From: Wales.Larrison@ofa123.fidonet.org (Wales Larrison)
Newsgroups: sci.space.shuttle
Subject: Re: Extended Duration Orbiter (2 of 2)
Date: Thu, 09 Apr 92 21:42:06 PDT
Organization: Universal Electronics Inc. (Public access BBS)

fuel cells to produce power.  The shuttle has the capability to 
carry 5 sets of LOX and LH2 tanks (1 each = 1 set).  The current 
pallet fits into the back of the payload bay and carries 4 
additional sets of tanks for a total of 9.  This gives the 
capability to generate an average of 18 KW for 16 days, plus 2 
contingency days at 12 KW.  [Note breathing oxygen is also carried 
in these LO2 tanks, but the amount is very small compared to the 
power needs]. 
 
  What vehicles have been modified: 
  As of this time, 2 vehicles have been modified for EDO.  On these 
vehicles typically only the "scar" mods are retained flight to 
flight.  ("Scar" mods are those necessary brackets, fittings, and 
attach points which are not removed flight to flight).  When an EDO 
mission is desired, the necessary GN2 and cryo kits (including the 
pallet) are hooked up. These vehicles are:
  o OV-102, which is "scarred" for 16 day missions, but has the EDO 
WCS, and RCRS installed. These mods were done by Rockwell during the 
recent overhaul at Palmdale.        
  o OV-105, which is "scarred" for 28 day missions. These mods were 
installed in OV-105 while it was being built by Rockwell. 
  There are no current plans to modify other vehicles. 
 
  What it would take to go to 28-day missions:
  If one were to use Endeavour (OV-105) two changes would be to 
implement the 8 GN2 tanks, and add either a second 16-day pallet 
(which would have to be built - although Rockwell installed the 
wiring to plug in a second pallet in OV-105) or add another 4 tank 
sets to the existing 16-day pallet (bringing it to the capability to 
carry 8 tank sets, for a total of 13 tank sets on an orbiter).  
Rockwell has published a design which makes some minor mods and adds 
the additional 4 tank sets on the existing 16-day pallet. 
 
  What are the plans for EDO:
  The USML-1 flight coming up in May/June (STS-50??) is planned to 
be the first EDO flight, with an orbital duration planned for 13 
days (if memory serves).  It will be use OV-102.   Later flights are 
planned to use EDO for 13 and 16 day missions at the rate of about 1 
or 2 missions per year.  There are no plans to use OV-105 for any 
EDO missions, nor any plans to extend to 28-days on orbit. 
 
   What if.....
   IF it is desired to go to 28-day missions it is assumed that 
the 13 day missions would be followed by 16 day missions, then 19-20 
day missions, then 22-24 day missions, then 24-28 day missions.  
However, either a new pallet would have to be bought, or the 
existing pallet modified - and there are no plans to do so. 
   IF even longer missions are desired, there are design studies to 
allow an orbiter to stay attached to an early assembly of space 
station parts to provide 30-, 60- or 90-day stays on orbit.  This is 
called the Long Duration Orbiter (LDO). In this case, the early 
parts of SSF would provide some power to LDO, allowing fuel cells on 
the orbiter to be throttled down, and allow a longer time on orbit 
with the same amount of LO2/LH2 carried on board.  However, without 
more substantial design changes to the shuttle, the lifetime of an 
LDO would be limited to the amount of time it would take to heat up 
and boil off the cryogenic LH2 and LO2, since it need some LH2 and 
LO2 to run the fuel cells for the flight back.  This boil-off limit 
currently looks like (depends on who you ask) to be from 80-120 days 
on orbit.  There are no plans to implement LDO capability, but 
there are some low-level on-going studies. 
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Wales Larrison                            Space Technology Investor

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Wales Larrison
Internet: Wales.Larrison@ofa123.fidonet.org
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