Landing on the mun

[Philae & Rosetta]

Hi all,

 

I tried for the first time (well, the second time, honestly the first time I completely crashed myself) to land on the Mun. 

And there is something in the game I can't understand. When I approach Mun surface, I slow my ship by retrograding, but when my speed is under 25m/s (approximatively),, the direction change and the ship goes up, instead of still going down...Then I need to stop retrograding (which is prograde because of the direction changed) and try again.

How can you go from 25m/s to -25m/s without transition?

Has anyone experienced it already? Is it a game bug?

Thanks,

P&R

[Aegolius13]

Is your display set to "surface" or "orbit"?  You want it on surface for landing.   Not positive that's the problem, but sounds like it could be involved. 

[Human Person]

Hmm. Are you in Orbit Mode or In Surface mode? The game switches to surface mode automatically at some point so that might explain the issue. Make sure you are in surface mode!

 

If you have problems landing on the mun in general, I can highly recommend the tutorial.

 

[Philae & Rosetta]

Ahahah you had the same idea both of you, at the same time.

Well yes I am on surface mode, completely perpendicular to the surface (the navball position is in the center of the blue part).

Usually when it happens I am between 5 and 10km high.

Well I could use the tutorial, that's true. But it's too easy after. I want to learn by myself. We are not in real life we can try, fail and retry (fortunately, otherwise I couldn't go very far )

 

 

Edited November 22, 2017 by Philae & Rosetta

[Kerbal7]

Make sure you're in surface mode on the velocity display. Also make sure your SAS is set to retrograde. Sometimes SAS resets on me, maybe when it switches from orbit to surface mode

[Plusck]

A screenshot just at the time you're talking about would help a lot to work out what's happening.

The normal, relatively efficient and easy way to land on the Mun is to burn retrograde in low orbit until the path hits the surface about a quarter of an orbit later. To make sure the next bit gives the right time, burn at full thrust only.
You then place a node on the surface and drag it retrograde until the orbital path starts going backwards. That should give you slightly less than 600 m/s to burn, and will tell you at what time you will hit the surface and how much time you need to come to a stop...
As you approach the surface, make sure the navball is set to "surface".
When you are about 2/3 of the time away from the node, burn retrograde at full thrust (ignore the maneuvre target). You should end up going very slowly a few hundred metres above the surface. Cut the engines, make sure "retrograde hold" is still on, then gently power up the engines so that you fall increasingly slowly as you approach the surface. Cut the engines the instant you touch the ground.

The main problem is that if you burn too hard and start going back up, the "retrograde hold" will make your ship flip around and face the wrong way.

The game protects against this by deactivating retrograde hold when you reach less than 1 m/s. However, if you never actually come to a stop, you will end up spinning around as you describe.

[bewing]

4 hours ago, Philae & Rosetta said:

Usually when it happens I am between 5 and 10km high.

The ground can often start as high as 5.5km. So 5km may be way too early or way too late.

Your technique needs to depend on how accurate you want to be, or whether you want to try to save as much fuel as possible. Your initial description sounds to me like somebody who is trying to be accurate. So I'll go over that quick.

As you burn, and as you go around the Mun, the direction that matches "retrograde" constantly changes. If you cancel half of your orbital velocity, then you will start to fall -- which adds an increasing amount of vertical velocity every second, and moves your retrograde marker around until it points "radial out" (ie. UP).

So the deal goes like this: you are happily flying along in orbit over the Mun, looking down from above, and suddenly you spot an area in front of you on the horizon that looks really flat and has almost no craters. You say "Aha! I want to land there." (You need to know about how long it takes your rocket to kill 550 m/s of orbital velocity -- but let's say you have a powerful engine.) So initially you want to burn retrograde -- but what you really want to do is kill your orbital velocity only.

Because the next thing you want to do is go down. So you don't want to kill your vertical velocity. So you wait until you are almost at the spot you want to land, the you set SAS retrograde, and then you set it back to stability mode. Because you do not want your nose tracking retrograde as you gain downward velocity. Now you burn. You watch the retrograde marker move. As you burn it will go from being straight in front of you, to straight over your head. That's when you stop -- because you've come close to a dead stop over the terrain. (You can also do this by going into map mode as you burn and watching the blue lines come together -- which gains you even more accuracy.) So now you know where you will land -- the spot straight below you. And then you just need to go back to Retrograde mode, and manage the speed of your fall until you gently touch the surface. Sometimes during your fall it's good to go into the engine's context menu and reduce its thrust. That helps you at the very end to accurately get your speed to 1 m/s just before you touch down. When you are most of the way down, it's often best to set your SAS to Radial Out. That helps to prevent accidents if you burn a little too much and start going up instead of down.

 

 

[Philae & Rosetta]

Thanks for all these answers.

 

But that doesn't very help me as i already do what you say.

I think the most appropriate is to show you screenshots Maybe you'll have a better understanding:

 

The first picture is:

 

 Two seconds later (you can see in the upper left corner), I took this:

. The ship is still going down (18 meters between first and second pictures) but for less than a second more.

Three second later, another screenshot:

 and you can  see that the ship is going up (6 meters between second and third picture).

And between second (15.2m/s down) and third picture (17.1m/s up), the velocity didn't go to 0 before the ship went up....The minimum was something like 14m/s, and after the ship went up...

 

Do you have any idea?

 

Thanks,

P&R

 

 

 

 

 

Edited November 22, 2017 by Philae & Rosetta

[Rocket In My Pocket]

Is it just happening too fast for you to see?

What kind of engine do you have on that? Seems like a pretty big lander.

Also, you may have better luck putting "hold retrograde" on and focusing on running the throttle to monitor your speed.

[Philae & Rosetta]

6 minutes ago, Rocket In My Pocket said:

Is it just happening too fast for you to see?

What kind of engine do you have on that? Seems like a pretty big lander.

Also, you may have better luck putting "hold retrograde" on and focusing on running the throttle to monitor your speed.

 

What do you want me to see?

I have 9 LV-909 Terrier Liquid Fuel Engine

Hold retrograde? I'm not sure it would be a good idea as the retrograde is moving and the ship will come back parralel to the surface...

Edited November 22, 2017 by Philae & Rosetta

[bewing]

No, the problem is that you have 15 m/s of sideways velocity, and you are using Stability Hold. So you are never cancelling your sideways velocity.

This means that your velocity on the navball never goes to zero.

In order for your velocity to go all the way to zero, you either must use retrograde hold, or you have to do some very careful maneuvering by hand to cancel your sideways velocity.

 

[Rocket In My Pocket]

23 minutes ago, Philae & Rosetta said:

What do you want me to see?

I have 9 LV-909 Terrier Liquid Fuel Engine

Hold retrograde? I'm not sure it would be a good idea as the retrograde is moving and the ship will come back parralel to the surface...

If managed carefully, (Ie. don't get carried away and start going back up or anything.) holding retro is fairly self correcting and will typically result in a very nice landing.

The only thing to watch out for is being to low to the ground, you may want to add some manual Radial out if you started your burn too late.

Holding retrograde all the way down is pretty efficient as you'll be killing your horizontal and vertical velocity at the same time; which is like walking diagonally across a large field instead of travelling two sides.

Also, not criticizing your build; if it works, it works. However that seems like serious overkill just to land on the Mun. 1 Terrier and a smaller ship would be plenty.

Edited November 22, 2017 by Rocket In My Pocket

[Philae & Rosetta]

Thanks, I understand better now.

First I didn't have an accurate straight down line (that's why I was moving sideways a bit -but enough to move too much).

And then I used too much fuel in one shot, and it's better by small amount to allow the retrograde point to still be close to the center of the navball.

 

So I managed to land at 1.8 m/s...My 21st July 1969 is done  Only 50 years late compare to real world...

 

Well, after I killed my Kerman on the Mun by going too high with EVA propellant but that's another story to tell our grandchildrens...^^

 

Thanks both of you for the help! I appreciate!

Edited November 22, 2017 by Philae & Rosetta

[Rocket In My Pocket]

23 minutes ago, Philae & Rosetta said:

So I managed to land at 1.8 m/s...My 21st July 1969 is done  Only 50 years late compare to real world...

Thanks both of you for the help! I appreciate!

Congrats!