Tag: space

Satellites Part 3: Deploying to Solar Orbit

by aubreygoodman, posted in Kerbalism

Vimeo: https://vimeo.com/308309765

YouTube: https://youtu.be/xpVvTuxP1XA

Welcome to Kerbalism! I’m your host, Aubrey Goodman. In this episode, we deploy two relays to solar orbit to become the backbone of our solar system communications relay network.

Before we can expand our horizons to visit other planets in the solar system, we need to have some infrastructure. Satellites sent to moons only need to communicate back to their planetary base. If we sent a satellite to another planet, we would need to make sure it has a very powerful radio to reach our home base. Also, as planets move around the solar system, the distance between them changes. In some situations, planets might find themselves on opposite sides of the star.

If we introduce a relay network in solar orbit, we can support a wider range of missions. Kerbin orbits around its star at 13.6 million kilometers. By placing a pair of relays in solar orbit at 8 million kilometers, the relays themselves are never more than 16 million kilometers apart, nor more than 16 million kilometers from Kerbin. This way, anything within range of a relay will be able to communicate with home base.

For orbital missions, such as placing satellites in orbit of other planets in the system, having a solar relay network is vital to maintaining connection with your probes. This will reduce payload antenna requirements and thus reduce costs, enabling more missions over time.

Observant viewers will note the two-node approach suffers the problem of having the star directly in the line-of-sight path between the relays. Using a three-node approach would eliminate the line-of-sight problem, at the cost of one extra relay. Also, positioning the relay itself is a very slow process, and making adjustments along the way would use too much fuel. Like so many things in space, it’s important to get it right the first time.

In this case, we settle for having two relays in circular solar orbits, and not quite exactly opposite each other. This gives us coverage for missions to all inner planets. The natural evolution of our relay network is to send smaller relays to each planet. This enables reduced cost missions with smaller radio equipment. If the probe only needs to communicate with the nearest relay network node, we can use the same equipment we used for lunar satellites.

So that’s all for relays. Now that we have the basis of our relay network, we can begin to discover more things about our solar system. One way we do that is by building stations in orbit. So, in our next episode, we’ll discuss orbital stations around our planet. Stay tuned!

And thanks for watching Kerbalism!

Satellites Part 2: Lunar Orbit

by aubreygoodman, posted in Kerbalism, Orbital Basics

Vimeo: https://vimeo.com/307753956

YouTube: https://youtu.be/qCvHz1n0qxU

Welcome to Kerbalism. I’m your host, Aubrey Goodman. In this episode, we’ll review the deployment of satellites to lunar orbit.

First, let’s expand to consider the nearest moon. It requires more deltaV to get there, and more still to stabilize in a circular orbit. The good news is our Kerbin orbital satellite is over designed for its task. Its first stage does almost all the work, and we have plenty of fuel left over in the second stage for transfer orbit burns.

Once the craft is in planetary orbit, we need to perform two maneuvers to stabilize into orbit around Mun. If we do a really good job executing the maneuvers, we will settle into a circular orbit.

Orbital transfer between Kerbin and Mun can be done really at any time from a mostly equatorial orbit. This refers to the inclination of the orbital plane relative to the rotation of the body. Kerbin and Mun have very similar inclination, making it convenient to transfer between them. As we’ll find later, Kerbin’s other moon, Minmus, has a different inclination.

While a transfer can be made between Kerbin and Mun at any time, there are optimal points along the orbit where fuel use can be minimized, due to favorable alignment. Sometimes, we can save a huge amount of fuel simply by waiting for 20-30 mins.

Once we find a transfer orbit we like, with a destination periapsis at the desired altitude – that means the periapsis of the resulting orbit around Mun – once we find that periapsis, we can proceed with executing the maneuver at the appropriate time. Even perfect execution will result in slight misalignment with your designed objective. This is expected. If necessary, you can make corrections with RCS, but this is generally not required.

Now, after some time has passed your craft has traversed its path and is now approaching the periapsis of the destination orbit. You must burn retrograde until you slow down enough to stabilize into an elliptical orbit. Then, bring the apoapsis down to around the same altitude as the periapsis, resulting in a circular orbit.

Kerbin has a second moon, called Minmus. Its orbital inclination is about 6 degrees higher than Kerbin, so any craft headed there must also perform a maneuver to align its inclination. This is ideally done during orbital ascent, which reduces the inclination difference.

Our over designed satellite has enough fuel to enter stable orbits of both moons. But it also does very little. As we add capability to our satellite, the payload mass increases, and the first stage fuel requirements increase exponentially.

So that’s it for lunar satellites. In the next episode, we’ll focus on solar satellites; that is, satellites on an orbit similar to a planet. Those will lead us to a place where we will be able to establish a relay network of satellites that allows us to explore a wider part of the solar system. So stay tuned for that and much more!

And thanks for watching Kerbalism!

Satellites, Part 1: Deploying to Low Orbit

by aubreygoodman, posted in Kerbalism, Orbital Basics

Vimeo: https://vimeo.com/307509709

YouTube: https://youtu.be/ZcPy605hAiM

Welcome to Kerbalism! I’m your host, Aubrey Goodman. In this episode, we’ll review the basics of deploying a satellite to low orbit. Let’s get started!

Long before we think about sending people into orbit, we need to send smaller unmanned probes. These serve as opportunities to learn about the perilous environment of low orbit. As we’ll show, they also present a solution to the issue of communication within the solar system. Without relays to boost the signal back to the origin planet, probes must carry heavy radio hardware powerful enough to reach home. Heavy things cost more to send to orbit. Lowering the cost is often a matter of reducing payload mass or using fuel more efficiently. There are many things to consider, even when designing a simple satellite deployment mission.

First, let’s look at the simplest case, deploying to planetary orbit. Here, we use Kerbin as our planet. It is similar to Earth, so it works very well as a learning and planning tool.

The simplest form of an orbital launch vehicle is a single stage configuration. This means the entire vehicle is one single unit ready to fly to orbit, from takeoff through ascent to low orbit. This is both inefficient and expensive for a satellite. There’s really no reason for the heavy lift stage to remain in orbit once the satellite has reached its intended orbit.

Rather than hauling heavy engines and fuel tanks into orbit to live forever awkwardly attached to our satellite, we will consider a more popular two stage configuration. In this case, we use a solid rocket first stage and a liquid second stage for orbital stabilization and precision maneuvering.

Using a solid rocket first stage has some side effects. The most important is they burn until the fuel is gone. There is no in-flight throttle control. Throttle can be achieved by narrowing the nozzle geometry, but this is a design-time decision and significantly impacts the construction cost.

Using a liquid first stage, we would be able to cut throttle on the ascent, and throttle back up at the peak of ascent to circularize the orbit for payload deployment. Then, if we’ve done well, we can burn retrograde to return the first stage back to the surface.

Terms & Concepts

by aubreygoodman, posted in Kerbalism, Orbital Basics

Vimeo: https://vimeo.com/309674273

YouTube: https://youtu.be/pAcyaTRn_JM

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!

01 – Intro

by aubreygoodman, posted in 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!