MechJeb2 Landing Guidance

[Popestar]

Playing on PC, v1.8.3.  Until today, I've had no problems.

I started a new career on Moderate a few days ago, and I'm in the process of unlocking Tier 5.  I sent a lander to the Mun, and tried using the scripting module to auto-land.  It seems like it wants to work, warping to the de-orbit point.  And then it...does nothing.  At all.  MJ refuses to complete the landing sequence.  I thought it may be a glitch of some small kind, so I reverted back to the launchpad, sent the lander up, tried using MJ again...with the same result.  So I backed out of KSP altogether, launched...and again, nothing.  MJ refuses to land.

So I tested to see if other parts of this work as expected.  And yes, Smart A.S.S. works, as does spaceplane autopilot.  I have never had an issue with the auto-lander before, and I've used it on several other career games that are both far more and far less advanced tech-wise as this one.

Why does this happen, and what do I need to do to correct it?  I've been under the impression that, regardless of technology unlocks, the scripting module works.  And that it works without having the MJ tech piece on board.

Any ideas?  This is really frustrating, especially when I cannot land manually (even with the tutorial).  I need to understand why MJ isn't functioning properly.  Do I need to uninstall and reinstall?

[paul_c]

I was going to ask......can the craft land manually with no issues or comms loss etc etc.

[Popestar]

I have full control over the craft before, during, and after the attempt.  In fact, on my last attempt, MJ did all the auto-warping, but I had to fire thrusters and all that jazz.  I have wondered if I need a relay in orbit of said celestial body, but on my Normal career (post-caveman, by the way), I was able to stick multiple landings on Minmus without a relay there.  So while I can try that, I am not confident that this is the issue.

[paul_c]

You don't need a relay if you have sight of Kerbin (and a decent aerial). If you time-warp (or plan the mission) so the landing occurs at full moon, it will be in daylight AND in comms. Obviously, there is an icon to show whether the craft has control (top left).

It does sound like a MJ issue but obviously there's a list of things which make a spaceship easy to land, or a nightmare. I dare say MJ could control even a nightmare craft if it had the necessary bits etc. I am surprised you say you need to handle the throttle, I would have thought an automated landing system did that. Otherwise, what is it doing differently to SAS retro hold?

[Popestar]

31 minutes ago, paul_c said:

You don't need a relay if you have sight of Kerbin (and a decent aerial). If you time-warp (or plan the mission) so the landing occurs at full moon, it will be in daylight AND in comms. Obviously, there is an icon to show whether the craft has control (top left).

It does sound like a MJ issue but obviously there's a list of things which make a spaceship easy to land, or a nightmare. I dare say MJ could control even a nightmare craft if it had the necessary bits etc. I am surprised you say you need to handle the throttle, I would have thought an automated landing system did that. Otherwise, what is it doing differently to SAS retro hold?

Exactly.  Why do I need to throttle when MJ does it for me?  I'm going to throw up a relay satellite just to see if this helps.  If it does, then it means that I'm not in range of Kerbin at the time MJ is trying to land, which then means no communications from the KSC.  And that would answer the question.  I'll post here in this thread when I do that with the results.

[paul_c]

Its very easy to determine if its a comms problem - saves needlessly sending a relay? (You might need >1)?

[Popestar]

1 hour ago, paul_c said:

Its very easy to determine if its a comms problem - saves needlessly sending a relay? (You might need >1)?

How is it easy to determine?

[paul_c]

There is a status bar on the top left of the screen which shows a green icon for full control; and signal strength (and a few other things).

[Popestar]

3 hours ago, paul_c said:

There is a status bar on the top left of the screen which shows a green icon for full control; and signal strength (and a few other things).

Link to a page that describes them please?

[paul_c]

circled

[Popestar]

I get what you are talking about.  What I can't find is information on it.

[dprostock]

I am a user (dependent) of the Mod, and I can tell you that it has some limitations that you should consider.
If the orbit is too low, causing sharp trajectories on descent, the MechJeb2 fails. ( In Mun, with orbits below 25 km. or at least my safety point)
If you change the checkpoint during descent, it fails. 
If you change engines or their power, on descent, it fails to shut down. At best, the descent point changes.
If you have any imbalance issues between the checkpoint and the motors, it fails or shuts down. 
The same goes for automatic ascent, control point change, or engine change while the upgrade program is running causes errors.
 
 

[Cant think of a username]

I did have the same problem once. I was above 25 km as @dprostock said, but it still didn't work (I was in sandbox mode) So I gave up on mechjeb and left it on while I went for normal landing. then ;like 5 seconds into the deorbit burn, Mechjeb just randomly started working again. IDK if this helps, but it did for me. Maybe Mechjeb doesn't like the Mun . Works always on Minmus ,or even EVE,.

[paul_c]

4 hours ago, Popestar said:

I get what you are talking about.  What I can't find is information on it.

What do you need to know, that isn't already there?

[Popestar]

1 hour ago, paul_c said:

What do you need to know, that isn't already there?

I'm looking for a wiki page or something that explains it in detail.

[paul_c]

There's the Commnet wiki entry https://wiki.kerbalspaceprogram.com/wiki/CommNet but it goes into much more detail/depth, way more than you need for this issue.

If your vessel has a lack of control, you can look at the icons and see that its not under command, and then look at the CommNet network or vessel links to see why it might not be under command. You can also look at the placement of various relays you might have, eg before a landing attempt, to figure out whether you're about to lose comms or whether they're good.

[Popestar]

28 minutes ago, paul_c said:

If your vessel has a lack of control

Not to sound harsh, but you obviously didn't read my original post.  I have full control over the rocket; it's only MJ that isn't functioning.

[paul_c]

Understood; but there was an element of doubt:

 

20 hours ago, Popestar said:

  I'm going to throw up a relay satellite just to see if this helps.  If it does, then it means that I'm not in range of Kerbin at the time MJ is trying to land, which then means no communications from the KSC.  And that would answer the question.  I'll post here in this thread when I do that with the results.

 

So I wanted to double-check its okay. I've seen situations where a relay is in place, the craft has an aerial, but it (for some unknown) reason, isn't controllable and the main screen shows it has no comms. Of course its difficult to do a back-to-back comparison at the exact same place/time but going back into the VAB, removing then re-adding the aerial then doing the same mission again, worked that time.

It might be a glitch, it might be a reason like a non-optimal positioning of the relay, it might be a graphics display issue where something is marginal but "looks" okay on screen. This was across the 1.11.1 update - a vessel was designed in the VAB in 1.11, flown in 1.11.1 and its aerial didn't work properly. One of those "difficult to replicate" issues!

Hence the suggestion, take MechJob out of the equation and fly it manually (or just tease the controls, make it pitch/roll/yaw/throttle up-down) as a sanity check. I've also seen situations where most of the controls work but there is no eg roll authority only. I am going to assume that MechJob doesn't directly relocate/change the physical aspects of a craft but, like a real auto pilot, manipulates the controls so that other effects such as electrical power used when reaction wheels need to produce a lot of torque, etc also occur.

If its a MechJob issue (it sounds like it is...) I wish you the best of luck with it but can't help further as I don't have it.

[dprostock]

Just a moment! I put together a visual guide and upload it.

[dprostock]

I use the KSP in Spanish, but if Sandra Bullock was able to press buttons in Russian on Gravity, I don't think language is a problem.

Let's look at the different modes that the MechJeb2 has to descend automatically, for that I will use a probe well tested for its capabilities of crashing, sorry, descending into Mun in one piece. 
In a snuff of enlightenment, I call it "Luna".

"Luna", for all tests, is in Mun orbit at 30 km. to 180º incline.

First let's try the mode "Aterrizaje en cualquier sitio", "Land somewhere".

Once that option is selected, the descent program runs...

And obviously the MechJeb2 has some problem, the ship has braked, but it does not slow down...

It belatedly turns on the engines to slow down, but this one is excessive, as is the drop speed...

And by logic, in the best KSP style, it has crashed and its remains bounce over the craters...

Again...

This time we will select where we want to crash... errrr... Descend.
For that we will go to the  "Elegir objetivo en el mapa" ("Pick target on map")

We carry the yellow symbol over the surface of Mun and select the location with one click. Latitude and longitude data are automatically recorded.
Then we select"Aterrizar en el Objetivo" ("Land at target") and the maneuver sequence begins.

First you will adjust the tilt of the orbit to match the descent site,

then an initial braking, stop,

and new braking over the site.

The engines stop at an altitude of 500 meters. and the ship falls freely, then ignites the engines for the last time before perching on the surface.

If you select coordinates, it works the same.

You should keep in mind that you have the engines activated beforehand, since the MechJeb2 does not take care of that task, it only turns them on and off.

I hope it works. Luck!

[Popestar]

@dprostock

Am I not articulating properly?  I have stated MULTIPLE TIMES IN THIS THREAD that MJ is not working when I use the exact procedure you just spit out.  I am doing EXACTLY WHAT YOU DESCRIBED and IT IS NOT WORKING.

Sorry, but it is frustrating to have to say this multiplie times and then get an answer that doesn't address the question. 

[dprostock]

On 2/4/2021 at 5:05 PM, Popestar said:

@dprostock

Am I not articulating properly?  I have stated MULTIPLE TIMES IN THIS THREAD that MJ is not working when I use the exact procedure you just spit out.  I am doing EXACTLY WHAT YOU DESCRIBED and IT IS NOT WORKING.

Sorry, but it is frustrating to have to say this multiplie times and then get an answer that doesn't address the question. 

Did you update the KSP version?

Did you update the Mechjeb version?

What version of MechJeb are you using?

Do you use CKAN?

Did you install another Mod to remotely control the ships?

It would be nice if you took at least one image of your ship and the situation you describe.

[snip]

 

Edited February 6, 2021 by Vanamonde

[Vanamonde]

Some remarks have been removed. Please don't make things personal. 

[Popestar]

Ok, let's try this again.

• KSP Version:  1.8.3
• MJ Version:  2
• CKAN:  Yes
• Other Flight Mods Installed:  No

I went to do a Mun landing again this morning, and again MJ failed to do anything other than warp to the deorbit burn.  I have multiple satellites orbiting, 2 around Kerbin and 1 around the Mun.  As you can see from the below image, I have a green line from the craft to Kerbin due to a pair of high gain antenna deployed.  And yet, when I attempt to do a Mun landing using MJ, it doesn't do anything other than warp to the high point deorbit burn.  I ended up having to follow along with what MJ said was the next step and manually land the craft, which I was able to do.  But that kind of defeats the purpose of having the mod installed, doesn't it?

Anybody know why this happens on the Mun?

[Popestar]

So, I have deduced that this is due to one of 2 things:

1. Advanced Flight Control; OR
2. R&D Level 2.

II upgraded R&D to level 2, and then before running a test I went around and collected a bunch of surface samples at the KSC to get enough science to purchase Advanced Flight Control.  I then sent a lander to the Mun...and MJ worked fine.

I will have to test these independently of one another, but st least I've got it working.  For now.