Author Topic: Basic Rocket Science Q & A  (Read 277987 times)

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #200 on: 05/09/2009 08:03 PM »
Anything you're going to find publicly is also going to be very generic.  In the real world, every single one of these is going to be mission unique.

It's like the cone vs the black line in hurricane forecasting.  You seem to be trying to calculate a black line that's the same for every mission.  In reality, there are just bounds on what the rocket can do (the cone).  How it flies on launch day, the black line withing the cone, is subject to a long list of variables, requirements and optimizations of same.  Where one rocket might be flying a steady zero or non-zero alpha, another one would be pitching.  It's truly unique to each mission.

Antares
That is perhaps the very best example I have ever seen for any rocket's actual performance vs. its predicted performance.

One of the jokes about trajectories and COLA's is that the one trajectory that the LV is not going to fly is the predicted one

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #201 on: 05/12/2009 02:16 PM »
How much easier would it be to make a battleship inline version of the ET than the real thing? Assuming it would still have enough payload to launch an Orion to the ISS. Since J-130 payload is predicted to be around 60mT, you'd have more than 30mT to play with.
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Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #202 on: 05/12/2009 02:18 PM »
How much easier would it be to make a battleship inline version of the ET than the real thing? Assuming it would still have enough payload to launch an Orion to the ISS. Since J-130 payload is predicted to be around 60mT, you'd have more than 30mT to play with.

That is a Direct question

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #203 on: 05/12/2009 02:25 PM »
I was hoping for an unbiased answer.
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Offline ugordan

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Re: Basic Rocket Science Q & A
« Reply #204 on: 05/12/2009 02:31 PM »
It's still a Direct J-130 question and there's no logic in expecting an unbiased answer here only because it's a general thread.

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #205 on: 05/12/2009 02:32 PM »
Very well, I'll ask it there.
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Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #206 on: 05/13/2009 07:37 PM »
Would a kerosene/LOX upper stage be easier to reuse on orbit than a LH2/LOX stage?
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Offline kevin-rf

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Re: Basic Rocket Science Q & A
« Reply #207 on: 05/14/2009 02:07 PM »
Would a kerosene/LOX upper stage be easier to reuse on orbit than a LH2/LOX stage?

I think you have coking issues (carbon buildups) with hydrocarbons that will limit how many times the engine can be reused. LH/LOX does not have "that" issue. With time and money you can design arround any issue.
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Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #208 on: 05/14/2009 02:18 PM »
And for a wet workshop?
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Offline kevin-rf

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Re: Basic Rocket Science Q & A
« Reply #209 on: 05/14/2009 02:40 PM »
And for a wet workshop?

Good luck getting that Kerosene smell out of the workshop. On the plus side, the Kero tank is much smaller than the LOX tank, so if you only use the LOX tank it is not an issue. With an LH/LOX stage, you will have a much bigger "workshop" due to the low density of LH and the fact you can use both tanks.

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Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #210 on: 05/16/2009 02:31 AM »
Do RP engines have to be cleaned after the acceptance hot fire test?  If not, then I fail to see how coking would be an issue on a properly designed and operated engine.
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Offline Notriverse

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Re: Basic Rocket Science Q & A
« Reply #211 on: 05/17/2009 03:42 PM »
Hello to everyone, I ve got 2 questions... 1. How fast is a Satelit? 2. Why cant a satelit collide with another one?
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Offline Danny Dot

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Re: Basic Rocket Science Q & A
« Reply #212 on: 05/17/2009 06:21 PM »
Hello to everyone, I ve got 2 questions... 1. How fast is a Satelit? 2. Why cant a satelit collide with another one?

About 17,000 miles/hours or 25,000 feet/second -- for the ones in low earth orbit.  And they can and do collide with each other.  When they do they turn into many, many smaller pieces and it makes a bit mess.

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Re: Basic Rocket Science Q & A
« Reply #213 on: 05/17/2009 06:25 PM »
Hello to everyone, I ve got 2 questions... 1. How fast is a Satelit? 2. Why cant a satelit collide with another one?

1) http://en.wikipedia.org/wiki/Orbital_speed

2) Satellites can collide - 2 of them did just a few months ago with stories about them all over the media and online.

Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #214 on: 05/22/2009 12:24 AM »
I've been reading a bit about augmented hydrazine thrusters and the discussion seems to focus on monopropellant thrusters. Is there a fundamental reason why bipropellant hydrazine thrusters couldn't benefit from thrust augmentation through electrical heating?
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Offline Antares

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Re: Basic Rocket Science Q & A
« Reply #215 on: 05/22/2009 04:04 AM »
What kind of power requirements are we talking about?  Most spacecraft are pretty power-limited.  It would be a trade of battery mass, I assume, against propellant mass.  Or if the power was drawn straight off the panels, would it be an appreciable gain in satellite life?  Is that the application envisioned?
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Offline mmeijeri

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Re: Basic Rocket Science Q & A
« Reply #216 on: 05/22/2009 02:15 PM »
Well, the background was I was trying to see if there was anything you could do to increase the Isp of storables if you had plentiful power, say next to a solar power satellite. This would only make sense if you had medium thrust. You can already do 500-600 s Isp with arcjet thrusters and ammonia or hydrazine, but with very little thrust. And of course you can do high thrust with storables, but only with mediocre Isp.

I did some more googling and found that people have tried bipropellant arcjet thrusters, but that there are problems with soot deposition. This wouldn't be a problem with hydrazine as a fuel, just with MMH or UDMH, but there may be other reasons why it's not done with hydrazine.
« Last Edit: 05/22/2009 02:25 PM by mmeijeri »
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Offline duane

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Re: Basic Rocket Science Q & A
« Reply #217 on: 05/24/2009 02:59 AM »
Got a crazy question that may have been answered already.

It's regarding the technology and manufacturing capability of private rockets capable of placing objects in orbit. Namely SpaceX's Falcon 1

My question is how much of a step up in technology or avionics etc would need to go into the rocket system to convert it to a small ICBM ?  I understand the guidance and rentry system would need to built/upgraded.

Just musing about how dangerous the technology, plans etc of these private rockets are if they fall into the hand of states such as Iran, Syria etc.. ?

Or is it a order of magnitude more difficult to get a ICBM working ?

Thanks for any high level insight on this.

Thanks a bunch
Duane
« Last Edit: 05/24/2009 03:00 AM by duane »

Offline StarStuff

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Re: Basic Rocket Science Q & A
« Reply #218 on: 05/24/2009 09:11 AM »
The first ICBMs were built using '40s and '50s technology, then it was a step up to man-rated rockets.

Offline Jim

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Re: Basic Rocket Science Q & A
« Reply #219 on: 05/24/2009 01:52 PM »

My question is how much of a step up in technology or avionics etc would need to go into the rocket system to convert it to a small ICBM ?

None.  A space launch vehicle is just a ICBM with longer range.