Accurate Landings in an Atmosphere

[Polstar]

I've managed to land my craft quite accurately on the Mun and Duna but I am struggling with this on Eve.

The problem is when I hit the atmosphere the drag naturally alters where I was heading as I suddenly slow down. Is there a trick to predicting this and getting an accurate landing spot? I have tried numerous times and the closest I've got is 70km of the target. On Duna I can get to within 1km due to the thin atmosphere.

I am only using the basic game with no mods, is this something that can be done without mods?

Thanks for any help

Edited November 13, 2013 by Polstar
Answered

[RocketPilot573]

I've been here too, so I got Mechjeb. It has a landing guidance system, I don't use the autopilot, but it still gives you readouts of where you will land and even your orbit after an aerobrake.

It's seriously the only reason that I use Mechjeb...

[700NitroXpress]

The best way I found to land accurately on Eve, is to have a lander that has a stage for the deorbit burn. You want an angle of about 5 - 10 degrees off of your landing zone so you're basically going to come in straight down on the LZ. I've landed things within 4km of each other doing this, mainly that far on purpose due to the terrain not being flat enough. Alternatively you can overshoot the LZ a little more, then when you're over the LZ and are going less than 400m/s, decelerate with the landing engines so you come in straight down. Make sure your lander has enough power to preform an atmospheric maneuver tho, otherwise I'd go with my first suggestion.

I landed on the little island in the middle of the huge crater along the equator of Eve surrounded by ocean using my method.

Here is my decent trajectory, first try.

Landed within 2.2km of my first Eve landing.

Edited November 9, 2013 by 700NitroXpress

[Kasuha]

When I need some accuracy with landing in atmosphere, I quicksave and retry till I succeed.

[Specialist290]

It's possible to do with stock, though tedious. You have to get a "feel" for the atmosphere of the planet you're landing on and adjust accordingly, so your first several attempts will probably be off target until you refine your technique a little. I still don't have it quite down myself for a lot of planets other than Kerbin, so don't feel bad since it does take tons of practice to get good at.

That said, you might find these charts by alterbaron to be of some use, as well as this tutorial.

[Vector]

This is an interesting problem, I had sorta written off before, but now that I think about it, there may be some interesting possibilities.

What if one were to enter a highly eccentric geosynchronous (not geostationary) orbit, then on one pass you could scope for landing places just prior to the periapsis and place a maneuver node at apoapsis to re-enter as steep as you can get away with.

I will have to experiment with this.

[Vector]

The geosynchronous orbit method appears to work decently well in getting in the general area, but for high accuracy it's not enough. I really hate to bring a ton of extra fuel just to de-orbit accurately. I think a really good solution is the geosynchronous orbit together with a glider for the last few dozen km in the atmosphere.

Below is a screen shot showing the general idea for the geosynchronous orbit method. Periapsis is about 100km and apoapsis is 20,560 km.

[sibrit]

Without mods, it's basically timing and learning from trial and error.

Once my ship has entered the Eve soi, I tend to burn until I get an equatorial orbit that has a periapsis at around 95km so that I skim through the upper atmosphere. Usually this is a very elongated orbit so it can make several passes before aerobraking causes a decent.

Then with an eye on where I want to land, I burn retrograde at apoapsis to get my periapsis altitude to between 30km & 60km. The lower the altitude, the stronger the aerobraking effect. You also need to take the planetary rotation into account in that if you set up the maneuver so that your touchdown is on your required point, by the time you get there Eve has rotated east by several degrees so that you end up landing far west of where you wanted to be.

This is why having a decent engine is useful, as you can either burn retrograde if it looks like you're going to overshoot, or a vertical burn to "float" over to your landing spot.

[Vector]

Using the orbital-period method (with wings to glide a little bit), I arrived on Laythe and landed on LAND for the first time!

Synchronous orbit is impossible for Laythe but it is possible to have an orbital period that is an even ratio of the rotational period, in this case 1/4. For this I used a periapsis of 56 km and an apoapsis of 3060 km.

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[Polstar]

Thanks for all the suggestions and advice