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...It only takes building 4 Space Solar Power satellites per yearto.....



 
 
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Old December 19th 09, 11:02 PM posted to sci.space.policy,sci.space.history,sci.physics
William Mook[_2_]
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Default ...It only takes building 4 Space Solar Power satellites per yearto.....

On Dec 17, 10:24*am, Me wrote:
On Dec 17, 3:06*am, "Androcles" wrote:

Three SRBs can lift the vehicle to orbit without the tank


No, they can't. *They would burn out at 2 minutes into the flight with
the orbiter still in the atmosphere and 1000's mph short of orbital
velocity. *The SSME's using propellant from the ET provide most of the
velocity.
The SSME and ET provide approx 588M pounds sec of total impulse. *One
SRB only provide 336M pounds sec of total impulse, not enough. *And
the burn is too short


Exactly right! A pound of SRB propellant will produce a pound of
thrust for 260 seconds. A pound of ET propellant will produce a pound
of thrust for 455 seconds. This is an important point captured in the
rocket equation;

Isp = specific impulse = 260 for SRB, 455 for SSME

Vf = Isp * g0 * LN(1/(1-u))

Where Vf = final velocity (9.2 km/sec)
Isp = specific impulse
g0 = gravity constant = 9.802 m/sec
u = propellant fraction needed achieve Vf given Isp
 




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