Ariane Economies of Scale

Ian Woollard wrote:

h (Rand Simberg) wrote in message ...
The problem is, that at a given technology level, you *can't*
have the same margins in a single-stage that you do in a multiple
stage.

Look, if you've got a SSTO, turning it into a TSTO is normally going
to be pretty easy and you certainly don't have to add margin and you
usually gain payload (for the same GLOW).

It may or may not be worth doing. But you can certainly do it.

I have been suggesting something similar for several years: Take
something like the SSX proposal and develop a reusable booster stage for
it (perhaps a cluster of modified ELV booster stages). By starting with
a 2-stage design, we relax the dry mass requirement for the Orbiter
stage, and have the option of turning it into an SSTO with some
additional engineering and technology development.

I mean, the whole point of TSTO is that it allows you to get away with
using a lower technology level doesn't it?

That's one way of looking at it, but it seems to go against what you
say above.

No, all I'm saying is you can add margin if you want to. You're saying
it's impossible, that you HAVE to add margin. Uh, why? No.

TSTO allows you to add margin. Increasing margins requires scaling up
the vehicle to maintain a given payload capacity. Not a big deal. A
lot of people disagree that you can get a positive payload in a
single-stage design even without margins.

On 16 Jul 2003 10:44:33 -0700, in a place far, far away,
(Ian Woollard) made the phosphor on my monitor
glow in such a way as to indicate that:

"Paul F. Dietz" wrote in message ...
Ian Woollard wrote:

Proof by assertion? No. Try again.

For a given level of technology (materials strength, engine
thrust/weight, etc.) a TSTO can be designed with larger margins
on the structure/etc. than a SSTO.

Not, if like me you consider the margins to be part of the technology.
The key phrase here is 'given level of technology'. I take that pretty
much to be measured by mass fraction.

You take it in a mistaken way. "Technology" is measured in no such
units.

We seem to be having trouble communicating, because you seem to have
different definitions (unique to you, AFAIK) for "technology" and
"margins" than most spacecraft designers.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

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On 16 Jul 2003 14:22:52 -0700, in a place far, far away,
(Ian Woollard) made the phosphor on my monitor
glow in such a way as to indicate that:

Not, if like me you consider the margins to be part of the technology.
The key phrase here is 'given level of technology'. I take that pretty
much to be measured by mass fraction.

You take it in a mistaken way. "Technology" is measured in no such
units.

Really? Then what is it measured in?

I challenge you to come up with a better one. Knock yourself out.
We'll even name it after you, how about that.

It's too complex to be amenable to such simplistic notions.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
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JRS: In article , seen in
news:sci.space.policy, Paul F. Dietz posted at Wed, 16
Jul 2003 07:15:41 :-

For a given level of technology (materials strength, engine
thrust/weight, etc.) a TSTO can be designed with larger margins
on the structure/etc. than a SSTO. You end up with more wiggle
room to add (for example) thicker TPS.

Moreover, with TSTO a significant proportion of the mass needs much less
thermal protection.

With TSTO, a single first stage design can be used with a family of
second stage designs. Let the second stages have the same mass,
mountings, shape, and CofG, so that they are indistinguishable as
payloads; but let there be versions with differing contents : differing
passenger/cargo ratios, for example.

The reusable first stage could also be used with a single-shot second
stage design matching those above (as much as required for
compatibility) but intended to be able to dispense a payload and to re-
enter terminally.

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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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h (Rand Simberg) wrote in message ...
On 16 Jul 2003 14:22:52 -0700, in a place far, far away,
(Ian Woollard) made the phosphor on my monitor
glow in such a way as to indicate that:

Not, if like me you consider the margins to be part of the technology.
The key phrase here is 'given level of technology'. I take that pretty
much to be measured by mass fraction.

You take it in a mistaken way. "Technology" is measured in no such
units.

Really? Then what is it measured in?

I challenge you to come up with a better one. Knock yourself out.
We'll even name it after you, how about that.

It's too complex to be amenable to such simplistic notions.

Ok, then I challenge you to even define it; frankly I think you're
full of it and using a term that is immeasurable and undefinable, but
go ahead make my day, define it as you used it in that context.

On 16 Jul 2003 21:20:39 -0700, in a place far, far away,
(Ian Woollard) made the phosphor on my monitor
glow in such a way as to indicate that:

It's too complex to be amenable to such simplistic notions.

Ok, then I challenge you to even define it; frankly I think you're
full of it and using a term that is immeasurable and undefinable, but
go ahead make my day, define it as you used it in that context.

Yes, I know you do.

I don't give a damn. I repeat my statement.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

"Kim Keller" wrote in message . com...
"Jake McGuire" wrote in message
om...
I assume that he's using "Big O" notation for the difficulty of a
task. It's a computer science term, and is generally used to
determine which algorithm is better on abitrarily large data sets.
It's not particularly useful for aerospace work since by definition it
completely ignores non-recurring costs.

I would assume he meant to say "roughly three weeks"

But I don't understand what effort he's referring to when he talks about
three weeks to recycle the shuttle. Recycle it after what? I could probably
give a semi-intelligent answer if he would elaborate.

I'm trying to ask a probably much too complex question; so a
semintelligent answer is probably too much to hope for ;-)

What I'm trying to understand or get a feeling for is why the Space
Shuttle takes whatever it takes (the three weeks I mentioned is
probably incorrect) to turnaround after a launch to prepare it to
launch again. I'm just trying to understand it, from the point of view
of looking at ways it could be improved upon in future launch
vehicles.

For example, some of the tiles need replacement, and I imagine it
takes atleast a week elapsed repairing that. Mating SRBs and main
tanks seem to take a week elapsed or so in total. I bet there are
repairs on the main engines etc. (SSMEs get removed and reinserted I
believe, don't know how long that takes), that kind of thing. Are
there any other long timescale items?

Any help or pointers to information about timescales would be much
appreciated.

-Kim-

"Paul F. Dietz" wrote in message ...
According to your definition, at the same level
of technology we'd be forced to use weaker and/or heavier materials on
the TSTO than on the SSTO.

Let's say you hypothetically manage to build an SSTO with a 5% dry
mass (dry mass here does not including payload mass). It just creaks
into orbit, but margins are terrible; it's rather unreliable.

You can then build a technologically equivalent TSTO having very
nearly 5% dry mass for each stage (not including payload mass). It
probably doesn't quite end up exactly the same dry mass, there's minor
differences due to scaling laws and the two sets of engines you have
in TSTO, but it will be pretty darn close.

But the margins would be the same. They have not INHERENTLY gone up.
That's all I'm saying. I'm not even saying that dry mass and
technology level are exactly the same, but they're very closely
related (in practice the actual dry mass will vary slightly with
vehicle size among many other things).

It's entirely a design choice to increase the margins for TSTO in this
scenario. You might want to just put more payload in orbit than the
SSTO, and leave the margins where they were. Or you might increase
margins because you want to manrate it.

Margins are not an independent variable, they are *derived* from
the technological inputs.

Right!

Paul

On Thu, 17 Jul 2003 00:43:34 -0500, in a place far, far away,
"Christopher M. Jones" made the phosphor on
my monitor glow in such a way as to indicate that:

For a given level of technology (materials strength, engine
thrust/weight, etc.) a TSTO can be designed with larger margins
on the structure/etc. than a SSTO.

Not, if like me you consider the margins to be part of the technology.
The key phrase here is 'given level of technology'. I take that pretty
much to be measured by mass fraction.

That's just about the most asinine definition of "level of
technology" I've ever heard.

Gee, you mean it's not just me?

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

Ian Woollard wrote:

Let's say you hypothetically manage to build an SSTO with a 5% dry
mass (dry mass here does not including payload mass). It just creaks
into orbit, but margins are terrible; it's rather unreliable.

You can then build a technologically equivalent TSTO having very
nearly 5% dry mass for each stage (not including payload mass). It
probably doesn't quite end up exactly the same dry mass, there's minor
differences due to scaling laws and the two sets of engines you have
in TSTO, but it will be pretty darn close.

But the margins would be the same. They have not INHERENTLY gone up.
That's all I'm saying.

But this is because you've optimized the TSTO design incorrectly.
You can prove lots of incorrect things through sufficiently stupid
mental engineering.

Paul