release the heat shield) fails?
2. Launch speeds are lower than reentry speeds...when shedding parts of a craft, you have to remove the pieces with enough energy to push them clear of the craft itself to avoid damaging the craft. The faster the craft is going, the faster you have to move the shedded material, and therefore the more force you have to use to remove it. You can't just assume that the air will push the debris out of the way
3. The parts of the space shuttle system that are shed during launch (solid rocket boosters and external tank) are positioned below the shuttle. When they separate, they fall away from the shuttle (even though the shuttle is upside down when the ET is shed, the fact that the shuttle is moving against the force of gravity helps it move clear of the ET).
By design, a heat shield has to point TOWARDS the direction of travel... so the heat shield is in effect in front of the vehicle when it is shed. This poses a danger because you will be sending the heat shield pieces backwards over the craft. All it takes is a little air turbulence to slam a chunk of the heat shield into the craft.
So yes, there are a few reasons why shedding pieces of a craft on launch is less dangerous (though, if this Columbia accident investigation turns out the way I think it will, still somewhat dangerous) than shedding a heat shield on reentry.
[This message has been edited by samuelk (edited 02-05-2003).]
Random ChaosActually Carefully-selected Order in disguise
This is an article on the problems with attempting to repair or rescue the crew of Columbia in orbit had they known of the damage prior to landing:
[url="http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html"]http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html[/url]
[quote]Originally posted by Random Chaos:
[b]This is an article on the problems with attempting to repair or rescue the crew of Columbia in orbit had they known of the damage prior to landing:
[url="http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html"]http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html[/url] [/b][/quote]
I really hate having to sign up for something just to read an article... [img]http://216.15.145.59/mainforums/mad.gif[/img]
[This message has been edited by JackN (edited 02-05-2003).]
Not to mention the pieces of heat shield landing on people. It's very fortunate that nobody on the ground was hit by shuttle debris. If it had broken up during a weekday rush hour instead of fairly early Sturday morning....
------------------
AnlaShok, Captain of the Gray Hand of Fate Squadron
Sidhe-1
Wielder of the Big Heavy Hammer of Obvious Truth
"FABRICATI DIEM, PVNC!"
If I may be so bold, I think we all agree the shuttle is old and possibly better technology exists.
Perhaps I could refocus to the topic. The primary consideration in both achieving and leaving orbit is velocity; you need enough to achieve orbit and you need to get rid of it to reach home (safely).
Unless I'm terribly mistaken (which is certainly possible), there is nothing that says you must come screaming into the earth's atmosphere. We just haven't devised a better way to reduce the velocity of our spacecraft. In theory, you could alter your orbit so that you'd arrive in the atmosphere at a much slower acceleration (picture Buck Roger's cigar-shaped rocket's slow tail-first descent, or even extremes such as the space elevator mentioned elsewhere), but this would require a much larger energy expenditure in orbit, which currently equates to bringing more fuel with you.
I also used to wonder why the heck did they have to come down so fast and face the heating + right angle problems and all that instead of just flying back on Earth like they go up, but then they would have to carry additional rockets and even more fuel up there making it all even more expensive and dangerous as it is now. It WILL be that way in the future, but only after we have a sufficient technology to do so. Such as the antigrav tech. [img]http://216.15.145.59/mainforums/biggrin.gif[/img]
Sam...(and the rest of ya I guess.. [img]http://216.15.145.59/mainforums/smile.gif[/img] )
go read some texts on psychology
in fact, here :
[url="http://keirsey.com/pumII/ns.html"]http://keirsey.com/pumII/ns.html[/url]
[url="http://keirsey.com/pumII/jp.html"]http://keirsey.com/pumII/jp.html[/url]
I can guarantee you that you Sam, fall into the "S " category, and I'd also be willing to bet "J"
I'm the extreme opposite of both of those, the "I" and the "N"
in fact here :
[url="http://keirsey.com/personality/nfep.html"]http://keirsey.com/personality/nfep.html[/url] [url="http://keirsey.com/personality/ntep.html"]http://keirsey.com/personality/ntep.html[/url]
I work in both these mindsets ,dependent on circumstance. I'm used to all sorts of abuse for being who I am, I'm one or two from one hundred and I'm seldom seen as valuable to those who fall on the opposite side of the S/N divide and seeing as the S persons outnumber me to a vast degree I'm always fighting...
Engineering should be an S pursuit....
Design should be an N pursuit....
if the world was fair.
It's not.. its about 50 to 1...so I take my lumps and give as many back as I can.
There is ****ing room for both of us, I hope you will eventually understand where I'm coming from.
Where did your hostility orginate ? Ask yourself that question and answer honestly and perhaps we may get somewhere.
I dont decry Engineering, I dont decry people who live in an S frame of mind... what pisses me off more than you can possibly imagine is boneheaded concrete booted hyperpragmatic champions of hidebound tradition and stagnation...
Sam, you're not one of those, neither is anyone else here that I know of.... but....
inside every Engineer lurks the above mentioned monster. I hate the SOB and I'm always sticking branches in its cage.... I cant bloody well help it...
it is responsible for a degree of misery for me and folks like me, that most probably cant even grasp...
but !! this is all well off topic.. so.. back to the case in hand
~~~~
As far as concrete heat sheilds go...there are such things as foundry bricks, fired at tempratures above that of what you find in re-entry, they stick em together with foundry clay, concrete/foundry clay... moon dirt... just slightly different moon dirt.
and the KISS principile still applies, hows this :
a big (perhaps slightly pointy) bucket .... bucket comes in arse first... steeply... aimed at the appropriate Ocean...chute deploys from pods exposed top....drags pod from bucket like the plunger from a syringe... viola
bucket becomes one with ocean floor at Mach whatever... pod drops to Ocean for splashdown.
Happy intact astronauts
My concern is the G's when the chute/s deploy...we need some sort of advanced crash couch to absorb it it somehow. Perhaps the 'extraction' chute is a separate jettisonable device used before the main chutes deploy..
[quote]Originally posted by shadow boxer:
Sam...(and the rest of ya I guess.. [img]http://216.15.145.59/mainforums/smile.gif[/img] )
go read some texts on psychology
in fact, here :
[url="http://keirsey.com/pumII/ns.html"]http://keirsey.com/pumII/ns.html[/url]
[url="http://keirsey.com/pumII/jp.html"]http://keirsey.com/pumII/jp.html[/url]
I can guarantee you that you Sam, fall into the "S " category, and I'd also be willing to bet "J"
I'm the extreme opposite of both of those, the "I" and the "N"
in fact here :
[url="http://keirsey.com/personality/nfep.html"]http://keirsey.com/personality/nfep.html[/url] [url="http://keirsey.com/personality/ntep.html"]http://keirsey.com/personality/ntep.html[/url]
[/quote]
I've already taken those tests. I fall somewhere in between an ENTJ and and INTJ (I've taken the test more than once, and tend to flip-flop between an E and an I).
[quote]I work in both these mindsets ,dependent on circumstance. I'm used to all sorts of abuse for being who I am, I'm one or two from one hundred and I'm seldom seen as valuable to those who fall on the opposite side of the S/N divide and seeing as the S persons outnumber me to a vast degree I'm always fighting...[/quote]
Maybe the reason you're always fighting is because you have a very hostile attitude towards people who disagree with you.
I've seen you insult and berate people here constantly. You've called people names and condescended to them with your "words of wisdom". You seem to have a very high-and-mighty attitude as if you have lots to teach and nothing to learn.
It's the arrogance that brings about conflict.
[quote]Engineering should be an S pursuit....
Design should be an N pursuit....[/quote]
Your mistake is separating engineering from design. They go hand in hand. Engineering is both an S and an N field. You're not going to get anywhere as an engineer if you don't pay attention to the world around you.
[quote]
if the world was fair.
It's not.. its about 50 to 1...so I take my lumps and give as many back as I can.
There is ****ing room for both of us, I hope you will eventually understand where I'm coming from.[/quote]
Of course there is. But I have a feeling that it's YOU who doesn't understand that, because you can't seem to accept the fact that someone else might know a little more than you do about a subject.
[quote]Where did your hostility orginate ? Ask yourself that question and answer honestly and perhaps we may get somewhere.[/quote]
I have no hostility towards you or anyone else here. I don't get angry about things I read on the web. If you think I'm angry or hostile towards you, then you're definitely misreading my posts (which is an easy thing to do, since it's only text).
[quote]I dont decry Engineering, I dont decry people who live in an S frame of mind... what pisses me off more than you can possibly imagine is boneheaded concrete booted hyperpragmatic champions of hidebound tradition and stagnation...[quote]
That's not a trait of engineers. It's a trait of [i]people[/i].
[quote]Sam, you're not one of those, neither is anyone else here that I know of.... but....
inside every Engineer lurks the above mentioned monster. I hate the SOB and I'm always sticking branches in its cage.... I cant bloody well help it...
it is responsible for a degree of misery for me and folks like me, that most probably cant even grasp...[/quote]
See, that's the attitude I'm talking about. I get the impression from reading that that you feel martyrd and misunderstood by everybody else because people just don't "get it".
[quote]but !! this is all well off topic.. so.. back to the case in hand
~~~~
As far as concrete heat sheilds go...there are such things as foundry bricks, fired at tempratures above that of what you find in re-entry, they stick em together with foundry clay, concrete/foundry clay... moon dirt... just slightly different moon dirt.[quote]
Have you ever hit a foundry brick with a hammer after it has been exposed to high temperatures? Very brittle. The force of impacted air molecules or micrometeorites is enough to crack something like that very easily.
[quote]and the KISS principile still applies, hows this :
a big (perhaps slightly pointy) bucket .... bucket comes in arse first... steeply... aimed at the appropriate Ocean...chute deploys from pods exposed top....drags pod from bucket like the plunger from a syringe... viola
bucket becomes one with ocean floor at Mach whatever... pod drops to Ocean for splashdown.
Happy intact astronauts[/quote]
I'm assuming it was your intention to perfectly describe the reentry procedure used during the Mercury, Gemini and Apollo missions...in which case I should point out that Gus Grissom almost died when his capsule sank in the ocean after the egress hatch blew prematurely. And he DID die (along with two others) in Apollo 1 when the capsule caught fire and the astronauts were trapped inside.
[quote]My concern is the G's when the chute/s deploy...we need some sort of advanced crash couch to absorb it it somehow. Perhaps the 'extraction' chute is a separate jettisonable device used before the main chutes deploy..
bring on commercially available spider silk..[/quote]
Keep in mind that even using the vehicle you mentioned, you're still going to need a heat shield, and you're still going to enter the atmosphere at extreme velocities. Chutes only work in thick atmosphere, and until you get below a certain altitude, the compressed air beneath the craft is going to create almost as much heat as that seen by the Shuttle.
That kind of reentry vehicle isn't really useful if you plan to take experiments with you into orbit (or bring cargo back).
The shuttle was designed to bring cargo into orbit and bring cargo back from orbit. No other spacecraft does the job better.
But of course that doesn't mean the shuttle is perfect for the job. There's always something better.
The other disadvantage of a small reentry vehicle is that there's no room to [i]perform[/i] experiments, sleep, move, etc.
The shuttle astronauts can stay in orbit for weeks. There's adequate oxygen, food and living space for them to stay up there for quite a while.
Plus, the shuttle has excersize facilities to prevent muscle atrophy.
The main thing to keep in mind is that the space shuttle is a multi-purpose vehicle.
It's a launch vehicle, a reentry vehicle, a mobile lab, a satellite deployment and recovery facility and a temporary space station.
[This message has been edited by samuelk (edited 02-06-2003).]
[quote]Originally posted by JackN:
[b]What about long space flight bone loss issues...
Anyone know what's the latest info one how to counter it?[/b][/quote]
It's still a major problem. I tihnk some experiments were done (or at least planned) for STS 102 back in 2001.
Here's what I've gleaned from stuff I've read recently....
There are two types of bone cell that are responsible for bone growth and decay. Osteoblast cells build new bone, and Osteoclast cells destroy old bone.
Osteoblast cells respond to stress. The normal stress of gravity regulates the activity of Osteoblast cells. If the normal everyday stress of gravity is taken away, Osteoclasts remove more bone than osteoblasts create, so the bone weakens and diminishes.
A chemical used in the development of osteoblasts is an enzyme known as "creatine kinase-B". There's a study underway at [url="http://www.mc.vanderbilt.edu/gcrc/space/#Bone"]Vanderbilt University[/url] that concerns finding out how the body regulates this enzyme and how that chemical is affected by weightlessness.
There are some other studies looking at how the ingestion of food affects bone growth...eating food causes an increase in production of a particular hormone that increases bone growth. It's possible that giving astronauts this hormone might prevent bone loss.
[This message has been edited by samuelk (edited 02-06-2003).]
My laymen’s understanding is that heat build up comes from air molecules clinging to the skin of the shuttle, and that these clinging molecules collide with other molecules, and that the friction between these air molecules causes the heat. Even if the skin of the shuttle were perfectly smooth, like glass, this phenomenon would still happen.
Could some form of modulated electrical and or magnetic force be used on the skin of a next generation shuttle to reject air molecules from sticking to the shuttle's skin?
I'm trying to imagine a system for allowing a craft re-entering the atmosphere to come through in an airless envelope, until means other than friction were used to slow the descent, to the point where these systems could be turned off, so that winged flight could take over.
I am aware that there are huge holes in this thinking. For instance, 'what' exactly will slow the vehicle, if not friction? It has already been stated that any system we know of that includes jets would be prohibitively heavy to carry into space, in order for this system to be used on descent.
Maybe this system I'm contemplating could be used simply to moderate the skin heating, so that some friction could still be used to slow the vehicle.
Where's anti-gravity when you really need it?
[This message has been edited by Randy (edited 02-06-2003).]
[quote]My laymen’s understanding is that heat build up comes from air molecules clinging to the skin of the shuttle, and that these clinging molecules collide with other molecules, and that the friction between these air molecules causes the heat. Even if the skin of the shuttle were perfectly smooth, like glass, this phenomenon would still happen. [/quote]
That's actually a very common misconception. The heat is caused not by air friction, but by air compression. The space shuttle is travelling so fast, the air doesn't have enough time to get out of the way, so it is compressed, which releases a LOT of heat.
In fact, the air is compressed so much, it no longer has the properties of normal "air", and is considered to be a chemically reacting mixture of atoms, molecules and ions. It is the ionized part of the air that disrupts communications on reentry.
If you've ever used a can of compressed air to blow dust out of your keyboard, you've probably felt the opposite of this process. The air in the can is already compressed. When you release the valve, the pressure of the air inside the can decreases rapidly, and you can feel the can become very cold.
[This message has been edited by samuelk (edited 02-06-2003).]
[quote]Originally posted by Randy:
[b]Maybe this system I'm contemplating could be used simply to moderate the skin heating, so that some friction could still be used to slow the vehicle.[/b][/quote]
Hmmm.... what if the system you described could be used to just "push" the friction and heat caused by it (air molecules) away from the ship just that much that the ship would be much less hot, like you were saying, but still have the same force by friction to slow it down, or at least nearly the same force. Kind of like a force shield to keep the heat and friction a few cents away from the ship, or whatever the necessary distance would be to make the ship less hot, but it would still have the frictional force to slow down the ship. In other words the force shield would take the friction instead of the ship hull, which is now the case.
[quote]Where's anti-gravity when you really need it?[/quote]
Indeed. Somebody keep a knife on scientists throats and make them invent antigrav in a few years ok? [img]http://216.15.145.59/mainforums/biggrin.gif[/img]
[quote]Originally posted by PJH:
[b]Hmmm.... what if the system you described could be used to just "push" the friction and heat caused by it (air molecules) away from the ship just that much that the ship would be much less hot, like you were saying, but still have the same force by friction to slow it down, or at least nearly the same force. Kind of like a force shield to keep the heat and friction a few cents away from the ship, or whatever the necessary distance would be to make the ship less hot, but it would still have the frictional force to slow down the ship. In other words the force shield would take the friction instead of the ship hull, which is now the case.[/b][/quote]
Heat can be transferred in three ways:
1 conduction (through solid material),
2 convection (through the air or other fluid--although this is really just a special kind of conduction)
3 radiation (the transmission of electromagnetic energy through "empty" space).
Much of the heat that the shuttle receives is heat of radiation, not convection. Radiated heat can pass from the ionized air to the surface of the shuttle even if the air isn't in contact with the shuttle.
[This message has been edited by samuelk (edited 02-06-2003).]
Samuelk, it's a mincing of words and you know it. What randy said is simply a laymans way of describing the forces that cause the heat.
Randy may very well have a good idea on his hands. If we can limit the amount of air that gets "stuck" or compressed or however you want to call it, it would allow a more controlled reentry as it would enable the shuttle to behave more like the glider it does in the last few steps before landing. OR if the energy barrier is what the air molecules "stuck" to instead of the shuttles skin.. well, I'm sure you can figure the rest out.
What appears to be a misconseption is often a simplified way of explaining something. Once more the self rightousness of the members of this board has proven itself. I'll take my non engineering degree having self elsewhere as its obvious that my kind isn't wanted here.
[quote]Samuelk, it's a mincing of words and you know it. What randy said is simply a laymans way of describing the forces that cause the heat. [/quote]
No, it's not. It's a very importnat distinction. If friction WERE the cause of the heat buildup, then it would be quite easy to get rid of it by keeping it away from the shuttle.
When you compress a gass, the temperature of the gas increases. This is shown using the ideal gas law:
PV=mRT (where P=pressure, V=volume, m=mass, R=gas constant and T=temperature)
The heat buildup has nothing to do with the air molecules "rubbing against" the shuttle surface. It's caused by the fact that the air is being compressed.
There's a huge difference between the two in terms of what Randy's proposing.
But it's not friction. It's pressure. The pressure is so high, it changes the properties of the air. Furthermore, the heat is passing to the shuttle via radiation more than convection or conduction. So even if you put a complete vacuum between the air and the shuttle, the shuttle would still heat up.
[quote]Randy may very well have a good idea on his hands. If we can limit the amount of air that gets "stuck" or compressed or however you want to call it, it would allow a more controlled reentry as it would enable the shuttle to behave more like the glider it does in the last few steps before landing.[/quote]
If you limit the amount of air that gets compressed, then you can't slow the shuttle down.
You're missing the fact that the air is what's used to slow the shuttle down. If we remove the compression of the air from the equation, then the shuttle will come screaming into the atmosphere and wouldn't be able to stop.
That's part of the reason why the shuttle doesn't dive into the atmosphere nose-first.
[This message has been edited by samuelk (edited 02-06-2003).]
No sam, the heat is caused by a combination of compression AND friction. At lower speeds those pressures are known as the forces of "lift" and "Drag" and are a result of the FRICTION between any objet passing through the air, and the air itself. What the shuttle deals with is an EXTREME of these pressures and THAT is where the heat comes from. Not from the compression of air alone, because the air would not compress if not for the friction present. What randy said is simply a simplified way of explaining the source of the heat.
[quote]No sam, the heat is caused by a combination of compression AND friction. At lower speeds those pressures are known as the forces of "lift" and "Drag" and are a result of the FRICTION between any objet passing through the air, and the air itself. What the shuttle deals with is an EXTREME of these pressures and THAT is where the heat comes from. Not from the compression of air alone, because the air would not compress if not for the friction present. What randy said is simply a simplified way of explaining the source of the heat.[/quote]
The heat is the result of the compression of air molecules. Friction between the air and the shuttle has nothing to do with the huge temperatures of reentry.
Period.
Friction only comes into play on a molecular level, concerning the friction of the air molecules between themselves, NOT friction between air molecules and the shuttle.
If you compress a gas, it's temperature increases. The friction between the air and the shuttle has a negligible impact on temperature.
Here's an exceprt from a web page that uncovers mistakes in school textbooks:
[quote]CORRECTED: RE-ENTERING SPACE CAPSULES ARE NOT HEATED BY AIR FRICTION
They are heated as they plow into the atmosphere and compress the air ahead of them. Ever pump up a bicycle tire and discover that the pump and the tire have become hot? The same effect causes spacecraft and supersonic aircraft to heat up as they compress the air at their leading edges. The heat doesn't come from *rubbing* upon the air, it comes from *squeezing* the air. This applies mostly to blunt objects such as Apollo reentry vehicles. It does not apply as much to the Space Shuttle: with wings oriented mostly edge-on to the moving air, the surfaces of the Shuttle ARE heated by friction. [b]But when the Shuttle first reenters the atmosphere, the bottom of the craft faces forwards, and in that case the Shuttle is heated by air compression, NOT by friction.[/b][/quote]
Here's another page:
[quote]How many times have we heard about how spacecraft turn into blazing fireballs when they reenter the atmosphere due to "the heat of friction." True, spaceships hit the upper atmosphere at Mach 25, and there are flames. But if the friction of air rushing across the spacecraft's skin really causes those flames, then how could the space shuttle's fragile protective tiles, which even a fingernail or a raindrop can damage and which come off with small hand tools, survive such a hypersonic blast without wearing or tearing away?
It turns out that the friction of air rubbing against spaceship skin (the boundary layer) has little to do with the fireball. Rather, compression mostly creates the heat as the thin air is squeezed in the shock layer ahead of the onrushing spacecraft. The air can't get out of the way fast enough, like snow in front of a plow, so it piles up. [/quote]
[This message has been edited by samuelk (edited 02-06-2003).]
I guess I'll just take everything else I've ever known and throw it out the window too... then bow down to the almighty knowledge of SamuelK and his sources.
I will simply disagree with you until such time as you can prove that pressure is the ONLY source of heat that the shuttle experiences on reentry.
[This message has been edited by Melkor (edited 02-06-2003).]
[quote]And if it's such a misconseption, then you should inform the publishers of the science books I was given in high school.[/quote]
Yes, it's a misconception. And it's a VERY popular misconception. Read my previous post.
Don't believe everything you read. Textbooks are notorious for getting stuff lik that wrong (see above).
[quote]You can lessen friction, but you can never take it away.[/quote]
I never said there was no friction. I said the friction between the air and the shuttle does not create the heat of reentry. The heat caused by air friction against the shuttle is negligible. It's PRESSURE that causes the 3000 degree temperatures.
Yes, friction causes heat. But friction between the air and the space shuttle does NOT cause the intense heat of reentry.
[quote]I will simply disagree with you until such time as you can prove that pressure is the ONLY source of heat that the shuttle experiences on reentry.[/quote]
Fine by me. Believe what you want, I'm just going on 5 years of college, testing and experience, and what my Space Flight professor (who worked for NASA for 36 years) told me.
[This message has been edited by samuelk (edited 02-06-2003).]
I'm not "beliveing what I want".. I'm beliveing what my teachers, text books, and multiple other pieces of material all say. Never, not once, have I ever read anything that would lend creedence to what you are now saying and would give me reason to doubt that which I have learned.
You are asking me to disbelieve everything I've learned from every source of information I could find. All on your words, and the words of your professor? Put yourself in my shoes sam.. what would you believe?
[quote]Originally posted by samuelk:
[b] Most of the heat that the shuttle receives is heat of radiation, not convection. Radiated heat can pass from the ionized air to the surface of the shuttle even if the air isn't in contact with the shuttle.[/b][/quote]
Then we would need a force field which would keep the heat radiation away as well. If only that would be possible with current tech though.
But there are materials which reflect the heat radiation like the aluminium foil, which as I undestand is actually been in use by space agencys around the world a long time already. Wasn't aluminium foil in fact invented by NASA and it came in civil use from there? So, what if the hull was covered with some material which reflects heat radiation. Something like that with the force field together could be a solution.
[quote]But there are materials which reflect the heat radiation like the aluminium foil, which as I undestand is actually been in use by space agencys around the world a long time already. [/quote]
Foil would be a bit too delicate for use in reentry. It's used a lot, but usually in situtations where the foil iself isn't put in stressful conditions (like high winds or debris).
It's possible that conduction/convection does play a part in heating up the shuttle (since the plasma created by the pressure wave can travel through the shock boundary to the surface of the shuttle), so I'm probably wrong in assuming that it's largely JUST radiation.
Randy's idea could have merrit, if a large enough power source could be found, and if the shuttle itself could be shielded from the affects of the field generated.
[This message has been edited by samuelk (edited 02-06-2003).]
Look sam, you don't go about saying things which fly in the face of conventional teachings by acting like what you're saying is how things are without citing some sources. Give me evidence, other than a blurb from an unknown source (which, though unlikely, could have been writen by you), that supports what you're saying and then I might have reason not to argue. I'm not saying that the pressures don't play a role, but to completely discount friction as a source of heat goes against every teacher and book I've ever listened to or read from. And considering I've been fascinated by air craft and space travel since I could walk, well, let's just say that the information I've read on it is substantial. Seriously.. I want to learn more.. if what I've been taught is wrong, tell me where I can find info that is RIGHT!
And as for the radiated heat.. well.. that's much easier to defend against than what we're currently dealing with.
[This message has been edited by Melkor (edited 02-06-2003).]
[quote]Originally posted by samuelk:
[b] Foil would be a bit too delicate for use in reentry. It's used a lot, but usually in situtations where the foil iself isn't put in stressful conditions (like high winds or debris).[/b][/quote]
Yes aluminium foil is indeed quite delicate material, but if the force shield would be possible to create then it would keep the air and it's pressure away from the hull and thus delicate materials could be used, right?
[quote][b]It's possible that conduction/convection does play a part in heating up the shuttle (since the plasma created by the pressure wave can travel through the shock boundary to the surface of the shuttle), so I'm probably wrong in assuming that it's largely JUST radiation.[/b][/quote]
Yeah, I'd think it's a combination of both radiation and convection/conduction.
[quote][b]Randy's idea could have merrit, if a large enough power source could be found, and if the shuttle itself could be shielded from the affects of the field generated.[/b][/quote]
Yup, and afterall even the small decrease in heat would be good unless it takes too much money and resources and would be too difficult to carry out.
Comments
[b]I have a degree in mechanical engineering. If it's one thing I was taught, it's how to think freely. Just because I'm educated in a certain area doesn't mean my thought process is restricted.[/b][/quote]
I'd just like to point out that Sam is entirely correct about what an engineering degree taught him. I have a degree in computer systems engineering, and if there is one thing I learnt from my 4 years there (and will further learn over the next 3 or 4 years there) it was how to think freely and flexibly to solve any problem.
------------------
[url="http://www.minbari.co.uk/log12.2263/"]Never eat anything bigger than your own head.[/url]
"Nonono...Is not [i]Great[/i] Machine. Is...[i]Not[/i]-so-Great Machine. It make good snow cone though." - Zathras
I pride myself on being onw of the most lateral thinkers out there... and yet.... I catch myself regularly resorting to routine, to 'tried and tested' methods without even thinking... never actually asking myself why on Earth I'm doing a specific task the way I am.
qualifications, experience, knowledge... all have handmaidens... cynsism, resentment of the new, jadedness. it happens to all of us to a degree, the important part is to recognise it and do our best to mitigate it and not get lost in 'when I was a boy' stories and 'whipper-snapper' bashing.
stop taking it personally, I'm as much having a go at myself as at anyone else.
excuse me Sam... was I referring to you when I asked if you had qualifications ?? I was referring to Davids post...
as far as concrete goes...ok sure... by the sounds of it its impractical, I can think of counters to some of your arguement but... its getting us precisely nowhere so I'm not going to continue in this vein.
I still think theres plenty of miles though.. in disposable re-entry shells, perhaps when mining stuff on the moon... we crudely smelt/process/refine ores and use them in re-entry shells, then.. collect them for final processing when they land.... precisely where of course is a big issue...
oh yeah... if you've shed your big heavy shell after the re-entry heat is gone.... 'wot me worry' about inertia... the actual re-entry vehicle can be much lighter/less robust
if we go up in stages... why the hell cant we come down in stages ??
[This message has been edited by shadow boxer (edited 02-05-2003).]
[B]any training is in essence 'a way of thinking', a learned pattern, even given the human minds ability to think laterally and to think in very flexible ways...you can fall unknowingly into a mode of thought which blinkers you to possibility...[/quote]
You're really stuck on this idea of structured education teaching closed-mindedness, aren't you?
College gave me the factual knowledge to think effectively. My experience in and outside of college working with various materials (concrete, steel, wood, etc.) gave me the knowledge to know that many of the things you suggest just aren't practical. It has nothing to do with narrow-minded thinking.
[quote]I pride myself on being onw of the most lateral thinkers out there... and yet.... I catch myself regularly resorting to routine, to 'tried and tested' methods without even thinking... never actually asking myself why on Earth I'm doing a specific task the way I am.[/quote]
It's easy to get caught up in one particular method. But one of the things I learned in college was how to effectively "brainstorm" a problem. Works wonders for coming up with new ideas.
[quote]qualifications, experience, knowledge... all have handmaidens...[/quote]
Yes, and so do ignorance and lack of experience and knowlage. If I had my choice, I'd go with knowing more than knowing less in this case.
[quote]cynsism, resentment of the new, jadedness. it happens to all of us to a degree, the important part is to recognise it and do our best to mitigate it and not get lost in 'when I was a boy' stories and 'whipper-snapper' bashing.[/quote]
But it's also important to recognize when someone is telling you your idea isn't practical because they may know a little more than you do about the subject (or may have experience to back it up).
[quote]stop taking it personally, I'm as much having a go at myself as at anyone else.[/quote]
As for me, I'm not taking anything personally. But I do find it amusing that you can't keep from insulting people or resorting to a condescending attitude (as if YOU know how to think and reason better than anyone else) and spewing out quaint little metaphors to teach the rest of us about life.
Skip the zen mysticism and just talk.
[quote]excuse me Sam... was I referring to you when I asked if you had qualifications ?? I was referring to Davids post...[/quote]
WHO you were referring to doesn't reall matter. I was talking about the fact that you continue to condemn qualifications, knowledge and experience even [i]after[/i] asking someone to back up his ideas with his qualifications, knowledge and experience (namely "concrete studies").
[quote]as far as concrete goes...ok sure... by the sounds of it its impractical, I can think of counters to some of your arguement but... its getting us precisely nowhere so I'm not going to continue in this vein.
I still think theres plenty of miles though.. in disposable re-entry shells, perhaps when mining stuff on the moon... we crudely smelt/process/refine ores and use them in re-entry shells, then.. collect them for final processing when they land.... precisely where of course is a big issue...
[/quote]
Disposable reentry shells are one thing. Disposable [i]concrete[/i] reentry shells are another.
But by all means, list your counter arguments...this is a discussion, after all.
[quote]oh yeah... if you've shed your big heavy shell after the re-entry heat is gone.... 'wot me worry' about inertia... the actual re-entry vehicle can be much lighter/less robust
if we go up in stages... why the hell cant we come down in stages ??[/quote]
Because when you reenter the atmosphere, you're at the whim of more forces than just gravity; you're also affected by air turbulence.
There are a few reasons why shedding parts of a craft on reentry is more dangerous than shedding parts of a craft on ascent:
1. When you shed part of a craft, it's weight aerodynamics change drastically. During seconds or milliseconds in which that weight is removed it only takes a small error to cause catastrophy. For the sake of simplicity, let's say your heatshield is designed to split in half and separate from the craft. If, during reentry, one side of the heat shield separates ONLY MILLISECONDS before the other half, the center of gravity of the craft will shift unexpectedly and it could start to tumble. Even worse, what happens if one of the explosive bolts (or whatever mechanism you use to release the heat shield) fails?
2. Launch speeds are lower than reentry speeds...when shedding parts of a craft, you have to remove the pieces with enough energy to push them clear of the craft itself to avoid damaging the craft. The faster the craft is going, the faster you have to move the shedded material, and therefore the more force you have to use to remove it. You can't just assume that the air will push the debris out of the way
3. The parts of the space shuttle system that are shed during launch (solid rocket boosters and external tank) are positioned below the shuttle. When they separate, they fall away from the shuttle (even though the shuttle is upside down when the ET is shed, the fact that the shuttle is moving against the force of gravity helps it move clear of the ET).
By design, a heat shield has to point TOWARDS the direction of travel... so the heat shield is in effect in front of the vehicle when it is shed. This poses a danger because you will be sending the heat shield pieces backwards over the craft. All it takes is a little air turbulence to slam a chunk of the heat shield into the craft.
So yes, there are a few reasons why shedding pieces of a craft on launch is less dangerous (though, if this Columbia accident investigation turns out the way I think it will, still somewhat dangerous) than shedding a heat shield on reentry.
[This message has been edited by samuelk (edited 02-05-2003).]
[url="http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html"]http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html[/url]
[b]This is an article on the problems with attempting to repair or rescue the crew of Columbia in orbit had they known of the damage prior to landing:
[url="http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html"]http://www.washingtonpost.com/wp-dyn/articles/A26641-2003Feb4.html[/url] [/b][/quote]
I really hate having to sign up for something just to read an article... [img]http://216.15.145.59/mainforums/mad.gif[/img]
[This message has been edited by JackN (edited 02-05-2003).]
------------------
AnlaShok, Captain of the Gray Hand of Fate Squadron
Sidhe-1
Wielder of the Big Heavy Hammer of Obvious Truth
"FABRICATI DIEM, PVNC!"
Same with the WTC disaster. If it had been say 11am-12md then the death toll would have been much larger.
Most disasters are like that. They are bad but could have been much worse if they happened at almost any other time during the day.
Perhaps I could refocus to the topic. The primary consideration in both achieving and leaving orbit is velocity; you need enough to achieve orbit and you need to get rid of it to reach home (safely).
Unless I'm terribly mistaken (which is certainly possible), there is nothing that says you must come screaming into the earth's atmosphere. We just haven't devised a better way to reduce the velocity of our spacecraft. In theory, you could alter your orbit so that you'd arrive in the atmosphere at a much slower acceleration (picture Buck Roger's cigar-shaped rocket's slow tail-first descent, or even extremes such as the space elevator mentioned elsewhere), but this would require a much larger energy expenditure in orbit, which currently equates to bringing more fuel with you.
------------------
bobo
<*>
B5:ITF
- PJH
Sorry to say that it takes something like this to make them increase the budget and be able to build a better mode of transport.
Fresh minds are needed to look at the problems, ie, Takeoffs and landing and methods their in, and rebuild the new shuddle.
------------------
[b]May You Live Forever, and The Last Voice You Hear, Be Mine! [/b]
go read some texts on psychology
in fact, here :
[url="http://keirsey.com/pumII/ns.html"]http://keirsey.com/pumII/ns.html[/url]
[url="http://keirsey.com/pumII/jp.html"]http://keirsey.com/pumII/jp.html[/url]
I can guarantee you that you Sam, fall into the "S " category, and I'd also be willing to bet "J"
I'm the extreme opposite of both of those, the "I" and the "N"
in fact here :
[url="http://keirsey.com/personality/nfep.html"]http://keirsey.com/personality/nfep.html[/url] [url="http://keirsey.com/personality/ntep.html"]http://keirsey.com/personality/ntep.html[/url]
I work in both these mindsets ,dependent on circumstance. I'm used to all sorts of abuse for being who I am, I'm one or two from one hundred and I'm seldom seen as valuable to those who fall on the opposite side of the S/N divide and seeing as the S persons outnumber me to a vast degree I'm always fighting...
Engineering should be an S pursuit....
Design should be an N pursuit....
if the world was fair.
It's not.. its about 50 to 1...so I take my lumps and give as many back as I can.
There is ****ing room for both of us, I hope you will eventually understand where I'm coming from.
Where did your hostility orginate ? Ask yourself that question and answer honestly and perhaps we may get somewhere.
I dont decry Engineering, I dont decry people who live in an S frame of mind... what pisses me off more than you can possibly imagine is boneheaded concrete booted hyperpragmatic champions of hidebound tradition and stagnation...
Sam, you're not one of those, neither is anyone else here that I know of.... but....
inside every Engineer lurks the above mentioned monster. I hate the SOB and I'm always sticking branches in its cage.... I cant bloody well help it...
it is responsible for a degree of misery for me and folks like me, that most probably cant even grasp...
but !! this is all well off topic.. so.. back to the case in hand
~~~~
As far as concrete heat sheilds go...there are such things as foundry bricks, fired at tempratures above that of what you find in re-entry, they stick em together with foundry clay, concrete/foundry clay... moon dirt... just slightly different moon dirt.
and the KISS principile still applies, hows this :
a big (perhaps slightly pointy) bucket .... bucket comes in arse first... steeply... aimed at the appropriate Ocean...chute deploys from pods exposed top....drags pod from bucket like the plunger from a syringe... viola
bucket becomes one with ocean floor at Mach whatever... pod drops to Ocean for splashdown.
Happy intact astronauts
My concern is the G's when the chute/s deploy...we need some sort of advanced crash couch to absorb it it somehow. Perhaps the 'extraction' chute is a separate jettisonable device used before the main chutes deploy..
bring on commercially available spider silk..
Sam...(and the rest of ya I guess.. [img]http://216.15.145.59/mainforums/smile.gif[/img] )
go read some texts on psychology
in fact, here :
[url="http://keirsey.com/pumII/ns.html"]http://keirsey.com/pumII/ns.html[/url]
[url="http://keirsey.com/pumII/jp.html"]http://keirsey.com/pumII/jp.html[/url]
I can guarantee you that you Sam, fall into the "S " category, and I'd also be willing to bet "J"
I'm the extreme opposite of both of those, the "I" and the "N"
in fact here :
[url="http://keirsey.com/personality/nfep.html"]http://keirsey.com/personality/nfep.html[/url] [url="http://keirsey.com/personality/ntep.html"]http://keirsey.com/personality/ntep.html[/url]
[/quote]
I've already taken those tests. I fall somewhere in between an ENTJ and and INTJ (I've taken the test more than once, and tend to flip-flop between an E and an I).
[quote]I work in both these mindsets ,dependent on circumstance. I'm used to all sorts of abuse for being who I am, I'm one or two from one hundred and I'm seldom seen as valuable to those who fall on the opposite side of the S/N divide and seeing as the S persons outnumber me to a vast degree I'm always fighting...[/quote]
Maybe the reason you're always fighting is because you have a very hostile attitude towards people who disagree with you.
I've seen you insult and berate people here constantly. You've called people names and condescended to them with your "words of wisdom". You seem to have a very high-and-mighty attitude as if you have lots to teach and nothing to learn.
It's the arrogance that brings about conflict.
[quote]Engineering should be an S pursuit....
Design should be an N pursuit....[/quote]
Your mistake is separating engineering from design. They go hand in hand. Engineering is both an S and an N field. You're not going to get anywhere as an engineer if you don't pay attention to the world around you.
[quote]
if the world was fair.
It's not.. its about 50 to 1...so I take my lumps and give as many back as I can.
There is ****ing room for both of us, I hope you will eventually understand where I'm coming from.[/quote]
Of course there is. But I have a feeling that it's YOU who doesn't understand that, because you can't seem to accept the fact that someone else might know a little more than you do about a subject.
[quote]Where did your hostility orginate ? Ask yourself that question and answer honestly and perhaps we may get somewhere.[/quote]
I have no hostility towards you or anyone else here. I don't get angry about things I read on the web. If you think I'm angry or hostile towards you, then you're definitely misreading my posts (which is an easy thing to do, since it's only text).
[quote]I dont decry Engineering, I dont decry people who live in an S frame of mind... what pisses me off more than you can possibly imagine is boneheaded concrete booted hyperpragmatic champions of hidebound tradition and stagnation...[quote]
That's not a trait of engineers. It's a trait of [i]people[/i].
[quote]Sam, you're not one of those, neither is anyone else here that I know of.... but....
inside every Engineer lurks the above mentioned monster. I hate the SOB and I'm always sticking branches in its cage.... I cant bloody well help it...
it is responsible for a degree of misery for me and folks like me, that most probably cant even grasp...[/quote]
See, that's the attitude I'm talking about. I get the impression from reading that that you feel martyrd and misunderstood by everybody else because people just don't "get it".
[quote]but !! this is all well off topic.. so.. back to the case in hand
~~~~
As far as concrete heat sheilds go...there are such things as foundry bricks, fired at tempratures above that of what you find in re-entry, they stick em together with foundry clay, concrete/foundry clay... moon dirt... just slightly different moon dirt.[quote]
Have you ever hit a foundry brick with a hammer after it has been exposed to high temperatures? Very brittle. The force of impacted air molecules or micrometeorites is enough to crack something like that very easily.
[quote]and the KISS principile still applies, hows this :
a big (perhaps slightly pointy) bucket .... bucket comes in arse first... steeply... aimed at the appropriate Ocean...chute deploys from pods exposed top....drags pod from bucket like the plunger from a syringe... viola
bucket becomes one with ocean floor at Mach whatever... pod drops to Ocean for splashdown.
Happy intact astronauts[/quote]
I'm assuming it was your intention to perfectly describe the reentry procedure used during the Mercury, Gemini and Apollo missions...in which case I should point out that Gus Grissom almost died when his capsule sank in the ocean after the egress hatch blew prematurely. And he DID die (along with two others) in Apollo 1 when the capsule caught fire and the astronauts were trapped inside.
[quote]My concern is the G's when the chute/s deploy...we need some sort of advanced crash couch to absorb it it somehow. Perhaps the 'extraction' chute is a separate jettisonable device used before the main chutes deploy..
bring on commercially available spider silk..[/quote]
Keep in mind that even using the vehicle you mentioned, you're still going to need a heat shield, and you're still going to enter the atmosphere at extreme velocities. Chutes only work in thick atmosphere, and until you get below a certain altitude, the compressed air beneath the craft is going to create almost as much heat as that seen by the Shuttle.
That kind of reentry vehicle isn't really useful if you plan to take experiments with you into orbit (or bring cargo back).
The shuttle was designed to bring cargo into orbit and bring cargo back from orbit. No other spacecraft does the job better.
But of course that doesn't mean the shuttle is perfect for the job. There's always something better.
The other disadvantage of a small reentry vehicle is that there's no room to [i]perform[/i] experiments, sleep, move, etc.
The shuttle astronauts can stay in orbit for weeks. There's adequate oxygen, food and living space for them to stay up there for quite a while.
Plus, the shuttle has excersize facilities to prevent muscle atrophy.
The main thing to keep in mind is that the space shuttle is a multi-purpose vehicle.
It's a launch vehicle, a reentry vehicle, a mobile lab, a satellite deployment and recovery facility and a temporary space station.
[This message has been edited by samuelk (edited 02-06-2003).]
Anyone know what's the latest info one how to counter it?
[b]What about long space flight bone loss issues...
Anyone know what's the latest info one how to counter it?[/b][/quote]
It's still a major problem. I tihnk some experiments were done (or at least planned) for STS 102 back in 2001.
Here's what I've gleaned from stuff I've read recently....
There are two types of bone cell that are responsible for bone growth and decay. Osteoblast cells build new bone, and Osteoclast cells destroy old bone.
Osteoblast cells respond to stress. The normal stress of gravity regulates the activity of Osteoblast cells. If the normal everyday stress of gravity is taken away, Osteoclasts remove more bone than osteoblasts create, so the bone weakens and diminishes.
A chemical used in the development of osteoblasts is an enzyme known as "creatine kinase-B". There's a study underway at [url="http://www.mc.vanderbilt.edu/gcrc/space/#Bone"]Vanderbilt University[/url] that concerns finding out how the body regulates this enzyme and how that chemical is affected by weightlessness.
There are some other studies looking at how the ingestion of food affects bone growth...eating food causes an increase in production of a particular hormone that increases bone growth. It's possible that giving astronauts this hormone might prevent bone loss.
[This message has been edited by samuelk (edited 02-06-2003).]
My laymen’s understanding is that heat build up comes from air molecules clinging to the skin of the shuttle, and that these clinging molecules collide with other molecules, and that the friction between these air molecules causes the heat. Even if the skin of the shuttle were perfectly smooth, like glass, this phenomenon would still happen.
Could some form of modulated electrical and or magnetic force be used on the skin of a next generation shuttle to reject air molecules from sticking to the shuttle's skin?
I'm trying to imagine a system for allowing a craft re-entering the atmosphere to come through in an airless envelope, until means other than friction were used to slow the descent, to the point where these systems could be turned off, so that winged flight could take over.
I am aware that there are huge holes in this thinking. For instance, 'what' exactly will slow the vehicle, if not friction? It has already been stated that any system we know of that includes jets would be prohibitively heavy to carry into space, in order for this system to be used on descent.
Maybe this system I'm contemplating could be used simply to moderate the skin heating, so that some friction could still be used to slow the vehicle.
Where's anti-gravity when you really need it?
[This message has been edited by Randy (edited 02-06-2003).]
That's actually a very common misconception. The heat is caused not by air friction, but by air compression. The space shuttle is travelling so fast, the air doesn't have enough time to get out of the way, so it is compressed, which releases a LOT of heat.
In fact, the air is compressed so much, it no longer has the properties of normal "air", and is considered to be a chemically reacting mixture of atoms, molecules and ions. It is the ionized part of the air that disrupts communications on reentry.
If you've ever used a can of compressed air to blow dust out of your keyboard, you've probably felt the opposite of this process. The air in the can is already compressed. When you release the valve, the pressure of the air inside the can decreases rapidly, and you can feel the can become very cold.
[This message has been edited by samuelk (edited 02-06-2003).]
[b]Maybe this system I'm contemplating could be used simply to moderate the skin heating, so that some friction could still be used to slow the vehicle.[/b][/quote]
Hmmm.... what if the system you described could be used to just "push" the friction and heat caused by it (air molecules) away from the ship just that much that the ship would be much less hot, like you were saying, but still have the same force by friction to slow it down, or at least nearly the same force. Kind of like a force shield to keep the heat and friction a few cents away from the ship, or whatever the necessary distance would be to make the ship less hot, but it would still have the frictional force to slow down the ship. In other words the force shield would take the friction instead of the ship hull, which is now the case.
[quote]Where's anti-gravity when you really need it?[/quote]
Indeed. Somebody keep a knife on scientists throats and make them invent antigrav in a few years ok? [img]http://216.15.145.59/mainforums/biggrin.gif[/img]
- PJH
[b]Hmmm.... what if the system you described could be used to just "push" the friction and heat caused by it (air molecules) away from the ship just that much that the ship would be much less hot, like you were saying, but still have the same force by friction to slow it down, or at least nearly the same force. Kind of like a force shield to keep the heat and friction a few cents away from the ship, or whatever the necessary distance would be to make the ship less hot, but it would still have the frictional force to slow down the ship. In other words the force shield would take the friction instead of the ship hull, which is now the case.[/b][/quote]
Heat can be transferred in three ways:
1 conduction (through solid material),
2 convection (through the air or other fluid--although this is really just a special kind of conduction)
3 radiation (the transmission of electromagnetic energy through "empty" space).
Much of the heat that the shuttle receives is heat of radiation, not convection. Radiated heat can pass from the ionized air to the surface of the shuttle even if the air isn't in contact with the shuttle.
[This message has been edited by samuelk (edited 02-06-2003).]
Randy may very well have a good idea on his hands. If we can limit the amount of air that gets "stuck" or compressed or however you want to call it, it would allow a more controlled reentry as it would enable the shuttle to behave more like the glider it does in the last few steps before landing. OR if the energy barrier is what the air molecules "stuck" to instead of the shuttles skin.. well, I'm sure you can figure the rest out.
What appears to be a misconseption is often a simplified way of explaining something. Once more the self rightousness of the members of this board has proven itself. I'll take my non engineering degree having self elsewhere as its obvious that my kind isn't wanted here.
No, it's not. It's a very importnat distinction. If friction WERE the cause of the heat buildup, then it would be quite easy to get rid of it by keeping it away from the shuttle.
When you compress a gass, the temperature of the gas increases. This is shown using the ideal gas law:
PV=mRT (where P=pressure, V=volume, m=mass, R=gas constant and T=temperature)
The heat buildup has nothing to do with the air molecules "rubbing against" the shuttle surface. It's caused by the fact that the air is being compressed.
There's a huge difference between the two in terms of what Randy's proposing.
But it's not friction. It's pressure. The pressure is so high, it changes the properties of the air. Furthermore, the heat is passing to the shuttle via radiation more than convection or conduction. So even if you put a complete vacuum between the air and the shuttle, the shuttle would still heat up.
[quote]Randy may very well have a good idea on his hands. If we can limit the amount of air that gets "stuck" or compressed or however you want to call it, it would allow a more controlled reentry as it would enable the shuttle to behave more like the glider it does in the last few steps before landing.[/quote]
If you limit the amount of air that gets compressed, then you can't slow the shuttle down.
You're missing the fact that the air is what's used to slow the shuttle down. If we remove the compression of the air from the equation, then the shuttle will come screaming into the atmosphere and wouldn't be able to stop.
That's part of the reason why the shuttle doesn't dive into the atmosphere nose-first.
[This message has been edited by samuelk (edited 02-06-2003).]
The heat is the result of the compression of air molecules. Friction between the air and the shuttle has nothing to do with the huge temperatures of reentry.
Period.
Friction only comes into play on a molecular level, concerning the friction of the air molecules between themselves, NOT friction between air molecules and the shuttle.
If you compress a gas, it's temperature increases. The friction between the air and the shuttle has a negligible impact on temperature.
Here's an exceprt from a web page that uncovers mistakes in school textbooks:
[quote]CORRECTED: RE-ENTERING SPACE CAPSULES ARE NOT HEATED BY AIR FRICTION
They are heated as they plow into the atmosphere and compress the air ahead of them. Ever pump up a bicycle tire and discover that the pump and the tire have become hot? The same effect causes spacecraft and supersonic aircraft to heat up as they compress the air at their leading edges. The heat doesn't come from *rubbing* upon the air, it comes from *squeezing* the air. This applies mostly to blunt objects such as Apollo reentry vehicles. It does not apply as much to the Space Shuttle: with wings oriented mostly edge-on to the moving air, the surfaces of the Shuttle ARE heated by friction. [b]But when the Shuttle first reenters the atmosphere, the bottom of the craft faces forwards, and in that case the Shuttle is heated by air compression, NOT by friction.[/b][/quote]
Here's another page:
[quote]How many times have we heard about how spacecraft turn into blazing fireballs when they reenter the atmosphere due to "the heat of friction." True, spaceships hit the upper atmosphere at Mach 25, and there are flames. But if the friction of air rushing across the spacecraft's skin really causes those flames, then how could the space shuttle's fragile protective tiles, which even a fingernail or a raindrop can damage and which come off with small hand tools, survive such a hypersonic blast without wearing or tearing away?
It turns out that the friction of air rubbing against spaceship skin (the boundary layer) has little to do with the fireball. Rather, compression mostly creates the heat as the thin air is squeezed in the shock layer ahead of the onrushing spacecraft. The air can't get out of the way fast enough, like snow in front of a plow, so it piles up. [/quote]
[This message has been edited by samuelk (edited 02-06-2003).]
I will simply disagree with you until such time as you can prove that pressure is the ONLY source of heat that the shuttle experiences on reentry.
[This message has been edited by Melkor (edited 02-06-2003).]
Yes, it's a misconception. And it's a VERY popular misconception. Read my previous post.
Don't believe everything you read. Textbooks are notorious for getting stuff lik that wrong (see above).
[quote]You can lessen friction, but you can never take it away.[/quote]
I never said there was no friction. I said the friction between the air and the shuttle does not create the heat of reentry. The heat caused by air friction against the shuttle is negligible. It's PRESSURE that causes the 3000 degree temperatures.
Yes, friction causes heat. But friction between the air and the space shuttle does NOT cause the intense heat of reentry.
[quote]I will simply disagree with you until such time as you can prove that pressure is the ONLY source of heat that the shuttle experiences on reentry.[/quote]
Fine by me. Believe what you want, I'm just going on 5 years of college, testing and experience, and what my Space Flight professor (who worked for NASA for 36 years) told me.
[This message has been edited by samuelk (edited 02-06-2003).]
You are asking me to disbelieve everything I've learned from every source of information I could find. All on your words, and the words of your professor? Put yourself in my shoes sam.. what would you believe?
[b] Most of the heat that the shuttle receives is heat of radiation, not convection. Radiated heat can pass from the ionized air to the surface of the shuttle even if the air isn't in contact with the shuttle.[/b][/quote]
Then we would need a force field which would keep the heat radiation away as well. If only that would be possible with current tech though.
But there are materials which reflect the heat radiation like the aluminium foil, which as I undestand is actually been in use by space agencys around the world a long time already. Wasn't aluminium foil in fact invented by NASA and it came in civil use from there? So, what if the hull was covered with some material which reflects heat radiation. Something like that with the force field together could be a solution.
- PJH
Foil would be a bit too delicate for use in reentry. It's used a lot, but usually in situtations where the foil iself isn't put in stressful conditions (like high winds or debris).
It's possible that conduction/convection does play a part in heating up the shuttle (since the plasma created by the pressure wave can travel through the shock boundary to the surface of the shuttle), so I'm probably wrong in assuming that it's largely JUST radiation.
Randy's idea could have merrit, if a large enough power source could be found, and if the shuttle itself could be shielded from the affects of the field generated.
[This message has been edited by samuelk (edited 02-06-2003).]
And as for the radiated heat.. well.. that's much easier to defend against than what we're currently dealing with.
[This message has been edited by Melkor (edited 02-06-2003).]
[b] Foil would be a bit too delicate for use in reentry. It's used a lot, but usually in situtations where the foil iself isn't put in stressful conditions (like high winds or debris).[/b][/quote]
Yes aluminium foil is indeed quite delicate material, but if the force shield would be possible to create then it would keep the air and it's pressure away from the hull and thus delicate materials could be used, right?
[quote][b]It's possible that conduction/convection does play a part in heating up the shuttle (since the plasma created by the pressure wave can travel through the shock boundary to the surface of the shuttle), so I'm probably wrong in assuming that it's largely JUST radiation.[/b][/quote]
Yeah, I'd think it's a combination of both radiation and convection/conduction.
[quote][b]Randy's idea could have merrit, if a large enough power source could be found, and if the shuttle itself could be shielded from the affects of the field generated.[/b][/quote]
Yup, and afterall even the small decrease in heat would be good unless it takes too much money and resources and would be too difficult to carry out.
- PJH