Land exactly at a desired area on a atmospheric planet (Like Kerbin)

[Vaporized Steel]

Hello there.

I have been playing KSP for a very long time already. I never showed my face around here as of yet. But I do now because I have a problem that I wish to solve.

I'm getting tired of the fact that there is no tool or way in which to accurately deorbit and land at or near KSC. And with "near" I mean within a radius of 10km. Since Mechjeb doesn't seem to be able to do that I do hope other mods / tools can.

There is some sort of a imho very inaccurate (noobysh) wiki article describing the procedures Click

Which steps don't work and are noobysh to say atleast.

However that article did help somewhat. I could get my deorbiting SSTO plane within a radius of 50-100km from the KSC. And would then be able to fly to the landing strip. Although I had to reload my quiksave a couple of times to get the exact periapsis right. IRL there is no quiksave and quikreload button and I intend to master game aspects without trial and this part of the game gives no alternatives to use the game over (reload) function.

However only a spaceplane can fly to a designated area once it's deorbited. That doesn't work for capsules and other non flying deorbiting modules with parachutes attached to them.

It is my hopes that there is some sort of mechjeb equivalent kind of autopilot and/or calculator. One where you can input total amount of drag by selecting the contained parts of the deorbiting module. A calculator where you can add such information like that and other parameters like the apoapsis and periapsis. So that it calculates based on you orbiting altitude at the apoapsis (which can be 100km but also 300km) to generate the sum where the periapsis should be.

I mean the exact place of splash down differs if you in scenario

A: retrograde burn at 200km altitude (apoapsis) to a periapsis of 35km

or

B: retrograde burn at 100km altitude (apoapsis) to a periapsis of 35km

In scenario A you land at a different spot then scenario B

Because in scenario A you come in steeper/faster and you probably land shorter from a designated target compared to scenario B

Other things like amount of drag also come in to play. Or whether you orbit kerbin 180 degrees on the navball (against the planets rotation) or with its 90degrees on the navball or if you deorbit from a polar orbit.

The only way I do now somewhat semi accurately land near ksc is by quiksaving hit for a altitude at the periapsis and see what happens and then reload and hit a few hundred meters lower or higher on the periapsis. Repeating that step until it's somewhat close to right. And from the retrograde deorbit burn a change of a few hundred meters to 1 km on the periapsis actually shifts your landing zone miles and miles further or shorter.

THIS^ issue is a problem. And I used the planet Kerbin as a example this time. I won't even begin about Duna. I

I honestly admit that although I wish to land nonflyable deorbiting modules to land at a desired area the real use of landing non planes at a desired area is on other atmospheric planets like duna or bodies like Laythe where you want to land near the base.

I have a base on the equator of duna. With the low dunar atmosphere it is even harder to calculate the landing zone. And for the sake of realism. Duna has no infrastructure. No cars or trains to transport kerbals landing miles ofcourse from the base camp. Preferably it should land near the base with the least amount of fuel.

I actually had to resort using unlimited fuel to navigate my dunar lander to the base as every attempt at deorbiting failed to hit the area of the base camp.

got any tips?

[LethalDose]

For precision landings on bodies with an atmosphere, the advice I've seen given is to come to a dead stop in orbit above your target, and drop straight down. You can use your engines to make correction on the decent, and don't forget to account for the rotation of the body as you descend.

To make a precision landing efficiently... I got nothing. Practice?

[rkman]

Since Mechjeb doesn't seem to be able to do that I do hope other mods / tools can.

Mechjeb does have Landing Guidance than can indicate where the craft will land. I would not trust it on autopilot but it's still a great help. It usually helps me land very close to KSC.

[MarvinKitFox]

Since Mechjeb doesn't seem to be able to do that I do hope other mods / tools can

.......

got any tips?

Use MechJeb.

Contrary to some evil rumours, it does work. You can use the landing prediction tool to get a landing within 10m on an airless world, and within about 150-250m on Kerbin.

It is not good enough to land me on the VAB roof, but I can hit the circle around the launchpad 7/8 of the time.

No, don't let MJ touch the controls. Its autopilot is a maroon, plus it steals all your fun. But as an interactive result-prediction-tool, it is very very good.

The only planet where landing prediction is too far off is EVE, where it consistently overestimates my travel distance by some 2-3km.. But thats easy enough to compensate, right?

Edited April 13, 2014 by MarvinKitFox

[Claw]

If I recall correctly, someone created a chart with optimum PE heights to hit your desired target on reentry based on your AP. (i.e. if you're doing LKO, Mun, Minmus type returns). I don't know which thread it's in, but you might be able to find it digging around a little.

MJ is the only addon I use. I find it less than helpful for airplanes, but seems to be okay for capsule craft. It does a much better job for craft that can retain a rocket during reentry so it can make corrections. Although I will also say that I don't use it very often. I typically set my PE to what I think works based on experience and accept what I get. But that clearly doesn't help you consistently land within 10km of a desired point.

[Geschosskopf]

Use MechJeb.

Contrary to some evil rumours, it does work.

......

The only planet where landing prediction is too far off is EVE, where it consistently overestimates my travel distance by some 2-3km.. But thats easy enough to compensate, right?

I agree, MJ does work extremely well for precision landings on almost all planets. There are a few caveats to using it, however. This applies to using it as an autopilot, not as a job aid.

1. When you select a target (either from the map or entering coordinates), that point needs to be at least 1/2 an orbit ahead of your ship. 1/3 is the minimum. Anything less and MJ panics, burns wildly, and doesn't come close to where you want to end up.

2. At places with Mun's gravity or more, MJ works best when your ship starts from an orbit between 100-200km. It has difficulty starting from lower orbits and wastes way too much fuel starting from higher orbits.

3. If you're landing point is significantly off the equator, you need to put your ship into an orbit of the appropriate inclination prior to initiating the auto landing. Do this very far from the planet to save on dV. If you're in a low equatorial orbit and tell MJ to land way off the equator, it will do a low-altitude plane change to line up with the target and thus waste tons of fuel.

4. I don't know if this still happens in the new MJ v2.2 but it used to be that it would get very **** about being right on target all the way down. If your target was off the equator a bit, this would often cause MJ to burn at very low thrust most of the way down, again wasting fuel. It was thus often better abort the autolanding after the main deorbit burn and let the thing coast most of the way before restarting the autolanding.

5. I haven't checked this in MJ v2.2 yet but it used to be that MJ just couldn't land on Duna to save its soul if your ship had parachutes. It just couldn't make up its mind how to use parachutes on Duna and would end up making a total hash out of it. So you if you plan on using MJ to land on Duna, it used to be almost required to not use parachutes and start from 100-200km. If you want to use parachutes to save fuel on the descent, you could well have to land it all yourself.

[Vaporized Steel]

As I actually thought that mechjeb didn't have a autoland function that can navigate through atmosphere.

Well, I guess I was wrong.

I couldn't get the hang of it.

I clearly did not yet know how it worked and assumed mechjeb couldn't do it.

google searching for "mechjeb autoland" and some YouTube videos hopefully does the trick. I'm gonna test it now.

[Specialist290]

Let us know how that works out, Vaporized Steel.

In the meantime, you may also find this chart handy if you want to try your hand at it manually, or if you want something to check MechJeb's results against.