Theory Play Share & Discuss

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Teach Getting to Orbit
with KerbalEdu

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Theory

Getting to Know Kerbals

In this lesson, we help out Kerbals - little green men - by building a rocket and getting to orbit. Simultaneously we will learn something new about orbits.

Teacher Resources

  • Theory: This lesson teaches your students to play KerbalEdu by having them undertake their first flights.
  • Play: Students learn to build their own rocket and launch it, with the goal of reaching orbit.
  • Share & Discuss: As students launch their rockets, they will encounter physical phenomena. The tasks focus on discussing these phenomena and how they influenced their rockets.

Friendship 7 (Mercury-Atlas 6)

  • Space flight with John Glenn as the astronaut.
  • February 20, 1961.
  • Three orbits around the earth.
  • Duration: 4 hours 55 min 23 sec, apoapsis of the vessel’s orbit: 247 km.

Gameplay screenshot

Teacher Resources

Today’s KerbalEdu lesson is a recreation of the historic Mercury-Atlas 6 flight. The very first orbital flight by Americans. John Glenn made three orbits around the earth with his spacecraft.

READ:

Image Source: Mercury-Atlas 6 launch, NASA.

What is an Orbit?

What is the definition of orbit?

Show Notes

Orbit is about falling.

In the picture we can see Newton's thought experiment about launched cannonballs. Can you explain what is happening in the picture below?

Show Notes
  • A and B cannonballs wouldn’t have enough velocity (also known as ‘orbital speed’) to achieve orbit.
  • C has enough velocity to stay in orbit, and it would hit the cannon from behind (the effects of atmospheric drag are ignored in this thought experiment)
  • D has more velocity than needed, so it makes elliptical orbit.
  • E has achieved ‘escape velocity’, meaning it slows down but gravity can’t hold it.

Gameplay screenshot

Teacher Resources

How Would You Fix This?

Jebediah has a problem. The trajectory looks like this and it is getting higher when he burns the rocket engines.

How would you remedy the situation? Using engines when and which direction?

Show Notes

Jebediah should shut down his engine (this is called ‘main-engine-cutoff’ or ‘MECO’) and coast to the highest point of the orbit. ‘Apoapsis’ is the best point for what the NASA calls ‘circulation burn’. At Apoapisis Jebediah should use his engines towards the horizon (prograde). Using engines now would just result higher orbit, while using them at the end of the trajectory would be vastly inefficient and probably not avoid the collision with the planet.

Gameplay screenshot

Teacher Resources

Good to know: The highest point of an orbit is called the ‘apoapsis’ (Marked ‘Ap’ in the game) and the lowest point (which indeed is the place of the cannon) ‘periapsis’ (Pe). In this picture the periapsis is inside of the planet Kerbin.

READ:

Ascent in the Game

  • Delta-v literally means "change (delta) in velocity", which simply means acceleration.

Gameplay screenshot

Teacher Resources

Question: “What forces reduce rocket velocity at launch?”
Answer: “Gravity and friction.”

  • Kerbin, like Earth, has 90% of its atmosphere in the troposphere. The troposphere is the section of atmosphere that is located below 20 km.
  • A lot of acceleration is lost to the friction of the atmosphere (see the picture). In the game, this lost energy is depicted as craft heating up during high-speed flight.
  • The rockets rise through the thickest part and then start the maneuver called ‘gravity turn’ - pitching so that in most optimal situation, when they leave atmosphere at 70km they would have all velocity towards the horizon. The speed should be over 2300 m/s at this point.

Notes:

  • The actual delta/v needed for orbit (in the KerbalEdu) is about 3500 ∆v. Since earth is ten times bigger than kerbin in the game the real life delta-v requirement would be 7.8 km/s (28,080 km/h).
  • In-game atmosphere ends at 70 km altitude. The real life athmosphere doesn’t have this limit.
  • In the Kerbal EDU Lowest orbit possible is 70 km and the amount of horizontal velocity required is 2200 m/s.

Play

Lesson Goal

The goal of the lesson is to build a rocket and launch it to orbit Kerbin. Optional goal is about returning the crew safely down.

Make note: How much delta-v the rocket needs to have to get into orbit?

How to Play

Gameplay screenshot

Teacher Resources

Note: Direct students to start the game in ‘sandbox mode’ and then click the tall building in the center of the screen (Vehicle Assembly Building).

KerbalEdu missions: Teaches the basics of the game and some basic physics while also demonstrating some vehicles from the early stages of human spaceflight.
Resume Saved: Resume a saved game from before (career, science or sandbox). Start New: There are several game modes:

  • Sandbox: The player has endless funds and all parts available (this is typically the best mode for lessons).
  • Science: The player needs to unlock different rocket parts by using science points. Science points are gained by radioing scientific information to Kerbin and doing experiments (both on and off the surface of the planet). Many experiments do not award points if the vessel does not return to the surface. You can use science points in the Research and Development Facility.
  • Career: In addition to science points, the parts cost and the player can earn more money by completing contracts.

Training: Simple missions that teach how the game works. It’s a good idea to let the students try these out!
Scenarios: Scenarios are challenging missions based on some topic and/or experiments.

READ:

Vehicle Assembly Building

Gameplay screenshot

Teacher Resources

Go through the main functions of the Vehicle Assembly Building.

  • Load, Save, Launch and Exit buttons are located on the right top corner of the screen.
  • You can name the rocket by clicking the ‘Untitled Space Craft’ on the top of the screen.
  • The selection of the rocket parts is on the left. You can select parts with left click and move them to the screen.
  • Use the search bar on the top left of the screen to find items from the vast catalog by typing part of the name or the type.
  • Design Data window is addressed in the next slide.

Building Orbital Rocket

  • Less mass means less resistance and better thrust-to-weight-ratio.
  • Thrust to weight ratio means how well the engine can fight the gravity. 1 meaning the craft that suspend itself in the air. Airbus has 0.227, F-15 has 1.04 and the Space Shuttle had 1.5 at launch.
  • Delta-v (∆v) is amount of which the rocket can change its velocity (without outside forces affecting). Orbit in Kerbal Space program needs at least 2300 m/s of delta-v, meaning the actual velocity rocket needs to have should be much higher.

Gameplay screenshot

Teacher Resources

Add the items pictured above and then take the rocket for the test launch. After that you are free to iterate the rocket as you see fit. Please select design data screen, click the data select and tap round button next of ‘Vehicle’. You can see the mass, Thrust to Weight Ratio and Delta-v from the information. These are key elements of deciding of the capabilities of your rocket. Optimal TWR would be around 1,5 meaning example rocket could be a bit more massive.

Read:

Controlling the Craft

Gameplay screenshot

Teacher Resources

You can see the keyboard controls above. Few hints to consider:

  • One important feature is ‘stability assist’ or SAS. It is enabled with ‘T’ Key. In short SAS keeps the craft orientation accordingly the selected mode.
  • The game’s navball is an important tool for the pilots.
  • The direction of travel is yellow prograde icon.
  • Burning the engines against retrograde icon will slow the craft down.

READ:

How to Orbit

  • Turn on SAS.
  • Launch by pressing Z.
  • Turn to 45 degrees east (use the Navball!)
  • Open map (press M)
  • When apoapsis is more than 70 km, turn off engines (press X)
  • When at apoapsis, thrust until you reach orbit around the planet.
  • Upon reaching orbit, turn off the engines again.

Gameplay screenshot

Iterating the Rocket

  1. Is your craft too heavy and taking too much time to fight the gravity?
  2. Is the craft ‘nearly getting there’ delta-v a bit?
  3. How would you make your craft lighter?
  4. Craft breaking up in the launchpad?
  5. Craft starting to spin or go out of control at some part of flight?

Gameplay screenshot

Teacher Resources

Note: This phase will take several iterations. Tell students to ask themselves what happens and why? How should they change the rocket to get the results they want?

Staging

Pressing ‘space bar’ activates the stage (engines, separators, and parachutes). Modern rockets are all about multi-staging: less extra weight you need to carry to orbit means more delta-v for the rocket. While It’s possible to build monolithic rockets, students are recommended to experiment with multi-stage rockets.

Stages are dropped in the predetermined order. Stages are dropped in the predetermined order. Students can adjust the stages either in VAB or during flight by hovering the mouse on the stage bar and dragging and dropping the icons to the stages.

Share & Discuss

Share & Discuss

  • What is a “gravity turn” and why is it only truly began at an altitude of 10 km?
Show Notes

A maneuver where gravity is used to direct the ship towards the right direction. It is started at about 10 km because less atmosphere causing friction at the higher altitude.

  • What forces affect the rocket at launch?
Show Notes

Both gravity and friction affect to the rocket.

  • What is Delta-v?
Show Notes

Delta-v is the maximum value that the rocket can achieve changing its velocity.

  • Why do some rockets cut the engines and coast to the edge of space without thrust?
Show Notes

Being in orbit is constant falling. When the highest desired point of the orbit is reached it is not necessary continue using the engines and fuel. Rather, the engines are turned off in this maneuver at the zenith of the orbit.

Teacher Resources