4. First orbit - Getting into a stable orbit and understanding orbital dynamics

[limpid gazelle]

This is Tutorial 4, click this pinned message to jump to the top.
Full view is highly recommended!

Table of contents:

1. [Ridin' higher yet higher](#1493421018117574877 message)
2. [Orbital basics - what the heck?](#1493421018117574877 message)
3. [Orbiting Kerbin](#1493421018117574877 message)
4. [Designing your first orbital rocket](#1493421018117574877 message)
5. [Thrust-To-Weight Ratio (TWR)](#1493421018117574877 message)
6. [Gravity Turns & Using the planet's rotation to your advantage](#1493421018117574877 message)
7. [The great orbital ascent](#1493421018117574877 message)
8. [Orbital activities - Managing solar panels and going on a spacewalk](#1493421018117574877 message)
9. [Going home](#1493421018117574877 message)

[Navigation](#1493421018117574877 message)

1. Ridin' higher yet higher

So at this point, if you've been following along with these tutorials, you've learned the basics of the tracking station/map view, engine efficiency, rocket construction and even gotten in a little flight experience, if you feel you want more flight experience feel free to keep launching or even modifying the starter rocket you built, you can test your heart out with no consequences thanks to the revert feature.

Once you're ready, it's time to go to orbit. Unlike our first joyride we'll need to be much more careful when flying this time, and we'll also need a deeper understanding of a key aspect of this game - Orbiting.

Buckle up - this tutorial is going to be quite the long one.

2. Orbital basics - what the heck?

Let's consider this Satellite I have in Low Kerbin Orbit (LKO), it is in a nice stable orbit.

There are two key orbital parameters we need to pay attention to here - the Satellite's Apoapsis and Periapsis.

• An object's Apoapsis represents the highest point of its orbit - this is also when the object will have the least velocity.
• An object's Periapsis represents the lowest point of its orbit - the point where the object will have the most velocity.

In spite of what a lot media might have you think, orbiting isn't really about going up - we only go up in order to escape the atmosphere, the most important part about orbiting is actually your horizontal velocity, that is, your velocity parallel to the body's surface, with our end goal being to pick up so much horizontal velocity that we "miss" the body as we fall towards it, I.E. an orbit.

The Satellite in this image is travelling around Kerbin with a velocity of 2,295m/s - around the minimum horizontal velocity required to not fall back into its atmosphere, while you can't see individual horizontal and vertical velocities in the stock game, this Satellite actually only has a vertical velocity of around 0.1m/s, and this would be zero if it were in a perfectly circular orbit (that is, its Periapsis and Apoapsis were the same).

3. Orbiting Kerbin

So, how do we get up there and stay up there?

To orbit Kerbin specifically, we need a periapsis outside of its atmosphere - Kerbin's atmosphere extends to exactly 70,000m - so we'll need to go at least this high to escape the atmosphere and not get pulled back down by atmospheric drag, furthermore we'll need at least 2,300m/s of horizontal velocity at this altitude to "miss" Kerbin's atmosphere as we fall around it.

All in all we need to construct a rocket that has at least around 3,600m/s of Delta-V (Measured relative to vacuum) in order to get high enough and then accelerate horizontally fast enough, however since your first orbital ascent profile is unlikely to be perfect it won't hurt to overpack for this, in this case let's design our first orbital rocket with at least 4,500m/s of Delta-V - This will give us plenty of margin to get to orbit.

Speaking of...

4. Designing your first orbital rocket

Let's go back to the starter rocket we designed back in Tutorial 2 (Hopefully you saved it) - we're going to need to beef this thing up a lot if we want to get it all the way to orbit.

Step-by-step

1. Firstly, let's attach a heat shield to the underside of the command pod - re-entering Kerbin's atmosphere is going to produce a LOT of heat and we'll fry without one, to do this detatch the rest of the rocket from the command pod by the decoupler, then attach an appropriately sized heat shield from the Thermal tab in the Parts Panel, then reattach the decoupler and rest of the rocket to the bottom node of the heat shield.

2. Next, let's swap out our "Swivel" engine for the much more efficient "Terrier" engine, althrough if you read the engine efficiency section in Tutorial 2 you'll remember that the "Terrier" engine does not work well inside an atmosphere, so we're going to need an extra stage below this in order to get it out of the atmosphere.

3. Now, add another decoupler below the "Terrier".

4. Add a pair of large 1.25m fuel tanks beneath this.

5. Re-add our trusty "Swivel" engines beneath this.

6. Add some fins to the bottom of the bottom-most fuel tank for aerodynamic stability, to do this find the "Basic Fin" part near the top of the Aerodynamics tab in the Parts Panel, press the C key to enable snapping if it's not already enabled (The hexagon icon in the bottom left) move it to the bottom of the tank and then press the X key three times to bring your radial symmetry up to 4x (you'll see the icon change in the bottom left), then click to place, finally hit Shift+X three times to return to 1x symmetry.

7. The final thing our rocket will need is some method of generating electricity - for this rocket I will simply be attaching two "SP-W 3x2 Photovoltaic Panels" to the top of the rocket beneath the decoupler using 2x symmetry.

This will leave us with a rocket that has around 4,700m/s of Delta-V (When measured in a vacuum), plenty to go to orbit!

The final thing to do is to ensure that our staging is correctly configured, make sure your "Swivel" engine is on the first stage, followed by your decoupler, then "Terrier", then decoupler, and finally parachute. You can also have your "Terrier" and lower decoupler on the same stage if you want to have your "Terrier" fire at exactly the same time you decouple your lower stage, up to you!
Remember that hovering over parts in the staging stack will highlight them on the vehicle itself, make sure your decouplers are the right way round or you'll be doing another hop instead of going to orbit!

5. Thrust-To-Weight Ratio (TWR)

Another important aspect of our rocket we need to account for is our Thrust-To-Weight Ratio - as the name suggests this is literally the ratio between how much upwards thrust is produced by our engines and how much downwards force on our craft is produced by gravity (I.E. its weight), you can see an engine's TWR by clicking on a stage, which will expand it to display extra information about it (You can toggle different parts of this information inside the Delta-V tool).

As we can see, the rocket we just built has a launch TWR of 1.17 - that is its thrust is 17% higher than the gravity pulling the rocket down at take-off, the optimal value for this is at launch is around 1.4, but it's okay to go below this a bit - the REALLY important thing is that our TWR is above 1, as if it is below 1 then the local gravity will overpower our engine(s) and we won't take off.

We can see this with our upper "Terrier" stage - it can only produce a thrust equal to 37% of Kerbin's gravity at sea level, so if were to immediately decouple our first stage on the launchpad and fire this stage, it wouldn't be able to lift off the ground. Once we get the "Terrier" stage out of the denser parts of Kerbin's atmosphere however its TWR skyrockets all the way to around 1.5, which is very good for an upper stage.

An extra thing to remember - since your TWR is based on your rocket's weight, it will increase throughout flight as you burn fuel and your rocket gets lighter.

6. Gravity Turns & Using the planet's rotation to your advantage

One last thing to explain before we give orbiting a shot - the concept of Gravity Turns.

You may recall from Tutorial 3 that when we switch our Navball mode over to Orbit mode our velocity magically increases - displaying the rotation speed of the planet we're on, well this isn't just for show, by turning into the planet's rotation (I.E. eastwards, or towards "90" on the Navball) as we ascend we can actually add this velocity to our final orbital velocity, giving us a free velocity boost.

You may be tempted to simply burn your engine all the way up, wait for it to run out, and then burn straight towards the horizon with your upper stage - and with this rocket that will indeed work to get you into orbit (Known as the Noob ascent profile), however we can do much, much better than this by instead gradually "tipping" our rocket over as we rise through the atmosphere until we're burning directly towards the horizon, doing this allows us to better balance our vertical and horizontal velocity (In short - the more horizontal velocity you have the less of a vertical component you need to maintain altitude), so gravity turns are an all around win-win for efficiency.

You don't need to be perfect with your gravity turn - Even a mediocre one will still grant large Delta-V gains versus a noob ascent profile, although be warned that turning over too quickly can cause you to incur extra drag losses or even burn up! As a general rule of thumb you want to be facing at least 45 degrees by the time you reach 10km altitude - although the specific optimal gravity turn will depend on how draggy your craft is.

7. The great orbital ascent

It's time.

With your upgraded rocket on the launchpad, we're finally ready to go to orbit!

• Make sure SAS is enabled and that your fingers are carefully rested on the WASD keys - this time we're going to need to be careful with our piloting.
• Ensure your throttle is at maximum with the Z or Shift keys.
• Additionally, make sure you enable Maneuver mode (The very bottom purple button) in the OKYS Panel - this will allow you to monitor your Apoapsis (Highest point in your orbit) and Periapsis (Lowest point in your orbit) in flight without needing to look at the Map View - remember that we're aiming for an Apoapsis of at least 80,000m (Air drag will slow us down as we ascend, so aiming 10km higher than the atmosphere will give us a good margin of error).

Ready?
Hit Space!

Step-by-step ascent

1. Don't turn over immediately! This rocket's fairly low TWR means that it will take some time to get to a higher altitude, wait until you're at around 1,000m before beginning your gravity turn.

2. To begin your gravity turn, gently tap the D key (Or W key if you rotated your rocket to face east) to slowly pitch over in the correct direction, you can use the below video to help guide you.

3. Again as before, you want to tune your ascent such that you're at least at 45 degrees of pitch (pay attention to the numbers on the Navball) by the time you reach 10,000m, then very slowly continue pitching over to the horizon from there - watching your Vertical speed indicator at the top of the screen, next to your altitude readout, and pitching up if you notice it beginning to get too low.

4. Once your lower stage is depleted separate and quickly fire up your upper stage, continue accelerating until your Apoapsis exceeds 80,000m, and then cut your engine with X.

5. You can use the < and > keys to decrease and increase your time warp, and / to cancel time warp (Remember from Tutorial 1?), keep an eye on your Apoapsis as you ascend however, it it ever drops below 70,000m you need to point prograde and fire your engine until it returns to 80,000m, once you're outside the atmosphere you can cancel and re-initiate your time warp to switch to a different time warp mode that's much faster but doesn't let you orient your craft or fire your engines, be careful not to overshoot your Apoapsis! (You can still use the atmospheric time warp mode by holding ALT when engaging time warp).

6. Once you've reached Apoapsis, all that is needed is to point prograde and fire your engine until your Periapsis is above 70,000m, and congratulations! You're officially in orbit!

8. Orbital activities - Managing solar panels and going on a spacewalk

Now that we're in orbit, we can pop open those solar panels we attached to begin generating electricity, to do this simply hover over them and right click to bring up a pop-up window, then click the "Extend Solar Panel" button, these specific solar panels can also be retracted again if need be, right click anywhere else to close this pop-up window, or click the pin icon to "pin" it to your screen, making it remain open until you unpin it.

Now that our electricity situation is sorted, let's get our pilot out and let them stretch their legs.

To get our pilot out, hover over their icon in the bottom right, a pair of buttons will appear.

• View - Allows you to view the insides of the spacecraft through their eyes, use the C key to toggle this view.
• Extra-Vehicular Activity (EVA) - Commands the crew member to exit the vehicle.

Click the "EVA" button and you'll find yourself in control of your Kerbal outside the spacecraft!

The EVA controls are quite a bit different to normal spacecraft controls:

1. Firstly, press Space to make your brave Kerbonaut let go from your command pod.

2. Next, ensure that RCS is enabled with the R key, this will activate the Kerbonaut's jetpack, this will likely push you away from your craft.

3. Now, the WASD keys control your lateral movement relative to wherever your camera is facing, and the Shift & Ctrl keys make your Kerbonaut go "up" and "down" - try and return to your craft before you fly too far away by pointing the camera in the direction you want to go and tapping W, using the other keys to adjust your trajectory (Try not to crash into your solar panels or you'll break them!).

4. While you're flying around be very mindful of your EVA Propellant level, visible in the Resources tab, this represents how much fuel your jetpack has, if it runs out your Kerbonaut won't be able to use their jetpack anymore and will likely drift off!

5. Once you're done flying around, approach your pod's door where you disembarked from, hit the F key when the prompt appears to grab back onto it, then finally hit the B key to board your spacecraft.

9. Going home

Now that we've had our fun, it's time to bring our brave kerbonaut home.

Deorbiting is a simple process:

1. Point retrograde and fire your engine until you have a periapsis around 35km (About halfway into the atmosphere).

2. Time warp until you enter the atmosphere (Your time warp will automatically stop).

3. Separate your command pod from your fuel tank with the decoupler, then hold retrograde so your heat shield protects you.

4. Once you've slowed down enough (Your parachute will turn from red to grey in the staging stack) simply activate your parachute as you did on your first launch and let it bring you to a soft touchdown.

5. Finally, hover over the top of the altimeter and recover your vessel.

Congratulations! If you've made it this far you've already achieved what a good percentage of this game's playerbase never do - you've made it to orbit!

Perhaps you may want to fly a few more orbital missions? Try messing around with different fuel tank and engine combinations to see if you can build a better rocket? Maybe even try putting a Satellite or two in orbit using unmanned probe cores instead of crew capsules!

Regardless, once you feel like you're ready to move onwards, the next tutorial will expand upon this game's Patched Conics system, the basics of building aerodynamic rockets as well as walk you through the process of getting to and landing on the Mun.