How to reach orbit, and a rocket that can do it; a walkthrough for newbies. (vARM)

[Vanamonde]

This is an example rocket that can reach orbit around Kerbin and splashdown again.

Download link to the craft file: OBSOLETE

Orbit is not a place or an altitude; it is a speed. It is the speed at which you are moving to the side at the same rate that the planet's gravity is pulling you down, so that you are constantly falling, but constantly missing the planet. This is how Isaac Newton figured it out a couple of centuries before anyone could actually do it, in a picture I stole from someone on the internet.

If one were to fire a cannon, Newton observed, the ball would travel a certain distance, gravity would be pulling it down the whole time, and it would soon hit the ground, as in path A. If you fired the cannonball a little faster, though, the earth would curve away beneath the ball as it traveled. The cannonball would still be falling the whole time, but it would go farther before hitting the ground, as in path B. But if the cannonball was fired at just the right speed, it would travel forever, falling the whole time, but always missing the surface of the earth. In path C, the cannonball is in orbit.

But this idea only works if there is no air to slow the cannonball down and cause it to fall to the ground. In order to reach orbit and stay in orbit, the cannonball or spaceship must not only reach the proper horizontal speed, but it must also climb above the atmosphere so that the air is not slowing it down. So to reach orbit in the game, you must compromise. You do need to go up a certain distance so that Kerbin's atmosphere is not slowing you down, but the important thing is to build up enough speed to avoid hitting the planet, so getting to orbit requires more effort to build up sideways speed than to go high. This will require starting off flying straight up and then gradually turning so that the ship is flying horizontally. You will hear many KSP players refer to this as a "gravity turn," though strictly speaking, that is something slightly different.

Flying can be disorienting, though, and you can't always trust your eyes or the picture on the game's screen. Real pilots and astronauts fly using their instruments, and so should you. Your navigation instrument is the navball display at the bottom of the screen, and there are 3 markers on it you will need to understand. Here they are, in another picture I stole from somebody on the internet.

As the illustration says, the prograde marker is the direction your ship is currently travelling, so if you point the nose of the ship that way and run the engine, you will be speeding up. The retrograde marker is the exact opposite direction, 180 degrees from prograde, so if you point that way and run the engine, you will be slowing down. The V symbol with the dot over it tells you exactly where the nose of your ship is pointed at the moment.

From the launchpad, turn on the stability assist mode (SAS) with the T key, throttle up to full, and hit the spacebar to ignite the engines. You are in the thickest part of the atmosphere and it is slowing you down, so fly straight up to 10,000m, where the air is much thinner.

Now you can turn to the side and keep running the engine to start building up the horizontal speed you will need to attain orbit. So use the WASD keys to point the prograde marker about 30 degrees to the east. Which way is east? One of the functions of the navball is to serve as a compass, and east is the vertical white line marked with the number 90 (for 90 degrees from north). It is surrounded by the yellow box in this illustration:

While you can reach orbit by turning in any direction, the reason it is best to turn to the east is that the planet rotates to the east, so even while sitting still on the launchpad, you are already moving east at 174.6m/s. And remember, the trick to getting to orbit is building up enough horizontal speed, so by taking off to the east, you get a speed boost from the planet that will help you reach orbit.

One thing that often bothers new players is that the ship may rotate around its long axis during flight, so that it is facing different directions at different times, and this makes it hard to figure out which way to fly to get where you want to go. But the fact is, this kind of rotation does not matter as long as the nose of the ship is pointed in the right direction, and this is why it is important and useful to orient yourself using the navball rather than try to figure out which direction to go on the game's main screen. So in this illustration, even though the ship has spun so far that it is almost upside down, the flight is still going well because the prograde marker is aimed to the east and 30 degrees from vertical.

As you keep flying on this path, the first stage of the rocket will run out of fuel and stop working. When it does, hit the spacebar. This will both eject the empty stage and instantly start the second stage.

Why is it useful to eject stages? The first stage had a big heavy fuel tank and engine that were required to get the fully loaded weight of the rocket off the surface of Kerbin, but now that the rocket is already high up and moving quickly and has burned off much of that heavy fuel, it no longer needs that heavy engine and tank. If you eject them, the remaining part of the rocket is lighter and can more easily build up speed, and any time you make your rocket lighter, it will require less fuel to get the job done. In fact, on a large rocket, the engines may actually crush the ship if they are pushing too hard for the remaining weight, so getting rid of powerful launch engines can actually be safer. So, almost all rockets are built in successive stages.

It is a waste of fuel to try to push the ship through the air faster than the air will allow it to go, but I have balanced the thrust/weight ratio of this ship for you, so that it will stay pretty close to the ideal speeds during ascent. So you do not need to change the throttle setting, and should leave it at full.

Also, as the second stage starts, continue to transition to horizontal flight by turning the ship until the attitude marker is at 45 degrees.

At this time you should hit the M key to switch to map view. Watch the pale blue line of the ship's projected path rise until the highest point marker, the apoapsis, reaches 50,000m. When it does, rotate the attitude marker to 70 degrees from vertical (as indicated on the navball in this picture),

and when the apoapsis marker reaches 60,000m, turn the ship fully horizontal.

Leave the engine running this whole time, at 100% thrust, until the second stage runs out of fuel. Then hit the X key to shut the engines down, and hit the spacebar to eject the second stage. Your ship will then coast up toward the apoapsis

While you are following these steps, the apoapsis marker will rise past 70,000m.

When the rocket gets that high, it will have entirely cleared Kerbin's atmosphere and the air resistence will no longer be holding the ship back. This is the minimum height required to achieve a sustainable orbit around Kerbin. However, it's possible that you might accidentally dip into the atmosphere if you are that close, so it's a good idea to let the apoapsis continue to rise to give yourself a safety margin. When that second stage does run out of fuel, the apoapsis marker should be sitting close to 80,000, which is high enough to orbit with a pretty good safety margin between your ship and the atmosphere.

(It is a very common newbie mistake to keep the engine burning at this time. This will make the ship go very much higher, but it will also just fall right back down again because it's not really in orbit yet.)

When your ship gets to the apoapsis point, you are already as high as you need to go, but remember that the important thing about achieving orbit is horizontal speed, and you do not have enough horizontal speed to stay in orbit yet. So turn the nose of the ship until it is pointing at the horizon (where the blue side of the navball meets the brown side) on the 90 line and, starting when the marker countdown reads 20 seconds to apoapsis (because the burn takes a few seconds and you don't want to start it too late) throttle up to full thrust. Then you will be applying ALL of the engine's power to building up horizontal speed. Remember, it doesn't matter if the ship has rotated as long as the nose is pointed in the right direction, like this:

As you build up speed, watch on the map view as your trajectory line elongates and rises. When it has met itself around the planet, a lowest point marker called the periapsis will appear. Although it looks like you will not hit the ground if the periapsis is above the surface, remember that the atmosphere is higher than that, and you can not allow your orbit to dip into the atmosphere at any point or your ship will be slowed and eventually fall. So keep watching that periapsis marker rise until it also is above the top of the atmosphere, at 70,000m or more.

When both the apoapsis and periapsis markers are above 70,000m, you are in orbit, and you should throttle the engine down to zero. It does not matter if your orbit is a tidy circle or an ellipse, as long as it never dips into the atmosphere. Your ship is now on a stable path and will circle the planet forever, unless you stop it. (In the real universe, other factors may cause an orbit to fail, but that doesn't happen in KSP.) From this point, there are several things you can do. You can just watch the planet roll by beneath you (always cool).

Or, if you're feeling brave, you can have the pilot get out and play around with EVA,

but it can be hard to fly him back to the door of the ship, so maybe save that for another day. Or, the ship will still have some extra fuel, and you can turn the nose and burn in different directions to see what effect this has on the orbital path. But when you are ready, you can also practice landing the ship.

Since the trick to achieving orbit is to go sideways fast enough, the easiest way to get out of orbit is to slow down and let the ship fall. This time, point the nose of the ship at the retrograde marker and burn the engine.

Switch to map view and watch as the projected path line dips into the atmosphere.

The ship will fall more or less slowly depending on how far you dip into the atmosphere, but once you have set the path you want, you can turn the engine off. In fact, the engine and any remaining fuel are useless weight now that will make the ship fall harder, which can be dangerous for the pilot. So, hit the spacebar one more time to eject everything but the capsule carrying the pilot.

As you re-enter Kerbin's atmosphere, flame effects will burn around the ship as air resistance slows the ship down and eliminates most of your orbital velocity. But the air will not eliminate ALL of your speed, and the capsule would crash into the surface and kill the pilot if you don't do anything more. That is why you should hit the spacebar one last time, to open the parachute on the capsule. The parachutes know when to open, and so it is never too early to activate them. However, it is possible to open the parachutes too late, so activate the parachute at least 3500m up, and you should be safe even if you happen to be coming down over the highest moutains on the planet.

Then watch the capsule float safely to the ground or water, and hit escape and "recover vessel" when you are done.

I hope this has been helpful.

Edited April 28, 2015 by Vanamonde
Update.

[pebble_garden]

Excellent work, Vanamonde! I'm sure it will be a huge help for newcomers to KSP.

[tommygunyeah]

Great tutorial, as written tutorials goes this is great for the new comers

[Gort]

Thanks so much! I'm one of those KSP noobs and really needed this well written tutorial (and with BIG pics too!).

[Vanamonde]

I'm glad it was helpful, and klaatu barada nikto.

[birky]

I just bought the game on Friday over steam and am enjoying it so far. I've watched a ton of videos, and get the concepts of how to get the ship into orbit (and back), asparagus staging, etc.

But I'm having a terrible time designing rockets that will actually hold their trajectory after lift-off. Even with very, very basic rocket designs and with SAS on. I get a few thousand meters off the ground and before I know it the nose of my ship is pointing back towards the ground. I'm guessing it has something to do with my CoM & CoL, but I've recreated several designs that I've seen on the forums or in videos and am having the same issue. Even having the issue with the Kerbal X stock ship. I'm having to turn off the SAS and manually make corrections the entire ascent, most of the time ending in disaster.

Any help?

[Vanamonde]

Is it possible for you to post some pictures of your ship? Screenshots from the game folder can be uploaded to a service like Imgur.com, and then you can use the link they provide in your post.

　

Meanwhile, here are some basic rules for building stable rockets:

1. The command part, the first piece you must choose when starting a new rocket design, is itself a guidance device that will help keep the rocket stable. The unmanned probe parts exert a small stability force, but the manned capsules are much stronger. Adding more command parts to a ship will give it more steering force, but also add weight to the ship, which makes it less fuel-efficient so that it won't fly as far.

2. As rockets increase in size, you will soon need more force than the command part provides to keep them stable. The simpleist method is to install an SAS module. There is considerable confusion among new players about what SAS does, so to be clear: when turned off it does nothing, when turned on it resists rotation, and it does not assist in turning even when it is turned on. But for small ships, it may be enough to keep you on course.

3. Once the ship becomes too big for SAS alone, you will need to substitute or add ASAS. ASAS is quite different from SAS, despite the similarity of names. ASAS does almost nothing by itself, but it does control the other kinds of parts that exert stabilizing forces, and those parts are gimballed engines, control surfaces, and RCS.

3a. If an engine is listed in the VAB description as having "thrust vectoring," that means the engine has a pivoting "gimbal" mount and will help steer the ship by pointing the thrust in different directions, and ASAS is the guidance device that tells the gimballed engines what to do. Without an ASAS, the engines will not gimbal. Conversely, a non-thrust vectoring engine can't pivot to assist steering, even if there is an ASAS on the ship. Engines work best and exert the most steering control when placed at the bottom of the rocket.

3b. A control surface is a flat slab which pivots to redirect airflow, and helps steer a rocket just like elevators and rudders work on airplanes. Not all the fin and wing pieces in the game pivot like this, though: only the ones listed as canards, winglets, or control surfaces. Again, control surfaces do nothing without an ASAS to give them instructions. Also, they only work while the rocket is passing through an atmosphere, and stop working in vacuum. This makes them useful for the first stages of rockets that are taking off, where they are quite powerful, and are the best way to stop a ship from spinning around its long axis. For complex reasons too lengthy to go into here, control surfaces are most effective when placed toward the bottom of the rocket, and can cause problems if placed in the middle or toward the front of the rocket.

3c. RCS is a set of small rockets that fire to the sides to help steer a rocket, and they need three things: RCS thrusters placed in a symmetrical way around the rocket, an RCS fuel tank on the rocket, and an ASAS to give the thrusters instructions. Although RCS does work while the rocket is in atmosphere, it's rather weak there and will quickly waste all the RCS fuel without doing much good. RCS is best left off until you get into space, where it becomes the strongest method of exerting stabilty control, but do keep in mind that it has a finite amount of fuel.

4. No ship ever needs more than one ASAS module, since all they do is give instructions anyway, but more than one SAS module will exert more stability force.

5. As for the shape of the rocket, wider ships are more stable than long ones, so it's often a good idea to attach parts to the sides rather than one on top of the other.

6. If the parts are swaying, the engines and mass will be moving around, imparting forces on the ship, so the more rigid the structure is, the straighter it will fly. The EAS-4 strut connector, the part you can stretch from one connection point to another, is the best response to this. Place them from one part to another, across gaps, and even between one stage and another, because these struts will automatically remove themselves when the stages separate. (Triangle arrangements of struts are strongest, because triangles can not flex.)

7. While wider ships are easier to keep flying in the right direction (pitch and yaw), their distributed mass is more likely to pick up a rotation around the long axis (roll). A bit of rolling makes a rocket a little harder to steer during manuevers, but doesn't actually hurt anything as long as the nose of the ship is pointed in the right direction. However, you can reduce or stop roll with fins or fins with control surfaces, additional SAS modules, and/or more struts between wiggling parts. Gimballed engines do almost nothing to prevent or stop rolling. But generally this is only a problem with very massive ships, so control surfaces should fix the problem for the kinds of small ships newbies should be learning with.

The VAB markers for center of lift, thrust, and mass are very important for airplanes, but don't help you much while building rockets. That's because, if you build the ship symmetrically, all 3 markers will automatically line up, so it's kind of hard NOT to have them aligned. Extreme distributions, if the center of mass is very far forward or very far back, can make the rocket harder to control and steer, but quite a bit of variation in the exact position of the COM doesn't have a big impact on the stability of the rocket.

Edited May 11, 2013 by Vanamonde

[birky]

Thanks for all of the useful tips. After playing around off and on for a few days, I think I've mostly gotten past the issue with the trajectory just through trial and error. I did, however, realize that I was using either the SAS or ASAS and not both and that my rockets were probably too long.

[SRV Ron]

My first orbital craft involved a two stage design that looks like the sub orbital Redstone Rocket. It has enough fuel to achieve low Kerbal orbit, 100,000 meters, with enough fuel left for a deorbit burn. As always, the key for the most efficient burn is when to make the gravity turn and to do so smoothly. Using the two step burn is a must to achieve a circular orbit and retain enough fuel for the deorbit burn. For landing on Kerbal, I aim for a point 15,000 meters in the atmosphere. That holds down the G forces on reentry.

[Vanamonde]

Updated for 21.1.

[Javster]

You're good at making tutorials! Could you make some kind of checklist for different types of craft (eg. station, lander, base etc.)?

[Vanamonde]

Thanks! I would like to make more tutorials, but I have to have the ideas clear in my head before I can write them out, and that's harder than it sounds. I tried writing a docking tutorial, for example, but it was turning into a mess because I had more exceptions than rules. What kind of checklists are you talking about? Flying or constructing?

[SRV Ron]

Simple two stage orbiter with thruster pack, from 0.202. For 0.2101, remove the ASAS ring and add solar panels. Mainsail first stage, skipper on the second. Makes 100k orbit easily when flown properly. Be sure to strut stitch the tanks on the first stage. Fins not needed in 0.2101

[Sentoki]

Thanks, I needed this a lot!

[Vanamonde]

You're welcome. I enjoy helping other players.

[Vanamonde]

Updated with a better ship design which benefits from recent changes in parts and game mechanics, and with a more efficient ascent method.

[velve]

I've been struggling for 6 hours to get a single orbit...this is in career so I'm a bit limited. I understand the process and am doing it correctly so I guess its just my ship.

[SRV Ron]

I've been struggling for 6 hours to get a single orbit...this is in career so I'm a bit limited. I understand the process and am doing it correctly so I guess its just my ship.

Try building and flying simple designs. As you gain experience, build on to that design and go for Mun.

This early career ship will not only achieve orbit easily, it can do a Mun and Minmus orbit and return for lots of science points.

Be sure to manage power use carefully as the LV-909 has no generator and transmitting will drain the battery.