Problems landing on the Mun

[synik4l]

Hi guys, new to this community and kerbal space program. I have a problem landing on the mun and not sure why. I sorta followed Scott Manleys tuts on building a decent rocket(changed it some). I have no problems getting to the mun or getting in orbit around it. My problem is landing. I get myself to a decently low altitude. Slow myself down a lot usually using my 2nd stage. Then i drop it, and here's where my problem lies. No matter what I do my lv-909 engine cannot slow my speed down. I can literally get to 10m/s using my 2nd stage. But as soon as I drop that one and go to the final landing stage. my speed will continue to increase even at full throttle. This happens all the way to the surface. In which at that point i'm back up to like 200m/s or more. What I am doing wrong? Weight? Has something changed where i need something bigger than the lv909 to properly land? Or am I missing something huge? Thanks for any advice anyone has.

My lander is equivalent to the one found in this video. The only difference from my rocket and scotts is my early stages.

[XenonSpark]

Your lander stage is exactly the same as Scott's and it's not working? No modifications to that stage at all?

At what altitude are you detaching your second-to-last stage?

EDIT: May have something to do that Scott starts his descent with about 2/3 fuel in his last tank - he's already burnt some performing other maneuvers. That lightens things up a bit for his descent. Not sure if that's your problem though.

Edited July 28, 2013 by XenonSpark

[Superfluous J]

Probably a stupid question, but are you sure your rocket's on? You may have to hit space again to actually engage that rocket depending on how your staging is set up.

If you could post a picture of your craft while it's having the problem, we may be able to help you more.

[reilem]

Are you using 0.21? It's possible that thrust/isp values have been changed of the engine, and also that ASAS that he has on his Mun lander is no longer neccessary due to the recent SAS changes. It is possible that the weight of the SAS has been increased and therefore causing your thrust/weight ratio being too low.

[Nurph]

That lander should have more than enough thrust to land with a full tank. Is the engine on? Is it getting fuel?

[synik4l]

Your lander stage is exactly the same as Scott's and it's not working? No modifications to that stage at all?

At what altitude are you detaching your second-to-last stage?

EDIT: May have something to do that Scott starts his descent with about 2/3 fuel in his last tank - he's already burnt some performing other maneuvers. That lightens things up a bit for his descent. Not sure if that's your problem though.

Thanks for all the quick responses guys...ill go in order.

No changes other than the SAS unit is that tiny one now..that can fit inside a decoupler without actually extending the length of the ship. Other than that..its the same.

I have tried different altitudes. I have tried getting into a orbit and then killing velocity. And then dropping stages immediately. Ive also tried doing the same, but dropping the second to last stage after the fuel in them is gone.

about your edit...i see how that could be possible. Although I can burn almost it all out and im still gaining velocity.

5thHorseman:

Yes my rocket is on. It is burning fuel. Just seems like something weight wise or something. Lemme grab a pic and ill post it. Ill post one with the stats module on.

reilem: I am on 0.21. ill try it without the SAS unit. In 0.21 its smaller than it used to be actually. I dont know if that made a difference on weight or not. As I said above you can now place it inside of a decoupler.

and nurph your questions have been answered above

General consensus, seems like it may be weight. but i dont know. I'll post a pic in a second. Then if I have changes to make ill do those and try it again and video it. So you guys can see whats happening.

Thanks again for all the help guys

Heres the pic-Yes I know my launch stage is huge. Maybe overkill. But it gets me to the moon with PLENTY of fuel. So thats why i built it like that.

I gotta be doing something way wrong. Cus it saying my TWR for S2 is 7.62 on mun.

Edited July 28, 2013 by synik4l
added picture

[Arkalius]

Based I what I can see in the screenshot, there's no reason the craft should be having this problem. The only thing I can think of besides pilot error is if you maybe have some part that is getting stuck to the bottom of the last engine, which is then eliminating the thrust it's producing. Do you have a decoupler facing the wrong way, perhaps, and thus sticking to the engine instead of the previous stage? Decouplers have a red arrow on them pointing to the side that will detach from it. It should be pointing upwards in most cases.

[Nurph]

The only other thing I can think of is that the decoupler under the 909 is clipped into the engine weirdly. The decoupler and the engine fairing both come off when you eject that stage, right? Can we see a landing attempt pic?

[espm400]

Based I what I can see in the screenshot, there's no reason the craft should be having this problem. The only thing I can think of besides pilot error is if you maybe have some part that is getting stuck to the bottom of the last engine, which is then eliminating the thrust it's producing. Do you have a decoupler facing the wrong way, perhaps, and thus sticking to the engine instead of the previous stage? Decouplers have a red arrow on them pointing to the side that will detach from it. It should be pointing upwards in most cases.

I'm pretty sure that decoupler is on the right way around (try zooming on the pic, you'll see).

If you can hear the engine firing, and a TWR that high, that little thing should stop on a dime, so there has to be something blocking the flow. My suggestion would be to pop off everything below that decoupler, remove and delete the decoupler and engine, then just replace them with new parts, then just put your launch stage back on. It could be as simple as an accidental, weirdly placed part blocking your engine exhaust. If it isn't that, then I'm drawing a total blank.

[Knas]

You don't need parachute for a mun landing Remove that and maybe it gets lighter.

[synik4l]

I'll try removing that stage and rebuilding it. That sounds like a good idea. Cus I know its firing. Something blocking it seems to be the most likely. I used the same ship to get to minmus tonight without problem. Of course it has like no gravity. so slightly different. Also Knas I brought the parachute for going back to kerbin. But good idea maybe i can just drop it and no go back to kerbin with this guy.

[rpayne88]

You don't need parachute for a mun landing Remove that and maybe it gets lighter.

Needs it to get back with out leaving a crater in the ground.

[GavinZac]

Try coming in from a higher orbit. Killing horizontal speed from a low descent is hard to do and leaves you less time for doing a perfect suicide burn.

[espm400]

I'll try removing that stage and rebuilding it. That sounds like a good idea. Cus I know its firing. Something blocking it seems to be the most likely. I used the same ship to get to minmus tonight without problem. Of course it has like no gravity. so slightly different. Also Knas I brought the parachute for going back to kerbin. But good idea maybe i can just drop it and no go back to kerbin with this guy.

The other possibility was that you just ran into some gool ol' alpha phase jank (always good times), because as I said, a ship that small with an LV-909 that's firing at full throttle should be able to kill several hundred m/s velocity in a few short seconds.

@GavinZac: You seem to be missing the point. The problem synik was having was that a firing engine wasn't producing any thrust, which happens if you inadvertently block the nozzle. Mind you, that also happens when the engine isn't firing at all, but we won't go there.

[Somerled]

I see you're using some mods. Are you sure you haven't grabbed some non-stock parts with different stats than you are expecting? For instance, I'm having a hard time believing that what looks like a FL-T400 fuel tank in your image is the same as the 0.21 stock version. It's too short based on where the legs are placed. The banding around the bottom doesn't look right either. Could it be much heavier than the stock version? What about the engine? Is it also a stock LV-909? The fairings look to be too short, but it's hard to tell given the perspective (and that could also mean a goofy connection to the decoupler).

Since I haven't been to the Mun in 0.21 yet, I thought I'd take your lander and give it a test. To confirm: I used the LV-909, FL-T400, Command Pod Mk1, Mk16 Parachute, TR18A Stack Decoupler, Telus-LV Bay Mobility Enhancer, and four LT-1 Landing Struts. All stock parts (no mods installed). That's also Scott Manley's design in the vid you linked, with a different ladder setup and no ASAS. It lands just fine at 1km elevation on the Mun. Weight is not an issue in the least. Fuel isn't a problem either; I landed took off and landed again 1/4 around the Mun with fuel to spare.

[Edit: scratched the rest, seemed irrelevant]

Edited July 29, 2013 by Somerled

[synik4l]

I see you're using some mods. Are you sure you haven't grabbed some non-stock parts with different stats than you are expecting? For instance, I'm having a hard time believing that what looks like a FL-T400 fuel tank in your image is the same as the 0.21 stock version. It's too short based on where the legs are placed. The banding around the bottom doesn't look right either. Could it be much heavier than the stock version? What about the engine? Is it also a stock LV-909? The fairings look to be too short, but it's hard to tell given the perspective (and that could also mean a goofy connection to the decoupler).

Since I haven't been to the Mun in 0.21 yet, I thought I'd take your lander and give it a test. To confirm: I used the LV-909, FL-T400, Command Pod Mk1, Mk16 Parachute, TR18A Stack Decoupler, Telus-LV Bay Mobility Enhancer, and four LT-1 Landing Struts. All stock parts (no mods installed). That's also Scott Manley's design in the vid you linked, with a different ladder setup and no ASAS. It lands just fine at 1km elevation on the Mun. Weight is not an issue in the least. Fuel isn't a problem either; I landed took off and landed again 1/4 around the Mun with fuel to spare.

[Edit: scratched the rest, seemed irrelevant]

You're right. I think this is the problem. I bet I overwrote some of those parts with mods. Ill wipe out the install today and reinstall. That is a good call Somerled. I didnt even think about that. Guess I need to watch more closely what i'm installing huh? n00b mistake.

Either way regardless of whether its what your saying espm or Somerled(or both). This should fix it.

So try it and report back tonight after work. Thanks for all the help guys. This community is super helpful.

[Somerled]

It's not a noob mistake. It's advanced design for research in underpowered hard Mun landings.

[synik4l]

It's not a noob mistake. It's advanced design for research in underpowered hard Mun landings.

Exactly....

[synik4l]

Okay so i reinstalled rebuilt it. Only installed Mechjeb and the stats mod. Was having problems even killing my velocity from over 200m meters away. When using mechjeb i go straight at it. Is it just not enough to stop the velocity of flying straight at the mun? Is the decouper blocking it? its on the right way i think. but it still looks like its in the way or something

EDIT: Got it :-D not the best landing area but its start. Atleast i know i can do it now. Thanks for the help guys

Edited July 30, 2013 by synik4l

[Somerled]

Okay so i reinstalled rebuilt it. Only installed Mechjeb and the stats mod. Was having problems even killing my velocity from over 200m meters away. When using mechjeb i go straight at it. Is it just not enough to stop the velocity of flying straight at the mun? Is the decouper blocking it? its on the right way i think. but it still looks like its in the way or something

EDIT: Got it :-D not the best landing area but its start. Atleast i know i can do it now. Thanks for the help guys

The added RCS tanks will make it take longer to reduce velocity, and flying straight at the Mun will mean you have to burn earlier to cut your high descent rate in time. But, it's all good.

Glad you made it!