NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/space/18217

Text File | 1992-12-25 | 4.0 KB | 88 lines

Newsgroups: sci.space
Path: sparky!uunet!spool.mu.edu!agate!rsoft!mindlink!a752
From: [e-mail] (Bruce Dunn)
Subject: Re: SSTO vs. 2 Stage
Organization: MIND LINK! - British Columbia, Canada
Date: Fri, 25 Dec 1992 18:45:27 GMT
Message-ID: <[e-mail]>
Sender: [e-mail] (Usenet)
Lines: 77

Regarding my comments that a DC-1 used as an upper stage in a two stage
vehicle would be able to survive an engine failure after separation...

> Edward V. Wright writes:
> However, you've overloaded the DC-1 to get that 5x payload capacity
> you talk about.  It's going to be over max takeoff weight.

      I am not quite sure what your argument is.   The following explanation
of takeoff conditions therefore may or may not answer your objections.

      Putting 5 times the payload on a DC-1 used as an upper stage only
raises the gross mass slightly.  A 500 ton DC-1 in SSTO mode with a 10 ton
payload has a total mass of 510 tons.  In two stage mode, the payload is
raised to 50 tons which increases the total mass to 550 tons.  I think you
are arguing that this increased mass makes it impossible to deal with an
engine out or engine start problem.  However, you have forgotten that in
contrast to a ground takeoff, the upper stage of a two stage vehicle is
operating in a vacuum and has increased thrust.  The increase in thrust
depends on the engine expansion ratio and chamber pressure, but might be
something like the 20% or so that the Shuttle SSME experiences in climbing
from sea level to space.  The increased thrust of a DC-1 in two-stage mode
more than makes up for the payload increase.

        If any problems are created by the increased payload, they will be in
the landing phase after an abort from a two stage launch.  Assuming the
payload isn't jettisoned, the landing mass will be roughly double that of am
abort landing of an SSTO DC-1.  This will require beefing up the landing gear
if the DC-1 is used as an upper stage.  In compensation, it would be possible
to eliminate complicated extendible nozzles for the majority of DC-1 engines,
with only a minimum set of engines capable of atmospheric operation in the
event of an abort situation.

>
> Or if you have negative separation, or separation followed by a
> collision, or several other scenarios you need to worry about.
>
> The problems of staging are not nearly as trivial as you make
> them out.


        We have been launching staged rockets for nearly half a century.  I
think the problems of staging, if not trivial, are solvable.  Certainly,
historical evidence indicates that staging is less of a technical challenge
than SSTO operation.

        For Edward and others tracking this discussion, I would like to again
note that I am strongly in favor of the DC-1 SSTO concept.  I am not
proposing that the DC-1 SSTO capability be scrapped, or that a "DC-0" (to use
Greg's nice name) be immediately developed.  I think of the DC-0 as a
potentially useful extension to an existing DC-1 flight program, to be
developed if and only if:

1)  Very large amounts of cargo have to be put into orbit.

2)  A full scale cost study suggests that it is ***clearly*** less expensive
to develop the two stage system than to simply build more DC-1s.

        I am of the opinion that when it gets closer to designing the DC-1,
it would be helpful to keep the two stage concept in mind so that where
possible design decisions favor approaches which would not rule out the later
use of the DC-1 as an upper stage (for instance, using landing gear which
could easily replaced with beefed up derivative rather than integrating the
landing gear deeply into the body).

        Finally, I think that the two stage concept should be kept in mind as
a potential backup strategy should the DC-1 fail to meet its performance
goals.  As I pointed out in a previous posting, an "obese" DC-1 which has
even a zero payload to orbit in SSTO mode still would make a very fine upper
stage for a two stage vehicle.






--
Bruce Dunn    Vancouver, Canada   [e-mail]