Author Topic: Basic Rocket Science Q & A  (Read 270761 times)

Offline Patchouli

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Re: Basic Rocket Science Q & A
« Reply #580 on: 02/07/2011 02:45 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.

Aluminum actually is one of the best thermal conductors there is though there are better ones which is why it makes pretty good cookware and engine heads.
http://en.wikipedia.org/wiki/Thermal_conductivity
Very thick aluminum would act like a heat pipe which is why they make CPU heat sinks from it.
« Last Edit: 02/07/2011 02:49 AM by Patchouli »

Offline scienceguy

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Re: Basic Rocket Science Q & A
« Reply #581 on: 02/07/2011 04:40 AM »
Thanks for all the responses! Actually what I will have is an almost vacuum compartment with cold hydrogen in it, the hydrogen of which I want to pass into another vacuum compartment with minimal spillage back into the first compartment. That's why I was wondering if I could just use an aluminum barrier. Also, this second compartment will be exposed to air on the outside of another barrier, and I want to keep O2 and N2 out while I build up cold H2 in it, for later use in a third compartment.

(please see attached diagram)
e^(pi)i = -1

Offline JayP

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Re: Basic Rocket Science Q & A
« Reply #582 on: 02/07/2011 04:03 PM »
It looks like you want some sort of molecular sieve as your barrier. That won't work in a one way application like you have laid out. You need a line between the two compartments with a check valve to prevent back flow or you could incrrease the preasure in the first compartment to something higher that the second compartment to ensure constant flow.

Offline Jason1701

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Re: Basic Rocket Science Q & A
« Reply #583 on: 02/09/2011 01:09 AM »
Thanks Jorge.

That got me wondering, would there be any need for a pitch maneuver if the rocket had some initial velocity at less than a 90-degree angle? In other words, could one select an initial velocity and angle that (with an engine burn) could place the vehicle in orbit following a gravity turn from the very start?

Offline Jorge

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Re: Basic Rocket Science Q & A
« Reply #584 on: 02/09/2011 03:28 AM »
Thanks Jorge.

That got me wondering, would there be any need for a pitch maneuver if the rocket had some initial velocity at less than a 90-degree angle? In other words, could one select an initial velocity and angle that (with an engine burn) could place the vehicle in orbit following a gravity turn from the very start?

Probably wouldn't be a good idea on Earth. The vertical rise is necessary to get above some of the Earth's thick atmosphere before starting the gravity turn. Otherwise max-Q is too high. You could do it if you beefed up the rocket's structure to withstand higher max-Q, but what would be the point? To avoid an extra guidance phase in the software? That's not a good trade; bits are cheaper than metal.
JRF

Offline Danderman

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Re: Basic Rocket Science Q & A
« Reply #585 on: 03/11/2011 02:49 PM »
What is the difference between the usual S-Band transponder that launch vehicles use, and the usual S-Band transponder used by satellites? Are these indeed different models, and if so, why?

I am guessing that rocket transponders are very high power, whereas satellite transponders are low power.

Offline baldusi

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Re: Basic Rocket Science Q & A
« Reply #586 on: 04/19/2011 09:04 PM »
This might have been answered hundreds of times. But I couldn't find my exact question. The issue is hammerheads. I understand that it all depends on the aerodynamics and rockets are not legos. But my question is. Let's suppose we have two TSLV. The first is 3.8m wide all the way. The second is 3.8m on the first stage and 5.2m on the second stage. Would it be easier, on the general case, to put a (just for the sake of it) 6.6m on the one with the 5.2m? In other words, the closer you get the general profile to a drop, the easier to increase the widest diameter at the top?

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #587 on: 04/20/2011 02:01 AM »
Probably, but aero is highly non-linear.  Look up stuff about area ruling (transonic drag) and center of pressure.  Acoustics are an issue too.
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Offline baldusi

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Re: Basic Rocket Science Q & A
« Reply #588 on: 05/05/2011 06:23 PM »
I've read that the RD-0120 development used more than 105 prototypes and test engines. Is that a normal number? I thought the plan of the J-2X has something like 10 to 20.

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #589 on: 05/05/2011 07:25 PM »
No, it's very much in the single digits in a modern engine program.  Frequently those are rebuilt as development goes on and improvements are made.
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Offline baldusi

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Re: Basic Rocket Science Q & A
« Reply #590 on: 05/05/2011 07:32 PM »
So, they might have count each rebuilt and new piece put together as a different engine? I do recall that they had something close to 106,000s of test by that time.

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #591 on: 05/06/2011 02:11 AM »
Hard to say for certain.  Usually the engine serial number follows a certain major component of the engine (every engine I can think of does this).  Then, some part of the serial number is incremented when a rebuild occurs (2 engines I can think of DON'T do this).  If they just change out minor components or remachine something, maybe neither increment or maybe they count it as a whole new engine.  Hard to say without seeing records and the source of 105 for the 0120.
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 Danderman

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Re: Basic Rocket Science Q & A
« Reply #592 on: 05/12/2011 07:37 PM »
For rockets where the 2nd stage engine is housed inside the 1st stage prop tanks, how exactly does the engine leave the tank during staging? Is the prop tank blown up?

Offline LegendCJS

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Re: Basic Rocket Science Q & A
« Reply #593 on: 05/12/2011 07:59 PM »
For rockets where the 2nd stage engine is housed inside the 1st stage prop tanks, how exactly does the engine leave the tank during staging? Is the prop tank blown up?

Do you know of a rocket where the second stage engine is immersed in the fuel of the first stage tanks before staging?  Don't you mean inter-stage volume?
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Offline kevin-rf

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Re: Basic Rocket Science Q & A
« Reply #594 on: 05/13/2011 01:48 AM »
I believe it was one of the concepts tspace was looking at.
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Offline Danderman

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Re: Basic Rocket Science Q & A
« Reply #595 on: 05/13/2011 04:55 AM »
For rockets where the 2nd stage engine is housed inside the 1st stage prop tanks, how exactly does the engine leave the tank during staging? Is the prop tank blown up?

Do you know of a rocket where the second stage engine is immersed in the fuel of the first stage tanks before staging?  Don't you mean inter-stage volume?

Sorry, I forgot to add the word "nozzle" in there, so the nozzle is in the lower stage prop tank.

Its quite common.

Offline sitharus

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Re: Basic Rocket Science Q & A
« Reply #596 on: 05/13/2011 05:02 AM »
For rockets where the 2nd stage engine is housed inside the 1st stage prop tanks, how exactly does the engine leave the tank during staging? Is the prop tank blown up?

Do you know of a rocket where the second stage engine is immersed in the fuel of the first stage tanks before staging?  Don't you mean inter-stage volume?

Sorry, I forgot to add the word "nozzle" in there, so the nozzle is in the lower stage prop tank.

Its quite common.


So the nozzle of the second stage forms part of the pressure structure of the first stage? I don't think I've ever seen such a design...

Offline Danderman

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Re: Basic Rocket Science Q & A
« Reply #597 on: 05/13/2011 06:46 AM »
For rockets where the 2nd stage engine is housed inside the 1st stage prop tanks, how exactly does the engine leave the tank during staging? Is the prop tank blown up?

Do you know of a rocket where the second stage engine is immersed in the fuel of the first stage tanks before staging?  Don't you mean inter-stage volume?

Sorry, I forgot to add the word "nozzle" in there, so the nozzle is in the lower stage prop tank.

Its quite common.


So the nozzle of the second stage forms part of the pressure structure of the first stage? I don't think I've ever seen such a design...

No, the nozzle extends into the first stage prop tank, saving loads of interstage area.

Offline yinzer

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Re: Basic Rocket Science Q & A
« Reply #598 on: 05/13/2011 07:56 AM »
Linear shaped charge around the circumference of the tank just below the upper dome, I'd imagine.  Not much different than cutting an interstage with an LSC, just stiffened sheet metal. Might be a pain to not have a pressurant diffuser or pressure relief valve at the very top of the tank, but that should be workable.

Maybe a plug in the throat of the upper stage engine that gets blown out during ignition.

I doubt anyone who actually knows will tell you given that the biggest use of this technique is making a missile short enough to fit in a silo or launch tube, thus ITAR.
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Offline kevin-rf

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Re: Basic Rocket Science Q & A
« Reply #599 on: 05/13/2011 01:15 PM »
I believe it was one of the concepts tspace was looking at.

Went and looked it up, got the wrong new space company. It was Airlaunch llc.

http://www.airlaunchllc.com/

It was part of the proposed "falcon". A two stage pressure fed Lox/Propane rocket dropped out of a C-17.

Look at the January 13th press release to see a nozzle extraction test. http://www.airlaunchllc.com/News.htm

A collage with a picture of the test.
http://www.airlaunchllc.com/AirLaunch%20Phase%202B%20Milestones%201&2%20Photos.pdf

My memory is fading, but I thought they also released a video of the test at the time.
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