Ariane Economies of Scale

"Paul F. Dietz" wrote in message ...
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.

'Incorrectly'? Incorrectly for what? Perhaps I just want a slightly
bigger payload. If I'm optimising for payload per GLOW (this is
frequently done for TSTO vehicles, for some bizarre reason), then I've
optimised it correctly.

Paul

"Ian Woollard" wrote in message
om...
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.

A typical orbiter flow is broken down into three segments. The first is its
stay in an Orbiter Processing Facility. The average stay is 80 days, and
during that period it is given a thorough inspection, the payload bay is
unloaded and reconfigured for the next flight, systems are tested to verify
their functionality, repairs are made as required, life-cycle-limited items
are replaced as required, small modifications may be performed as time
allows, and some fluids are added for the next flight (ammonia, deionized
water, freon, etc.).

The next segment takes place in the VAB and involves integrating the orbiter
into the complete shuttle "stack". This takes between 5 and 7 days. The
orbiter is mechanically and electrically attached to the ET/SRB stack, and
the interfaces are tested.

The final segment takes place at the pad and runs about 25 days. Hypergolics
are added to the orbital propulsion systems, hydraulics are tested, the main
propulsion system is leak-tested, payload is loaded into the payload bay (if
it wasn't already loaded in the OPF), work on open items from the OPF flow
continues, and final closeout inspections are performed.

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?

Tile repair is worked in parallel with all other processing work. SRBs take
about a week per booster to stack, but require more work beyond that - say,
a month. The ET doesn't require much work once it arrives at KSC; a small
day-shift team takes care of that. The SSMEs are pulled from the orbiter
after landing and taken to the engine shop for inspection and maintenance. A
fresh set is installed in the orbiter near the end of its stay in the OPF.

The Columbia accident will probably lead to a longer stay in the OPF to
accommodate more extensive inspections. United Space Alliance had plans in
place to gradually reduce the length of an OPF flow to just 30 days by
around 2010, but the mission schedule simply isn't going to require that
kind of effort.

What else can I tell you?

-Kim-

"Ian Woollard" wrote in message
om...
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.

A typical orbiter flow is broken down into three segments. The first is its
stay in an Orbiter Processing Facility. The average stay is 80 days, and
during that period it is given a thorough inspection, the payload bay is
unloaded and reconfigured for the next flight, systems are tested to verify
their functionality, repairs are made as required, life-cycle-limited items
are replaced as required, small modifications may be performed as time
allows, and some fluids are added for the next flight (ammonia, deionized
water, freon, etc.).

The next segment takes place in the VAB and involves integrating the orbiter
into the complete shuttle "stack". This takes between 5 and 7 days. The
orbiter is mechanically and electrically attached to the ET/SRB stack, and
the interfaces are tested.

The final segment takes place at the pad and runs about 25 days. Hypergolics
are added to the orbital propulsion systems, hydraulics are tested, the main
propulsion system is leak-tested, payload is loaded into the payload bay (if
it wasn't already loaded in the OPF), work on open items from the OPF flow
continues, and final closeout inspections are performed.

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?

Tile repair is worked in parallel with all other processing work. SRBs take
about a week per booster to stack, but require more work beyond that - say,
a month. The ET doesn't require much work once it arrives at KSC; a small
day-shift team takes care of that. The SSMEs are pulled from the orbiter
after landing and taken to the engine shop for inspection and maintenance. A
fresh set is installed in the orbiter near the end of its stay in the OPF.

The Columbia accident will probably lead to a longer stay in the OPF to
accommodate more extensive inspections. United Space Alliance had plans in
place to gradually reduce the length of an OPF flow to just 30 days by
around 2010, but the mission schedule simply isn't going to require that
kind of effort.

What else can I tell you?

-Kim-

Ian Woollard wrote:

h (Rand Simberg) wrote in message ...
On Sat, 12 Jul 2003 22:44:16 GMT, in a place far, far away, Michael
Walsh made the phosphor on my monitor glow in
such a way as to indicate that:

The payoff of the SSTO would be from expected lower operational
costs.

Yes, but because SSTO would have much less margin than a
(technology-equivalent) two-stage, lower operational costs may end up
being an illusion at current technology levels.

Not quite. By definition, SSTO has the same margin as a
technologically equivalent two-stager.

By what definition?

The SSTO is much more sensitive to weight growth during the
development phase than a two-stage vehicle with the same
payload.

At this point I just need some more information about your
remark. I can't argue about it unless I understand what you
mean.

Mike Walsh

Ian Woollard wrote:

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.

I have been away for a week so I made my first reply about
not understanding your definition before reading the other
messages.

The replies and counter-replies followed the usual Usenet
standard of increased huffiness.

Are you claiming that a two stage vehicle, to be at the
same level of technology, would have to have the same
mass fraction as a SSTO with the same payload to be
at the same technological level?

Mike Walsh

Ian Woollard wrote:

Michael Walsh wrote in message ...
The only virtue that a SSTO has over a TSTO (two stage to orbit) reusable
vehicle is the reduction in cost by developing and using only one vehicle
instead of two. If the SSTO does not show a cost advantage then there
is no reason to build one.

That's not necessarily the case, there may very well be reliability
advantages of SSTO, due to system simplicity.

I have made the implied assumption that safety should not be
compromised.

I should not have made the mistake of using the term "only virtue" but
there is still no reason to build a SSTO unless it shows a cost advantage.

In addition, SSTO does not have the strong tendency of TSTO to drop
stages onto occupied land that can preclude many orbits.

If we are talking about fully recoverable systems then I would expect a
the recovery to take place in a controlled location, even if it was not
a "flyback" system.

For example Soyuz would have been unable to reach Columbia's orbit due
to these constraints- (however, overflying the land would still entail
some risk, but it might well be considered acceptable on a rescue
mission.)

The Russians continually launch over land areas and the Soyuz reaches the
ISS on a regular basis. I am not sure what the flight path would have been
for a Columbia rescue mission. That is somewhat of a special case.

Mike Walsh

Michael Walsh wrote in message ...
Ian Woollard wrote:

Michael Walsh wrote in message ...
The only virtue that a SSTO has over a TSTO (two stage to orbit) reusable
vehicle is the reduction in cost by developing and using only one vehicle
instead of two. If the SSTO does not show a cost advantage then there
is no reason to build one.

That's not necessarily the case, there may very well be reliability
advantages of SSTO, due to system simplicity.

I have made the implied assumption that safety should not be
compromised.

I do not see how you implied that.

I should not have made the mistake of using the term "only virtue" but
there is still no reason to build a SSTO unless it shows a cost advantage.

Yes, you said that. It's not totally clear why you said that. If the
cost was much the same for example, then SSTO may be more desirable.

In addition, SSTO does not have the strong tendency of TSTO to drop
stages onto occupied land that can preclude many orbits.

If we are talking about fully recoverable systems then I would expect a
the recovery to take place in a controlled location, even if it was not
a "flyback" system.

Yes, that may help.

The Russians continually launch over land areas and the Soyuz reaches the
ISS on a regular basis. I am not sure what the flight path would have been
for a Columbia rescue mission.

There isn't one, first stage drops on China IRC.

That is somewhat of a special case.

No, not at all. It heavily constrained the location of the ISS itself;
the ISS is where it is because the Russians could reach it even though
many other orbits were within delta-v range of the Soyuz vehicle. The
ISS is constained by the multiple stage vehicles used to reach it.

Mike Walsh

Ian Woollard wrote:

Michael Walsh wrote in message ...
Ian Woollard wrote:

Michael Walsh wrote in message ...
The only virtue that a SSTO has over a TSTO (two stage to orbit) reusable
vehicle is the reduction in cost by developing and using only one vehicle
instead of two. If the SSTO does not show a cost advantage then there
is no reason to build one.

That's not necessarily the case, there may very well be reliability
advantages of SSTO, due to system simplicity.

I have made the implied assumption that safety should not be
compromised.

I do not see how you implied that.

Written in between the lines. I made the assumption, but did not
state it.

I should not have made the mistake of using the term "only virtue" but
there is still no reason to build a SSTO unless it shows a cost advantage.

Yes, you said that. It's not totally clear why you said that. If the
cost was much the same for example, then SSTO may be more desirable.

Nope. The cost of developing the SSTO would, in my opinion, be higher
than that of a two stage vehicle. If you disagree with this, that is your opinion,
but not I believe a sound one.


In addition, SSTO does not have the strong tendency of TSTO to drop
stages onto occupied land that can preclude many orbits.

If we are talking about fully recoverable systems then I would expect a
the recovery to take place in a controlled location, even if it was not
a "flyback" system.

Yes, that may help.

I could go on at greater lengths about my opinions on the probable
costs of SSTO development vs. costs of developing a multi-stage
system.

Basically, a SSTO is a more difficult technical problem than the
TSTO systems. NASA claims that SSTO is beyond our current
technological level. However, this looks more like a way of
excusing management failures that resulted in them giving up on
the X-33 and X-34 rather than hitting technological barriers.

Mike Walsh

Ian Woollard wrote:

Michael Walsh wrote in message ...
Ian Woollard wrote:
Yes, you said that. It's not totally clear why you said that. If the
cost was much the same for example, then SSTO may be more desirable.

Nope.

So you are opposed to SSTO even if it turned out to cost the same?

Interesting...

An interesting misinterpretation of what I, perhaps not too clearly said.

I was referring to equal operational costs where I would expect that
the multi-stage system would have lower development costs than the
SSTO.

Then equal operating cost means you never get back the total cost
of your system.

The cost of developing the SSTO would, in my opinion, be higher
than that of a two stage vehicle.

Perhaps. However some of the early Atlas first stages demonstrate SSTO
mass fractions (about 5.5% dry mass); and they weren't even trying to
build an SSTO vehicle. Granted, the Atlas engines were only capable of
delivering an ISP of around 300 seconds; you would need around 330
seconds to make a single stage vehicle, but other engines are capable
of this level of performance, so it would seem not impossible to do
this.

Since the original Atlas was parallel staged there was a significant hunk
of booster engine that was dropped off about two minutes into the flight.
The Atlas is frequently put forth as an example of a non-reusable SSTO
vehicle, but it really was not.

Discussion of mass fractions of expendable SSTO vehicles is an
interesting exercise, but not one I would expect to see anyone
actually try to produce.

If you disagree with this, that is your opinion,
but not I believe a sound one.

This from a man who doesn't think that SSTO is worth it if it cost the
same?

Please try to carry out a reasonable discussion instead of distorting
my remarks.

Basically, a SSTO is a more difficult technical problem than the
TSTO systems.

Possibly; although it's easy to forget how complex a vehicle like the
Shuttle really is, and it's unclear whether an SSTO is more difficult
or easier than that overall, since whole structures disappear. It may
very well be somewhat easier/cheaper overall. (If done right; done
wrong it is impossible of course).

NASA claims that SSTO is beyond our current
technological level. However, this looks more like a way of
excusing management failures that resulted in them giving up on
the X-33 and X-34 rather than hitting technological barriers.

Definitely, although the X-33 atleast deserved to die from what I
could see.

I regard the process that resulted in the failed composite tanks as
primarily a management failure rather than a technical failure.
When the original project manager, David Urey, accurately points
to the composite, conformal tanks as the highest risk for the project
and the program just rolls on with the full-size flight tanks coming in
and failing in construction and ground test I call that a management
failure.

By the time the X-33 got to the point where NASA canceled it,
it deserved to die.

Mike Walsh