This isn’t Rocket Science

Anibal X Diaz Ortiz

My dream has always being to work in a career field where the aspect of space and the universe were involved. This has led me to research a lot of companies and the company that supersedes the rest to me is the NASA. I gained interest in this area as a result that I would always hear the famous irritating phrase, “its not rocket science,” to mock me for the supposed easy task I was performing. So if this phrase is a synonym to one of the most rigorous disciplines, then I knew I would dedicate myself to one day become a rocket scientist.

Rockets are not as common as airplanes or helicopters, but they indeed fly. But the question is how does this occur? “The simple answer is that rockets fly by using Newton’s third law, for every action there is an equal and opposite reaction.” So in layman’s term the thrust the rocket expels, pushes the rocket upward to exit the atmosphere. The physics used to calculate the acceleration needed to depart is the conservation of momentum, “That is, for a given system, in our case the rocket-gas system, the total momentum will remain constant even if individual components move around. So if some component of the system (the gas) moves in one direction with a given momentum, some other object (the rocket) will have to move such that the two momentums exactly cancel each other out.” So if I heard the phrase “its not rocket science” so much, what was the deal with understanding this, as the equation needed to figure out the momentum is P=MV, where p equals momentum, m equals mass, and v equals velocity. Even though this equation is certainly true, its too simple to solve a complex problem, such as finding the momentum of this system, as thrust also needs to be incorporated, making it complex. And it becomes complex, because “you now have two masses to deal with, and two momentums to deal with. However, keep in mind that the total momentum of the system remains unchanged. So if we call the change in the velocity of the rocket dV, the mass of the gas emitted dM, and the velocity of the gas emitted relative to a stationary observer U, then the situation becomes Pf=U*dM+(M-dM)(V+dV), since the momentum of the system is equal to the momentum of the gas plus the new momentum of the rocket.” With this I really started to appreciate the work and time dedicated to understand the principles and concepts needed to realize such million dollar experiments.

Momentum isn’t the only physics concept applied when dealing with these complex systems; specific impulse, thermodynamics, and many others are also found. But specific impulse, “the change in momentum per unit mass for rocket fuels, or rather how much more push accumulates as you use that fuel” also needs to be calculated as it’s found by dividing the total impulse by the weight. This is crucial, because according to the NASA, “First, its a quick way to determine the thrust of a rocket. Second, it is an indication of engine efficiency. Third, it simplifies mathematical analysis of rocket thermodynamics. Fourth, its an easy way to "size" an engine during preliminary analysis.” In conclusion both momentum and specific impulse are probably the most important themes in rocket science, because the goal of launching a shuttle is to move the rocket as fast as possible, allowing maximization in cargo capacity, which is done none other than making the thrust faster and stronger.  

References:

Benson, Tom. "Specific Impulse." NASA.com NASA Glenn Research Center, 11 July 2008. Web. 29 Apr. 2011. .

"The Physics of Rockets." The Physics Behind The Rocket. Http://www.uaf.edu/. Web. 30 Apr. 2011. .

"What Is Specific Impulse?" Welcome to QRG. Www.qrg.northwestern.edu. Web. 29 Apr. 2011. .