🚀 go-pugleaf

David Anderman writes:
  
>Using a 50,000 lb. payload for the Shuttle to calculate its cost
>per pound does not take into consideration the trivial fact that
>the Shuttle never carries 50,000 lbs into orbit. Maximum payload
>weight for a safe abort is 40,000 lbs, and the shuttle rarely
>carries that much weight.
  
   There are several other factors here, and I believe, a
misstatement.  The factors are that many shuttle missions do not go
to 150 nmi, 28.5 deg. circular orbits.  If the shuttle goes to a
higher orbit such as was done for Space Telescope deploy, its
performace decreases (as does every other launch vehicle).  So I
would not expect the shuttle to carry its max rated capacity for 150
nmi to 250 nmi or so.  Similarly, if the shuttle launches to a
higher inclination orbit than 28.5 deg, say to 50 deg inclination,
then its performance also decreases (as does every other launch
vehicle).  Again, I would not expect the shuttle to carry its max
rated capacity for 28.5 deg inclination 150 nmi orbits to 40 deg
inclination 150 nmi orbits.
   On that basis, yes, the shuttle rarely carries its maximum
achievable payload, if that maximum payload is measured to 150 nmi,
28.5 deg circular orbits.
   Probably a better comparision is to compare the percentage of
maximum payload possible (based upon vehicle performance to that
altitude and inclination) to what was actually achieved.  Based upon
my analysis of this, incorporating the masses of the primary
payloads (IUS/TDRS, Spacelabe etc), plus secondary payloads (middeck
locker experiments, GAS cans, crew experiments), and compared to the
expected vehicle performances into the altitudes and inclinations
the shuttle was launched into,  I find the shuttle manifest
typically runs about .95-.97 full.
   I found this result rather surprizing (I was trying to justify ET
propellant scavenging into unused payload performance to fuel a
resuable space tug), but the simple answer I found what that
secondary payloads (GAS cans, crew experiments, middeck locker
experiments) are used to fill up unused primary payload
performance -- yet typically only pimary payloads are listed on the
manifest.  And there is quite a long waiting list of secondary
payloads who want opportunities to fly ...
  
   The misstatement is the 40,000 lbs safe return weight.  There are
actually two safe return weights, with a much higher value based
upon a 1 time safe return, versus a routine return.  Please read the
following, which is a repeat of a November posting (which is a
repeat of an earlier posting).
  
   ORBITER RETURN PAYLOD CAPABILITY
   Orbiter return capability is totally different from orbiter
delivery capability.  The orbiter return delivery capability is
calculated on an individual vehicle and mission capability - based
upon total return landing weight.  Furthermore there is a 1-time
contingency landing capability as well as a regular mission limit.
   The limit is driven at (from memory) about 240 Klbs routine
return weight on the landing gear/tires.  OV-102, since it is about
9,000 lbs heavier than any other vehicle, is certified for regular
returns of about 32,000 lbs of payload. OV's-103, -104, and -105 are
much lighter weight vehicles and can accommodate higher weight
payloads, typically in the 40,000 lb or higher category, on a
regular basis without exceeding the 240 Klb limit.
   However, there is also a higher certified safe limit for a 1-time
contingency landing.  If the shuttle is launching a 45,000 lb
TDRS/IUS, it obviously can't dump the payload before landing in a
RTLS or TAL abort, yet it must be able to land safely.  And there
might be a heavy payload that won't deploy.  So the orbiter is
certified to land, at least once, with a gross weight at landing of
about 275Klbs, which is about a 75,000 payload on OVs -103, -104,
and -105.  After such a landing, it would be necessary to reinspect
and recertify the landing gear, but it has been exhaustively
certified that it won't crash or collapse in such an event. I called
and talked to a Shuttle landing gear designer I used to work with,
and he thought an inspection would be sufficient in such an event,
based upon the landing data from the previous 45 [now closer to 52,
I believe] or so flights.
  
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 Wales Larrison                          Space Technology Investor

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