Derek Lyons wrote:
wrote:

Derek Lyons wrote:
A Shuttle can launch a wide variety of missions without requiring
that there be something for it to meet in orbit. It carries it's
purpose
with itself.

A CSM is quite limited in what it can do usefully on orbit without
requiring a second launch.

First, I don't see exactly what advantages this has (other
than bundling launch failures together so that they affect
multiple aspects of the mission rather than being more or
less isolated).

Lets see.. It utterly eliminates the need for rendezvous procedures,
docking hardware, and independent flight capability for the payload.

Except when it doesn't. Such as when rendezvous with the
payload is unnecessary and the sole goal of the launch is
to place the payload in orbit (e.g. when independent
flight capability for the payload is already a requirement,
which is quite a lot more often than never, e.g. HST,
many ISS components, etc.).


It eliminates the parasitic weight of a shroud for the payload.

No, it just moves the weight of the shroud onto a different
balance sheet. You may recognize it as the weight of the
"cargo bay".


It
ensures that the payload and it's operators arrive on orbit,
together,
always.

Except when it doesn't. And when it doesn't, it ensures that
rather than just missing putting one payload in the proper
orbit (or in orbit at all) you miss two or more. This could
be an advantage, or at least a minimal disadvantage, if done
right. The Shuttle is not an example of doing it right,
however.


And those are just the ones that occur off the top of my head.

That's *not* to say the Shuttle is the is the best way to do things,
or that it's advantages outweigh the disadvantages. But to pretend
the Shuttle has no advantages is nothing but handwaving FUD.

Certainly. As you say, the Shuttle as it exists currently
has many fewer advantages than a hypothetical shuttle
system of somewhat similar design. And that sort of
practical concern is precisely what we need to keep in
mind when devising practical, real world systems.


And contrary to vigorous handwaving of the Capsule Cabal, the cargo
will not tend to itself. Provisions must be made for it.

Provisions must be made in either case. The question is
whether the cost and capabilities of one method are
clearly superior than the other, to date we do not have
enough data in the form of actual, working systems to
make that determination outside of theory. What data we
do have is not supportive of the Shuttle's method.


Second, this is a non-issue with regards to the subject of the
sub-thread. If there is a payload that can be launched into
LEO that can serve as a "target" for the Shuttle, in that it
serves as a mission that is sufficiently useful to warrant
launching the Shuttle with said payload in the cargo bay,
then that same payload would obviously warrant a cargo-only
launch for rendezvous (if necessary) in a cargo-bay-less
manned spaceflight scenario.

No, it's not obvious. You fail to account for all the things a
'target' payload needs that a 'piggyback' payload doesn't. It also
ignore the problem that in few instances is a 'target' payload
recoverable, whereas a 'piggyback' payload always is.

This, at least, is a real advantage of a cargo vehicle
system such as the Shuttle. However, you can get the
same or similar advantages with systems that are
significantly different from the Shuttle. I'll grant
that this could be an issue with a hypothetical, low
cost access to space system such as a high flight rate
RLV or such like. In such cases it may be significantly,
or even just incrementally, more expensive to launch
separate payloads, and that might make just enough
difference to not justify such a launch even though it
might be justified with the other system. However,
that sort of hypothetical scenario lives in a realm
that is completely off the radar of the present
discussion. Moreover, it is in a realm where the
concerns brought up here are almost entirely moot.

Here we are talking about big ticket items which
justify the existence of the whole manned spaceflight
program. And there it is beyond ridiculous to assume
that there are such which are just small enough to
justify Shuttle operations but not, say, a capsule
based vehicle aimed at LEO operations. The history
of the Shuttle is not one of cutting edge cost
effectiveness. I think the existing examples
throughout spaceflight history back up my
interpretation fairly soundly on this point.


So, it's a distinction without a difference.

Hardly.

You have accreted onto your original statement a series of
statements regarding the advantages of the Shuttle, not all
of which are related. With regard to your original statement
that there is some sort of difference in the validity of the
*justification* for a mission between a shuttle vehicle
bringing its "target" with it and a vehicle rendezvousing
with its target. I continue to maintain that there is none,
regardless of the other advantages and disadvantages of
either method.