Author Topic: Basic Rocket Science Q & A  (Read 282456 times)

Offline madscientist197

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Re: Basic Rocket Science Q & A
« Reply #120 on: 03/23/2009 08:19 AM »
There's no way that a crew could survive either a solid stage or a HTP stage detonating without another stage as a buffer in between -- no LAS could relocate the capsule fast enough.

Using HTP for stage combustion is an interesting idea, it certainly would reduce the temperatures involved a lot and make production cheaper. Not sure if it would give the best performance though.
« Last Edit: 03/23/2009 08:21 AM by madscientist197 »
John

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #121 on: 03/23/2009 09:42 AM »

On the Explosion Hazard and LAS. If the Ares I LAS can pull a crew away from an exploding SRM then I wouldn't be so sure that one couldn't be devised to protect a crew from a HTP stage.


SRM's don't detonate

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #122 on: 03/23/2009 10:56 AM »
Unlike LOX one, which can only burn ...

gospacex, this is a general comment and not aimed specifically at you.

I keep seeing this statement ("Unlike LOX one, which can only burn") and others like it all over the place, and while I know it's a fine distinction, it is *not* true that LOX (oxygen) burns. Oxygen does not burn. It is not a fuel. It is an oxidizer. Fuel cannot burn without the presence of an oxidizer to support combustion, and oxygen, in this case, is that oxidizer. In fact the term "burn" is common speech for combustion and actually means "oxidizing" the fuel, such as hydrogen, kerosene, RP1, gasoline, paper, wood, etc. Combustion requires at least 2 things, a fuel to burn and an oxidizer to support the burn. The fuel burns, the oxidizer does not. It molecularly combines with the fuel to create the "oxidation process", called combustion. There are other oxidizers as well besides oxygen. All of them are oxidizers, not fuel, and none of them "burn". They all support combustion and allow the fuel, whatever it is, to combust, or “burn”. Chemistry 101.

Likewise it is incorrect to describe LOX as explosive. It is not. What is generally being referred to when this term is misapplied is that the ET, as a "pressure vessel" can rupture under the high internal pressure. That does not take a spark or ignition or combustion of any kind, just a structural imperfection in a weld or some other less than satisfactory "mechanical" property of the structure of the tank. Granted, the end result is often the same, especially if the rupture also releases large quantities of fuel to mix with the released oxygen (Challenger) which then supports the "fuel" exploding, but the oxygen did not explode, the structural pressure vessel ruptured.

Can we use the correct terminology please?
« Last Edit: 03/23/2009 10:58 AM by clongton »
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Re: Basic Rocket Science Q & A
« Reply #123 on: 03/23/2009 11:10 AM »
Can we use the correct terminology please?

From where I stand, gospacex did use the correct term - a "LOX one" as in engine means it has a fuel in addition to LOX. If the two are not well mixed, no detonation is possible. Any by definition, keeping both fuel and oxidizer (in this case LOX) in separate tanks prevents them from mixing. I don't see that statement as implying it's LOX itself that burns.

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #124 on: 03/23/2009 11:20 AM »
Can we use the correct terminology please?

From where I stand, gospacex did use the correct term - a "LOX one" as in engine means it has a fuel in addition to LOX. If the two are not well mixed, no detonation is possible. Any by definition, keeping both fuel and oxidizer (in this case LOX) in separate tanks prevents them from mixing. I don't see that statement as implying it's LOX itself that burns.

Oxygen does *not* burn.
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Re: Basic Rocket Science Q & A
« Reply #125 on: 03/23/2009 11:30 AM »
What did I just say above? He did NOT say "Unlike LOX, which can only burn" he said "Unlike LOX one [i.e. fuel/LOX combo], which can only burn".

I'd think the vast majority of people here know oxygen doesn't actually burn, but maybe it's just my impression.

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #126 on: 03/23/2009 12:07 PM »
What did I just say above? He did NOT say "Unlike LOX, which can only burn" he said "Unlike LOX one [i.e. fuel/LOX combo], which can only burn".

I'd think the vast majority of people here know oxygen doesn't actually burn, but maybe it's just my impression.

Google "LOX one" and you won't get the reference you refer to. You will gets hundreds of hits something like this:
"Lyrics for One Two Three Four by The Lox. Album DJ Clue "
So that's just another example of what I was trying to get at and afaik, that term isn't found in a technical manual or reputable dictionary either.

My post was in regards to the use of proper terminology, especially when discussing things of a technical nature. Introducing coloqual terms into a technical discussion is not appropriate given the nature of the subjects. It can and has led to misinterpretations.

I have seen professors ask students to leave the class when they did that, and my request was for folks to take pains to use the proper terminology and use it correctly. This isn't a rap around a campfire. Perhaps I'm old school, but I like to know that the terms I see used in a technical discussion are actually there in the dictionary and continue to mean what they have always meant.

But that's just me.

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Re: Basic Rocket Science Q & A
« Reply #127 on: 03/23/2009 12:10 PM »
I have seen professors ask students to leave the class when they did that, and my request was for folks to take pains to use the proper terminology and use it correctly. This isn't a rap around a campfire. Perhaps I'm old school, but I like to know that the terms I see used in a technical discussion are actually there in the dictionary and continue to mean what they have always meant.

Fair enough. I'll drop this subject now.

Offline gospacex

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Re: Basic Rocket Science Q & A
« Reply #128 on: 03/23/2009 12:23 PM »
Unlike LOX one, which can only burn ...

gospacex, this is a general comment and not aimed specifically at you.

I keep seeing this statement ("Unlike LOX one, which can only burn") and others like it all over the place, and while I know it's a fine distinction, it is *not* true that LOX (oxygen) burns.

You are right. My phrase was "Imagine a manned rocket at the pad fueled by HTP. Unlike LOX one..."

Correct phrase should be "Imagine a manned rocket at the pad fueled by HTP. Unlike LOX fueled one..."

(I'm not sure whether it's 100% correct to say "fueled by [some oxidizer]", but nothing better comes to mind)

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #129 on: 03/23/2009 12:42 PM »
Unlike LOX one, which can only burn ...

gospacex, this is a general comment and not aimed specifically at you.

I keep seeing this statement ("Unlike LOX one, which can only burn") and others like it all over the place, and while I know it's a fine distinction, it is *not* true that LOX (oxygen) burns.

You are right. My phrase was "Imagine a manned rocket at the pad fueled by HTP. Unlike LOX one..."

Correct phrase should be "Imagine a manned rocket at the pad fueled by HTP. Unlike LOX fueled one..."

(I'm not sure whether it's 100% correct to say "fueled by [some oxidizer]", but nothing better comes to mind)

That’s fine. I take your meaning and I understood what you were getting at in the first place. That wasn’t the point, and is why I started by saying it was a general comment, not specific to you.

I see so much these days of folks allowing their English to slip into word usages that are not correct, being linguistically lazy. Folks like me who speak English as a native language often forget that English is *THE* most difficult language on earth to learn as a foreign language. That’s why it is so important, especially in a technical conversation, to take pains to use the correct terminology and to apply it correctly. There are many people on this forum from non-English speaking nations and what they are reading here is a foreign language to them. We English-speakers too often forget that. When we allow ourselves to become casual with how we use our terms, it can make it difficult for them. Hell, it is even difficult for English speakers sometimes to figure out what someone has said.

So like I said, my point was to encourage folks to think about what they want to say before they post it, not only so that it is conceived correctly, but also that it is spoken correctly. Set your language bar high and then reach for it. That’s all I was getting at. I used “burning oxygen” as the example, because I see that incorrect usage so often.
« Last Edit: 03/23/2009 12:44 PM by clongton »
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Offline sbt

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Re: Basic Rocket Science Q & A
« Reply #130 on: 03/23/2009 06:24 PM »

On the Explosion Hazard and LAS. If the Ares I LAS can pull a crew away from an exploding SRM then I wouldn't be so sure that one couldn't be devised to protect a crew from a HTP stage.


SRM's don't detonate

Ok – I picked that up a while ago (and didn't say they did).

Just to fill in the gaps, does anyone know:

a) Whether HTP actually Detonates in the true sense (i.e. reacts along a shock front) or if it deflagrates (or something else)?

b) If the behaviour of bulk HTP in a stage is understood – does the 'whole lot go up' in one instantaneous bang or does the oxidiser disperse so that only part goes up?

Mind you, this is for info only, not because I actually believe that anybody is going to build a large HTP stage nor am I particularly advocating one – just doing thought experiments.

Rick
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Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #131 on: 03/23/2009 06:41 PM »

a) Whether HTP actually Detonates in the true sense (i.e. reacts along a shock front) or if it deflagrates (or something else)?

b) If the behaviour of bulk HTP in a stage is understood – does the 'whole lot go up' in one instantaneous bang or does the oxidiser disperse so that only part goes up?


It rapidly decomposes (explodes)  and hence its use as a monopropellant.

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Re: Basic Rocket Science Q & A
« Reply #132 on: 03/24/2009 01:44 AM »

Mind you, this is for info only, not because I actually believe that anybody is going to build a large HTP stage nor am I particularly advocating one – just doing thought experiments.


There is water on Mars so ISRU H2O2 could be used in a Mars ascent stage.

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #133 on: 03/24/2009 02:56 AM »
Another thing that needs to be pointed out: solids can only ignite under a very hot ignition source to begin with.  I don't think even a typical match already burning would do it.  Please correct my impression if I'm wrong.
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Offline Steven Pietrobon

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Re: Basic Rocket Science Q & A
« Reply #134 on: 03/24/2009 05:17 AM »
From HTP safety manual

"HTP Explosion Hazard: The action of detonators on HTP has shown that it is possible to partially explode 90% material if it closely confined, and under severe conditions of shock and confinement it has been known to detonate at 80%-85% strength."

100% HTP has the same freezing point as water, 0 C. So if you can keep large volumes of water from freezing, you can do the same with HTP.

If anybody wants a scan of various paper and manuals relating to HTP, email me and I will send them to you.
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Offline Steven Pietrobon

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Re: Basic Rocket Science Q & A
« Reply #135 on: 03/24/2009 05:48 AM »
BTW, do you have data on HTP/C3H8 pair?

I don't have it on hand, but the program I use gives a density of 1.2284 kg/L, exhaust speed of 3242 m/s, impulse density of 3982 Ns/L and a mixture ratio of 7.8. This is better than O2/RP-1, but worse than HTP/RP-1 as a first stage propellant.
Propellants  MR   dp (kg/L)  ve (m/s) Id (Ns/L)
O2/H2        5.0  0.3251     4455     1448
O2/H2        6.0  0.3622     4444     1610
O2/H2        7.5  0.4120     4365     1798
O2/CH4       3.6  0.8376     3656     3062
F2/H2       14.6  0.6553     4704     3083
O2/C2H6      3.2  0.9252     3634     3362
O2/C3H8      3.1  0.9304     3613     3362
O2/C3H4      2.4  0.9666     3696     3573
O2/RP–1      2.8  1.0307     3554     3663
O2/C7H8      2.4  1.0954     3628     3974
HTP/C3H8     7.8  1.2284     3242     3982
HTP/C3H4     6.5  1.2553     3319     4166
HTP/RP–1     7.3  1.3059     3223     4209
HTP/C7H8     6.6  1.3496     3288     4437
F2/NH3       3.4  1.1770     4115     4843

By the way, the highest impulse density propellant I know of is F2/NH3 (liquid fluorine and ammonia). F2 has a density of 1.505 kg/L and NH3 0.676 kg/L. With such high density propellants, at a MR of 3.4 you get dp =  1.1770 kg/L, ve = 4115 m/s and Id = 4843 Ns/L, 32% better than O2/RP-1 if you don't mind a hydrofluoric acid exhaust. :-) I've also added data for F2/H2 which has an Id more twice that of O2/H2 with a better ve.

Any other propellant combinations the readers here would like me to try?
« Last Edit: 03/24/2009 06:08 AM by Steven Pietrobon »
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Offline duane

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Re: Basic Rocket Science Q & A
« Reply #136 on: 03/25/2009 02:26 AM »
I have a simple question. How do you destroy a solid rocket booster that is out of control ?

More specifically how are the shuttle SRB's destroyed by the range safety system ?

I read a Wikipedia article on the SRB's and it quoted it using a linear shaped charge, but where exactly is the charge located, and what/how does it destroy the SRB ?

Cut it in half, cut the nozzle off etc.... ??

Thanks for any info
Duane

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Re: Basic Rocket Science Q & A
« Reply #137 on: 03/25/2009 02:31 AM »
Along the side of the case.  It's a zipper.

There's occasionally talk of being able to shut down a solid without destroying it by jettisoning the nozzle with ordnance, but that joint itself would be unsafe.
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Offline duane

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Re: Basic Rocket Science Q & A
« Reply #138 on: 03/25/2009 02:54 AM »
Along the side of the case.  It's a zipper.

There's occasionally talk of being able to shut down a solid without destroying it by jettisoning the nozzle with ordnance, but that joint itself would be unsafe.

Is this charge down a significant length of the SRB ?
Does this zipper cause it to break apart, and does this propellant continue to burn as it falls to splashdown ?

What the heck happens if they abort Ares I before, or shortly after clearing the tower ? Would you have a mass of solid rocket fuel burning on/near the pad til it was exhausted ? Even if the SRB was zipped open  ?
 
Thanks a bunch!
Duane

Offline TrueGrit

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Re: Basic Rocket Science Q & A
« Reply #139 on: 03/25/2009 02:54 AM »
I've also heard of a concept of blowing off the top of an "out of control" solid...  But the fact is that the nature are solids such that they don't go "out of control" in a standard sense.  They quickly transistion to and overpressure situation and blowup.  So while NASA claims the RSRBs don't blowup...  I'm having trouble believing them.