[PLUG-TALK] Wingspan of 385 feet - bigger than the Spruce Goose - for satellite launching
keithl at kl-ic.com
Thu Jun 1 13:31:13 PDT 2017
On Thu, Jun 01, 2017 at 10:10:25AM -0700, Michael wrote:
> Paul Allen has constructed a twin fuselage airplane monstrosity to
> lower the cost of satellite launches.
Software people doing rocketry. Hmphf. Hey guys,
learn the physics. Reality is not an #IFDEF
Specifically: Real rockets launch straight up.
They must be AT LEAST 50 kilometers up before
they start accelerating horizontally. Otherwise,
the atmospheric drag is gynormous. Learn about
MaxQ, maximum aerodynamic overpressure.
Once above the high drag atmosphere (80 km or higher)
aim horizontally. Below that, the drag is high enough
to slow down fast and reenter. Space shuttle Columbia
burned and broke up at 70 km altitude.
Orbits are ellipses. If the entire orbit is not above
the dense atmosphere, you slow down the next time you
pass through. If the ellipse intersects the Earth, this
is called "lithobraking", which is like aerobraking,
except the aerodynamic media is granite. Ouch.
There are some small air-launched orbital rockets.
These have lousy reliability, because they must
transition from "fuel at the side" to "fuel into
the turbopumps". Many other structural problems,
plus a tendency to destroy the launch airplane if
things go really wrong.
The main reason for an air launch is that it allows
the launch airplane to fly under the orbit of an
existing space satellite and launch into that orbit.
A fixed position launch site like Kennedy Space Center
only rotates under a satellite orbit twice a day,
and one of those passes is a launch to the south,
a trajectory passing over Bermuda, risking lives in
case of a failure. An air launch from a plane over
the ocean does not have this problem. Instead,
there's the long flight over the ocean, carrying a
huge fuel-air bomb.
So ... this is silly. Paul Allen needs better advice,
or time to read some good books on space launch.
Keith Lofstrom keithl at keithl.com
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