How to I stop myself from moving sideways when trying to land on the Mun?

[bandman232]

Hey. I'm trying to land a one man ship on the Mun. I get my transfer and everything right, but when I'm close to the surface when landing, I keep moving sideways and when I touch the ground, tip over. I tried burning tward retro grade, but it still keeps going sideways. What do I do? Could I try using RCS to stop it?

[Ziff]

I made a short video about this when .16 was released to answer that question for a few people.

is a link for it.

[Nibb31]

Use your navball. When you are way above the ground, make sure that your retrograde marker is as close to the center as possible. This means that you are going straight down with no lateral motion.

[Vanamonde]

I tried burning tward retro grade, but it still keeps going sideways.

Then you are starting too late and/or not burning hard enough. Try killing your horizontal speed while you're higher up.

[MET?]

You have to make sure that the retrograde marker on your navball is straight up. That is to say, directly on top of the blue half.

When you are landing on the moon, before you slow down on descent, you will be moving down at several hundred meters per second. Your retrograde marker should be very near the top of the blue. However, you also, inevitably have some horizontal speed. Lets say your moving west at 2m/s and down 250m/s. Your trajectory is going to be pretty straight down. Right?

Now when you slow, and you kill that 250, you are still moving 2m/s west, and since your not moving as quickly down, your trajectory changes. To the point where if you aren't moving down at all, all your velocity is west! So your marker is going to be on the 270 line, and your other on the 90 line. That's why as you slow down, your retrograde goes let or right or whatever, even though your not burning that way.

SO: On your descent, cancel out downward velocity periodically, and correct your trajectory. Depending on your lander size, linear rcs helps with this. Also, the wider your lander, the more fudge factor there is. If you have a skinny lander, you will have to be much more precise.

Hope this helps.

[EndlessWaves]

Also hit caps lock to make your corrections smaller.

[bandman232]

Well, I've done it! Thanks for the help! Now the real challenge will be making a rocket that has enough fuel to get him back...

[hjalfi]

I had an 'aha!' moment the other day, and suddenly I can do landings. Hell, last night I managed to land on Minmus for the first time ever. *Twice.*

The secret is, keep the retrograde marker in the middle of the navball. This means that you are thrusting in precisely the right direction to cancel out both your vertical and horizontal velocity. As your velocity decreases, you'll see this move towards the middle, which means that you're going straight down. Your goal is for your velocity to be as close to zero as you can manage just as you touch the ground, but a good lander design and the heavy duty lander legs can absorb quite a lot --- you just have to be careful not to bounce.

If you apply too much thrust and start going up, the retrograde marker will go nuts and vanish. This just means that it's flipped to the other side of the navball because you're moving in the other direction. Don't follow it, just point the vehicle straight up, reduce thrust, and once you start going down again it'll come back. Note that this means that aborting landings is easy! If you start to topple over after landing, throttle up, get off the ground, get the nose pointed straight up and just try again. Also, quicksave is your friend.

If you have a flight stick, use it; it's much, much easier that way than using the keyboard. (If you don't have one, you can get one off Amazon for less than the price of KSP, but of course I have no idea if those are any good.)

My last lander had a huge RCS tank (this was the one I landed twice on Minmus with). I never used it.

[Aescwulf]

Yeah I had this drift problem as well when I was landing on Mun the first time I ended up losing control and well bouncing poor Jebs face off the surface of Mun and the second time ( thank the maker for quick save and load ) I almost lost control but managed to land.

When I'm in Muns orbit I try to kill off all horizontal speed and land that way and start doing a slow burn around 30K M

[Will_hynes]

Well, I've done it! Thanks for the help! Now the real challenge will be making a rocket that has enough fuel to get him back...

That should be the easy part, you can return with 1-2 tanks of fuel.

[hjalfi]

To get back, get yourself into a roughly equatorial orbit around the Mün, wait until you're travelling in the opposite direction to the Mün's motion, and throttle up. Once you've left the Mün's sphere of influence you should be in a nice elliptical orbit taking you back down to Kerbin.

You shouldn't have any trouble with that. I've gotten back from the Mün using nothing but RCS thrusters in the past (including the takeoff).

[EndlessWaves]

To get back, get yourself into a roughly equatorial orbit around the Mün, wait until you're travelling in the opposite direction to the Mün's motion, and throttle up.

Isn't burning ahead of the mun better so your apoapsis extends back along the moon's orbital track?

[Kosmo-not]

To get back, get yourself into a roughly equatorial orbit around the Mün, wait until you're travelling in the opposite direction to the Mün's motion, and throttle up.

Isn't burning ahead of the mun better so your apoapsis extends back along the moon's orbital track?

Actually, both of your are wrong. The correct burn point is roughly halfway between those two.

[bandman232]

That should be the easy part, you can return with 1-2 tanks of fuel.

Sadly I have less than a tank. Need to redesign my rocket.

[draeath]

I only needed 3 short bursts to get back into Mun orbit - one to ascend, one to gravity turn (straight up, then one lateral, and then lateral again at apoapsis to circularize), and I only needed about 5 seconds of burn time from then to fall back to Kerbin. You won't need much!

Wait until your orbit is (relatively) slinging you towards the Mun's retrograde. When you are about 90-degrees from where Mun's retrograde orbit line crosses your own orbit line, burn towards Mun's retrograde.

Edited September 30, 2012 by draeath

[hjalfi]

Hmm. That's about where I do my burns, but I need a lot more than five seconds of burn time. My epic atomic interplanetary explorer lander pulls about 1/3 of a gee on full thrust. Is there a better way to do this?

...incidentally, Jeb got his wish: full instrument landing. Bob was flying because he's the only one who can see the radar altimeter and a window at the same time, but this turned out to be pointless as he's flat on his back and the only thing he could see was stars. I would video it and put it on Youtube but it would make for really dull watching.

Next time I do this I need to take more care about the landing site. I ended up on a mountainside but was lucky and stayed upright. In the Apollo landers the astronauts stood upright, and could see out --- I should investigate the other capsules and see if any have better sightlines for use as landers.

[VernKerrigan]

This is where the brand new center of mass readout is supremely helpful. All you have to do is remove the stages below your lunar lander, and place rcs ports around the center of mass with 4 way symetry. As long as it doesn't have an ASAS, you can turn your RCS on while keeping your rocket pointed stright up, and use the RCS translation to cancel out any persistent horizontal velocity that you have as you get close to the lunar surface.