Tag Archives: Big Ideas

Big Ideas – Rocket Science

I hope you view my contributions to the Teen Blog as an invitation to challenge yourself, think hard, and learn new things. This entry marks the start of a new series on the teen blog, Big Ideas. So far, I’ve only introduced major themes and academic concepts obliquely, and as they happen to come up in the course of talking about something else in depth. In these Very Special Episodes, we’re going to tackle them head on, so you can prove to yourself that you can think Big Thoughts fearlessly. Very few things indeed are truly Too Hard or Too Complicated to comprehend the outline of. If you do, though, you’ll understand everything around you in a deeper way. Tragically, you won’t unlock most of these Big Ideas until sometime in college, maybe. I think this is deeply stupid and unfair, so that’s why I’m writing these, to introduce you to as many really Big Ideas as possible, in an approachable way.

To prove to you that you do have the ability to understand Big Ideas, let’s start with the most proverbially Big Idea of all.

This IS Rocket Science

Actually, it’s physics, mostly, and a little bit of chemistry.

Since I’m never one to do anything half-way, let’s make an example, where we can explore some of the math and concepts needed to put a living thing in orbit. That’s right: we’re going to model a solo orbital mission. For this, you’ll need Newton’s laws of motion. (Spoiler Alert: FOR NOW, you need Newton’s laws. I’m planning to cover special and general relativity later.) I’m going to write a summary in modern English, because here’s how Newton put it.

Yeah. So, basically everything academic that was published back then was in Latin, so everyone across Europe with a high level of education could read it. This is also the book in which Newton details calculus (Don’t forget about Liebniz too!), and also there’s universal gravitation in there, and also some extensions of Kepler’s laws… the Principia is kind of a big deal.

Are you ready? Here’s your cheat sheet!

newton's laws, the gravity equation, and the gravitational constant in a cheat sheet.

Tricky. How about we pick a model, where someone’s done something similar before?

Mercury-Atlas 8 summary, comparing the mass of the capsule to the launch vehicle.

Now, let’s chart a path to orbit by thinking through what we have to do to get something to orbit the Earth and come back. The objective is less to do the math than it is to get an intuitive idea of what the math means, and therefore a feel for the physics. It’s all about how much the mass of the rocket escalates as you add more mass it needs to carry.

why a Syrian Hamster is perfect for a space mission.
escalating rocket size.
escalating rockets 2
escalating rockets 3

P. S. A note on just how dang fast these rockets have to get the capsule to. Sigma 7’s orbital period was a little under 89 minutes. Imagine circling the entire Earth in just under an hour and a half. That’s how fast something has to go to stay in orbit. Given that F = ma, you don’t have to do the exact math to figure that even a tiny chunk of space junk slamming into a satellite or something at these velocities would be a Very Bad Thing, especially since this sort of collision would result in even more space junk orbiting at stupidly high speeds.

P. P. S. For a nice illustration of how the need to accelerate to a high enough speed fast enough impacts rocket design, compare the Atlas D series to the Saturn V rockets. “But Katherine,” I hear you whine, “what about the outer solar system probes, like New Horizons, or Voyager? Those rockets were way smaller.” Indeed. Probes can’t suffocate, die of thirst, or starve. Spacefaring humans definitely can. With a probe, you just need to get it out of Earth’s gravity well, and coast to a bigger planet or several to get a boost from their gravity wells to gain more speed. If it takes decades to do it, who cares, because it’s powered by Plutonium pellets. It’ll be fine, probably. With people, they need to breathe air, drink water, and eat. You gotta get ’em to the Moon and back, FAST. The Saturn V is a balancing act between how much fuel you need to accelerate to speeds that will save you on mass in terms of air, water, and food vs more fuel. It weighs 2,970,000 Kg. That’s a gobsmacking 5,940 Thoroughbred race horses. Glorious.

P. P. P. S. (Post-Post-Post Script) It should be self-evidently clear by now that Newton was right about that First Law. There’s precious little to exert a force to slow you down in space. The Earth doesn’t need rocket engines to keep going around the Sun. The Moon doesn’t need rocket engines to keep going around the Earth. I’m sorry if I just ruined several space odyssey movies for you. No stern chases in space. If your ship is already going faster than your pursuers’ top speed, you already got away, past tense. Just NO. Also, no sneaking up on things in space. Don’t even get me started on the consequences of relativistic speeds and Faster-Than-Light-Travel. We’ll get to ruining space movies in devastating detail later, when we do relativity, I’m sure.