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Two Stage to Orbit

Posted by: campbelp2002 - Fri Nov 11, 2005 5:22 am
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Two Stage to Orbit 
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Post    Posted on: Tue Nov 29, 2005 8:06 pm
Ooh, but then you get to deal with the FAA, who are loath to admit that there is any place above God's Green Earth that they do not have some measure of control over.

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Post Re: My 2 bits   Posted on: Wed Nov 30, 2005 4:34 am
SawSS1Jun21 wrote:
... The trouble with VTVL rockets is not that you can't make them big enough, it's that you can't use them easily enough. Ask Musk...


Why ask Musk? He's not trying VTVL. He is trying VTSSHIDS. *

Ask Carmack, he can test several times a day.

The advantage of an Armadillo style VTVL is frequent, incremental, flight testing. You don't have to be perfect for the whole flight profile the first time you fly. Your first flights are low altitude hovers, then you expand the envelope. This gives you confidence and lots of experience by the time you launch to orbit.

Not that I don't think Musk is doing a great job. For a traditional 2 stage, he's setting a new standard.

* (Vertical Takeoff Sea Splashdown, Hope It Doesn't Sink)


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Post    Posted on: Wed Nov 30, 2005 5:04 am
campbelp2002 wrote:
In the VTVL scenario there is no reason to stay with a low separation velocity. That constraint is to allow a reasonably cheap winged, air breathing launch aircraft. You can easily (well, more easily) get a higher velocity separation from a rocket powered first stage.


There are a few reasons. The first stage should be optimized to get out of the effective atmosphere on a ballistic path that will stay out for a while, and give a head start on orbital velocity. More velocity is better, but not if it increases expense & complexity, while decreasing margins. Also the faster/higher it goes, the more heating during re-entry, and the further it will travel down range.

The first stage can be big, strong, simple and inexpensive, because it doesn't have to do too much. With moderate flight rates, the one I described might cost less than $1 million per launch.

The second stage would cost a bit more, especially if not reusable.


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Post    Posted on: Wed Nov 30, 2005 7:45 am
Hello, SawSS1June21,

what do you mean by your issue
Quote:
but due to the development and maintenance costs, it won't be economically cheaper until thousands of such systems have been built


precisely?

Are you speaking about total development and maintenance costs or are you speaking about development and maintenance costs per vehicle or are you speaking about development and maintenance costs per flight or are you speaking about development and maintenance costs per sold ticket (which is "per customer") ?

It is likely that the results are different between these four questions because of the Arithmetics to be done - according to the theoretical Costs-thread in the Financial Barriers section as well as to the threads about two vehicles.



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EDIT: This would tend to belong to the Financial Barriers section - perhaps I find a way to handle it there by including two-stage-vehicle into the theoretical Costs-thread or by a new thread which is unlikely currently-


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Post Re: My 2 bits   Posted on: Wed Nov 30, 2005 4:24 pm
WannaBeSpaceCadet wrote:
Why ask Musk? He's not trying VTVL. He is trying VTSSHIDS. *

Ask Carmack, he can test several times a day.

The advantage of an Armadillo style VTVL is frequent, incremental, flight testing.


...granted. But John is only allowed fly the 'dillo to 10Kft or something equally silly.

Don't get me wrong, I really like what both John and Elon are doing. I am just looking at different scenarios because they are interesting to me. It is completely feasible to build the ship we are talking about as a ballistic first stage, I just have a preference for HT--whether it makes sense economically or operationally is still up for grabs, but when Burt wanted to fly, he did. Falcon still waits... Also, I am extrapolating based on known technological achievements, so at this point RLV means HL from orbit; hence HTHL is implicit in my anlysis. So my method is based on a possibly irrational personal prejudice and a desire to copy things that are known to work. Its just speculation in any case, it ain't like you're gonna have to pay for it :)

P.S. Why shouldn't one call you "dude" ...is that because you prefer "mate" or is it a gender issue? If the latter, you should know that in popular US usage, the term is gender-neutral... I'm sure no offense was intended.[/i]


Last edited by SawSS1Jun21 on Wed Nov 30, 2005 4:37 pm, edited 1 time in total.



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Post    Posted on: Wed Nov 30, 2005 4:35 pm
Ekkehard Augustin wrote:
Hello, SawSS1June21,

Are you speaking about total development and maintenance costs or are you speaking about development and maintenance costs per vehicle or are you speaking about development and maintenance costs per flight or are you speaking about development and maintenance costs per sold ticket (which is "per customer") ?


I was referring to:

1) The cost of development and subsequent manufacture of a hypersonic bulk transport aircraft.
2) The operational and maintenance cost of said vehicle.

The thermodynamic margin (achived by the higher efficiency of turbojets compared to rockets) is not large enough to offset the costs mentioned above until the flight rate and system count gets really high, as such it constitutes only a marginal reason for developing the HTHL concept. The flexibility of basing and the regulatory ease of operation are the only significant reasons (on paper, anyway) for investing the kind of money required for this kind of project. All of which was only a passing reference on my part, I have no immediate desire to examine the economies involved at this point, only the technology.


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Post Re: My 2 bits   Posted on: Wed Nov 30, 2005 5:45 pm
SawSS1Jun21 wrote:
But John is only allowed fly the 'dillo to 10Kft or something equally silly.
He is limited to a 15 second engine burn. That limits him to very low altitudes in practice, but I am not aware of an actual altitude limit the FAA has imposed on his tests.


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Post    Posted on: Wed Nov 30, 2005 6:14 pm
John Carmack makes mention of a 3500 AGL waiver for flying at his ranch


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Post    Posted on: Wed Nov 30, 2005 6:55 pm
OK, that makes sense. The FAA only has to ensure that no aircraft below 3,500 feet enter that area. That would effect only a few light aircraft. For something like a 50,000 foot limit, the FAA would have keep all airliners out too.


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Post    Posted on: Wed Nov 30, 2005 8:24 pm
From the little I know about the FAA, they would *not* like doing that....

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Post    Posted on: Thu Dec 01, 2005 8:05 am
Hello, SawSS1June21,

I too don't want to discuss the economics of the vehicles here but simply felt troubled a little bit because the issue might have caused misunderstandings.

So Thank You Very Much for clarifying. 1) is what I call total development and production costs here while 2) are costs per vehicle except the development and except the production costs. 1) don't have been considered in the Financial Barriers section yet except in the theoretical Costs-thread a little bit. 2) are involved in the theoretical Costs-thread and the threads about the Accunmulation in deatil and the CXV.



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Post    Posted on: Thu Dec 01, 2005 5:15 pm
OK, kids... after some feverish scribbling and a breif workout on xcalc, I have decided to subvert my reputation for laziness and formally publish my thoughts on this particular topic. I will post a white paper on HTHL TSTO RLV sometime in the next few weeks.

I have a demanding full-time job and a new baby and an unfinished home remodeling project, so it will be a little while and I ask you to be patient; but after running some of the numbers it seems that something reasonable can be put together without the blue-sky fantasies concocted in the RASC and Air Force Academy papers previously featured in this thread.


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Post    Posted on: Thu Dec 01, 2005 7:27 pm
I just wish somebody would rescue/assemble that second AN-225 and use it as a first atage. This way all Rutan would need is an interim Hotol type craft that should be well within his ability.


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Post    Posted on: Fri Dec 02, 2005 11:07 pm
SawSS1Jun21 wrote:
Well, before I answer, can we establish an approximate relationship between velocity and altitude in this equation?
(...)
You're the expert and I'm lazy, otherwise I'd dig it out myself :)


OK then:
For me, velocity and altitude are just measures of energy:
E=1/2 m v^2
E=Integral(m*g(h)dh) or for g=const. E=m*g*h (applicable for low altitudes, such as below 100kft)
So, if you look only at the end result, v^2=2*g*h would give you the relationship between velocity and altitude for "low" altitudes.

Considering the "expert", you said that. I didn't. I feel flustered. :o

Sorry for the late answer, was away a few days.


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Post Re: My 2 bits   Posted on: Fri Dec 02, 2005 11:15 pm
SawSS1Jun21 wrote:
The only reason that HTHL is better in the near term is basing and mission flexibility.

Thermodynamically it is cheaper (the 'ISP', such as it is, of air-breathing turbojets is well into the thousands), but due to the development and maintenance costs, it won't be economically cheaper until thousands of such systems have been built.


Hey! Unexpectedly fast, we're coming close to common ground! :D
You're right about the operational flexibilty. On the cost, however, I'd argue it'll be cheaper when "thousands" of missions have been flown, not necessarily built. Remember, the starting point was that they should be reusable!


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