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It seems a large amount of rocket fuel during launches is spent to get the mass moving; indeed according to QuickLaunch, Inc. it takes 40% of the rocket fuel to get to Mach 1.3. It seems as though the engines are firing quite a while before liftoff, and considering that the full launch weight of the space shuttle is 4.4 million pounds (~2 million kg).

Would it be feasible to add a counterweight system to help it get started? It seems as though one could be built with a structure a few hundred meters above the launch vehicle, which could significantly reduce the launch weight and get the upward motion started sooner.

What I'd imagine is four cables attached to the launch vehicle, running up to the structure and each having ~400,000kg weights attached. This would make the rockets only need to lift ~400,000kg for the first, say, 200m, which would lead to much greater acceleration for this span and it'd be to Mach 1.3 much sooner.

Is this too hard to make? Would it have any noticeable effect on the fuel requirements, or would it be negligible? Is the acceleration already near the limits of the astronauts' bodies? Or would it just be one other thing that could fail? The reason I ask it just because of the seemingly ludicrous amount of weight that needs to be launched.

Are there any other methods in the works to assist the launch besides rockets for manned vehicles? It doesn't seem space guns or sky ramps are ever planning on having humans in the launch vehicles.

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All are probably waiting for Superconductor maintenance man. Once it's in hand, everything would become handy..! One more thing: Even though you've used some counterweight methods for conserving fuel, the total energy required would be the same. But instead of fuel, the counterweight requires a lot of manpower and new bills..! I've already answered your Trebuchet question with Mass Drivers. Please refer Wikipedia..! – Ϛѓăʑɏ βµԂԃϔ Sep 12 '12 at 17:02

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I think the main reason why this is not done is that the first stage in most rockets burns for several minutes. The acceleration from a counterweight cannot be higher than $g$ and for a falling distance of $200$m the total speed of $g\cdot t \approx 63$m/s is not significant enough to warrant such a huge engineering challenge.

On the other hand this looks very different if a higher acceleration is used, e.g. in a railgun or mass driver. Here the acceleration and terminal velocity is much higher but this is still only done on a research level.

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In addition liquid rocket engines run for a few seconds to get pumps upto speed and temperature. The engine gimbals are also used to balance the rocket as the support clamps are released – Martin Beckett Sep 12 '12 at 15:14
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Using a pulley system or something you could achieve an acceleration greater than $g$ using a counterweight. (Probably not practical for a rocket, though) – David Zaslavsky♦ Sep 12 '12 at 18:27
@DavidZaslavsky: Yes, I thought of that after I wrote the answer but a pulley for a rope that holds 400 tons is beyond my imagination and it does not really help as the kinetic energy is the same for the same counterweight. – Alexander Sep 12 '12 at 20:08

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