From: Wales.Larrison@ofa123.fidonet.org
Newsgroups: talk.politics.space
Subject: Re: Re: More Soyuz as ACRV
X-Sender: newtout 0.06 Jan  3 1993
Date: 26 Jan 93  22:32:02

Hi David!
  
>Needless to say, I have some questions about your stated
>assumptions:
> 
>It has not ever been tested in orbit for 3 years.
    True -- but Soyuz systems (or so I have been told) have been
ground tested in environmental tests over several years.  (That's
supposedly where the 3 years cert data from the Russians came from -
- according to the NASA documentation on Soyuz).   I don't think an
orbital test is really called for here as the problem is the thermal
cycling of the specific quality of hydrazine in a sealed container
under those thermal conditions for x number of cycles.  Zero gravity
isn't a driver for the fuel degradation, from what I've seen.
Running a new set of cert and qual life tests on a sealed Soyuz
propulsion system is something I expect anyone proposing a Soyuz
launch in the shuttle will propose.  And it ought to be fairly cheap
-- I'd ROM it at a $1M or so.
  
> There are other factors besides the fuel lines in limited the life
>of a Soyuz in orbit
    True as well -- but you had focused your discussion on the fuel
line issue of the discussion in your previous posting, so I only
addressed that.  From your original posting:
DA>  Currently, the Russians are reluctant to allow the Soyuz to
DA>remain operational in orbit for more than three of four months
DA>due to its fuel lines degrading. Exposure over long periods to
DA>the thermal stresses of low earth orbit cause Soyuz fuel lines to
DA>lose integrity.  However, these same fuel lines have a longer
DA>lifespan if they have not yet been used. ...
  
   There are numerous issues in extending the lifetime of any space
vehicle.  Specific pertinent issues for Soyuz might include: pyro
degradation, softgoods lifetime limits, outgassing, solar array
degradation, battery cycling, chute pack limits, radioactive source
limits (used in the descent system), and many others.  What other
ones would you like to discuss?
   There are limits, but there are also off-the-shelf solutions to
virtually all of these problems to get a moderate increase in
lifetime to to few years.  The trade is (which I admit up-front I
haven't got a full answer on), is to trade the cost of adding
additional orbital life versus against the cost of increased
orbital replacements (holding reliability and availability the
same), and also against different deployment options.  One boundary
condition is changing out Soyuzes every 180 days, for which ELV
launches are probably the best answer.  Another boundary condition
is to extend orbital ifetime as long as possible by launching a set
of Soyuzes unused in in Shuttle, and change them out at a longer
period of time (say, 3 year intervals).
   And it should be pointed out that another boundary condition is
merely to leave a Shuttle at SSF as an "emergency ride home".  A
shuttle capable of staying at SSF for 90 days would also solve this
issue, and from what data I've seen, the modifications to do this
are about $ 300 M for the entire shuttle fleet.  This might be the
lowest cost answer.
   And there are intermediate solutions along the trade parameter of
varying periods on orbit with a Soyuz  (as a function of $ for
increased lifetime) versus deployment method (as a function of
$/flight) to SSF.
   As I said, I don't know the full answer to this trade since I
haven't seen the detailed technical assessments and preliminary
Soyuz/ACRV design studies, but I can identify the boundary
conditions and ROM some cost comparisons.
  
>Would you really want to risk your life on a lifeboat in orbit that
>had never had its engines fired?
   Considering the alternative -- to die in orbit.  Yep.  Same as
I'd risk my life in an ejection seat in a high-performance jet
aircraft if the alternative was the same.
   And I assume enough redundancy in the Soyuz propulsion system
(the Russians are good spacecraft designers) that any single failure
in the propulsion system (sticking valves, failed engines, failed
ignitor circuits, etc.) would not prevent the system from separating
and deorbiting.
   We (the US) and the Russians have a pretty good experience base
in high-reliability sealed hydrazine propulsion systems -- ICBM RV
buses for example, are designed for instant readiness after several
years of being sealed.
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 Wales Larrison                          Space Technology Investor

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