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How to estimate the landing zone?


Cairol
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How do you estimate or calculate by rule of thumb where your lander will end up on the ground of a A) pressureless B) pressurized body?

(Assuming you do not perform a suicide burn - which for me is really suicide...)

I often have the problem to miss my desired landing spot because I can't eyball what influence my braking bursts have on my glide path.

Most of the time, I come down way in front of my desired landing zone. Often ending up in some crater-rich area instead of a flat spot when landing on Mun or Minmus for example.

EDIT: Can a mod please move this to "Gameplay Questions" ? Thanks.

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For airless bodies I generally aim to overshoot, then refine the trajectory by burning somewhere between the horizon and retrograde. I usually try to kill all lateral movement relative to the surface by ~1km above the landing target. Adjust as needed during decent.

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For most of the airless bodies, you can get pretty close just using map mode maneuver nodes. However, for a few of them (Gilly and Pol in particular) there is something wrong with the map mode which makes this not work very well. (I think the map mode model of the moons is rotated or something.)

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For most of the airless bodies, you can get pretty close just using map mode maneuver nodes. However, for a few of them (Gilly and Pol in particular) there is something wrong with the map mode which makes this not work very well. (I think the map mode model of the moons is rotated or something.)

Map mode does not represent planet rotation. I see massive divergence of body fixed trajectory even on Mun and Minmus.

If you are doing target ladings, overdo the thrust but plan to land on â…†throttle. Having buffer allows corrections.

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Map mode does not represent planet rotation. I see massive divergence of body fixed trajectory even on Mun and Minmus.

If you are doing target ladings, overdo the thrust but plan to land on â…†throttle. Having buffer allows corrections.

Yes, but that's not what I'm talking about. On most bodies, you can use the maneuver nodes to get yourself into the area you want to land, and the closer you are (so the less time the planet has to rotate), the more accurate you can get. With some practice you can land very close to where you want to land just using map mode and maneuver nodes until switching to ship mode for the final landing burn.

But with Gilly and Pol (and maybe others?) what you see in map mode is not what you get in ship mode. You can crash into the surface even when map mode shows you way above the surface. You can also be shown on the surface in map mode but actually be a couple of km above the surface.

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Might be right, might be wrong, I don't know but for atmo... I try to put my PE over my target (initially anyway) usually about 35-40k altitude (for kerbin)

For non-powered landings this usually has me around 2-3k in the air above my landing zone and on a almost dead drop trajectory so when I hit chutes I am never too far off.

For powered landings (spaceplanes specifically) it allows me to make breaking maneuvers and final adjustments before landing.

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On airless bodies I use the reverse gravity turn technique. This allows me to land precisely where I want to be.

On bodies with atmospheres, it's from experience. If you set your apoapsis at a certain altitude over a location, you'll end up landing right about there. It varies with the properties of the lander, but you get the feel for that over time.

Best,

-Slashy

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How do you estimate or calculate by rule of thumb where your lander will end up on the ground of a A) pressureless B) pressurized body?

(Assuming you do not perform a suicide burn - which for me is really suicide...)

I often have the problem to miss my desired landing spot because I can't eyball what influence my braking bursts have on my glide path.

Most of the time, I come down way in front of my desired landing zone. Often ending up in some crater-rich area instead of a flat spot when landing on Mun or Minmus for example.

EDIT: Can a mod please move this to "Gameplay Questions" ? Thanks.

Lets say you were going to land on the Mun and you are traveling at 20k making your radius 220km. The circumference of your orbit is then 1382.6km. Each degree is then 3.83km

If you are traveling 540 m/s along the equator, and your craft can accelerate at 1 g, then it takes 55 seconds of horizontal velocity to stop all horizontal or rotational vector.

distance travel = 1/2 a * t^2 14.877, (correct formula is =V0T + 1/2AT2, but magnitude is exactly the same as traveling from a dead stop to 540 m/s) therefore you will travel about 3.9degrees when decelerating full along the horizontal vector. If you know the targets longditude you can begin decelerating about 3.9 degrees before you reach it. The lead degrees increases at higher latitudes along the 090, because the span per degree gets smaller. The degrees decrease accurately to about 045 or 135 (prograde) because the distance traveled per degree increases. So for instance if you are crossing the equator at 45 degrees you would begin the retro 2.7 degrees before the targets longditude, and 2.7 degrees before its latitude.

If you are traveling at more than 045 or less than 135 you need to set targets latitude coordinate as your primary trigger.

Also since you are burning horizontal the craft will fall according to 1/2 grav T^2. Since grav is 1.63 you will travel 2.5 km downward (a little less because of curvature) and be traveling 89 m/s meaning at 1 g it will take you 11 seconds or 500 meters meaning that the burn will need to end at least 3000m below a flat horizontal start. Thus you should not attempt a horizontal burn unless you have more than 1g accel and are at least 3000m above the target points true altitude. Of course you probably won't know this unless you have mech jeb or some other program (or you have a flag planted with its elevation in its name). This assumes that at the end of the horizontal burn you immediately point up and burn, if not you can add 100m per second travel to this in the time it takes to reorient the craft.

It is actually most efficient to calculate this along the retro surface velocity vector starting from a minimal orbit (say 250 to 500meter above the minimum) and burn retro surface velocity down to around 200 meters, then a final 2 second burn a few meters up. Its also very risky, but represents the least amount of time fighting gravity. The orbit above starts at 20,000 and would be suitable for a landing between 15,000 and 16,500 meter altitude(true), there are none of these on the mun. Landing in a crater generally will require a starting retro altitude of much lower 5000-8000 meters. The problem is that there are terrain around the craters at this altitude so you would need to create an elliptical orbit with a periapsis close to the retroburn point that will have slightly more velocity. Alternatively you can do a small retro burn at the maximum terrain elevation that then bring your craft down a few thousand feet before you start your retro. Programs like MechJeb give some of the transition points (different from the above but relative) is you use the landing guidance ap. You can also plant flags and put the biomes, elevations, even the longditude in the flag name, and show the flags in mapview. I used to do this, and also I would find the flattest near-by spot to plant the flag, that why when I return with my expensive geared out lander I am going to have a safe landing.

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I've never been able to really do it. It's always looked like it'll be in the kind of area I want, but then I either forget to account for planet rotation or just do something to mess it up :rolleyes:

Kerbals is teh hards.

EDIT: mostly I get put off because the solutions seem to involve math and some form of calculating/figuring it out. I don't really want to be doing that.....

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You can also plant flags and put the biomes, elevations, even the longditude in the flag name, and show the flags in mapview. I used to do this, and also I would find the flattest near-by spot to plant the flag, that why when I return with my expensive geared out lander I am going to have a safe landing.

I used to do this a lot more, until I realized I almost never return to that same biome. Why would I? It has no more science left in it.

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I used to do this a lot more, until I realized I almost never return to that same biome. Why would I? It has no more science left in it.

Early game career/science mode you'll not have unlocked all the science experiments. Especially if you have mods that add more experiments like DMagic.

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I used to do this a lot more, until I realized I almost never return to that same biome. Why would I? It has no more science left in it.

I have a refinery on Mün and perciese landings is a must for when I want to refuel for tourist contracts. And since I like to refuel in orbit as I play stock. More ove a must then.

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I have a refinery on Mün and perciese landings is a must for when I want to refuel for tourist contracts. And since I like to refuel in orbit as I play stock. More ove a must then.

A Mun refinery is not nearly as delta-v efficient as a Minmus refinery. And if the Minmus refinery is on one of the "flats" there is no need to look around for an easy landing spot, because the whole area is an easy landing spot. But to each his own.

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On airless bodies I use the reverse gravity turn technique. This allows me to land precisely where I want to be.

On bodies with atmospheres, it's from experience. If you set your apoapsis at a certain altitude over a location, you'll end up landing right about there. It varies with the properties of the lander, but you get the feel for that over time.

Best,

-Slashy

How would one do the reverse gravity technique? I know what it is in theory but have no idea how I would pull it off.

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How would one do the reverse gravity technique? I know what it is in theory but have no idea how I would pull it off.

Start by pointing retrograde. Burn. Keep pointing retrograde. Time the burn such that the delta-V used is exactly equal to your orbital velocity + vertical velocity from the fall (IE you land at exactly 0 m/s when hitting the surface). It's really just reversing the steps of a normal launch, with the rocket facing the other way.

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Unless you use mods (cheaters!) you mostly have to eyeball the landing burn in the map view. Burning retrograde will cause your landing point to go short of where it is; burning radial-out will cause it to go long. The direction you have to point your ship to keep the landing spot stationary is somewhere in between the two, but the sweet spot varies depending on your speed and descent angle.

The most reliable way to hit--errrrrr.....REACH a desired landing spot is to fly above it, burn horizontal along the retrograde heading to bring your ship to a lateral halt, then drop straight down. Uses more fuel, but is much easier to aim.

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