=space
These are my favorite systems to help put stuff into orbit that aren't rockets.
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Rockets are often considered inefficient, but they're actually
quite efficient at expelling gas at ~3 km/s. The inefficiency generally
comes from mismatch between rocket speed and exhaust speed.
So, any
reasonable launch system should probably involve rockets, and any launch
assist system should probably involve launching a rocket at under 1500 m/s.
If you're launching something at under 2 km/s a gun using high-pressure
gas will almost inevitably be lighter and cheaper than an electromagnetic
gun.
If you're launching something at low altitude, drag will be much
higher if it's supersonic.
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#1: big trebuchets
Aircraft catapults on aircraft carriers are the closest thing in real
life to rocket launch assist systems, and if you extrapolate the costs,
they're too expensive. Something cheaper is needed to be practical.
Something...low tech.
Sometimes, the best solution to a modern
problem is to use an old design, but bigger and with modern materials.
Trebuchets have historically been effective for launching heavy projectiles
at moderate speeds.
Build a concrete tower maybe 300m high. Put a
large steel arm on it, with plain bearings. Put a counterweight on the arm,
maybe a big water tank. Attach a cable to the other end of the arm. This is
a trebuchet assembly.
We want to launch straight upwards, so let's
use a pair of trebuchet assemblies, sharing a single cable. The center of
the cable goes under a hook on the side of the rocket. This trebuchet pair
is similar to a
springald, but it uses gravitational potential energy and can only fire
upwards.
We need to support both sides of the rocket equally, so
let's add a second trebuchet pair on the other side.
Construction
cost might be similar to bridges with towers of similar height.
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#2: the jet lifter
Connect maybe 20 large turbofan or turbojet engines pointing upwards, maybe in a "V"
shape. Add fuel tanks. Connect that to your rocket.
Start the jet
engines and take off vertically.
The thrust of the jets will decrease with altitude. When the craft starts
slowing down, start the rocket and separate it from the jet engine assembly.
Shut down most of the jet engines, and land the jet assembly vertically near the launch
site.
This is certainly not a new idea, and it's been
analyzed
a few times. I figure this type of system should be economical if it was used
for 100
launches, possibly fewer.
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Of course, these would have a smaller impact on launch costs than development of cheaper rockets could. But most people find novel configurations more interesting than thoughts on turbine manufacturing and thermodynamic cycles, and I don't really feel like blogging about turbine technology either.