

Aerotow to Orbit: The Eclipse Project - rfreytag
http://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-02-DFRC_prt.htm

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dysfunction
My only claim to expertise is playing a lot of Kerbal Space Program, but I'm
not sure this is practical. I don't think an air-breathing tow plane could
fully replace a rocket first stage.

Even if it can lift a launch vehicle to the same altitude as a rocket first
stage, velocity is the more important component of getting to orbit. A Falcon
9's first stage gets it to 11,000kph, about 3 times the top speed of an SR-71,
the fastest jet aircraft.

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zelos
You're eliminating the first part of the flight, so the rocket just has to
provide the delta-V for orbital insertion, not lift the fuel to do that from
sea level.

The Tsiolkovsky equation suggests that's going to be a big saving:

[http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation](http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation)

And yes, my only qualification is Kerbal as well ;-)

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lmm
> You're eliminating the first part of the flight, so the rocket just has to
> provide the delta-V for orbital insertion, not lift the fuel to do that from
> sea level.

Sure, but the altitude gain is almost "free" \- you need to accelerate by
something like 6 km/s laterally (number pulled out of somewhere, it's 2.3 in
kerbal space program but the planets are smaller there) and 1 km/s vertically
(depending on ascent profile, 0 for an instantaneous ascent and infinite for a
slow hover upwards, but it ends up something like that), so by Pythagoras it's
sqrt-37 = really not a lot more than the 6 kms/s you'd have to spend if you
could start at 100km altitude.

Intuitively we assume rockets go "upwards" partly because that's the part we
see, but actually the gravity turn occurs very early and most of the
acceleration is closer to horizontal. E.g. the less-crazy of the space shuttle
abort plans if something went wrong early in flight was to land at Shannon.

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birk5437
I do that in Kerbal all the time....but I just use detachable jet
engines....works great!

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birk5437
Why not lift something up with a balloon? As computers get smaller you could
probably pack more useful stuff into something like a CubeSat.

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keenerd
Think bigger!
[http://jpaerospace.com/atohandout.pdf](http://jpaerospace.com/atohandout.pdf)

(I had posted this link on its own 30 minutes ago, but it is going nowhere.)

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msandford
That's bananas! I love it.

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curtis
A related more recent NASA project is TGALS, the Towed Glider Air-Launch
System:
[http://www.nasa.gov/centers/armstrong/Features/TGALS_first_f...](http://www.nasa.gov/centers/armstrong/Features/TGALS_first_flight.html).

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jackgavigan
Interesting patent:
[http://www.google.com/patents/WO1996015941A1?cl=en](http://www.google.com/patents/WO1996015941A1?cl=en)

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mrfusion
How is this better than the Pegasus concept?

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ohitsdom
Exactly my question. Also, Virgin Galactic.

