Mitch wrote:
Hi there,

Why would one not
use something like a modified commercial airliner (make it airtight and
so forth) and then perform a regular take off and fly up to the
altitude where the air still supports the lift on the wings (using
plain old kerosene) and then once that barrier has been reached utilize
a rocket engine to make it the rest of the way.

Gaining altitude and actually getting outside of the atmosphere is
easy. The space shuttle does that in under a minute. The whole rest
of the flight is gaining speed. So when you see the shuttle sitting on
the launch pad and you look at that huge tank of fuel, don't make the
mistake of thinking, "wow, it takes all that fuel to get up into
space." The truth is, it doesn't take much fuel at all to get into
space. It takes A LOT of fuel to get up to speed.

Your 747 idea is a way of using wings to gain altitude. That would be
a good idea if altitude was the problem.

To actually use an aircraft to launch a spaceship (the way Burt Rutan's
Spaceship One worked), you need to have a mothership that can lift the
spaceship *and* the fuel needed to gain orbital speed. So, imagine an
airplane carrying a big heavy tank of fuel like the shuttle's external
tank. The shuttle's main fuel tank holds 800 tons of fuel. That's
pretty heavy. The largest aircraft in the world is the An-225, and it
can only lift 275 tons. You'd need a much larger airplane to carry
enough fuel to get up to orbital speed.