a question ive always had about landing on the mun, but never asked

[putnamto]

so i circularize a low orbit to pick my landing spot, then burn off my horizontal speed and point my ship with the engines and landing gear facing the planning, falling straight down.

when burning to reduce my vertical speed sometimes my ship will start gaining horizontal speed when i have a few hundred meters left before landing, this usually ruins my plans and i have to quick load, why does this happen?

[bewing]

The basic answer is that zero orbital speed is not the same as zero surface speed. Or, in other words, "straight down" has two possible meanings.

If you burn to zero orbital velocity, then you really do fall straight toward the center of the CB. However, the surface is continually moving underneath you -- so you miss your landing spot by a ways every time. You would have to know how many seconds the landing would take, and lead your landing point by the surface velocity multiplied by the time -- and then cancel your negative surface velocity just before you land.

OTOH, if (in orbit) you burn to zero surface velocity, then you still have a horizontal component to your velocity in the grand scheme of things (because the surface is moving horizontally). At that point you need to understand what the navball means by zero surface speed. Let's say you're on a CB with the equator rotating at 175 m/s, and a radius of 600km.  If you are sitting on the equator at zero surface velocity and switch to orbital navball mode -- it will say 175m/s. If you are orbiting at an altitude of 3463330m (keosynch) and you check your surface velocity, it will also say zero -- however, your orbital velocity will be 1009.8 m/s. So what the navball means by "zero surface velocity" is the velocity you need at your current altitude in order to stay over a particular spot. But the velocity is a function of altitude. The higher you are the faster you need to be going, in order to achieve "zero surface velocity". If you have that horizontal velocity, and then you teleport down to the surface -- you will be going somewhat too fast compared to the actual surface. And then you have to cancel out your positive surface velocity just before you land.

So basically there is a small fundamental problem with this landing method. If you come to a stop with respect to the surface while you are in orbit -- then you are starting over the right spot, but your horizontal speed is a bit too high and you will land east of your target. If you slow to the correct surface speed or slower, then the surface will rotate under you while you descend -- and you will end up west of the spot you are hovering above. However, these effects are small for a slowly rotating CB such as the Mun.

On the third hand, landing on a precise spot by hand is always inefficient. So this is actually a pretty good method without going to the full "push the retrograde marker on top of the anti-target marker" method, or a mod.

 

Edited December 16, 2018 by bewing

[Superfluous J]

Also, perspective may be causing your issue. If you don't kill your speed exactly along your velocity vector and only kill your vertical speed, as you get closer to the ground it will look like you're going sideways. Also, if you are tilted slightly in a direction (but can't tell because the navball can't show you EXACTLY vertical) then you may actually be slowly accelerating in that direction, actually speeding yourself up.

There are 3 ways to stop this if it's the problem:

1. "Aim retrograde." Like @bewing states above, make sure you're in surface mode and click the little picture to aim retrograde. Then every time you burn you're guaranteed to be killing your velocity and not just your vertical speed.
2. Get a mod that will help you. There are mods that handle part or all of the landing process. In particular there are ones that will automatically kill your horizontal velocity (so you're sure you're coming straight down), or automatically kill your vertical velocity (so you can hover), or both (so you can go get coffee and come back landed).
3. Practice, practice, practice. Landing is hard and like anything hard, you have to do it a lot before you get used to it. There are no less than 10 buttons on your right hand (11 if you need to stage, more if you need to do action groups) that you may have to hit at any given time, under a time limit with the threat of total mission failure. Until you can hit them without even thinking about them, you're going to have trouble.

[Rocket In My Pocket]

It would be more efficient to do them both at once, killing horizontal then vertical speed is like walking two sides of a large field instead of crossing it diagonally.

Just lock retro in Surface mode and burn at the last (reasonably) possible moment.

[putnamto]

thanks for all the info guys, its an issue not because i miss my landing spot, i dont even really have a precise spot i want to land at, i just want to land. i end up gaining so much momentum that i tip when i do land.

im using KER and im getting rid of horizontal speed at 500-1000m, it starts to go horizontal when im burning my last 5-15ms surface speed on the navball.

9 hours ago, Rocket In My Pocket said:

It would be more efficient to do them both at once, killing horizontal then vertical speed is like walking two sides of a large field instead of crossing it diagonally.

Just lock retro in Surface mode and burn at the last (reasonably) possible moment.

i tried lock in retro but accidently burn past 0 when im close to the ground causing my ship to "bodyslam" itself into the ground lol. is their a key for lock retro/pro on the keyboard so i dont have to constantly reach back and forth to my mouse?

[Plusck]

6 minutes ago, putnamto said:

i tried lock in retro but accidently burn past 0 when im close to the ground causing my ship to "bodyslam" itself into the ground lol. is their a key for lock retro/pro on the keyboard so i dont have to constantly reach back and forth to my mouse?

If you're using KER, you can "cheat"* and use the landing countdown to tell you when you absolutely need to burn at full blast.

* "cheating" in this context means, basically, having modern navigation and guidance computers on board, giving you a HUD telling you how far you are from the surface and how hard you need to burn to come to a stop in time. "Not cheating" means winging it with a radar altimeter that you have to squint to see at the edge of the screen in cockpit view...

On retrograde hold, just start a few seconds early (10-20 seconds early to be sure), and cut the engines as soon as your surface velocity is about 10 m/s. Then slowly ramp up the throttle until the velocity stabilises and starts falling. Keep it at about 10 m/s or so until you're only a few tens of metres high, then increase thrust until you're down to about 5 m/s for a while, then down to about 3 m/s until you touch the surface. Kill the engines immediately.

If you're on retrograde hold, you'll never gain horizontal velocity. Rather, you'll constantly reduce your horizontal velocity as you come down.

 

Of course, for this to work properly you really must have thrust aligned with the centre of mass. If they're significantly misaligned (and KER shows this during the build and in the vessel info (thrust offset) during flight) there is a very good chance that the problem gets worse the more fuel you burn, and therefore the closer you are to landing.

[bewing]

36 minutes ago, putnamto said:

i tried lock in retro but accidently burn past 0 when im close to the ground causing my ship to "bodyslam" itself into the ground lol. is their a key for lock retro/pro on the keyboard

Lock retro until you are 30 meters or so above the surface and still moving down at 5 m/s or so. Then switch to Lock Radial Out. There is no assignable key for it, unfortunately.

Also, this "burn past zero" problem generally means that you have the thrust on your engines turned up too high. Try turning the thrust limiter down to 20 or 30 percent after you eliminate most of your horizontal orbital velocity to give yourself more control during landing.

Edited December 16, 2018 by bewing

[putnamto]

thanks guys, its weird how a year break from this game can make something like landing on the mun seem impossible.

[Superfluous J]

Also get used to throttling up with shift and down with x. That way you'll never massively overthrust and if you have a slight overthrust you'll cancel it immediately.

Be careful though to keep your speed down if you do that. You can't brake from 50m/s in 3 seconds by tapping shift a couple times.

[putnamto]

best part about building a lander that seperates and leaves the landing part on the mun is leaving all the science in the lander.......:(

[Draalo]

4 hours ago, putnamto said:

best part about building a lander that seperates and leaves the landing part on the mun is leaving all the science in the lander.......:(

You know that you can collect the data from the instruments and store that into the pod?

Edited December 17, 2018 by Draalo

[Superfluous J]

8 minutes ago, Draalo said:

You know that you can collect the data from the instruments and store that into the pod?

I'm pretty sure he does. I think he could have cross posted to the Thread To Complain About Stuff.

[linuxgurugamer]

Hmmm. Seems that a mod to kill all engines at surface contact might be useful

[Gargamel]

10 hours ago, linuxgurugamer said:

Hmmm. Seems that a mod to kill all engines at surface contact might be useful

Stahp.   Just Stahp.

But yes you're right it would. 

[putnamto]

12 hours ago, 5thHorseman said:

I'm pretty sure he does. I think he could have cross posted to the Thread To Complain About Stuff.

i sure do, but i didnt remember the science until it was to late. curently theirs a bunch of science sitting in a sci jr. a goo can, a thermo, and a baromat all attached to four fuel tanks and four landing legs sitting on the mun.

[Superfluous J]

9 minutes ago, putnamto said:

i sure do, but i didnt remember the science until it was to late. curently theirs a bunch of science sitting in a sci jr. a goo can, a thermo, and a baromat all attached to four fuel tanks and four landing legs sitting on the mun.

This is why I won't play the game without ForScience.

[pincushionman]

On 12/16/2018 at 5:02 PM, putnamto said:

…I tried lock in retro but accidently burn past 0 when im close to the ground causing my ship to "bodyslam" itself into the ground lol. is their a key for lock retro/pro on the keyboard so i dont have to constantly reach back and forth to my mouse?

Kind of. It’s “T”.

When you’re both very close to the ground and close to zero speed, you really need to disengage all SAS and finish the job flying relative to surface features. SAS is a simple tool, and is not an autopilot.

[Superfluous J]

45 minutes ago, pincushionman said:

disengage all SAS

Yikes no. Stop locking to prograde/retrograde/radial/etc? Sure. Maybe. Turn SAS off entirely? NO WAY that can ruin an experienced player's landing little alone someone new to the whole thing.

[pincushionman]

8 hours ago, 5thHorseman said:

Yikes no. Stop locking to prograde/retrograde/radial/etc? Sure. Maybe. Turn SAS off entirely? NO WAY that can ruin an experienced player's landing little alone someone new to the whole thing.

Know what? You’re right. I didn’t think that all the way through before I wrote it. You do want hold direction.

What I meant when I wrote it was “no SAS is better than SAS wigging out and flipping you around” but I guess once it starts to turn you then you’re already hosed.

[Kryxal]

If you want to just switch to SAS hold, a quick tap of F should do it, I believe ... unless they changed the behavior there.  If you've scrubbed off all your horizontal velocity, it should be fine unless you try to hover a while.

[bewing]

Yeah, tapping F will do that. But I find that Radial Out works better when you are touching down, because if you bounce and tip over a little then Radial Out will try to stand you back up again and Hold won't.

[klesh]

On 12/17/2018 at 8:50 AM, linuxgurugamer said:

Hmmm. Seems that a mod to kill all engines at surface contact might be useful

 

If you end up making it, I would like to humbly suggest the name “3, 2, 1... Contact!” named after that classic educational kids show from the 80’s.