Best way to kill horizontal movement for landing

[zapman987]

Trying to land for first time on the moon. Ive got the vertical down, but how do you kill the horizontal efficiently. best i can try to do is point at an angle, which kills my fuel (and still I tip over).

[John FX]

Have you tried using RCS?

[jackercrack]

the line that turns blue to brown on your nav ball is your equatorial line, you draw at straight line from the very top of the nav ball that passes through your retro grade marker and burn on it untill the retro marker is at the top of the nav ball.

[700NitroXpress]

Kill horizontal and vertical equally as you come in for a landing. Since you're traveling in an arc, if you point the nav marker behind the retrograde marker, then it will kill the horizontal velocity with the vertical velocity and you'll come in straight down. If you gain any horizontal velocity while angling your craft during landing burns, using the RCS translation controls of JKLI you can counter the horizontal movement.

[zapman987]

I dont think Ive learned RCS yet. Early career moon lander.

Jackercrack, thats how you get down. Im getting down just fine. Even if you are moving side to side, retrograde will be at the top.

[konokono]

Let "o" be the top of your navball and let "+" be your retrograde marker. Burn at the "x"

Navball:

o

+

x

That is, burn in a direction such that your retrograde indicator is between the burn and the top of the navball. This will push your retrograde marker towards the top. When your retrograde marker is at the top, you have only vertical velocity

[Tripod27]

I generally go from a circular orbit around the mun to an orbit where my periapsis is at 5000m and on the light side so I can see easily (most of the mun is under 5000m tall but there is one mountain that is about 6000 so watch out)

Now at my periapsis I'll be basically traveling along the surface of the mun about 500-1000 meters above it. I kill horizontal speed while pointing my engines down just enough to maintain altitude and glide a few hundred meters above the surface until my horizontal speed is 0 (point between the horizon and the reverse velocity marker until it points down at the planet). Then I use gravity to bring me down the other 500 or whatever vertical meters using some thrust to stay at a reasonably slow speed ("reasonable" depends on the thrust to weight ratio of your rocket) until I get really close to the ground where I slow down to under 4m/s and land.

By being so close to the ground for the entire landing burn, it makes it easy to judge how much fuel you're using for "not going down" since fuel you spend hovering or going up is wasted due to gravity pulling you back down while fuel used for slowing down horizontally is never really wasted unless you're flying back and forth or in circles or something.

[Guest]

The navball has 3 modes : orbit, surface, and target. In this screenshot you can see it's in surface mode :

You can switch between modes by clicking on the top center of the navball inside the box where the speed is displayed. While in surface mode, aim for the retrograde marker (the greenish circle with an x in the middle) and burn until it says zero. This will kill horizontal and vertical at the same time. Suicide burns are the most efficient, meaning the closer you are to the surface when reaching zero surface velocity the better. I like to reach zero at around 100 meters, hopefully having time to engage SAS with the rocket pointing straight up, then it's just a matter of keeping the descent slow enough to keep the landing gear from breaking. Helpful tip : you can see your actual altitude above the surface while in IVA. The altitude given at the top of the screen in flight mode is not your actual altitude above the surface.

[Dunbaratu]

Put the navball in "surface" mode and watch the green "x" : the retrograde marker. To be falling vertically with respect to the ground you have to have the green 'x' at the very center of the sky. So when you get near the bottom and want to kill your relative horzontal speed, use the navball to steer by and try not to look too much at the 3-D view on the screen - just keep your eyes on the ball. The goal is to get it going vertical a little bit above the ground. And you do that by "chasing" the marker while adjusting your throttle to make sure you never stop falling, but you fall slowly. To "push" the marker, put your aiming crosshairs on the other side of it. You'll "push" the retrograde marker away from your crosshairs. Like this:

X = retrograde marker
. = where you want to move the retro marker to
+ = your current crosshairs.



  +

     X

       \
        \| 
	~ 
	   .

"push" the "X" with your crosshairs, toward the center.

[Tripod27]

I made a quick tutorial >here< explaining my landing process if you're more of a visual guy

The first step got cut out (get into orbit) and the audio is offset by 3 seconds because adobe aftereffects hates me, but besides that it should be easy to follow

[RSF77]

If you aren't opposed to using mods, mechjeb has a very nice way of doing this buried deep within its menus.

1) Go to your Smart A.S.S. (<~ hilarious btw)

2) Choose the ADV tab I think its called, the last one.

3) Click the arrow until you see the mode called "SURFACE_VELOCITY".

4) Just below that, click the other arrow over one so it says "BACK" or "REVERSE" or something like that.

5) Execute and your craft should orient itself.

6) Burn until you're lander is vertical.

7) Profit.

It will want to get wacky on you if you happen to burn all the way until you are ascending again because it will attempt to turn your lander upside down because reverse direction actually changes to up, just be sure to keep that in mind and disable it if this happens. If you burn slowly and steadily to kill horiz velocity without being so much to nullify your vert then it lands if perfectly.

Without using mods, a pretty inefficient but fairly easy way to get close is make a maneuver node above where you want to land and drag the retrograde marker until your projected path is a line directly down or a little forward or back depending on which direction you are orbiting. If you're quick about it you can do this as well while already on a descent path, just make a node close to the ground and it should get you at least close to where you want to be.

Otherwise when you are low enough and near 0 horiz velocity you can just look almost directly down and pay attention to which direction your ship is oriented then turn and burn until the ground stops moving under you. Just make sure you are always burning upward and toward your retrograde marker (when descending) and eventually you will kill horiz velocity. While still moving downward at an angle at some point the retrograde marker may quickly change to the opposite side, cut your throttle at this exact moment and face upright for your landing.

Edited November 13, 2013 by RSF77

[Frederf]

As others have stated for main engine only technique you'll want to devote a fraction of your hovering (or slow descent) thrust counter to your lateral motion. Once you have your lateral motion under control (~20m/s or less) turn your craft for landing and tilt 5-10 degrees from vertical toward the retrograde marker. This will proportion 5-10% of your thrust to lateral motion which allows easier fine tuning. Assuming you are slowly descending through the process the retrograde marker will drift toward the center position indicating no lateral motion. At that time return your attitude to vertical to not induce any lateral motion now that it is zero.

The less your descent the more sensitive the the retrograde marker will be to lateral motion.

[celem]

It's most efficient to burn away the horizontal and vertical together. Basically you come in like an uncontrolled meteor and dump both lateral and vertical together with an angled burn timed to leave you at a dead-hover right above the ground.

However without knowing the true ground-height and without knowing your craft's decceleration this will result in craters a lot in early career.

Whilst less efficient i find it easier early on to cancel the horizontal first using methods listed above (switch to surface speed and burn on the retrograde), then drop vertically.

You should be aware that with a low gravity, 0-atmosphere body like, say, minmus, once you've killed horizontal and start the vertical drop the planetoid is still spinning beneath you, and you will pick up a little horizontal surface velocity as you descend anyway, always make a final correction nice n low. Higher gravity bodies tend to pull you in fast enough that this rotation is less relevant, while bodies with atmosphere wont display this at all really as the atmosphere spins you with the planet during the descent

[Kasuha]

Very efficient landing method for bodies without atmosphere:

1/ Bring your periapsis down, just clear of terrain (check wiki for what's the safe height)

2/ At this periapsis start burning retrograde.

3/ As your horizontal speed decreases, your altitude will start dropping. Watch your vertical speed (how fast the altimeter is rolling) and keep it low by burning slightly above the retrograde marker (i.e. between the marker and the center of the blue part).

4/ Once you slow down enough that the retrograde marker climbs to about 45 degrees (while your vertical descent is still low) start burning retrograde and modulate your descent with thrust.

The only tricky part is not hitting anything while you're still killing your horizontal speed.

[sjwt]

You should be aware that with a low gravity, 0-atmosphere body like, say, minmus, once you've killed horizontal and start the vertical drop the planetoid is still spinning beneath you, and you will pick up a little horizontal surface velocity as you descend anyway, always make a final correction nice n low.

And also why you should always change from orbital to surface velocity readings before starting your burn. You still pick some up, but you are countering it as you are burning, not as efficient DV wise, but more often safer.

[Xiphos]

I would suggest practicing landings on minimus. One of the large, flat frozen lakes ought to serve you well. The gravity is so low you should have plenty of time to learn the fine tuning required for landing in higher G. Since it takes such little fuel, you can land, take off, make orbit, and land again many many times with the same ship you used to get to the mun. I aim for the lowest Pe possible when adjusting my orbit for landings, then I do the rest by eye when I am over a spot I want to land, I full burn on the horizon, then it's just little adjustments from there. Eventually you can land within a couple hundred meters of your target each time. Good luck, let us know how you are progressing.

[capi3101]

If you're tipping over on landing, try redesigning your lander so that you shorten and widen it - this lowers the lander's center of mass and increases the surface area around which the lander can pivot after touchdown, both of which makes the design more stable. For example - let's say your lander uses a single FL-T400 tank. If you've got access to fuel lines, change that out to four FL-T100 tanks, one in the center and three outboard. Run fuel lines from the outboard tanks to the center, and put your lander legs on the outboard tanks. You'll have successfully widened your lander without changing its mass in the process.

Now, if you are just using an FL-T400 as your sole fuel tank, you need to watch your fuel level as you land. Most basic low-tech landers (a Mk16 chute, Mk1 Command Pod, FL-T400, LV-909 and 3-4 lander legs) will reach "bingo fuel" around 80 fuel units. If that's what you're using, think about heading back to Kerbin when it reaches 90, and when it gets to 80 either hit space or plan on not returning to Kerbin.

[Dun Kirk]

helps to see your craft....

[Killerdude8]

Burn around your Retrograde Marker (prograde if you flipped your pod during construction) until its at the top of the nav ball.