Precision landing guides or videos?

[pRoSpA]

Hi everyone,

This is my first post, and first week of playing KSP. I have to say, i'm hooked!

In my career mode i currently have ten flights in progress. Six of those are stranded Kerbals lol. It's started off with two being stranded, one in space, one on Mun. Now i have four Mun and two in space! My biggest problem on Mun isn't landing. It's actually landing where i want to land without using too much fuel. Because by the time i've made corrections and got close enough to EVA/fly a kerbal to the rescue ship it's past the point of no return.

I've been looking on YouTube for help on this, but not found one that specifically tells you how to judge your landings consistently. Can anyone point me in the right direction?

[breakthrough]

Lower your apoapsis as far as you can and the speed at periapsis will be lower thus requiring less burn time to come to a stop. Also, consider putting a high TWR stage under the rescue lander and ditch it after killing your horizontal speed.

[Captain Sierra]

What I do is kill all lateral velocity at orbital height (25km) and then do a series of short burns to kill off velocity (I usually overbuild my transfer stages and can use them for this).

From a 25km orbit, you want to place your orbit line about 1/2 to 3/4 cm ahead of your target at the highest zoom. F5/F9 are your friends. It usually get's me down to the surface within no more than a km of the target.

[Aphobius]

I'll post a video tomorrow with a precision landing.

[pRoSpA]

Hi,

Thanks for the replies!

Lower your apoapsis as far as you can and the speed at periapsis will be lower thus requiring less burn time to come to a stop. Also, consider putting a high TWR stage under the rescue lander and ditch it after killing your horizontal speed.

Yeah that makes sense. By "TWR Stage" do you mean a small/medium tank with an angine just to kill off the speed before ditchingit and attempting to land?

What I do is kill all lateral velocity at orbital height (25km) and then do a series of short burns to kill off velocity (I usually overbuild my transfer stages and can use them for this).

From a 25km orbit, you want to place your orbit line about 1/2 to 3/4 cm ahead of your target at the highest zoom. F5/F9 are your friends. It usually get's me down to the surface within no more than a km of the target.

That is actually how i try to do it, it's just i suppose i must be spending too much fuel messing around to get it right. I did make a wider lander and had better luck with it because it didn't tip over so easily if i had any horizontal speed. And yeah, when i realised about the quicksave button it was a great revelation lol. I'll do longer overshoots and time it better. Trial and error i suppose. Plus today i've been doing quite well, i think i'm getting the hang of it more. Not missing by too much now.

I'll post a video tomorrow with a precision landing.

Awesome, it would be good to learn as a procedure. P;us there's lot's of Land on Mun vids but (maybe i missed them) not any "how to land at a specific location" vids.

Thanks again guys, you've helped already!

[Mystique]

If there is no atmosphere, get you orbit circular and lowest possible first (so that you won't hit any high rocks). Burn retrograde so that end of your trajectory points to your target; when to do it depends on your TWR, the less it is - the sooner you need to start or you may not have enough time to decelerate. Next step - kill horizontal velocity while keeping end of your trajectory at the same point. To do this, point "higher" than retrograde (between retrograde and directly "up") and start burning. This way you will lose your horizontal velocity less efficiently than 100% retrograde burn, but you'll also fall down slower. Idea is to find that sweet spot that will keep vertical velocity close to 0 and reduce horizontal velocity. If end of your trajectory points at the same spot and your horizontal speed is decreasing - you're doing it right. It's actually like hovering at same altitude while decreasing horizontal speed. Just don't get your vertical speed positive unless you need to correct trajectory - it'll be a waste of delta-v. As you'll get closer to landing zone, retrograde marker will move up (better to switch to surface mode). I prefer killing horizontal velocity a bit earlier rather than a bit later, this way it'll be easy to control descent. If you miss even a few hundred meters from your target you can alway make small burn to correct trajectory. To land softly, I usually keep vertical speed below 20 m/s at 200 m radar altitude, then 10 m/s at 100 m and decrease it to 1-3 m/s before touchdown, depending on surface flatness and lander stability (some builds allow rough landings while other may flip over).

[Kasuha]

...

Horizontal landing is efficient and useful but I did not find it very useful for landing at a precise spot. In most cases you'll either overshoot a lot or you'll need to spend considerable time hovering to get to your target.

My way is more of setting a suborbital trajectory going right above the target (slightly overshooting it) and then braking to pull the terrain intersection near my target as I get closer. Selecting the target in map to see it on navball also helps.

[pRoSpA]

Text moved.

Edited January 23, 2014 by pRoSpA

[pRoSpA]

Text Moved.

Edited January 23, 2014 by pRoSpA

[pRoSpA]

Hmm, strange, i don't get intersection markers when i target a landed craft. I wonder if i don't have it switched on somewhere...

Mystique - Yeah, each time i get a little better at judging how soon to burn or stop burning, and getting the retro into the up position. I'm not sure how you'd judge your TWR against your velocity without burning, stopping, burning stopping, you know, kind of stuttering. I suppose if i'm going the perfect direction to the target and watching the distance from it tick down it'll get easier each time to hit it spot on after a few tries.

Thanks for replies guys

Ahhhh, i actually just worked it out i think. I haven't yet done it, i'm about to on the game but i rough orbit to circular 20k alt, created a movement to be completely stopped directly above the site, so it's like a 90' angle. But i wont actually do the movement as planned, i'll the burn meter to judge how much horizontal speed i still need to kill and ill also start to kill the vertical speed together. I'll edit this when it's done.

Wow. you guys are AWESOME It just kind of clicked in my mind, after reading over and over what you all said and right now my game is paused but im just about to land right next to Jeb to rescue him. This is the first time i've had the target and the retro indicator both on the Up dot on my navball! Woop!

Edited January 23, 2014 by pRoSpA
Condensing Replies

[Aphobius]

Here's the promised video.

My ship is a little strange (weak engines), I've made it for a challenge.

[breakthrough]

Aphobius, is there supposed to be commentary in the video? I see the mouse gesturing, but I don't hear anything besides a pair of ant engines firing continuously for 15 minutes.

[Aphobius]

Aphobius, is there supposed to be commentary in the video? I see the mouse gesturing, but I don't hear anything besides a pair of ant engines firing continuously for 15 minutes.

And here's all the commentary you need.

Joking. I just wanted to show you, probably, the hardest precision landing ever made. There are enough tutorials with commentary on youtube.

[Collin Dow]

A good way to estimate twr is to open the map, and then hit the "I" for info, and check your mass. Then, recall what the thrust in kN is on your vehicle. Divide the thrust by the mass. In null g, that is twr. You have to multiply mass by gravity. However, for killing horizontal speed over the mun, that isn't important. Fun fact, in null g that formula will also approximate your accelerative ability.

Thrust (kN)/mass (t)*grav(m/s2)

[Aphobius]

When you divide thrust by mass you get your acceleration in m/s^2. If you divide that acceleration with the gravitational acceleration of a planet, you get your acceleration in Gs.

Example:

thrust = 1500kn

mass = 100t

gravitational acceleration = 10m/s^2

acceleration = 1500kN / 100t = 15m/s^2

acceleration in Gs = 15m/s^2 / 10m/s^2 = 1.5Gs

The actual formula use N and kgs, but 1kN = 1000N and 1t = 1000kg, so you can use it with the units you get in kerbal, without changing them to N and kgs.