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KSC Next Gen Site ___Questions? Comments? Highly Reusable Space Transportation Study |
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rocket works by combining fuel with oxidizer, but all the
oxidizer, unlike cars or airplanes, all the oxygen, is
carried aboard the rocket. Not so for cars or airplanes.
The physics of a rocket mandates that most of the rocket
at lift off is thus propellant. Most of the rocket is not
rocket structure holding the propellant nor other parts
of the rocket. By weight, it's mostly propellant. Some
numbers - a typical passenger jet plane may be 30%
propellant, in this case jet fuel, and 70% aircraft, by
weight. For a rocket the propellant may be in the range
of 85% propellant and 15% rocket, by weight. This 15%
does not make for an easy design, one that will be robust
and can preoccupy itself with affordability, ease of
operation, reliability or safety. Mostly at 15% of
something to hold 85% of something else, the
preoccupation is just to get of the ground, and if need
be return, such as with the Space Shuttle. Expendable
launch vehicles do not significantly depart from this
basic reality. Separating / dropping stages during ascent
is simply a means of discarding structure that is no
longer required for the rest of the ride, but which was
still just as fragile and weight limited. Now imagine some of the oxidizer was taken from the air as the spaceship traveled through the atmosphere. The topic of Rocket-Based Combined Cycle spaceships was explored extensively in the HRST work as to it's effects on affordability of operations, reliability and safety. Potentially, in theory, such extreme machines using SCRAM cycles, if the barrier of thermal management and materials, both external and internal, could be overcome, could get to where an aircraft-like spaceship, taking off horizontally, would be as much as 35% "ship" and *the rest propellant, vs. 15% today with stages and the throwing away of stages. The possibilities are explored here in the broader context of the effect such technology could have on creating routine, affordable access to space. *...see the wiki for more on what the term "mass fraction" means... *...also see the NASP wiki... 1998
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1995 _____________________ Also see: _____________________ Website Contact: Edgar Zapata, NASA Kennedy Space Center |