Why Is Rocket Science so Hard?

Somewhat apocryphally, rocket science has been cemented in our culture as one of the hardest things you can possibly do. Right up there with brain surgery (which, of course, lead to the comedic portmanteau “rocket surgery,” but which is actually a thing), the science that goes into launching our big metal birds into the starry beyond is utterly incomprehensible to the layman. But, why is that?

If you break it down, you’re really just inflating a really big balloon and letting it jet across the room when you let it go. But instead your breath is millions of pounds of highly explosive chemicals, and you actually want to get somewhere instead of careening wildly about. And, therein lies the problem.

Rockets Are Hard (in part) Because Earth Is Heavy

Credit: NASA, RS-25 engine test

The big issues really come into play because getting into space is really hard — on Earth. If we, for instance, lived on an asteroid, then yeah, you could actually launch something with just compressed air. That wouldn’t be terribly difficult except all the things you’d to gather and compress air, much less manufacture the tanks and other machinery wouldn’t comfortably fit on such a tiny rock. And that’s the issue. For us to really be, we kinda have to be on a planet. As far as we know, anyway. And that means there’s a minimum level of mass the planet would likely have, as well as a certain atmospheric density. Otherwise, life would be tough — if not impossible.

So, Earth has the right conditions to make us, but to have that combo, it kinda needs to be heavy and big. That means there’s a lot of gravity — a planet’s worth, in fact — that we have to fight against. And compressed air just isn’t strong enough.

Instead, we need something that can pack a huge amount of energy into a tiny space. And the best and safest place to get that kind of energy, at least for now, is explosives.

The thing about explosives, though, is they tend to rip apart whatever they’re put in. And that’s exactly the problem rocket engineers need to control. Unless you’re working with solid rocket fuels, which just burn on their own, you’ll want some means of controlling how the fuels mix together so you can adjust temperature, pressure, power, etc. as you go. And that means a combustion chamber where you mix your cocktail of zany flame-y chemistry and get the lift you need to let slip the surly bonds of Earth.

In many ways, your car runs on the same basic principle — making a bunch of booms and using that power to go.  And, though it may be impressive, doesn’t exactly inspire entire generations of children. Rockets use much more potent chemicals and manage to keep all that burning fury on just enough of a lease that it can do something useful. But, much like your car’s fuel injectors, spark plugs, etc. must be carefully controlled so you can actually go anywhere, rockets are very, very finely calibrated to do the same.

Therein lies a good chunk of the complexity in building out modern rockets. Combining a series of some number of liquids and gasses in such a way that you get enough power to push millions of pounds of steel and science into orbit, but without causing the whole thing to… y’know. Explode. Or melt. Or anything. Because car engines get hot, of course, but they are contending with chemicals that can give TNT a run for its money.

Respect the Chemistry

NASA_HDR_rocket_test

NASA/JPL

That leads us to the next big obstacle — the chemistry. While the principles of rocketry have been more or less understood for a few hundred years, starting with fireworks and the like, the complex combo sciences hadn’t been explored to the point where the devices were practical.

Metallurgy was still in its relative infancy — and believe me, it takes a lot more than cast iron to stand up to these heats — not to mention the field of chemistry itself. We had yet to discover high explosives, or even grasped what oxygen truly was. And for as much as rocket science relies on Isaac Newton’s laws of motion, so too does it need a good founding in the chemical.

There are dozens of different types of rocket fuels — each with their own advantages and disadvantages. Monopropellant, for instance, is a liquid fuel that will burn on its own. As you might suspect, this is often super dangerous and happens to be phenomenally toxic. Hydrazine, one of the more common types is infamous for its toxicity. But, still, it has its uses — namely in chemical thrusters out in space, where simple, fast, and reliable is more important than chemically safe.

While some rockets have used this on Earth, conventional wisdom has kept people closer to the kerosene end of the spectrum. And while that’s obviously pretty nasty stuff too, as chemicals go, it’s not too bad.

The Space Shuttle’s main engines, on the other hand, used hydrogen and oxygen, creating water as an exhaust. That’s not only pretty environmentally friendly; it’s incredibly efficient. But, the tech is also a lot more expensive than earlier American rockets like the F-1 (the Saturn V’s main engine), just about any Soviet-era engine like the RD-170 or even the Merlin Engine on SpaceX’s Falcon line. And, as expensive as rocketry already is, it can be hard to justify the added expenditures of safer rockets with cleaner exhausts.

These are Big Bois

Stop. Alright. How big do you think the Saturn V rocket was? It was the monster that took people to the moon and is among the most powerful machines of any kind humans have ever constructed. So. Now. Really think. How big do you think it was? Unless you’ve seen a rocket up close, it can be impossible to grasp just how gargantuan they are. But, to put it into perspective, Neil Armstrong and Buzz Aldrin and that other guy sat atop and a mountain of explosives and steel that stretched almost sixty feet higher than the Statue of Liberty — pedestal included. All of which, may I remind you, was designed to be discarded during launch. Huge chunks of metal and gear the size of national landmarks just dropped into the sea/space all to get a couple of dudes to that white rock we sometimes see at night.

If your mind isn’t blown, you really need to let that sink in. One of the largest bombs ever conceived is needed to get a few thousand pounds of anything basically anywhere.

Controlling the Damned Thing

NASA

An artist’s rendering of a rocket launching with the InSight spacecraft (via NASA/JPL-Caltech)

Alright, so putting that all together, we have the insanely complex chemistry of combining super-hot incredible powerful explosive thingies into a chamber that can’t explode or melt and then controllably flinging the explosion outside the ship and using that to control a mountainous machine. So, let’s take it another step and make it a bit harder.

Rockets, you see, can’t go straight up. Or, at least, that’s a big waste of fuel. The thing is, Earth is spinning pretty fast, and you also want to orbit the thing — generally. Going straight out is surprisingly hard because it means 100% of your rocket’s power goes to fighting the Earth’s gravity, and if you don’t have enough fuel, you’ll just become the world’s most ridiculously expensive vertical gunshot.

That’s another misconception. Most rockets don’t actually escape Earth’s gravity. They get a little further out. Those that do, often try to take advantage of gravitational slings to help. Rockets, as powerful as majestic as they are, still aren’t what you’d need to really get away from the planet.

So, your job is to steer the thing. And how do you just… drive the Statue of Liberty? Well, that’s the thing. Adjusting individual rocket nozzles, additional thrusters, controlling chamber pressures, and good ol’ aerodynamics get you there. But along the way, you realize another important problem — as you fly, Earth’s atmosphere gets thinner. When that happens, the hot, expanding gasses literally rocketing out of your engines can get unstable or lose efficiency. That’s where we get into another layer of chemistry, as well as understanding how rocket nozzles are shaped and how they need to operate. Going back to the Saturn V, it actually ran super-cooled fluid through the nozzle to help prevent the extreme heat from melting. That caused some unburned fuel to appear on the sides of the rocket exhaust — and cost a bit of power.

All of these and the thousands of little issues that crop up when you’re building a machine the size of a skyscraper are the real nature of the field. And that’s even before we get to considering how you’d literally build the thing and get people inside of it.

Honestly, the deeper I’ve looked into this, the more impressed and amazed I’ve been. Rocket science truly is a marvel of our modern world. And it deserves a huge nod of respect from us all.

But also boom-towers are just fuckin’ cool.

Written by | Geek.com


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