Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 18/05/2016 09:45:06

Title: Can one rocket piggy-back on another to travel faster?
Post by: thedoc on 18/05/2016 09:45:06

Can a rocket or some sort of spacecraft be mounted on another - say travelling at 1000 km/h and then the mounted one fired at 1000 km/k to travel at 2000 km/h and another mounted on the second rocket to be fired and double the speed? If this is feasible, why is it not done to speed up the probes for the journey to Mars?
Asked by Loyiso


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Title: Re: Could we use Einstein's theory of relativity to get probes to Mars faster?
Post by: chris on 14/04/2016 19:06:38

Why have rockets on rockets? That achieves nothing more than if you just made the first rocket bigger and faster. The mass that you are accelerating is the main determinant. More mass means more fuel is required.

Title: Re: Could we use Einstein's theory of relativity to get probes to Mars faster?
Post by: evan_au on 14/04/2016 22:31:33

Quote

Can a rocket or some sort of spacecraft be mounted on another?

That is exactly the concept of a multi-stage rocket (https://en.wikipedia.org/wiki/Multistage_rocket), and it is used for space probes to Mars (as well as most rockets trying to reach space from ground level).

Most of the mass at launch is the mass of the fuel, and the tanks to hold the fuel. Once you have burnt all the fuel, the tank is just dead weight, which slows down the rocket unnecessarily. So the empty fuel tank is dropped, and another, smaller rocket starts firing.

This allows rockets with far greater range and payload than a single-stage rocket.

But there is a limit to how far you can take this concept - eventually adding another stage can double the mass (and cost, and risk), to give you a 1% increase in payload at the destination.

This is why concepts like a Space Elevator (https://en.wikipedia.org/wiki/Space_elevator) appear much more attractive than very large rockets to reduce the cost of launching payloads into space.