This NASA document has been around for a while, but it remains relevant. If you’re going to engage in space travel, you have some unyielding scientific and engineering realities to contend with. This article is a bit dry, but it’s a pretty good introduction into the realities of spaceflight.
Tyranny is a human trait that we sometimes project onto Nature. This projection is a form of rationalization, perhaps a means to cope with matters that we cannot control. Such is the case when we invent machines to free us from the bounds of Earth, affecting our escape into space. If we want to expand into the solar system, this tyranny must somehow be deposed.
Rockets are momentum machines. They spew gas out of a nozzle at high velocity causing the nozzle and the rocket attached to it to move in the opposite direction. Isaac Newton correctly defined the mathematics for this exchange of momentum in 1687. Conservation of momentum applied to a rocket was first done by Russian visionary and scientist Konstantin Tsiolkovsky in 1903. All our rockets are governed by Tsiolkovsky’s rocket equation.
The rocket equation contains three variables. Given any two of these, the third becomes cast in stone. Hope, wishing, or tantrums cannot alter this result. Although a momentum balance, these variables can be cast as energies. They are the energy expenditure against gravity (often called delta V or the change in rocket velocity), the energy available in your rocket propellant (often called exhaust velocity or specific impulse), and the propellant mass fraction (how much propellant you need compared to the total rocket mass).
read the rest at NASA – The Tyranny of the Rocket Equation.
There is, of course, another tyranny this article doesn’t mention: the tyranny of economics. In truth, you can brute force your way through the tyranny of the rocket equation if you have enough resources. But to get those resources, there has to be a payoff.
We often hear talk about the spirit of exploration, evoking the age of discovery when Europe explored the rest of the world. What is often not mentioned is that the age of discovery was motivated by economics. Initially it was to find alternate trading routes to the spice islands (other than the difficult and dangerous overland routes through Asia), but later the incentives became extracting resources from far flung colonies.
I’ve said it before, but for the space age to really get started, it will need an economic incentive. We need a space age version of the spice trade, only much bigger since space is much more expensive. Until we find it, most of our exploration will continue to be by robots (of increasing intelligence and sophistication) with a few symbolic manned missions. We may even put a colony on Mars, just to prove we can do it, but without an economic incentive, it’s unlikely to last.
So yes, the tyranny of the rocket equation must be contended with, but so must the tyranny of economics.