Wanted: Precision Landing Tips and Tricks

[Srpadget]

Now that I've figured out (even if not precisely 'mastered') rendezvous/dock so I can 'routinely' fly Apollo-profile missions and visit space stations, it's time to add another skill to the mix. Namely, precision landing at a predetermined site (on a vacuum world).

I've seen plenty of screenshots of bases/colonies that clearly required multiple landings at the same site, so I know there are folk out there who've mastered it. I've managed to get kinda-sorta close (within a couple km, anyway) to a desired landing site on Mun or Minmus by the simple, if fuel-wasteful, expedient of killing ALL my orbital velocity when essentially directly over my desired landing site, plummeting for a while, then burning to remove the accumulated vertical velocity in order to accomplish a "landing" rather than a "new crater". But there has to be a more elegant (and fuel-efficient!) method than that. One that more closely resembles a launch-in-reverse (short "decircularize"/deorbit burn something less than halfway around the Mun from the desired landing site, cruise in to low altitude and some distance uprange of desired landing site, fire engines and come down in a 'reverse gravity turn'). I can do that kind of landing without too much problem (as long as no mountains/crater walls are near the LZ!), but the actual touchdown site is...well, let's just say I can hit the correct biome pretty much every time, and usually come down in the desired area of that biome. But it sure as heck isn't likely to be within convenient EVA distance of the actual target point, let alone the precision I've seen in screenshots, where multiple landing craft are lined up like a suburban housing subdivision.

Any tips/hints/tricks/techniques from you more experienced KSP'ers?

(Yeah, I know, "MechJeb". But I'm looking for all-stock, all-manual solutions. And that's NOT a declaration of religious crusade, or saying that anyone else is 'doing it wrong', or anything like that. I just happen to play stock/manual, myself; YMMV, and that's fine.)

Edited July 9, 2014 by Srpadget
Mark as "Answered"

[Kerba Fett]

If you want to make a base the first thing is to send a small lander down to scout the area. Find a flat area and mark a landing spot with a triangle of flags.

To get down to it from orbit make a maneuver node with the end point at your base site. After you complete the burn you should be on track to crash directly at your base site. Next go to your map view and use that to fly most of the trip down. As you burn to slow your descent watch your projected course line and using the navball adjust your attitude to keep your impact point at your base. Once you're within a few KM of the surface you can leave the map view and land as normal.

Don't forget to turn labels on (F4) to make it easier to spot your landing zone.

[Superfluous J]

I agree with most of what Kerba Fett says, except the start of your descent. You should aim a little bit past your base because the act of slowing down will pull your orbit inward. Depending on the paths you end up taking with each method, it could be anything from slightly to surprisingly more fuel efficient than the above method.

I would suggest sending up a ship with a half dozen or so small landers attached to a mothership. Land one of them and then just keep practicing landing the others as close as you can get. Experience will tell you far more than we can, after these basic explanations of the strategy.

Also, practice first on Minmus. It's far more forgiving. Once you've got the basics down try again on Mun. Once you can pinpoint a landing on Mun with regularity you can pretty much do it anywhere. Well, anywhere without atmosphere.

Edited July 8, 2014 by 5thHorseman

[Sirine]

Learn to be really understand/read your Nav-Ball,

The tricks are near the end of the video. (Recommended practice at Minmus.)

[Alshain]

In addition to what has been said, once you have your scout ship down, use it as a target. As you start to land, you want the pink circle marker to be close to the retrograde marker during the last few steps in the descent. You can adjust it's position by putting the retrograde on the opposite side of the navball. Try to get it fairly lined up without doing that as mentioned by others because it eats fuel, but by the point you start building bases you should have some really efficient engines anyway.

EDIT: Sorry I realized that wasn't very coherent. If you line your target up by way of inclination as mentioned by earlier posts then you should be coming 'close' already but because the map is way zoomed out it won't be exact. This is where you target. As you get close you want to push the pink marker just like how you push the retrograde marker to stop your lateral speed. In this case, don't be afraid to go back up a little. You want to push the pink marker near the top of the ball, but in this case it's not a big burn like slowing lateral movement, instead you want to get your arc headed that way a little past the target and wait for the lateral movement to bring you in close to where the pink marker is near the top of the ball and then finally kill the lateral movement using the way you already know.

One last note, you want the pink marker very close to the top of the nav ball... not on the very top like with retrograde (doing that would set you down right on top of the target)

Edited July 8, 2014 by Alshain

[Blind Dead McJones]

I know you said stock, but besides mechjeb you could also look into Kerbal Engineer Redux (gives you all sorts of information including speed, delta-V, apoapsis and periapsis...) and Scansat (make maps of the surface of a planet, which also shows you your orbital path and exactly where it ends).

As for going all stock, remember that you want to start from a lower orbit, because stopping will take less DV. It's tempting to kill all vertical speed and then fall straight down, but this actually costs more fuel and isn't a very accurate way to land due to the fact that the planet will rotate under you.

For the reason of rotation as well as killing momentum, remember to put the end of your suborbital arc slightly past where you want to land. Lastly, don't get discouraged and don't expect a pinpoint landing. When I go to my munbase, I generally consider it a success if I land within 1/2 kilometre and chose a flat valley area specifically for this reason. I also gave them a mun buggy to go back and forth, because flying them around with the EVA jetpack individually takes forever.

[Moss]

Mostly it's intuitive. Practice is essential. Here are some common tips:

-Let your trajectory either lead or fall short of your target, depending on your heading and the rotation of the planet/ moon. This is because as you're falling the planet may rotate under you, taking the target with it. Also applies for landing in atmosphere, as the map trajectory doesn't account for air resistance and you'll need space to slow.

-Some people like to come to a dead stop (no horizontal speed) above their target and then fall onto it. This typically uses a lot of fuel.

-Target markers can be helpful.

[Lheim]

Yep, make a maneuver to come down a little past your intended target. Keep adjusting that - the planet will rotate, and you want to do it relatively shortly before the landing so you're not knocked too far off whack by that rotation.

Then target the ship/flag at your landing site. If you go into target mode - you'll see the pink icons that represent the target's position and velocity vectors relative to you. You can use that to trim your direction of motion on top of your target.

It's a total art, though, seriously.

[LethalDose]

Mostly it's intuitive. Practice is essential. Here are some common tips:

-Let your trajectory either lead or fall short of your target, depending on your heading and the rotation of the planet/ moon. This is because as you're falling the planet may rotate under you, taking the target with it. Also applies for landing in atmosphere, as the map trajectory doesn't account for air resistance and you'll need space to slow.

-Some people like to come to a dead stop (no horizontal speed) above their target and then fall onto it. This typically uses a lot of fuel.

-Target markers can be helpful.

This pretty much sums up everything I've learned so far. Especially "Practice is essential" and "Lead your target" due to planetary rotation.

[MockKnizzle]

Assuming you already have a flag or ship or something at the targeted landing site, the first step is to get into a low circular orbit (as low as possible, ideally <10km) that passes over the target. Oftentimes this requires an inclination change, so try and get that sorted before you begin your landing. Next, pop into map mode and set up a maneuver for a retrograde burn about a quarter circumference before the target, such that your trajectory intersects the ground a few kilometers past the target zone. If there are any particularly tall mountains or ridges in the way, you may need to execute the burn later (and come down steeper) so you don't smash into them.

Now, once you've started your descent, the exact procedure depends on the TWR of your vehicle. A high-thrust craft can coast for longer and brake harder, whereas with a low-thrust craft you will need to manage your descent a little more carefully. Once you've coasted down to about 6km or so (I'm just basing these numbers off the Mun), you'll want to start braking and managing your vertical speed. Stay in map mode, and watch your trajectory as you brake. Ideally, your landing point should slowly approach your target. This is where I like to have a data readout plugin like Kerbal Engineer, so I can watch my vertical speed, horizontal speed, and radar altitude while still in map mode. Commonly you'll find that your landing point will shorten up too quickly and move uprange of the target; this means you're braking too hard and need to either ease up on the throttle or pitch up or both. You also might need to correct your trajectory to one side or the other if you find it drifting sideways. Continue to manage your trajectory in map mode until you're very near the target. At this point you should be within a few kilometers and closing at only a hundred or so m/s.

For terminal descent and an eventual pinpoint landing, controlling vertical speed is the most important. As long as your initial descent was good, your horizontal speed should be low and steering towards the target should be relatively straightforward. It's better to come up a little short than to overshoot, as you can just ease back your descent rate and glide on down. It's really quite simple to park your lander right next to the target once you're close enough, it's just like flying over and landing on the VAB.

[Kerba Fett]

Seems like lots of people have some good tips on targeted landings. MockKnizzle raised a good point about an inclination change often being needed to put you at your base. Normally I do that when I set up the node for the de-orbit burn. I also start from a lot higher. I keep a refueling depot in orbit around the Mun in a 100km orbit so that's usually the altitude I enter orbit of the Mun and the altitude I de-orbit from. I usually start about a quarter orbit before my base and don't touch the throttle till I get down to about 15km. Like the others I set my de-orbit to overshoot my target so I can use the retrograde marker to decelerate.

I don't like to start my descent from too low an altitude since the Mun has a lot or hills and ridges and I don't like too much surface speed close to the ground. I've flown into hillsides because I was moving too fast to get over them even at full throttle.

On the subject of throttle, when flying manually I sometimes like to tweak my engine power down once I get close to the ground and have gotten rid of most of my velocity. A lower TWR lets you use more of your throttle range and gives you more precise control at low descent rates. (like for your final landing)

This is only practical for single engine setups though since you'd usually have to spend more time than you can spare tweaking a bunch of engines to the same settings.

Finally for the players reading this that don't mind using mods, There's 2 that will make landings a lot easier.

One is Diazo's vertical speed controller, the other is MechJeb.

For MechJeb you want to make a custom window. (they're real easy to make)

The info you want for landing is: True altitude, vertical speed, surface speed, time to impact, time to suicide burn, and remaining dV. The time to suicide burn is the most useful for me as it tells me when to start braking hard from my de-orbit trajectory. I usually start decelerating when it gets to 15 seconds and try to slowly work it down to about 5 seconds.

Once you get to about 500m on manual throttle you can use the vertical speed controller to manage your descent. This lets you concentrate on managing your horizontal speed for a precise landing.

If a ship is fairly tall and I'm landing it among buildings I also like to put a ring of linear RCS thrusters right at the top and use the IJKL keys to operate them. The reason I only use the top mounted RCS is that if your ship is drifting forward and you activate the forward RCS thruster it will kill some of your velocity. It will also cause the ship to pitch back a bit which also slows you. When you stop thrusting with the RCS MJ or the SAS will return the ship to vertical.

If you've got enough fuel to hover for a while this lets you place things exactly where you want them letting you make your base a nice tight cluster of buildings.

Edited July 8, 2014 by Kerba Fett

[Taki117]

[Aphobius]

What's that? Hovering at 10km and going straight down after that? Beginners shouldn't make tutorials.

[Taki117]

What's that? Hovering at 10km and going straight down after that? Beginners shouldn't make tutorials.

It's Scott Manleys tutorial on precision landing. The reason he goes straight down from 10km is because the surface isn't at sea level, it's at about 4km, meaning he's only about 6km up.

[NecroBones]

Here's one of Scott Manley's tutorials on precision landing (in the context of a rescue mission):

EDIT: Sorry, hadn't noticed that someone linked it already. But this is posted inline, so enjoy.

[Kerba Fett]

Even if you want to drop straight down onto your target he sure made the process a lot more complex that it needs to be. If he knows he wants to be stopped over his target and he knows that the burn to do it will take 71 second, then why not just start burning at T-71 seconds? By the time he gets to the node his speed should be 0 and he can start descending. Seems like he's adding a lot of math that may not be needed.

Also, I keep forgetting to mention one of the most important things. Quicksave before your de-orbit burn.

[EdFred]

Someone declaring Scott Manley a beginner. Best laugh I've had today.

[Master Tao]

Even if you want to drop straight down onto your target he sure made the process a lot more complex that it needs to be. If he knows he wants to be stopped over his target and he knows that the burn to do it will take 71 second, then why not just start burning at T-71 seconds? By the time he gets to the node his speed should be 0 and he can start descending. Seems like he's adding a lot of math that may not be needed.

Also, I keep forgetting to mention one of the most important things. Quicksave before your de-orbit burn.

Because the burn slows you down, so if you burn starting 71 seconds before the maneuver node, you'll stop without ever reaching that position. To stop over a precise position, you have to calculate how far you'll travel during the burn, then start that distance away, rather than that much time before.

[John FX]

I have an Apollo craft I use and through a test run where I quicksaved, did a test landing and saw the stopping distance of my lander (It`s good to have some performance figures for these things) so I knew when to start the deceleration burn (about 63km) I used a low Pe orbit (6.3km) and could pinpoint a landing point within a rough circle of 5-6km centered at 60km (TWR 0.3 kerbin/2 mun)

[Superfluous J]

Because the burn slows you down, so if you burn starting 71 seconds before the maneuver node, you'll stop without ever reaching that position. To stop over a precise position, you have to calculate how far you'll travel during the burn, then start that distance away, rather than that much time before.

dividing 534 (I think that was it) by 2 and then multiplying that by 71 is the same as taking 534 and multiplying that by 71/2. So just start 35 seconds before the node.

Other than getting a calculator out, his way does look a bit cleaner than mine. I think I'm going to try it a few times and see how it works. I really don't like how long he dropped vertically though.

If it's not too fuel inefficient though I'm all for it.

[-root]

A little more on planetary rotation. When you get down lower to the planet, you may over burn when trying to kill your horizontal velocity. Don't worry about correcting it if its along the orbital plane, the planet's rotation will actually help null that out for you.

That and "slow and steady" is a good plan. If I've got the altitude, I normally pause for an extra second or two to orientate things. Too many times I've overcooked a burn and missed my landing because I was hurrying when I didn't have to.

[Srpadget]

Thanks, all!

It sounds like I've had the right approach all along, I just need either a) more practice, give up "pure stock" and set up a mod that gives me better/more-accessible data, or c) both.

Last night I managed a reasonably-fuel-efficient descent/landing and wound up aligned with but 8km short of the target, in a less-than-ideal mostly-flat-but-cratered area (craters really screw with techniques that rely on velocity as a function of height above ground...). Sounds like I'll get there with patience and practice.

I do rather like the idea of tweaking the engine thrust after deorbit but before landing. I hadn't thought of that. I deliberately built this lander with an overpowered engine to see if I could reduce my total fuel requirements with a) better Isp (ooooh, that seductive 390 secs of the LV-909!) and lower gravity losses. It seems to have worked for that, but at the cost of reduced fine control in terminal descent as noted in this thread.

Thanks again!

[Kryxal]

If you want to manage finer control, you could also use multiple small engines and set an action group to toggle out half or two-thirds of them. So long as the active engines still have symmetry, you should be good.

[Claw]

... I think I'm going to try it a few times and see how it works. I really don't like how long he dropped vertically though. ...

I often recommend people start out with the PE around 5 to 6km. It gives a bit more time to get oriented and get practice burning. As you get more experience, you can lower the PE down. I think Scott's technique is still valid with a lower PE, it's just that things happen a little faster. It might not be the most efficient, but if a newbie's alternative is crashing, then it's infinitely more efficient.

... give up "pure stock" and set up a mod that gives me better/more-accessible data,

Hopefully you never feel forced into this. Do it if it makes you more comfortable and have more fun. But don't feel like you MUST do it...

[John FX]

Thanks, all!

It sounds like I've had the right approach all along, I just need either a) more practice, give up "pure stock" and set up a mod that gives me better/more-accessible data, or c) both.

Last night I managed a reasonably-fuel-efficient descent/landing and wound up aligned with but 8km short of the target, in a less-than-ideal mostly-flat-but-cratered area (craters really screw with techniques that rely on velocity as a function of height above ground...). Sounds like I'll get there with patience and practice.

I do rather like the idea of tweaking the engine thrust after deorbit but before landing. I hadn't thought of that. I deliberately built this lander with an overpowered engine to see if I could reduce my total fuel requirements with a) better Isp (ooooh, that seductive 390 secs of the LV-909!) and lower gravity losses. It seems to have worked for that, but at the cost of reduced fine control in terminal descent as noted in this thread.

Thanks again!

Sounds like you have your tools, now you just need practice. A `surface data` readout of some form is handy, although some people just do it by eye (not me)

I`ve started landing on Mun IVA mostly using instruments and some external cameras. It`s very scary and almost impossible to tell the slope of the ground your are heading for. You have to land almost purely on the instruments and can only really tell if there is a very very obvious thing you should avoid.

Much fun.

I`d recommend trying to get an orbit, or Pe of about 6.3km and keeping that height for your deceleration burn. It`s one of the most fuel efficient descents. adjust throttle to control slowdown initially and adjust your angle to manitain height then once you are tipped more than 45 degrees, adjust throttle to maintain height and adjust your angle of attack to maintain a suitable descent speed (20-30m/s) slow your descent as you approach the ground and your horizontal and vertical speed will be very low by the time you reach the ground. It has the control of a powered descent but the efficiency of a suicide burn (pretty much)

throttle control is a much needed skill for landings.

win-win