# What happens if we place a hydraulic platform under rocket exhaust

Imagine I place a hydraulic platform mechanism under a rocket where its engine exhaust is placed.This hydraulic platform is fixed on the ground. During propulsion we actuate/lift platform to certain height (assume 100meters) with a pump. We can do some maths and find the initial velocity of the rocket and with same velocity we will lift the platform.

Will it double the velocity of rocket? Will there be any issues apart from the platform design?

## 1 Answer

A rocket motor doesn't have to push against anything. It works by accelerating the exhaust gases to very high velocities. There is more on this in the various answers to Rocket/Thrust/Gas/Free Expansion of Gas.

So putting a platform below the rocket motor is not going to change the thrust by any significant amount. However it is likely to blow up your rocket motor by reflecting hot gases back towards it and overheating it.

• You will get a little more thrust due to the higher pressure difference, but I also wonder if you lose thrust due to this, since the specific impulse of an rocket engine decreases with higher atmospheric pressure. Commented Jan 24, 2014 at 10:48