launch assist

=space launch



These are my favorite systems to help put stuff into orbit that aren't rockets.




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.




#1: the pulley launch tower

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.

Build a pair of towers maybe 400m high, probably with guy wires.

Partway up the towers, suspend a large water tank between them using compound pulleys. Run those compound pulley cables to pulleys at the top of the towers, then back down to the ground, and connect them to hooks on a rocket.

Put an identical tower pair on the other side of your rocket. Fill the water tanks with water from pipes going up the towers.

When the water tanks are full and the rocket is released, the water tanks fall down and pull the rocket up. The water tanks land in pools of water, and the cables fall off the hooks on the rocket.

After a launch, the water tanks are drained and lifted back up.



#2: the jet lifter

Connect maybe 20 large turbofan engines pointing upwards, maybe in a "V" shape. Add fuel tanks. Connect that to your rocket.

Start the turbofans and take off vertically.

The thrust of the turbofans will decrease with altitude. When the craft starts slowing down, start the rocket. When the rocket has higher T/W than the turbofan assembly, separate the turbofan assembly and shut down most of its engines.

Land the turbofan assembly vertically near the launch site.

This is certainly not a new idea, and it's even been analyzed a few times. I figure this type of system should be economical if it was used for 100 launches, or maybe less.



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.



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