🚀 go-pugleaf

In article <ewright.726181992@convex.convex.com>, ewright@convex.com (Edward V.
Wright) says:
>
>[me]
>>Rather depends on how many heavy cargoes there are, doesn't it?
>
>No, I don't think so.  Building and testing a new two-stage vehicle
>would be more expensive than building and testing a new one-stage
>vehicle.  So costs would be greater no matter how many, or how few,
>payloads you spread them out over.

Huh?  Rather depends on the vehicle, doesn't it?  And the design team,
and the funding situation, and...

The Bruce's proposal seemed to assume an off the shelf DC-1, with
all the mating hardware (or as much as possible) going on the
lower stage.

>>As I understand it, the point to an SSTO is to make expendables
>>non-cost effective.  So there *won't* be another vehicle fairly
>>soon after DC-1's get flying in numbers if they work as advertised.
>
>I don't think Boeing gave up when McDonnell Douglas introduced
>the DC-3.  If one company demonstrates a successful space
>transportation system that makes money, other companies
>won't let them have the market all to themselves for long.

This pre-supposes a significant market; what basis to believe
that there will be one do you have?  How many comsats are backlogged
waiting for launch?

>>If there's one or two heavy cargoes a year, Bruce's quick and simple
>>second stage might make a great deal more sense than scaling up
>>an SSTO design by a factor of five, which I would expect to be quite
>>difficult, since it's a complete re-design and probably needs new
>>engines.
>
>Bruce's "quick and simple" concept requires *two* new designs.
>You couldn't just put 5x the cargo into an existing DC-1.  Unless
>it was unusually dense, it wouldn't fit into the cargo bay.  Even
>if you could, the vehicle's balance would be off.  So you're talking
>a major redesign, then component testing of both the first and second
>stages, then testing both the first and second stages together....
>
>And I can't understand why a larger SSTO would need new engines
>while a TSTO with a comparable liftoff weight wouldn't.

What is the assumed specific gravity of a DC cargo?

The TSTO *does* need new engines; however, they might be more
readily available (being kerosene burners) than the whatever
a 50 tons to orbit SSTO needs.  (It won't be just more of what
DC-1 uses; square cube law and aerodynamics don't leave the bottom
of the cone having enough room.)

As for cargo stacking - hammer-headed payloads don't seem to
bother the expendables; I suspect that you don't need to redo
the entire vehicle.  I also suspect that the payload bay is
designed to have as much volume as it possibly can, to give
more leeway for odd structures.

The point is in any case moot in the abscence of a real engineering
study done *after* DC-1 flies.

Graydon