Kerbal Space Program How-to Series: 3 – Halfway to Anywhere (Orbit Kerbin)

(Current for KSP version 0.25)

In this chapter you will learn:

  • To have a vessel orbit Kerbin, then return to the ground safely
  • The difference between liquid-fuel engines and solid-fuel boosters
  • How to “tweak” parts

“If you can get your ship into orbit, you’re halfway to anywhere.” — Robert Heinlein

In this chapter, you will put your first ship into orbit of Kerbin, do some more science, and return safely.

First off, go to the Research & Development Center. Ensure that General RocketrySurvivability, and Science Tech are researched. Science Tech unlocks a new experimental tool, the SC-9001 Science Jr. You know the drill; you can “launch” vessels with nothing but a pod and a Science Jr to get more science points from the Launchpad and Runway.

Getting into orbit will require a vessel that is a little more complicated than the ones you built in the previous chapter. You can either try to recreate it from the picture and description below, or you can download the vessel file. Read this appendix to learn where to put the vessel file.

This is what the vessel looks like:
ksp-kerbin-orbiter-3

The top consists of a Command Pod Mk1 with a Mk16 Parachute on top of it, as usual. Below it is a TR-18A Stack Decoupler, then below that is an FL-T100 Fuel Tank, an FL-T200 Fuel Tank and an LV-909 Liquid Fuel Engine. Place three SC-9001 Science Jrs symmetrically around the fuel tank. Below it are two layers of alternating TR-18A Stack Decouplers and RT-10 Solid Fuel Boosters, similar to the K-2. Below that is another TR-18A Stack Decoupler, then a Rockomax BACC Solid Fuel Booster.

Adjust your staging. Ensure the stages are properly ordered from the bottommost booster to the topmost engine, and that they are paired with the decoupler directly below them.

Stage 0 (topmost) should contain the parachute and topmost decoupler.

If you remember the K-2 launch, you may have noticed reentry effects going upward as well as downward. We don’t want that on this craft, as it’s a sign of extremely high drag. We thus have to control our thrust on the upper stages.

Right click the topmost RT-10 Solid Fuel Booster and set the Thrust Limiter to 60%. (Some parts can be “tweaked” this way; you may note that you can also adjust the amount of fuel it has, for example) Likewise, the second-topmost booster should have the Thrust Limiter set to 90%. Solid boosters, unlike liquid engines, cannot be throttled or turned off, so this is the only way to control their thrust.

Name your vessel (from now on, vessel names in this guide will be descriptive, sometimes followed by a “nickname”. I named this one ‘Kerbin Orbiter “Fastok”’. This helps with remembering what each vessel is for when loading). The cost should be 8,037 funds.

You may want to go to the Space Center view, press Esc, and save your game before launching (I generally save to “prelaunch” before launching a mission, and “mission acc” after completing it. Do not rely on Revert Flight always being available; it becomes unavailable after a certain amount of time, and it is possible that the game might crash or you might have to exit the game in the middle of your mission.)

OK, now we can launch the vessel! Go back to the VAB, ensure the Fastok is loaded, and click the Launch button.

Wait a few seconds for it to load, then Press T to engage SAS.

Press Z to set throttle to full. Note that solid fuel boosters cannot be throttled or turned off. However, we want the LV-909 to be activated at full power as soon as the last booster drops.

Press Spacebar to launch!

The bottom solid fuel booster should be activated and propel you upward. Use your first Science Jr. kit to complete the lower atmosphere experiment. Press Spacebar again as soon as each booster runs out to activate the next one.

By the time the first two boosters run out of fuel, you should be at about 10,000m.

We’ll pause here for a bit to talk about what exactly we need to achieve orbit. Orbiting is often described as “falling and missing the ground”, and that is essentially accurate. You can’t achieve orbit just by continuing to propel upward; you’ll eventually either fall back to the ground, or you may escape Kerbin’s gravity altogether and orbit the Sun instead. Orbiting requires two things: horizontal speed (you need to be going sideways fast enough that when you fall toward Kerbin, the ground would have curved away), and height (you need to be above the atmosphere, so that atmospheric drag doesn’t slow you down and cause you to deorbit. On airless bodies, you still want to stay above any mountains, for obvious reasons).

You could just propel yourself toward the desired height, then fire sideways for horizontal speed, but that is rather inefficient. It is more efficient to perform what is known as a gravity turn, where we gradually transition from moving upward to moving sideways.

As such, unpause the game, then turn toward the right, toward the 90° heading mark (east). Why east? Well, remember that you launched from a rotating planet. It rotates from west to east, so you already have some horizontal velocity. Since this is your first attempt to get into orbit, it is thus easiest to have that working for you rather than against you. Do not turn too much; a 45° pitch (midway between the zenith [white dot in the middle of the blue half] and the artificial horizon [line that separates the blue and orange halves of the navball]) should be sufficient for now. Your navball should look something like this:

ksp-pitchover

Now press M to switch to the orbital map view. You will see a small blue curve indicating the projected trajectory of your vessel. What you need to do is find the Ap flag and click it. This displays the height of your apoapsis; it should be increasing rapidly. There is also a T value, which indicates the projected time to the apoapsis if you turned your engines off (we don’t want to do that yet though).

You can view the navball from  within the map view by clicking the arrow at the bottom of the screen. Continue burning until the ksp-prograde prograde marker on your navball moves close to the level indicator in the center. Then, slowly turn the vessel eastward, such that you stay slightly east of the prograde marker. Don’t turn too quickly; ensure that the T value of your apoapsis continues increasing.

You’ll likely run out of fuel soon. Once you do, hit M to exit map view, hit Spacebar to activate your LV-909 stage, then hit M to return to the map view.

You should be almost horizontal by the time your apoapsis reaches past 50,000m. You may also see your prograde marker jump; this is because the navball automatically switched from the surface reference frame to the orbital reference frame. You can switch between them by clicking at the small window on top of the navball. Keep in on “Orbit” for now though. Continue burning until your apoapsis is above 80,000m. As soon as that happens, hit X to turn off your engine. Your apoapsis will start decreasing slightly due to drag, however the atmosphere is so thin at this point that it should easily stay above 70,000m.

You’re now on a course out of the atmosphere. Exit map view, use your second Science Jr. kit to complete the upper atmosphere experiment, and return to the map view. You have a good amount of horizontal velocity, but not quite enough for orbit. You will thus need to make a second burn near the apoapsis.

Go back to the map view. Click on your path at the point of the apoapsis, and click Add Maneuver. Start pulling the ksp-prograde prograde marker outward. Note that you’ll begin to see an orange Pe flag; that indicates your projected periapsis. Continue pulling until the apsides start to “run” around the path; if you hover over them you should note that they are very close; ensure that both are over 70,000m.

Turn your craft slightly past the artificial horizon, at the ksp-maneuver maneuver node marker. Note that you get an “Estimated burn time” value. Wait for your time to apoapsis to be roughly half of that. (you can speed this up a bit by using the time warp control at the top left corner of your screen. Be careful not to go too fast though!). Then press Z to activate your engine again.

As your horizontal speed increases, your trajectory should begin to circularize. After some time, you’ll see the blue Pe flag rising out of the opposite side of Kerbin. Click it, and you’ll see the height of your periapsis. To achieve orbit, you must get this above 70,000m before turning off your engine. Then delete the maneuver node by clicking the cross or checkmark on the bar to the right of your navball.

Congratulations, you have achieved orbit! Exit map view, and use your third Science Jr. kit to complete the “space near Kerbin” experiment. To savor your victory, you may use time warp to run several laps around Kerbin. Sunrises and sunsets are common in low orbit.

You may note that the Science Jr. kits are placed below the decoupler. This is not an accident; keeping them will result in more weight on our parachute, which may endanger the Kerbal. However, it means you will need to get the data out of the Science Jr. kits into the pod to actually get any science points. As such, press F5 to quicksave, then do an EVA. Press to activate your Kerbal’s EVA pack, and carefully maneuver him toward one of the Science Jr. kits. Rightclick on it and click “Collect Data“. You will get a warning message that the kit will be rendered unusable; go ahead and remove the data, since you won’t need them anymore. Repeat with the other two kits, then return to the pod.

Now it’s time to return to Kerbin. Press F5 to quicksave again. Align your vessel to the ksp-retrograde retrograde marker, and press Z to activate your engines. This will cancel some of your hard-earned horizontal speed, so your periapsis will now begin to lower. Press X when it reaches below 30,000m. You don’t need to get it under Kerbin, because once you’re deep enough into the atmosphere, the drag will be sufficient to get you toward the ground.

As you achieve reentry, you want to ensure your navball is set to Surface mode (it should switch automatically, but just check to be sure), then align and keep your vessel on the ksp-retrograde retrograde marker; this minimizes stress on the parachute when you deploy it. Press Spacebar when you’re about 10,000m up to activate the parachute and jettison everything below your pod (it is likely to “stick” to the pod; twist around a bit to push it away).

As usual, the parachute will automatically fully deploy when you’re close to the ground. You’re likely in a new biome, so you can do a crew report for “flying” above it. Adjust your pod so that it touches down flat on the ground. (If you’re unlucky, you may end up landing in a very hilly region and have a hard time touching down without rolling uncontrollably. In which case, you should press F9 to quickload, and do your deorbiting burn at a different part of your orbit.) Then do an EVA, EVA report (again you may be able to get one for “flying” while on the ladder, in which case store it on the pod, get down, and do another EVA report), Surface Sample, Take Data from the pod, and reenter it. Then do another Crew Report for the ground in that biome. Then recover your vessel.

Congratulations on a successful mission! You should now have a bunch of science points to spend. If you’re playing Career Mode, I suggest you research Flight Control. This unlocks your first unmanned pod, the Stayputnik Mk. 1.  Try completing some of the suborbital and orbital part test contracts from Mission Control; using an unmanned pod means you don’t have to worry about returning safely. You’ll have to design your own vessels for these; however, modifying the K-2 (suborbital) and Fastok (orbital) vessel designs should be quite sufficient as long as your cargo isn’t too heavy.
Tip 1: you can empty solid rocket boosters you wish to test to lighten the load, or “thrust limit” liquid engines to 0% to avoid accelerating your craft; as long as you activate the part via staging at the correct altitude, the test will still be complete.
Tip 2: The Stayputnik Mk. 1 does have some disadvantages: it does not produce as much torque (turning power), and constantly uses electricity. If you have trouble with controlling your vessel, try adding a Small Inline Reaction Wheel under your Stayputnik to increase your torque. If you have trouble with electricity, stick on a Z-100 Rechargeable Battery Pack to extend your lifetime.

Glossary:

apoapsis /ˌæpoʊˈæpsɪs/, pl. apoapsides /ˌæpoʊˈæpsɪdiːz/ n. The point at which an orbiting object is farthest away from the body it is orbiting. According to Kepler’s laws of planetary motion, an object is slowest at the apoapsis. In the map view, the apoapsis is indicated by an arrow marked “Ap”. Antonym: periapsis.

apsis /ˈæpsɪs/, pl. apsides /ˈæpsɪdiːz/ n. Refers to either the apoapsis or the periapsis.

periapsis /ˌpɛɹɪˈæpsɪs/, pl. periapsides /ˌpɛɹɪˈæpsɪdiːz/ n. The point at which an orbiting object is closest to the body it is orbiting. According to Kepler’s laws of planetary motion, an object is fastest at the periapsis. In the map view, the periapsis is indicated by an arrow marked “Pe”. Antonym: apoapsis.

prograde /ˈpɹoʊˌɡɹeɪd/ adj. In the same direction, “forward”. In Kerbal Space Program, the ksp-prograde prograde marker on your navball indicates the direction in which your vessel is moving, relative to your chosen reference frame. Antonym: retrograde.

retrograde /ˈɹɛtɹɵˌɡɹeɪd/ adj. In the opposite direction, “backward”. In Kerbal Space Program, the ksp-retrograde retrograde marker on your navball indicates the opposite direction to that in which your vessel is moving, relative to your chosen reference frame. Antonym: prograde.

zenith /ˈziːnɨθ/ n. The imaginary point vertically above the observer. On the navball, the zenith is indicated by the white dot in the middle of the sky (blue) half. Antonym: nadir.

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