Kerbal Space Program – First Orbital Mission

OK, let me see if I can walk you through an orbital launch in Kerbal Space Program.

I’m going to start by designing a new-pilot-friendly ship. This can get to orbit and have plenty of fuel left to play around with when you get there. It’s a bit over-engineered but also shows some concepts that will help a lot when you move up to bigger ships.

Go to the VAB and start a new ship. I like to start with the Mk 1 Cockpit just because the in-vehicle views are nicer. Switch to the “Utility” tab and add a Mk2-R Radial-Mount Parachute right behind the cockpit. (It will clip through the cockpit but that is OK; try to make the “bottom” end of the parachute just above the bottom of the cockpit.) Drag the cockpit higher in the assembly building; we’re going to need space to put things below it.

Now go to the “Structural” tab and select the TR-18A Stack Decoupler. Put it on the bottom of the cockpit. Now when your mission is complete you can separate the cockpit from the final stage and the parachute will let it float gently back to the surface of Kerbin.

Let’s move on to the actual rocket part. Switch to the “Control” tab and put a S.A.S. Module and an Advanced S.A.S. module below the decoupler. (Be careful these two don’t clip inside each other; that sometimes causes problems.) Then switch to “Propulsion” tab and put a FL-T800 Fuel Tank on the craft and a LV-T45 Liquid Fuel Engine on the bottom. This is the orbital stage.

Now we get a bit more complex. Look at the bottom of the parts menu and there are two buttons there for “Symmetry Mode” and “Angle Snap”. (They aren’t labeled, just hover over them to see which is which. Symmetry Mode probably looks like a yellow dot and Angle Snap like a yellow dot with a circle around it right now.) Set Symmetry Mode to 3 (three yellow wedges) and Angle Snap to on (the circle turns into a hexagon). This makes it easier to balance things.

Switch to the “Structural” tab and select the TT-70 Radial Decoupler. Attach it about the middle of the fuel tank. Since you have symmetry mode on you should get three decouplers.

Now, switch back to the “Propulsion” tab and select the FL-7800 Fuel Tank again and attach it to the decouplers. Again you should get three. (Pan around to make sure they are centered on the decouplers; sometimes they snap to it at odd angles and that will cause you problems.) Pick up a second FL-7800 and put them below the three you already have. Then, select the LF-730 Liquid Fuel Engine and put it below the two fuel tanks. (Note that this is a different engine from the one we put on the center stage.)

Finally switch to the second page of the “Propulsion” tab and select the FTX-2 External Fuel Duct. Click on the “inside” one of your outer tanks and drag it to the center tank. This will create a “fuel pipe” from the outer tank to the inner. (I’ll explain why we’re doing this in a second.)

Our rocket is done but we need to do one more thing. Look at the bottom right. You should see several little orange boxes with icons for engines and decouplers in them. Drag the top engine icon (should be in box 2) down to the box with the other engines (should be box 4). Now we’re ready for launch. Your rocket should look close to this.

Let’s talk about this design for a minute. The first thing to think about are the S.A.S. and Advanced S.A.S. modules we added. Despite the similar names these actually do two different things.

The S.A.S. module is basically a big gyroscope. It holds your ship steady while flying. This will help keep the ship flying straight at launch and will aid in maneuvering in orbit. Without it it is more difficult to control your ship. (Note: All cockpits actually have a small S.A.S. unit built in but they are too small to affect much more than just the final stage.)

The Advanced S.A.S. module is a controller that uses *all* the control systems on your ship to help maneuver it. This includes the S.A.S. module but also fins, gymbaled engines, RCS thrusters and anything else it can find. We don’t have any fins or thrusters on this ship but we do have a gymbaled engine.

That’s the LV-T45 we put on the center stage. If you look at the description for it you will see that it has “thrust vectoring”. That means the engine itself can move around to help steer the rocket.

We *don’t* want this on the outer stages. If those start firing anywhere other than straight ahead then they can tear themselves off the side of the rocket, which is a bad problem and will mean that you will not go to space today. There are ways around this but we don’t need to worry about them here.

The other thing to talk about is staging. By default “stages” are defined by decouplers, in our case the one between the cockpit and the central fuel tank and the ones between the central and outer fuel tanks. Normally the game wants to run the engines on the bottom or outermost stage then, when those fuel tanks run out, jettison them and start the engine on the next stage.

While this is fine it really isn’t very efficient. The engine on the center stage isn’t doing anything to get itself off the launch pad and instead is just being lifted by the engines on the outer stage. By dragging the engine down from stage 2 to stage 4 we make it start at the same time as the outer stages, meaning we get more work out of them at the beginning.

But what’s the point of putting all the engines in differnt stages if we’re run them at the same time anyway? That’s where that fuel line we added comes in. As the engine is firing, fuel is coming from the outer tanks into the center tank. So as long as the outer tanks are there the central engine is using fuel from the outer tanks. When the outer tanks run dry, we can jettison them and keep using the central engine which will still be attached to a full tank. So we can have the engine run on the lower *and* the upper stage.

KSP players call this “asparagus staging” because someone thought the clusters of fuel tanks that are created this way looked like a bunch of asparagus.

Asparagus staging is essential for lifting larger craft into orbit. This minimal craft could have gotten into orbit without it but it is such an essential element of KSP design I thought it should be introduced as early as possible.

OK, theory out of the way, let’s head for the launch pad.

Here we are and ready to go.

Wait until the rocket completely loads (you can tell it is ready when the Kerbal appears at the bottom right). Hit the “T” key. This turns on the S.A.S. and Advanced S.A.S. modules. Then hold the shift key until the throttle is at full.

Ready to go? Hit the space bar and we have liftoff!

Keep an eye on your rocket. The S.A.S. and Advanced S.A.S. should be keeping you flying straight up but we have a few other things to keep an eye on. First, keep watching your speed (at the top of the nav-ball at the bottom). When it gets up to around 150 m/s start throttling back your engine to try to keep the speed between 150 and 175 m/s.

This is because of air resistance. If you wave your hand around right now you won’t notice the air, but stick it out the window of a car going down the highway and you will definitely feel the air pushing on it. The same is true for your rocket. You don’t want to waste all your fuel forcing your way through the atmosphere so back off until you get to an altitude of around 10 kilometers (10,000 meters on your altimiter at the top).

When you hit 10,000 meters you will need to do several things. First, disengage your S.A.S. modules long enough to tilt your rocket over to about a 45 degree angle. (Hit “T” to disengage, hold down “D” long enough to tilt the ship over then hit “T” again to lock it on your new heading.) This is called the “gravity turn” and is a key part of getting into orbit.

When you are done, bring the enginges back up to full thrust again then switch to the map view by hitting “M”. Bring up the nav-ball if it is hidden.

Most of the rest of your flight will be spent in this view. The grey triangle is your rocket, the blue line shows the path your rocket is taking and the blue triangle is your “apoapsis”, the highest point in your orbit. As you can see, right now our rocket is destined to fall back to Kerbin.

Keep an eye on your apoapsis. If you hover your mouse over it it will show you what it is. As soon as it gets close to 100,000 meters, hit “X” to kill your engines completely.

(Note: It is possible your outer stage will run out of fuel somewhere around this point. Keep listening to your rocket; you will hear a “fwoomp” sound when they burn out. If this happens, flip back to the view of your rocket briefly, hit space to jettison them, then flip back to the map view.)

Now you need to wait until your craft reaches apoapsis. In general, things are much more efficient if you make orbital changes at certain key points in your orbit. The most efficient place to change your “periapsis”, the lowest point in your orbit, is at apoapsis. Since your periapsis is currently inside the planet (since you aren’t in orbit yet) we are best off waiting until this point to make our final orbit maneuver.

In the meantime, turn off your S.A.S. modules again and, using the nav-ball, turn the ship until it is pointed directly at your “prograde” vector. This is the thing that looks like a yellow circle with two horizontal and one vertical line coming from it. This is the direction your ship is moving in. It will slowly move as your ship moves towards the top of its arc so you will have to slowly adjust to follow it. We’re going to make our final burn at the point the prograde vector is on the horizon; the place where the blue and orange hemispheres on the nav-ball. If you made your gravity turn cleanly enough it should be obvious where that is going to be and you can go ahead and aim your ship at that point.

(Note: There are things called “maneuver nodes” that make it easier to line your ship up for orbital changes like this but they would require some explanation of their own. For what we are doing here we are ok without them but you will definitely want to learn them once you get beyond basic orbits.)

When you get close to your apoapsis, lock your orientation by activating S.A.S. again and go to full thrust. Keep watching the map screen and you will see the blue line indicating your path geting wider and wider. (As before, listen for your outer stages to burn out if they haven’t already. As soon as they do, jettison them then switch back to map mode.)

Keep watching your orbit and you will soon see a periapsis triangle appear on the far side of Kerbin. A few seconds later the apoapsis and periapsis triangles will suddenly “spin around” the planet. The instant this happens, hit “X” to kill the engine.

Congratulations! You are in orbit. It’s probably a bit lopsided at this point (mine here is a bit inclined and varies from 106 to about 120 kilometers), but welcome to space!

When you are ready to come down point your rocket at the “retrograde” vector, the opposite of the way you are going. This one looks like a yellow circle with three lines radiating out at equal angles. Burn your engine until your periapsis drops inside of Kerbin again. Jettison the final stage (you don’t need it anymore), switch back out of map mode and wait until the re-entry effects are done.

Watch your altitude. When it drops below around 2000 meters hit space one last time to activate your parachue and watch as your Kerbal drifts safely back to the surface of Kerbin.

Congratulations on your first successful mission. Now, let’s go to the Mun!

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