Air Launch Advantages
Below are some of the Advantages of Air Launch. For a really small
to get into space,
air launch can make the difference between making it and not.
Interesting Air Launch Links
Air Resistance for Small Rockets
Air resistance is much more of a problem for a small ground launched rocket than a large one.
The total energy of the rocket is determined by the amount of fuel, which goes up with
the volume of the rocket, or the cube of the dimensions. The air-resistance is going
up with the cross-sectional area, which goes up with the square.
Rockets in Vacuum
The ISP for a rocket is usually rated at sea-level and in a vacuum. If the ISP is 300
at sea-level it might be 350 in a vacuum. Launching at 60,000 feet is much closer to
a vacuum than sea-level, so the rocket is more efficient.
If you can design the rocket to operate in low pressure/vacuum and not
sea level, then you don't have to compromise the design so much.
Better Failure Modes
A rocket taking off from a launch pad will probably fall back and explode if the engines
fail during lift off. An air launched liquid fueled rocket should be able to dump
fuel and land if the engines fail. This is called "intact abort" and is a very good thing,
since the rocket and any cargo can live to fly again.
By starting out high the rocket can aim more horizontally. Since orbit
depends mostly on horizontal velocity, this is efficient.
If you start from the ground you are better off to go mostly vertical
at first to get out of the air faster.
Starting from higher up gives you the potential energy of that height
before you even start the rocket. This is a smaller effect than
the above 2, but every bit helps.
Lower/Shorter Aerodynamic Loads
Starting out at 60,000 feet you have less aerodynamic pressure
and less heating.
You can also get rid of a payload shroud earlier. Getting rid
of mass saves your rocket energy for the other mass.
Lower Acoustic loads
In a ground launch acoustic energy is reflected from the
ground back to the vehicle, but this doesn't occur in an air launch.
The thinner air of an air launch also reduce
An air launched vehicle can avoid turbulance during the rockets
flight, so can be designed a bit lighter. You can also avoid lightning.
An air-launch is going to have less red tape to deal with than a
rocket using a government launch site. The only private
launch site so far is Sea-Launch.
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Copyright (c) 2002, 2003 by Vincent Cate. All rights reserved.