[[Tutorial] Planetary intercepts - or how to orbit in the right direction]

Thanks Al-Rabban for the kind words!

Temstar - I'm not going to argue with that ribbon! I'll give your second method a try and see how it works for me. Not that I'm doubting that it works per se, but having just gotten my head around one way of thinking about this it may take some time to adjust Thanks for the reply.

[[Tutorial] Planetary intercepts - or how to orbit in the right direction]

This is probably old news to the seasoned Kerbalnauts out there but it's something that took me a while to figure out. So I thought I'd write a tutorial in case anyone else out there was having the same problem. That problem being - how do I set up an intercept with a planet (or moon) so that I end up in a consistent prograde or retrograde orbit?

The Mun isn't a problem. It's big enough to have a significant effect on your spacecraft's trajectory and I could set up a recognisably similar trajectory for everything I sent to the Mun by eyeballing it. For Minmus though it wasn't so easy. It's a smaller target, it's a lot further away and setting up a consistent trajectory was proving difficult. As a result, my early Minmus missions ended up in prograde or retrograde orbits more or less at random.

This is fine for 'footprint and flag' missions but not so helpful for building space stations or for docking larger craft in orbit. And if Minmus wasn't working, then what chance Duna, or anywhere further afield? It was time to figure this out properly, so without further ado.

A guide to consistent orbiting

1. To figure out your eventual orbit, you need to know your velocity relative to the planet as you approach.

Here's a rough diagram to illustrate the point. In each case we burn retrograde at periapsis (Pe) to drop into orbit around Minmus. If our velocity relative to Minmus is pointing in one direction, we get a clockwise (retrograde) orbit. If it points in the other we get a counterclockwise (prograde) orbit. The trick is working out the relative velocity ahead of time, so lets look at that next.

2. We can do this the complicated way...

Here's a simple example. To a reasonable approximation we're on course to cut straight across Minmus's orbit. We can therefore estimate our relative velocity by considering motion along Minmus's orbit and normal to it. Our velocity along Minmus's orbit is essentially zero, so our relative velocity becomes 0-x where x is whatever Minmus's orbital speed is. The exact numbers don't matter, the point is that relative to Minmus we are travelling back along its orbital path. In contrast, we have a small velocity normal to Minmus's orbital direction and at any given time Minmus has zero velocity in that direction. So our relative velocity becomes y-0 or in other words nothing changes. Add the two up and we get our relative velocity.

This is a whole lot easier to see on the diagram. Red lines are our relative velocities along Minmus's orbit and normal to it. Green line is the resultant velocity.

3. Or we can do this the easy way.

A much easier way of doing this is simply to mouse over the 'Minmus encounter' point on the Map to display the Minmus' location at that encounter point. We can then estimate our direction of travel relative to Minmus by drawing an imaginary line between the encounter point and Minmus. As you'll see, that works out to be fairly similar to the direction we estimated in Step 2 by fiddling around with adding vectors.

4. But does that work in practice?

Lets try. Minmus is way over there at the encounter point, so draw that imaginary line. Looks like our relative velocity is angled back along Minmus's orbit at about 20 degrees to its direction of travel. Remembering back to that first diagram, we can predict that our eventual orbit will be clockwise (or retrograde) around Minmus.

Once we cross into Minmus's sphere of influence, the Map will show the correct relative velocity and we can see if that prediction is correct. A quick burst of timewarp and

Not bad!

5. So lets set up the Minmus insertion burn.

Note that our prograde marker on the maneuver node is pointing in the direction we expect. That's a nice check.

And there we have it. I've added a maneuver node to highlight our orbital direction. As predicted - a nice retrograde orbit.

Hope this all made some sense. Have fun planning those missions!

[Mün Landing?]

What these good people have said. One other thing though - trust your instruments. It's much easier to use the Navball to zero out your horizontal velocity than to try and do it by eye. When you're heading vertically downwards, the Navball should be entirely blue with your retrograde marker dead centre. If it's not you can tilt your lander a bit to push it to the centre. Takes a bit of practice but it's not so bad when you get the hang of it.

Last thing - sometimes it's easier to just stop your engines a couple of metres above the surface and drop, rather than trying to fly right down to the surface. Just make sure you're not doing more than about 5m/s when you touch down, maybe slightly less if you're landing a probe on those spindly wee legs.

[Halp i need tips on dockin!]

Welcome to the community SolidSnivy

Landing on the Mun does take some practice, I suggest you get into a low orbit, something like 10km is good, that way you don't have to land until you are ready.

When you see a place you want to land at, slow down so you are descending vertically (you'll see the marker at the top of the navball) and gently descend on your main engine thrust.

Don't forget to extend your landing legs

What are these things you call 'landing legs'?

SolidSnivy - it's not a very exciting ship to land on the Mun as its unmanned. It's easy to get to the Mun though as it's very light - but it also handles quite nicely for the actual landing. Take a probe core, put the smallest 'engine for ants' on the bottom and fit a toroidal tank around the engine. A standard decoupler will fit around the tank and will work just fine. The rest of it is just for the look really. I'm using these as navigation beacons to mark out landing sites and I figure a navigation beacon should have some communication gear!

[Go for liftoff!]

Hey KSP community. I've got to say, I'm very intrigued by this cool game. It's hard, but rewarding all the same. Before KSP, I messed around on Orbiter for a little while, but never could seem to figure things out besides getting into LEO.

The KSP devs have really helped with the UI on this one, on my first day I've:

1) Put a probe in a polar orbit.

2) Put a probe in a horizontal orbit.

3) Shot a probe off into deep space ( I missed the Mun, and then missed Minus, so now it's renamed the deepspace1!)

4) Put a probe into orbit around the Mun.

Right now, I'm working on landing an automated rover on the moon.( I can't seem to get into orbit with enough fuel for a moonshot with all that extra rover-weight) After that, I figure I'll move on to get some Kerbalnauts up there.

Anyways, I'll be around, mostly to ask for help here or there, and perhaps ogle at people's rocket designs.

Also, does this game come with joystick support? I'm half-tempted to build some aircraft and try 'em out with a joystick.

Definitely with you on the hard but rewarding part. It makes those successful flights all the sweeter though! Congrats on the successful probe launches, especially the one around the Mun! That's good going for day 1. Not sure about joystick support - I think the answer is yes but I don't have a stick myself so I havn't tried it out.

Not going to spoiler this thread but I have a design for a very compact (unmanned) Mun lander if you want to try it. It doesn't do much when you get there but it flies very well and makes a nice practice lander. Also it's very light - if you can get a probe into orbit around the Mun you can definitely get this to the Mun too.

[[Theory]]

This is no joke. Only the truth.

The truth is out there. Likewise this theory

[[Stock] Mun Base]

Howdy, this is That1Guy, asking for opinions on my Munar base... I am looking to make a video on how to build this style of base.

Nice base! I see how you're putting it together from a single standard module. I'd definitely like to know how you line them all up and dock them together though. I presume you're not building it in orbit and then landing the whole thing in one piece?

[Working Soyus with stock parts]

Nice design! The solar arrays look a little large for a Soyuz - I think maybe the smaller ones would work better. Apart from that - *thumbs up*

[Here we go again... :P]

Since I had to create a new account after the forum crash, I will introduce myself again

Hi, I'm turbu from France.

Space made me dream since as long as I can remember, and I jump on every occasion to play a game about it. Some of them are good, some of them are, unfortunately, really bad. But I have to say Kerbal Space Program is definitly one of the best of them, if not THE best.

I play KSP since 0.18.2, and I'm loving it !

Fly safe fellow kerbalnauts !

(Pardon me if my english is not perfect ^^)

Welcome Turbu. Your English is great - way better than my French!