Why isn't MechJeb landing?

[briligg]

I just try to use MechJeb to get over the parts of the game i'm not interested in learning right now, landing being one of them. So i got my ship in an orbit around the Mun with a periapsis a bit above 26km and an apoapsis of 138, and activated autoland. And it isn't doing anything. It says it is doing a deorbit burn, but it is lying. I've tried closing the game and restarting it, i've tried aborting the autoland and reloading it. I fear the file is corrupted and i am going to have to launch all over again.

I am finding the learning curve on this game deeply aggravating. I stick with it because there is nothing else like it for getting an intuitive feel for orbital mechanics. But OH how i would love to have TWO quick save slots.

[technicalfool]

Unsure about the Mechjeb issue, but you should be able to use alt+F5 to create named quicksaves. Alt+F9 to load one.

[Taki117]

A picture of the situation would help, but barring that Make sure you have fuel and an activated engine. You might also need to circularize your orbit a bit more.

[Starman4308]

I just try to use MechJeb to get over the parts of the game i'm not interested in learning right now, landing being one of them. So i got my ship in an orbit around the Mun with a periapsis a bit above 26km and an apoapsis of 138, and activated autoland. And it isn't doing anything. It says it is doing a deorbit burn, but it is lying. I've tried closing the game and restarting it, i've tried aborting the autoland and reloading it. I fear the file is corrupted and i am going to have to launch all over again.

I am finding the learning curve on this game deeply aggravating. I stick with it because there is nothing else like it for getting an intuitive feel for orbital mechanics. But OH how i would love to have TWO quick save slots.

Can't tell you for certain what the issue with Mechjeb is, but the stupid possibilities:

#1) You haven't specified a spot for it to land.

#2) It's refusing to land because it doesn't do well with an eccentric orbit. It is best to start your landing from a very tight (~10 km) circular orbit, as that minimizes loss to gravity drag.

[Axelord FTW]

I've had MJ land with some pretty eccentric orbits before.

If you don'T have enough d/v, MJ might just refuse to land your ship, however.

Do you have auto-warp on? MJ will do the most-ish efficient deorbit burn it can if you don't specify a landing spot. If auto-warp isn't on, it'll take a while for MJ to do anything.

Can we get a pic or your orbiting ship with delta-v stats page open and in all stats mode?

[Zylark]

1: Get into a nice stable orbit. Low, high, doesn't matter.

2: Bring up the MJ Landing Autopilot window and then go to map view if not there already.

3: Select 'Pick target on map' in the MJ Landing autopilot window. You'll get a crosshair. Left click anywhere you'll like to land on the Mun.

4: Now press 'Land at target' in the MJ Landing Autopilot window.

5: Go back to vessel-view and enjoy the show

Edited October 27, 2014 by Zylark

[Tex_NL]

Before clicking any of the two 'Land' buttons make sure you've killed time warp. 2x time warp is easy to overlook.

And of course make sure you still have electricity. If your batteries are dry your craft is dead and even MJ won't be able to land it.

[briligg]

Many great tips here, thanks to all. Especially, thank god for that alt F5 option. That was not on the key bindings cheat sheet i downloaded.

I don't have the rep for my posts to go up before checked by a moderator, so i muddled until i got it and didn't check this until now. Yes, i had discarded the previous stage and not pressed the spacebar again to activate the new one.

But next time, in consideration of these tips, i'll try to create a tighter, circular obit before activating the autopilot. And eventually i'll try it myself, after watching MechJeb a few times. I really find watching it go through a near ideal execution of something is helpful in learning to do it properly yourself. I think the 1.0 version should really comes with it or something like it. Some of us need time in order to fully nerd out.

My batteries have indeed now run dry because i forgot to fold away the landing gear after takeoff and one of the legs is blocking sunlight from reaching the solar panel. Now this is the kind of detail i really find trying. Hereafter i will save named files, and this will not be a big dea, but sheez, there is a lot of stuff you have to figure out by repeatedly screwing up.

All the same... KSP is great.

[bakanando]

Try the in-game tutorials. These will help a lot to get yourself accustomed to the game's mechanics. It has tutorials for going to the Mun, landing in it, rendez-vous maneuvers and docking.

[Andrew Duff]

I have the same problem with Mechjeb. I am running 0.25 with Mechjeb 2-2.4.0.0. I have tried landing on Kerbin, Mun and Minmus using Mechjeb and it does not kill the horizontal velocity correctly. I have managed to land manually with all craft (with infinite fuel...) so I know the Delta V is ok. Seems to me that there is something with this version of Mechjeb?

[numerobis]

I find it most reliable to land by first firing retrograde to set Pe at the surface just ahead of where I want to land, then I estimate a good time to fire in the SVEL- (surface-retrograde) to kill most of the horizontal motion, and only then do I use the landing assistant to polish off the landing and get a nice soft 5m/s landing.

The landing assistant has always had trouble with anything unusual, where "usual" isn't really well defined.

[Oafman]

Every time I ask MJ to do something, and it doesn't seem to be do0ing it, it's because I have neglected to activate the engine.

[lorax284]

Make sure you have enough fuel in your ship. If you don't have enough fuel, Mechjeb will still point at the node and attempt at a burn.

[goldenpsp]

Also,

Not that I am an anti MJ type. I use it plenty to do things that have become redundant at times. But now that you know the ALT-F5 way of making saves I do highly recommend taking the time to learn to land properly. Even if after that you use MJ for 100% of your landings, it is something important to get familiar with. It is a great feeling to finally accomplish that first landing. And well, it's fun.

Use ALT F5 to make a save in orbit right before you begin.

I usually make another alt f5 once I've made my initial deorbit burn

Then i just use regular F5 to save on my way down if I feel I need to (usually just dark side landings these days).

That way if you botch the landing you have 3 places you can reload from depending on how far back you want to go.

[Geschosskopf]

MJ has several issues with landing. The main one is that its algorithm seems a bit picky about the orbit you start in. Generally it seems to prefer somewhere around 100-150km. It works for higher orbits but uses a lot of excess fuel, but it has great difficulty with lower orbits. Besides this, it doesn't like to use parachutes at all unless that's the only way to get slow enough to avoid a crash. If it can land without using the parachutes, it will, even you tell it give it permission to use the chutes. I assume this is because it is, after all, trying to hit a precise point on the ground and wants to maintain control as long as possible. But this becomes an issue for you if you designed your lander to rely on the chutes for landing to save fuel for taking off again afterwards, because MJ will use fuel instead of chutes on the descent.

Now, as to your problem with MJ saying its doing the de-orbit burn but nothing actually happens, this is because the landing engine isn't activated. The usual cause of this problem is not having the lander engine in the same stage as the decoupler below it, so you have to hit spacebar twice, once to drop the stage and again to activate the lander engine. If you only hit spacebar once, the engine won't be activated and MJ won't turn it on by itself. So either you have to hit space again or right-click on the engine and select the activate option. Then MJ will use the lander engine.

Once you've got the engine turned on MJ has another little quirk. It will never finish a deorbit burn until it hits the atmosphere or gets below a certain altitude on an airless world. Instead, it will constantly burn at minimum throttle all the way from where the burn started to the edge of the atmosphere, saying it's doing a course correction of like 0.1m/s. This makes the landing process take a huge amount of time (no warping during this) and burn more fuel than you'd like. But if you use MJ for landing, you've got to deal with this.

[FleshJeb]

In addition to the fantastic advice in the rest of the thread, MJ has trouble with really low and really high TWRs.

The high TWR (over 4 ish) will give it trouble with the fine-tuning burns. Likewise, the suicide burn at the end gets mistimed occasionally, causing unplanned lithobraking.

Low TWR will sometimes make it miss the deorbit burn because it doesn't have time to finish the burn before passing over the landing site. MJ will just keep circling the planet indefinitely while saying "Warping to deorbit burn". I have some ion Mun landers that have to start from a 30km orbit instead of my normal 8km because of this.

[Pecan]

...Besides this, it doesn't like to use parachutes at all unless that's the only way to get slow enough to avoid a crash. If it can land without using the parachutes, it will, even you tell it give it permission to use the chutes... It will never finish a deorbit burn until it hits the atmosphere or gets below a certain altitude on an airless world...

These are things I've never seen. MJ sometimes engine-brakes so much the chutes get cut, then it runs out of fuel and crashes (doh!)* but I've never had it fail to deploy the chutes at all. Although, rarely, I have seen MJ keep 'hunting' for a correction heading aborting and re-issuing the "land at target" solves it. Unless there's next to no SAS/control authority of course and it can't turn. The biggest problem I have with MJ's landing at the moment is that it over-does its deorbit burn (at Kerbin) by 20-200km short of the target and then wastes time and fuel turning prograde to correct it (abort and re-issue fixes that too).

[*actually, this happens so much that once the ship's nearing full-deployment altitude (ie; 500m for normal chutes) I "abort auto-land" then tell MJ to "land somewhere" once they are safely open]

[FleshJeb]

I think it refuses to open the chutes if you're going (or will be going) above ~105 m/s (Kerbin landing) to prevent chute tear-off. Frequently, it will fire a burst at full chute deployment to get you below this number, and then cut off. I think those short intermittent bursts also serve to let it know what the actual TWR at the current engine configuration is. (This is just speculation from having watched about 1000 landings.) I REALLY need to dig into the code to check it out, because the behavior fascinates me.

[ExavierMacbeth]

How long have you guys let MechJeb sit before determining its not functioning?

I have had the same problem but its not completely failing but rather the "warp" function is stalled. For me this can happen when its trying to switch between High & Low orbit burn mode. Instead of autowarping to the burn point it will sometimes remain in 1x speed ALL THE WAY to whatever invisible maneuvering node it is using for that phase. I had it get stuck for 1/4th an orbit once where I just left it and when it finally got to the point where I am use to seeing it do its de-orbit burn it kicked in properly the rest of the trip down.

Also just a side note, If you have to tweak the engines for any reason (realized you don't want to give Mechjeb 6+ TWR with the way it likes to flare the engines sometimes), make the changes BEFORE you initially engage the autoland. You may not be able to see the maneuver nodes but it still follows them, and changing anything thrust related (including staging) after you tell it to calculate the path initially will result in bad contact with the ground since the path doesn't get updated for drastic changes.

[numerobis]

I think those short intermittent bursts also serve to let it know what the actual TWR at the current engine configuration is. (This is just speculation from having watched about 1000 landings.) I REALLY need to dig into the code to check it out, because the behavior fascinates me.

MechJeb calculates the thrust directly. It's around here that mechjeb does this. Good luck working with sarbian to fix anything though.

[CyberDroog]

When I first started using the auto land feature I made the same mistake and found myself in the same position. It said it was doing a deorbit burn but was actually doing nothing. Then I hit the spacebar... Make sure the engine available for the burn is staged and ready to go.

[FleshJeb]

How long have you guys let MechJeb sit before determining its not functioning?

I have had the same problem but its not completely failing but rather the "warp" function is stalled.

My experience with that case is that MJ hasn't rotated to the node completely. Give it a bump with the WSAD; it will re-steer to the node and then it will warp. "Percussive Maintenance"

MechJeb calculates the thrust directly. It's around here that mechjeb does this. Good luck working with sarbian to fix anything though.

Thanks for that.