rocket – Page 2 – Kerbalism

Welcome to Kerbalism! I’m your host, Aubrey Goodman. Space is strange and foreign. There are lots of terms and concepts you probably haven’t heard before. We will use this terminology throughout the show, so let’s review the basics!

First, you blast off straight upward until your orbit reaches the desired altitude. The point with highest altitude along your orbit is called the apoapsis. Accelerating upward will raise your apoapsis. This is called a prograde burn; prograde means adding energy to the vehicle. When the craft reaches the apoapsis, we initiate a second maneuver (also a prograde burn) to accelerate sideways and increase our speed.

This raises the periapsis, or point with lowest altitude, up to the same altitude as the apoapsis, resulting in a circular orbit. In a circular orbit, the craft’s velocity doesn’t change very much. If we are orbiting a body outside of its atmosphere, there are no forces to accelerate the craft. This is referred to as a stable orbit.

If we wanted to land from a circular orbit, we would need to slow down, performing a retrograde burn. Retrograde means removing energy from the vehicle. Wherever we are along a circular orbit, burning retrograde will cause the apoapsis to settle at the craft’s location while the periapsis descends toward the planet’s surface on the opposite side of the orbit.

As the craft descends, its velocity increases. To be clear, we slow down now to speed up later at a lower altitude. If the periapsis is inside the atmosphere, we will begin to lose energy to drag forces. As we drop lower into the atmosphere, drag increases and vehicle speed decreases.

If instead we wanted to visit a moon orbiting the planet, we would need to burn prograde to speed up and raise the apoapsis to a higher altitude. This has the opposite effect as before. As the craft ascends, its velocity decreases. This time, we speed up now to slow down later at a higher altitude.

Each of these maneuvers is introducing a change in velocity, known as delta-v. As we compare different aspects of spacecraft design, we will be focused on optimizing delta-v. Many of the tools we use include automatic calculations for delta-v.

At this point, you might feel confused. In an elliptical orbit, the velocity changes along the path, so isn’t that the same as delta-v? Well, not exactly. As the craft moves around the ellipse, it speeds up toward the low point (or periapsis) and slows down toward the high point (or apoapsis). Each time the craft travels around the path, it returns to the periapsis with the same speed as it had the last time. Unless there is some other influence acting on the craft, it must obey the laws of physics and mathematics.

That’s all for this quick review. Stay tuned for satellite deployment!

And thanks for watching Kerbalism!

Vimeo: https://vimeo.com/305384440

YouTube: https://www.youtube.com/watch?v=wMqwyPoBY5k

Space is dark, lonely, and cold… most of the time. Rockets are dangerous; sometimes they explode. Atmospheric re-entry is violent. Sometimes parachutes don’t deploy. In short, space is hard.

From the very first rocket tests in the 1930s, rocketry has been a dangerous field. Early rocket tests had no passengers of any kind. We didn’t want to risk sending humans into the unknown.

After the early rocket tests started to stabilize and launches were starting to succeed more frequently, we expanded to biological payload. Yes, we sent a monkey into space. While we may want to believe he looked like an astronaut in a space suit, in reality it was different. The world saw it on the cover of Life magazine in 1961.

Once we proved we could keep a monkey alive, we started sending manned missions. Over the years, many brave men and women gave their lives so we could learn how to protect living passengers. The stakes are very high, and even the smallest mistakes can lead to catastrophe. Make no mistake, this is a high risk high reward scenario.

We continue in the face of adversity because the benefits are nearly limitless. The cultural and scientific value of visiting other planets is hard to imagine, let alone calculate.

You can read about all the heroes, tragedies, and triumphs in history books. You can also read textbooks about orbital mechanics. But how do we make it easily accessible to everyone? With games! Video games rely on simulated environments to represent the physical world with stunning accuracy.

We can use tools like Kerbal Space Program (KSP) to learn more about space in a fun and emotionally compelling way. It empowers intrepid explorers to design, build, and fly rockets and experience the challenges of space flight in a hyper-realistic way. Before we get into the details, let’s start with something we can sketch on paper.

Here’s a thought experiment: draw a small circle beside a larger one and label them Moon and Earth, respectively, and ask people to draw the path a spacecraft might follow in order to travel from the Earth to the Moon. Many will draw a straight line from one circle to the other. Few will connect the two circles with an ellipse.

While you could try to aim your rocket straight at the Moon, your path would be anything but a straight line. This is because of the immense power of gravity. Inside the sphere of influence of any massive body, everything moves along clean mathematical curve shapes.

As long as you’re not actively accelerating using engines of some kind, your spacecraft is adrift in the cosmos, confined to a fixed orbit forever. In many cases, this is the final goal of the craft, to maintain a stable orbit around some stellar body.

This is achieved by executing a series of maneuvers, where we burn fuel to accelerate and change to a different orbital curve. Then we wait for gravity to pull the craft to an intersecting point on another curve. The rules are simple, but there are a lot of variables to consider when designing a launch system.

And that’s the trick – we’re never just designing the spacecraft; we’re designing the craft, as well as the plan to execute its successful deployment at some point in spacetime. We’re not just driving on paved roads to the local supermarket. Launch planning sometimes involves several maneuvers, docking with other craft for fuel, supplies, and crew transfer. Orbital alignments wait for no one.

This is the essence of Kerbalism. Thanks for watching and stay tuned!

Tag: rocket

Terms & Concepts

01 – Intro