Author Topic: Basic Rocket Science Q & A  (Read 271771 times)

Offline Nikola

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Re: Basic Rocket Science Q & A
« Reply #160 on: 03/29/2009 03:15 AM »
The cube/square relationship of volume to surface area means that smaller LVs have higher aero losses. You get similar effects with the minimum gauge of materials.

That's true - smaller LV will have higher relative air drag. Can you, please, give some example of the effects that appear "with the minimum gauge of materials"? That's what interest me the most.

For example if you reduce the dimensions of a fuel tank by half and reduce the thickens of walls by half, tank will still have same mass fraction. I would guess this is example where scaling is possible. I don't have any experience in building rocket hardware so I could be wrong.

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #161 on: 03/29/2009 03:16 AM »
Danny, if you or anyone else would like, I could port that code to C, C++, or Java, since some people might find it easier to read or use that way. I was thinking of doing that anyway, since I'm one of those who, despite having started with QB, finds C-like languages more readable, but it occurred to me that others might find such a translation useful...

c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)
Danny Deger

Offline Oberon_Command

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Re: Basic Rocket Science Q & A
« Reply #162 on: 03/29/2009 04:00 AM »
Slightly off-topic:
Once upon a time, I thought the same as you... then I actually switched to C, used it for a few years, and I came to see the beauty and simplicity in single-character braces as opposed to constantly capitalized potential polysyllabic keywords (woo, alliteration!), shorter type-names, and always declaring your variables before using them. Then again, I do find myself working with regular expressions from time to time, which are of a whole order less readable than BASIC or C... :P

This is not to say that beautiful BASIC code is impossible, or that ugly C-syntax code is impossible. Idiomatic C++ is particularly hard on the eyes at times, for sure.

I'll do that port tomorrow, then, when I have more caffeine in my system.
« Last Edit: 03/29/2009 04:04 AM by Oberon_Command »

Offline strangequark

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Re: Basic Rocket Science Q & A
« Reply #163 on: 03/29/2009 06:40 AM »
Steven,

Thanks for reminding me about HTP. I might have to think about acquiring some for my garage project. The catalytic decomposition eases ignition, and it doesn't have any nitrogen in it to murder your Isp.

Be very, very careful!   

HTP is catalyzed by a lot of organic sustances, including leather and human skin. Have plenty of water around to dilute any spills and a shower for any one exposed.  Never work alone as the pain from exposure can prevent someone from treating themself.

IIRC, an amateur rocketry enthusiast died a couple of years ago working with HTP.

Do plenty of research.

Definitely planning on it. I have a few brains at KSC I will likely pick, regarding general safety practices with strong oxidizers. Might invest in something like a butyl coverall if I do go through with it. The "hypergolic with test engineers" issue is definitely not to be taken lightly.  ;)
Don't flippantly discount the old rules of this industry. Behind each one lies a painful lesson learned from broken, twisted hardware. Learn those lessons, and respect the knowledge gained from them. Only then, see if you can write new rules that will meet those challenges.

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #164 on: 03/29/2009 12:05 PM »
The "hypergolic with test engineers" issue is definitely not to be taken lightly.  ;)

"Peroxides kill chemists" is another warning I've heard.
We will be vic-toooooo-ri-ous!!!

Online hop

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Re: Basic Rocket Science Q & A
« Reply #165 on: 03/29/2009 10:34 PM »
That's true - smaller LV will have higher relative air drag. Can you, please, give some example of the effects that appear "with the minimum gauge of materials"? That's what interest me the most.
Described here as:
Quote
Note also that to get high mass ratios you need BIG rocket ships. That follows because there are minimum weights to many rocket parts. This is known as 'minimum gauge', meaning that you can't make it any thinner or lighter. Combustion chambers have to be rugged. Pipes must be thick enough to hold pressures that don't get smaller just because you're trying to make a small sized rocket.
But this is sort of specialized case of a larger issue: A lot of things just don't scale arbitrarily. See 3-5 here http://www.av8n.com/physics/scaling.htm#htoc14

For rockets, engine cooling is a good example: You need to cool the surface area of your combustion chamber, but propellant flow scales by volume. Small engines are harder to cool.
Quote
For example if you reduce the dimensions of a fuel tank by half and reduce the thickens of walls by half, tank will still have same mass fraction.
Tank mass does scale roughly with volume over a fairly large range (see http://yarchive.net/space/launchers/fuel_tank_scaling_laws.html ), but at extremes other things would start to take over.

strangequark:
If you haven't already, I suggest you read armadillos update archives. They did quite a lot with H2O2.

Offline kkattula

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Re: Basic Rocket Science Q & A
« Reply #166 on: 03/30/2009 05:48 AM »

...
strangequark:
If you haven't already, I suggest you read armadillos update archives. They did quite a lot with H2O2.


NB:  Armadillo started with HTP then moved to a 'mixed mono-prop' of 50% conc. H2O2 mixed with Methanol. (in a 92%:8% mixture IIRC).

50% conc. H2O2 mixed with Methanol is fairly stable, but tricky to decompose.

HTP mixed with Methanol tends to DETONATE (not just decompose) if you look at it wrong.
« Last Edit: 03/30/2009 05:48 AM by kkattula »

Offline sbt

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Re: Basic Rocket Science Q & A
« Reply #167 on: 03/30/2009 07:10 PM »
Danny, if you or anyone else would like, I could port that code to C, C++, or Java, since some people might find it easier to read or use that way. I was thinking of doing that anyway, since I'm one of those who, despite having started with QB, finds C-like languages more readable, but it occurred to me that others might find such a translation useful...

c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

And, if you don't object, I'll have a bash at putting it into Python.

Any particular wishes concerning a licence to be attached? Otherwise I'll tag it as being GPL which will keep your name attached and prevent somebody rolling it into their commercial product yet allow others to make improvements.

Rick
I am not interested in your political point scoring, Ad Hominem attacks, personal obsessions and vendettas. - No matter how cute and clever you may think your comments are.

Offline Steven Pietrobon

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Re: Basic Rocket Science Q & A
« Reply #168 on: 03/31/2009 04:03 AM »
Checkout Peroxide Propulsion which has rocket grade HTP at 80%, 85% and 90% concentration.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #169 on: 03/31/2009 07:21 AM »
Danny, if you or anyone else would like, I could port that code to C, C++, or Java, since some people might find it easier to read or use that way. I was thinking of doing that anyway, since I'm one of those who, despite having started with QB, finds C-like languages more readable, but it occurred to me that others might find such a translation useful...

c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

And, if you don't object, I'll have a bash at putting it into Python.

Any particular wishes concerning a licence to be attached? Otherwise I'll tag it as being GPL which will keep your name attached and prevent somebody rolling it into their commercial product yet allow others to make improvements.

Rick

Thanks for asking.  Sounds like a good idea.  Is that what GNU does to their code?

Danny Deger
Danny Deger

Offline vt_hokie

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Re: Basic Rocket Science Q & A
« Reply #170 on: 03/31/2009 04:06 PM »
c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

I never liked C, but then I never really used it beyond an intro course in college.  Hate to say it, but I haven't really done any programming since my FORTRAN 77 days in school! 
« Last Edit: 03/31/2009 04:06 PM by vt_hokie »

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #171 on: 03/31/2009 04:16 PM »
c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

I never liked C, but then I never really used it beyond an intro course in college.  Hate to say it, but I haven't really done any programming since my FORTRAN 77 days in school! 

So you should do fairly well with both POST and OTIS code.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline William Barton

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Re: Basic Rocket Science Q & A
« Reply #172 on: 03/31/2009 04:25 PM »
c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

I never liked C, but then I never really used it beyond an intro course in college.  Hate to say it, but I haven't really done any programming since my FORTRAN 77 days in school! 

I saved my Fortran text for years, though what box it's in now... probably the same box as the Prolog, Pascal, and LISP books. I do most of my work with Visual Studio, these days, so that means C#, which is charitably described as "C-flavored."

Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #173 on: 03/31/2009 04:43 PM »
c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

I never liked C, but then I never really used it beyond an intro course in college.  Hate to say it, but I haven't really done any programming since my FORTRAN 77 days in school! 

I saved my Fortran text for years, though what box it's in now... probably the same box as the Prolog, Pascal, and LISP books. I do most of my work with Visual Studio, these days, so that means C#, which is charitably described as "C-flavored."

Oh - now I 'C'. (grin)

You may find this a little strange, but I actually prefer VB. It's very conversational and sufficiently structured that I can do just about anything I want. Of course C is more powerful; it's just not as much fun. Plus most Macro applications for Window-based software is executed by VB. Makes it convenient to be conversant with it.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline sbt

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Re: Basic Rocket Science Q & A
« Reply #174 on: 03/31/2009 07:05 PM »

And, if you don't object, I'll have a bash at putting it into Python.

Any particular wishes concerning a licence to be attached? Otherwise I'll tag it as being GPL which will keep your name attached and prevent somebody rolling it into their commercial product yet allow others to make improvements.

Rick

Thanks for asking.  Sounds like a good idea.  Is that what GNU does to their code?

Danny Deger

Yes. There are a few variations on a theme. The LGPL (also GNU) is the main one - which allows inclusion into commercial products as a stand alone library.

There are lots of small variations, if you really want to get deep into things.

Two reasonably simple comparisons (assuming you want to be Open Source)

http://itmanagement.earthweb.com/osrc/article.php/12068_3803101_2/Bruce-Perens-How-Many-Open-Source-Licenses-Do-You-Need.htm

http://developer.kde.org/documentation/licensing/licenses_summary.html

Really deep and 'political':

http://www.gnu.org/philosophy/license-list.html

Personally I would have to have a very good reason to licence something that was my creation (and mine alone) as anything other than GPL. But this is a port of your code so you get to choose.

Anyway - back to the Rockets...

Rick
I am not interested in your political point scoring, Ad Hominem attacks, personal obsessions and vendettas. - No matter how cute and clever you may think your comments are.

Offline butters

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Re: Basic Rocket Science Q & A
« Reply #175 on: 05/04/2009 05:36 PM »
Are there any general guidelines for sizing diameter versus length for a cylindrical ELV with a given LEO payload capacity, specific impulse, and propellant density?


Suppose you wish to launch a payload with a relatively large diameter for its mass.  Would it be better to launch it in a fat PLF on a skinnier LV or to launch it on a relatively short and squat LV that matches the PLF?


In other words, is there a "golden aspect ratio" for earth-launched rockets, and to what extent does the diameter of the payload affect the optimal diameter of the rocket?

Offline mdo

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Re: Basic Rocket Science Q & A
« Reply #176 on: 05/06/2009 10:53 AM »
Are there any general guidelines for sizing diameter versus length for a cylindrical ELV with a given LEO payload capacity, specific impulse, and propellant density?


Suppose you wish to launch a payload with a relatively large diameter for its mass.  Would it be better to launch it in a fat PLF on a skinnier LV or to launch it on a relatively short and squat LV that matches the PLF?

- drag is proportional to frontal area per lift-off mass

- this ratio improves with rocket mass; for Shuttle sized vehicles it becomes negligible - Orbiter, Tank, SRBs fully exposed; only small sounding rockets need to be tall

- spherical tanks have the best volume/weight ratio

- constant cylindrical LV diameter has two advantages
1. PLF is lighter; it need not reach inwards to skinny rocket body
2. less turbulent air flow

- payload dimensions vary; so adapt the LV to a certain mass and adapt the fairing to individual volume requirement

Quote
In other words, is there a "golden aspect ratio" for earth-launched rockets, and to what extent does the diameter of the payload affect the optimal diameter of the rocket?

Don't know about golden rules:
Suggest to let the denser one of the two fuel/oxidizer 2nd (upper) stage components drive the diameter of its spherical tank. The other three tanks of upper and core stage will be more cylindrically elongated corresponding to their larger volumes. The 4 tank stack gives a rough estimate of length to diameter ratio for a given propellant.

Mind you, I do not build these things myself; others please correct or expand on solid propellants.

Apropos, some say the SRB was designed by a horse's ass:
http://greyhorsematters.blogspot.com/2009/04/interesting-history-lesson.html

edit: typo
« Last Edit: 05/08/2009 06:36 AM by mdo »

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #177 on: 05/07/2009 07:13 PM »
Rule of thumb for solid motor length:diameter seems to be 12:1.
If I like something on NSF, it's probably because I know it to be accurate.  Every once in a while, it's just something I agree with.  Facts generally receive the former.

Offline mdo

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Re: Basic Rocket Science Q & A
« Reply #178 on: 05/08/2009 06:28 AM »
What is the desired angular change to the flight path achieved by the pitch maneuver performed after clearing the launch tower?

What are typical pitch angles for current LVs such as Atlas V, Ariane 5 etc.?

Offline William Barton

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Re: Basic Rocket Science Q & A
« Reply #179 on: 05/08/2009 07:18 AM »
c might be useful to many out there.   Lot is c code in the world today.  By the way, you must be a really strange dude if you think c is inherently more readable than QB ;-)

I never liked C, but then I never really used it beyond an intro course in college.  Hate to say it, but I haven't really done any programming since my FORTRAN 77 days in school! 

I saved my Fortran text for years, though what box it's in now... probably the same box as the Prolog, Pascal, and LISP books. I do most of my work with Visual Studio, these days, so that means C#, which is charitably described as "C-flavored."

Oh - now I 'C'. (grin)

You may find this a little strange, but I actually prefer VB. It's very conversational and sufficiently structured that I can do just about anything I want. Of course C is more powerful; it's just not as much fun. Plus most Macro applications for Window-based software is executed by VB. Makes it convenient to be conversant with it.



I don't find it strange at all. When you're working in a tool like Visual Studio, the difference between the languages is a matter of style more than anything else, and if inaccurate Microsoft would rationalize the .Net object model, the differences would be negligible. I sell VB code to my clients along with their projects, based on the theory they can have it maintained by bottom feeders if need be, and will never have trouble finding a programmer if they need one and I'm not available anymore (or they've decided I'm too annoying for the money I charge). There's really nothing you can do in C# you can't do in VB, so the main advantage of C# is, I get to charge more.

I would love to get my hands on some of the flight software for modern LVs and spacecraft. I'm sure I could have no end of fun with it.

Footnote: another posting intervention! When I type i-d-i-o-t (without the spaces," it rendered as "inaccurate." (Idiot?)
« Last Edit: 05/08/2009 07:21 AM by William Barton »