🚀 go-pugleaf

In article <ewright.726343877@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <1993Jan5.215441.21415@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes:
>
>The Shuttle also has zero availability, if your time frame is the
>next few days.  Your car has zero availability, if your time frame
>is the next 30 seconds.  (I'm assuming you're not a track star.)
>Soyuz spacecraft/launchers purchased from the Russians have zero
>availability, if your time frame is the next six months.  DC-1
>has zero availability, if your time frame is the next four years.

and...

>Switching from the Shuttle to Vehicle X would certainly delay
>some payloads and missions currently planned to fly aboard the
>Shuttle.  But remaining with the Shuttle might delay other 
>payloads and missions that are not yet planned but could be
>flown on Vehicle X.  You can't just look at one side of the
>equation; you need to do a complete cost-benefit analysis.

<plus discussion on "turf battles" by shuttle deleted>

While your arguments about availability are sound in principle, they
ignore the element of risk.  Shuttle availability has a long time window
to availability, in months, but it is reasonably likely to be available
when predicted to be, with some error margin <error margin because the
schedule is ill-controlled, only "reasonably likely" because of the
possiblity of another crippling accident shutting the STS down>

While I believe the DC-X and DC-Y programs should continue (although I'm
not as sold as I once was), the uncertainty associated with the "four
year" time frame is, to say the least, very large.  While I THINK that
the program can be managed with reasonable deadlines, and I THINK that
DC-Y, if funded, will eventually demonstrate that SSTO is feasible, there
is a very significant risk with both of these.  One point that gets lost
is that while DC-X is "bent metal" and will solidly demonstrate the
"quick turn" aspects of a launch vehicle (or not), it will NOT demonstrate
the key SSTO capability of a vehicle with the extremely small "dry mass"
necessary to make SSTO work -- that is left for DC-Y.  So, in spite of
the encouraging signs, such as DC-X maintaining a close adherence to 
schedule, the risks are still very, very significant.

This is not a criticism of the DC program -- far from it! If there were no
risk associated with the program, it would, by definition, have to have
extremely conservative targets, and "If you always do what you've always
done, you always get what you've always got".  So it is essential that the
DC program take some risks if it is to demonstrate new concepts.
Intelligent management (which I will never accuse NASA of), can reduce those
risks, but not eliminate them.

This is a fairly long-winded lead in to say that no matter how great DC
may be, you cannot stop shuttle flights before an operational DC capability
exists, or else your "downside risk" is an undetermined period of years,
with no upper bound, before a manned spaceflight capability is
reestablished.  Given the current political/budgetary climate, that might be
a very, very long time.  This is NOT because of any advantage of the shuttle
-- in my opinion it probably has none -- but because it is the ONLY system
which we PRESENTLY have.

Murphy willing, the DC program might change that, in which case we can (and 
should) retire the shuttles to the Smithsonian.

Disclaimer:  All opinions expressed are my own, and do not reflect the 
     position of Intel, Portland State University, or Zippy the Pinhead.  
============================================================================
Jeff Greason                  "You lock the door ... And throw away the key.
  <greason@ptdcs2.intel.com>   There's someone in my head, but it's not me."