Author Topic: Basic Rocket Science Q & A  (Read 271758 times)

Offline deltaV

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Re: Basic Rocket Science Q & A
« Reply #560 on: 01/21/2011 06:20 AM »
I'm looking for a comparison of the operational and safety difficulties of nitrous oxide, hydrogen peroxide and liquid oxygen as oxidizers. If performance (e.g. density and specific impulse) isn't a distinguishing factor which would you rather deal with? Here are the principle safety issues that I'm aware of:
* Liquid oxygen is cryogenic.
* The decomposition of hydrogen peroxide is catalyzed by an inconveniently wide range of substances including various contaminants and human skin.
* An ignition source in gaseous nitrous oxide will cause catastrophic deflagration. Organics dissolved in liquid nitrogen may make it shock sensitive.

Hydrogen peroxide engines can be ignited easy by simply catalytically decomposing the peroxide before injection. Liquid oxygen doesn't allow any ignition shortcuts. Nitrous oxide is in between, with catalytic decomposition possible but only at high temperatures.

There's some discussion of hydrogen peroxide in the following post and in a few pages of posts before and after:
http://forum.nasaspaceflight.com/index.php?topic=13543.msg380864#msg380864

Webpages on hydrogen peroxide and nitrous oxide safety respectively:
http://www.solvaychemicals.us/static/wma/pdf/6/6/0/4/HH-2323.pdf
http://www.spg-corp.com/nitrous-oxide-safety.html

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #561 on: 01/21/2011 09:47 AM »
Heh, I've just been thinking about a related topic, triggered by a discussion on Paul Breed's blog.

Way out of the box presure system...
Is nitrous oxide safe?
Hybrid safety

I was thinking that using nitrous oxide as a pressurant for a storable oxidiser instead of as a (self pressurising) storable oxidiser itself might be a nice way to get the best of both worlds. And by using it as an oxidiser for a (continuously running?) torch igniter instead of a cat pack you might be able to add lots of stabilisers to the peroxide without getting into trouble with poisoning now unneeded peroxide cat packs. You could similarly use propane or acetylene to pressurise a storable fuel (although the vapour pressure of propane is a bit low), or use a diaphragm and pressurise it with the oxidiser or perhaps with a diaphragm and nitrous.

But the safety problems associated with nitrous oxide may make this uninteresting. On the other hand, peroxide has its own safety issues, and "there are no nice oxidisers". Which would be safer, liquid high test peroxide or gaseous nitrous oxide? Most of the time your nitrous would be liquid, but at engine cut-off it would be mostly gaseous. Still not a good time to go boom. On the other hand isn't nitrous used safely with acetylene welding torches? Some googling suggests that flashback arresters are standard practice for acetylene, but I haven't been able to find a nitrous compatible one. The ones I've seen explicitly warn they are not suitable for nitrous (and silane, both for unexplained reasons). On the other hand, the hybrid safety document I linked to above suggests a flashback arrester for nitrous should be easier than for most gases, because it has a larger quenching distance than typical fuel/air mixtures. One potential reason is that even the pure nitrous upstream of the arrester, being a monopropellant, is an explosion hazard whereas a pure fuel wouldn't be. But that reason doesn't apply to silane and doesn't take away from the larger quenching distance.
« Last Edit: 01/21/2011 09:49 AM by mmeijeri »
We will be vic-toooooo-ri-ous!!!

Offline Downix

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Re: Basic Rocket Science Q & A
« Reply #562 on: 01/26/2011 07:21 AM »
Satellites
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline MP99

Re: Basic Rocket Science Q & A
« Reply #563 on: 01/26/2011 07:50 AM »
Deep Space 1.

Dawn.

cheers, Martin  :)

Offline pathfinder_01

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Re: Basic Rocket Science Q & A
« Reply #564 on: 01/26/2011 08:56 AM »
One more probe to add. ESA's Smart 1.

Offline ugordan

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Re: Basic Rocket Science Q & A
« Reply #565 on: 01/26/2011 02:59 PM »
Hayabusa.

Offline kevin-rf

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Re: Basic Rocket Science Q & A
« Reply #566 on: 01/26/2011 03:14 PM »
Many GEO comsats for station keeping
If you're happy and you know it,
It's your med's!

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #567 on: 01/26/2011 11:51 PM »
GOCE, which is a pretty cool application of it - to overcome aero drag.
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 blue sky

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Re: Basic Rocket Science Q & A
« Reply #568 on: 01/28/2011 03:46 PM »
how can i find the detail about the current satellite that use electric thrusters? i need sources and i want to do a research about them.

Offline blue sky

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Re: Basic Rocket Science Q & A
« Reply #569 on: 01/28/2011 04:37 PM »
One more probe to add. ESA's Smart 1.
thanks. but i want the detail about these satellites.

Offline Jason1701

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Re: Basic Rocket Science Q & A
« Reply #570 on: 01/29/2011 01:44 AM »
Hello,

In my research I'm trying to optimize the path of my theoretical Centaur-based craft. This has led me to wonder how pitch programs are optimized for real rockets. Do the engineers just try a whole bunch of pitch kick time and delta-angle values and see which are the best? Would this need to be repeated if a mission required a new set of orbital parameters? Or is there a more analytic way to find a good pitch program?

Your help is much appreciated.
Jason

Offline Jorge

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Re: Basic Rocket Science Q & A
« Reply #571 on: 01/29/2011 02:23 AM »
Hello,

In my research I'm trying to optimize the path of my theoretical Centaur-based craft. This has led me to wonder how pitch programs are optimized for real rockets. Do the engineers just try a whole bunch of pitch kick time and delta-angle values and see which are the best? Would this need to be repeated if a mission required a new set of orbital parameters? Or is there a more analytic way to find a good pitch program?

Google "powered explicit guidance".
JRF

Offline scienceguy

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Re: Basic Rocket Science Q & A
« Reply #572 on: 02/06/2011 10:37 PM »
Hi there,

How thin does aluminum have to be for H2 boiloff to occur? How thick does it have to be to prevent N2 or O2 boiloff?
e^(pi)i = -1

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #573 on: 02/06/2011 10:41 PM »
Hi there,

How thin does aluminum have to be for H2 boiloff to occur? How thick does it have to be to prevent N2 or O2 boiloff?

You mean how thick to prevent boil off?

feet of aluminum

Offline scienceguy

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Re: Basic Rocket Science Q & A
« Reply #574 on: 02/06/2011 10:43 PM »
No, actually I wanted boiloff of hydrogen in this case. I just figured there would be lots of people on this forum who knew about this.

So it takes feet of aluminum, you say, to prevent N2 and O2 boiloff?
e^(pi)i = -1

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #575 on: 02/06/2011 10:58 PM »
Actually, there is always boil off.   Only active cooling would prevent boil off

Offline Scotty

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Re: Basic Rocket Science Q & A
« Reply #576 on: 02/06/2011 11:43 PM »
LH2 boiloff is a result of heat leaking into the tankage.
Bare aluminum will have a high boiloff, as aluminum is a very good thermal conductor.
To reduce boiloff, you have to reduce heat leakage into the tankage.
That is where foam insulation comes into play.

Offline sitharus

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Re: Basic Rocket Science Q & A
« Reply #577 on: 02/07/2011 01:48 AM »
Hi there,

How thin does aluminum have to be for H2 boiloff to occur? How thick does it have to be to prevent N2 or O2 boiloff?

As long as ambient temperature is above the boiling temperature of the liquid there will be boiloff. Insulation will help but insulation is never 100% effective, even in a vacuum flask there's still a path for heat conduction.

The only way to prevent boiloff is to alter the environment so the ambient temperature is below the boiling point. Generally this means increasing the pressure, which raises the boiling point..

Offline Nomadd

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Re: Basic Rocket Science Q & A
« Reply #578 on: 02/07/2011 02:13 AM »
No, actually I wanted boiloff of hydrogen in this case. I just figured there would be lots of people on this forum who knew about this.

So it takes feet of aluminum, you say, to prevent N2 and O2 boiloff?

 Not sure why you think thick aluminum would help. Aluminum is a pretty lousy insulator. That's why they make radiators out of it. Thicker would just give you more mass to warm the H2 and make boiloff worse to start.
« Last Edit: 02/07/2011 02:15 AM by Nomadd »

Offline Propforce

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Re: Basic Rocket Science Q & A
« Reply #579 on: 02/07/2011 02:40 AM »
No, actually I wanted boiloff of hydrogen in this case. I just figured there would be lots of people on this forum who knew about this.

So it takes feet of aluminum, you say, to prevent N2 and O2 boiloff?

 Not sure why you think thick aluminum would help. Aluminum is a pretty lousy insulator. That's why they make radiators out of it. Thicker would just give you more mass to warm the H2 and make boiloff worse to start.

You guys are not approaching this problem correctly.  You'll need to know what the boiling point of each gases you 1) want to boil off, and 2) to prevent from boiling off.  Then you'll have to ask what is the "heat source" coming into this "system"? Is it the sun radiation? on the ground? in space?  Finally, you'll need to ask what is my insuation system?  Is it a vaccuum-jacked dewar? MLI blankets?

In your case, LH2 boils off at -423 def. F, while the LO2 boils off at -297 deg. F and LN2 at -320 deg. F, So if you want to boil off LH2 while keeping LO2 & LN2 liquid, then depending on your 'system' and 'environment, you'll just need to keep the temperature in between -423 and -320 deg. F. You'll not only need to cool it down bt also able to draw heat away afterward.

The above numbers assume you're doing this at 1 atmosphere.  Different numbers if you are dong this at lower pressure.