Author Topic: Basic Rocket Science Q & A  (Read 281887 times)

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #280 on: 06/01/2009 01:30 AM »
Seems to me that making all those incremental steps and designing for missions that do not exist would be awfully, awfully expensive.

Likely expensive, don't know about awfully expensive. Constantly flight-certifying new designs would certainly take a lot of effort. I suspect this is a major difference with software development, where most of the equivalent of that can be automated. On the plus side: you'd get really good at it and the guys doing it would have plenty of job security. :)

But the real point is that the individual steps would be much smaller than the existing steps. One or more steps could happen every election cycle. Is there anyone here who believes Ares I + Orion will fly before Obama leaves office? Each step could be undertaken in much less time, with less risk and with a much lower yearly budget. It's yearly budgets and near-term milestones politicians and the public care about. Total amounts, who cares?

Quote
Some of those steps (for instance, "use composites") should come at the very beginning, and others ("- switch to deeply throttleable engine, add landing gear, extend flight software for landings - lunar surface missions") would be better left to a vehicle designed for that mission when the requirement arose, rather than try to cut-and-paste existing into a frankenship.

Yeah, the idea was to have the single ship evolve into a separate Altair, Orion and perhaps a hypergolic (and later cryogenic) small (and later large) EDS. Much like different species evolve from a common ancestor. The stretch limo was an intermediate step, likely destined to be preserved in the fossil record only. The idea is to get from an SDLV + Orion but without an upper stage to a lunar architecture in small steps, with every step being a working system and leading to increased capability or performance. The NEO mission for instance is there in order to be able to do something useful with only a subset of the systems required for a lunar landing.
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Offline mrskyking737

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Re: Basic Rocket Science Q & A
« Reply #281 on: 06/03/2009 02:47 AM »
I have a question about reentry heating that can't seem to find easily, and have no rocketry background.  Forgive me if the question turns out to be stupidly easy. 

I was thinking about how orbital vehicles need to withstand several thousand degrees during reentry, but suborbital vehicles do not.  I don't have any way to quantify how fast is too fast to not need TPS protection. 

I understand that the White Knight reached 367k and mach 3.09 on it's first flight without anything special in regard to it's construction.  Could the same craft with increased duration been able to handle mach 4 and 367k?  Mach 6 and 450k?  How much is too much for simple aircraft materials to be able to handle the heat? 

How can we figure out in simple fashion where any given speed & corresponding given altitude will experience a certain calculated amount of heat? 

Dave

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #282 on: 06/03/2009 03:56 AM »
Heat is a function of shape, altitude and speed.  Too complex for be reduced to a table.

Offline veryrelaxed

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Re: Basic Rocket Science Q & A
« Reply #283 on: 06/03/2009 04:35 AM »
Jim's response is correct.  Thermal loads, as well as the G-loads are complex...  Here *duration* is also important as in any G-load analysis.  The question should be framed "this many Kelvins/Centigrade" *for how long*, and *how even a distribution across the heat absorbing components*?  For example STS due to the higher Lift/Drag ratio provides lower Kelvins but higher durations (especially on the leading edges of the structure) , while lower L/D shapes* provide higher absolute heat loads but for shorter durations... What is 'better'.  It is a complex analysis of trade-offs.

*like capsules or lifting bodies
« Last Edit: 06/03/2009 04:38 AM by veryrelaxed »

Offline DMeader

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Re: Basic Rocket Science Q & A
« Reply #284 on: 06/03/2009 01:01 PM »
I understand that the White Knight reached 367k and mach 3.09 on it's first flight without anything special in regard to it's construction. 

SS1, not White Knight.

Offline fredm6463

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Re: Basic Rocket Science Q & A
« Reply #285 on: 06/05/2009 05:41 PM »
Does any one know how NASA obtains the hydrogen and oxygen it uses to  fill the Space Shuttle's External Tank.

What process is involved and specifically what devices are used to separate the two elements? And does NASA do it or is it done by a contractor?

Thanks.
« Last Edit: 06/05/2009 05:43 PM by fredm6463 »

Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #286 on: 06/05/2009 06:01 PM »
The hydrogen is produced by Air Products, I think, near New Orleans, by cracking hydrocarbons IIRC, then trucked in.  Fun fact: NASA couldn't get hydrogen after Katrina because Homeland Security took over distribution of LH2 since it's used in food production (look for partially hydrogenated whatever in your ingredients).

The oxygen is produced in Mims, FL, in a typical air separation unit.  Praxair, I think.

Suggest moving this to the Shuttle or basic rocket science Q&A thread.
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Offline fredm6463

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Re: Basic Rocket Science Q & A
« Reply #287 on: 06/05/2009 06:39 PM »
thank you

Offline padrat

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Re: Basic Rocket Science Q & A
« Reply #288 on: 06/05/2009 06:51 PM »
The hydrogen comes from steam-reforming natural gas. Actually, after Katrina, we gave most of our hydrogen back to Air Products because Katrina shut down their New Orleans plant for a while at the same time their Canadian plant was down for maintenance, so they didn't have any for their other customers.
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Offline clongton

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Re: Basic Rocket Science Q & A
« Reply #289 on: 06/05/2009 07:30 PM »
Just thinking outside the box here but wouldn't it be *forward looking* if there were a THORIUM (not uranium) nuclear power plant nearby that generated electricity, drew in seawater, and then used some of that electricty to distill and crack the purified water into hydrogen and oxygen gasses? Send the remaining electricity into the grid and send the gasses off to be liquified, maybe even on site at KSC.

Thorium generators (molten salt coolant) can't "melt down" and do not produce any byproducts that can be reprocessed into weapons grade material. And thorium byproduct half lives are extremely short, unlike uranium.

Just musing. Returning you now to your regular programming.
« Last Edit: 06/05/2009 07:32 PM by clongton »
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Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #290 on: 06/26/2009 04:28 AM »
All things being equal, where is the aerodynamic center of a rocket?
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 whitewatcher

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Re: Basic Rocket Science Q & A
« Reply #291 on: 06/30/2009 12:39 PM »
1.) I would like to do a WSB transfer from LEO to LLO.

To which extent is the delta-v and the travel time dependant on inclination of departure/destination orbit?

2.) Are there WSB transfers from LLO to LEO? Where can I find information on that subject? (delta-v's, travel times)

3.) Which transfer options are there for travel between EML-1 andd EML-2?
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Offline Bob the Avenger

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Re: Basic Rocket Science Q & A
« Reply #292 on: 06/30/2009 05:55 PM »
WSB meaning Weak Stability Boundary?
If so I'd suggest you start with "Fly Me to the Moon" by Edward Belbruno. Its an excellent introduction to how ballistic capture orbits work, but for more indepth information, he has written "Capture Dynamics and Chaotic Motions in Celestial Mechanics: With Applications to the Construction of Low Energy Transfers" which I haven't read so I dont know how much thats got in it that you're looking for.
If I remember the basics of it all correctly (big if), then the chaotic nature of the orbits that it utilises means you need to simulate the transfer in reverse, i.e. you start with the object in orbit around the moon(-ish) and you 'run time backwards' in the simulation, and see where it ends up.

I hope that helps, if not, then sorry.


Offline irex31i

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Re: Basic Rocket Science Q & A
« Reply #294 on: 06/30/2009 07:10 PM »
Thanks a lot guys.. I have been reading this forum for a long while now. i hold a degree in electronics and am working in a small research company.. I just wanted to appear for the interview at indian space research org. Can someone please guide me about the questions.. i was reading some interview questions here about radio and rf. Pls i need more.. can you suggest some books.. thanks in advance..
« Last Edit: 07/01/2009 06:52 AM by irex31i »

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #295 on: 06/30/2009 07:19 PM »
All things being equal, where is the aerodynamic center of a rocket?

Is the rocket in or out of control?   ::)

On an aircraft wing, aerodynamic center is the point on the wing that the pitching moment is NOT a function of the angle of attack.  It needs to be aft of the center of gravity for the "aircraft" to be stable.

I'm not sure it is even used on rockets, because they don't have wings.  They mostly use the point that the pitching moment is zero.  This is called the center of pressure. 

For a layman, mixing the two terms up is probably OK.  Might even be OK for a pilot.  But an engineer MUST know the difference to do his or her job.

Danny Deger
« Last Edit: 06/30/2009 07:27 PM by Danny Dot »
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Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #296 on: 06/30/2009 07:21 PM »
All things being equal, where is the aerodynamic center of a rocket?

In the center of its longitudinal area projection.

Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #297 on: 06/30/2009 07:26 PM »
All things being equal, where is the aerodynamic center of a rocket?

In the center of its longitudinal area projection.

I think that is center of pressure.

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Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #298 on: 06/30/2009 10:17 PM »
All things being equal, where is the aerodynamic center of a rocket?
In the center of its longitudinal area projection.
I think that is center of pressure.

You're both right.  For an airfoil, the rule of thumb is quarter-chord subsonic, half-chord supersonic.  Just wondering if there was an analogue for rockets, without airfoils.

Which would be like a plane with no wings, which would be a fuselage.  Except this would be a variable area fuselage... I think I answered my own question.
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 Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #299 on: 07/01/2009 12:27 AM »
All things being equal, where is the aerodynamic center of a rocket?
In the center of its longitudinal area projection.
I think that is center of pressure.

You're both right.  For an airfoil, the rule of thumb is quarter-chord subsonic, half-chord supersonic.  Just wondering if there was an analogue for rockets, without airfoils.

Which would be like a plane with no wings, which would be a fuselage.  Except this would be a variable area fuselage... I think I answered my own question.

With no fins the center of pressure would be in the middle.  Thus the need to add fins to shift it aft.  But most modern rockets are not aerodynamically stable, by are stabilized by moving the thrust.

Danny Deger
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