It’s Just Rocket Science

Aerospace engineering: it’s the branch of engineering that is concerned with the science and technology of aircraft and spacecraft.  This branch is responsible for all the missions to the moon, Mars, and even your short airplane ride to visit Uncle Jim out in Wyoming.

 To juxtapose the common expression:

That’s right folks, this IS rocket science we’re talking about here.

So you’re probably all wondering, how do those certified geniuses at NASA get those mammoth multi-ton monstrous flying contraptions in the air.  The answer is quite simple: they blow stuff up.

Well maybe it’s a bit more complex than that, but its all based on the basic chemical concept of combustion.  In traditional classroom chemistry, a combustion reaction is when a hydrocarbon (a molecule composed of hydrogen, carbon, and sometimes oxygen) reacts with oxygen gas to yield carbon dioxide, water, and a significant amount of energy.

When launching a rocket, all the basic concepts are still there, but with minor changes.  All combustion reactions require a fuel (or propellant) and an oxidizer.  Fuels are substances that burn when combined with oxygen to produce thrust, and heat.  In rockets, the fuel is combusted in what is called a combustion chamber down at the bottom of the rocket.  This reaction produces thrust which is pointed in a specific direction to achieve a velocity in the opposite direction by Newton’s 3rd Law.

In Earths atmosphere, there is generally enough oxygen around to complete the reaction without any need for extra O2.  However, in the vacuum of space, oxygen is not present.  This brings in the need for oxidizers, which can provide the necessary O2 needed for the reaction to run.  Therefore, oxidizers are not only limited to pure oxygen gas, but can also be compounds with oxygen in them where the oxygen is easily separated from the compound.

There are many different types of fuel with varying chemical formulas and efficiencies.  One way to compare these fuels against one another is to use specific impulses.  This is measured in pounds (or Kilograms) of thrust generated by one pound (or Kg) of propellant per one second. This helps gauge the efficiency of a fuel based on its chemical and physical characteristics.

Two large subdivisions of fuels are solid propellants and liquid propellants:

The simplest fuel type is solid propellants. It is stored easily within a cylinder with the oxidizers packed in.  A spark gets the process going, which cannot be stopped, and reset easily.  However, this is generally the lightest, and has less mechanical and electrical parts.

Liquid based propulsion systems are more complex than solid fuels with storage tanks and intricate pumping systems, but carry some more benefits.  Fuel flow can be adjusted on command by simply adjusting the flow of propellant into the combustion chamber by way of a valve.  By doing this, one can throttle, decelerate,  stop, and restart the engine with ease.

Within this category of liquid propulsion systems is the important subcategory of cryogenic propellants.  As a crucial part of astronautics and aeronautics dating back to the 1940s, cryogenic propellants are liquids of typical gases at STP, such as liquid hydrogen (LH2) and liquid oxygen (LOX) as its oxidizer as the most common example.  Sub-zero methods are utilized to freeze these gases into liquid fuels that are known to have specific impulses 30-40% greater than their gaseous counterparts.  This is solely due to the change in state; liquid hydrogen, though not at all dense by normal standards, (0.071 g/ml), is ultimately more dense than its gaseous form.  Therefore, due to this increase of actual fuel per unit volume, a smaller volume of liquid fuel can replace a larger volume of gaseous fuel, making it more efficient.  Not to mention, as a liquid, it can be pumped into the combustion chamber more easily, again emphasizing the difference in energy obtained just by the difference in state.  Hence, the cyrogenic liquid propellant provides, to quote funk band Zapp and Roger, “more bounce to the ounce.”

RL10 engine: common cryogenic propulsion system used in jets and rockets (note : LOX and LH2)

However, there are still multiple different types of propulsion techniques still being researched.  One method that has made recent advancements involves applying a charge to liquid propellant to create a stream of ions, released from nozzles as charged gas, producing thrust.  The upside to this is that a device like this is about the size and the weight of a Lego brick, and it can be used for smaller satellites as to not “clunkify” them by attaching large, heavy thrusters.

Overall, getting these just giant flying contraptions in the sky isn’t as complicated as most people think it to be when they say it’s “rocket science.”  When simplified into basic chemistry terms such as combustion, density, and states of matter, this process is not nearly as threatening as the harrowing pillars that it launches into space.


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