I was watching a video of a Saturn 5 Rocket launch and I was amazed at how much fuel was used and how massive the explosion at the beginning was (and how massive the continuous fuel burn was).
But it got me thinking can we, in the future, develop rockets which can lift more payload per gallon of fuel or are all of our rockets equally efficient in terms of the rocketry version of “Miles per Gallon” because of some law of physics which we already mastered?
And I know there are alternatives like Space Elevators, but I’m specifically curious about rockets.
In: 6
Lots of people have talked about specific impulse, which is *part* of the picture, but not all of it.
What we want in a rocket is “delta-v”, which is the amount a rocket is able to change its velocity. Distances between places in space are largely measured in terms of delta-v; to get from the ground to orbit takes about 9 km/s of delta-v to be successful.
The rocket equation is:
delta v = 9.8 * specific impulse * ln(mass ratio)
The specific impulse is a measure of engine efficiency. It’s partly controlled by the fuel that is used, and partly controlled by the design of the engine. Specific impulse is important but it’s overblown by many people.
The mass ratio is the mass of the rocket when it takes off divided by the mass of the rocket when it is out of fuel. ln is the natural log function.
So, a higher specific impulse means more delta v. And a rocket that holds more fuel for a given amount of structure has more delta v.
So you can make a rocket a little more efficient if you can increase the specific impulse, or if you can make it a little lighter. But those are small, incremental gains.
Rockets do use a lot of fuel, but the cost of propellants for Falcon 9 is less than a million dollars, and the rocket itself is on the order of $50 million. The big improvement will be rockets that are fully reusable.
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