Mitch wrote:
Hi there,

One thing that I always wondered about space flight is why most
agencies (NASA, etc.) do not use a more efficient way of lifting into
space. The vertical rocket takeoff seems to use so much energy and does
not take advantage of the physics of regular flight. 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. Should this not allow
for much greater payloads to be carried since less fuel is needed to
get up to 30,000 ft? Plus one could use established procedures such as
in-flight refuling at altitude to lessen the need for fuel at take off
even more.

Just imagine how much could be hauled into space and how much cheaper
it would be if one would modify a 747 and use the cargo capacity of
such a plane. I realize that this is a little simplistic in its
description (put a rocket motor on a 747 and have it lift off), but
nevertheless, why not take advantage of wing designs, etc. to get into
space.

I am sure that there is a very good reason why this has not been done
yet, since there are thousands of very smart people working on these
problems. I would just like to know what the negatives are to this idea
that would make it not feasible to implement. I can't imagine that it
would be cost, since they spend a boat load on the shuttle program as
it is.

Thanks for taking the time to answer this question.



Regards,
Mitch

Others have talked about the fact that you need horizontal as well as
vertical speed. The reason rockets start out vertically is to get up out
of the most dense atmosphere, as soon as possible. Orbital speed is
something like Mach 27, but you can't do that in the earth's atmosphere;
aside from the fuel it would take, you'd burn the spacecraft to a
cinder. Boost trajectories are designed to start out vertically, but
transition to horizontal flight as the atmosphere gets thinner. As a
matter of interest, boost trajectories today are designed by computer
programs that calculate the most efficient path.

Having said that, your idea of using an airplane to lift the rocket to a
higher altitude is a good one, and as someone else has pointed out, it's
one that was used by Burt Rutan, in capturing the X-Prize. The White
Knight served the same purpose as your 747, and lifted Starship 1 to as
high an altitude as it could. For all practical purposes, this meant
that the space ship could start out with a full tank of fuel, rather
than having expended a bunch of it getting up to there.

A booster that is becoming popular lately is the Pegasus. It's carried
under a jet plane (sorry, I don't know which one) to altitude. Since it
must be carried by a plane of reasonable size, it's too small to boost
astronauts, but works just fine for smaller payloads.

Way back in the 50's, researchers in White Sands were firing "sounding
rockets" vertically, to learn more about the atmosphere at high
altitudes. A popular booster was the Wac Corporal, which could reach a
few hundred miles, launched vertically. Someone got the same bright
idea you did, and built the "rockoon," which was a Wac Corporal lifted
to altitude by a huge balloon. With most of the atmosphere beneath it,
the rockoon went to an altitude of four _THOUSAND_ miles. That's the
difference an atmosphere makes.

Jack