PTNLemay

How is the MEM meant to be used, exactly?

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I've built a few landers using the MEM part, and I'm a bit perplexed by it.  On it's own, it has a built in fuel tank.  But if you try and put any kind of engine on it, you get a big 1.875m "skirt" that appears and apparently you can't get rid of.  So you have to either live with it, or make it look more aesthetically pleasing by adding a medium sized tank.  Even with the smallest such tank, this gives the lander a massive 2 km/sec of deltaV in most configurations I end up with.  It just feels sort of out of character.


Also, the integrated RCS jets seem to be very off center.  And not off center in a way that would help once you add the engine.  Either with or without added tanks and engines, they seem way too high relative to the center of mass.  Unless they are only meant to be used to rotate the craft (which might explain why the pod has no reaction wheel).   I'm wondering if there are things about the part that I'm missing.  Or is it meant to be like this?  They're not big issues, but I'm curious.

 

The skirt that can't be toggled:

FgEIFMb.png

 

The part with and without added tanks & engine that have off-center RCS in both case.

kgozoiL.png

 

The part with the center of mass adjusted so the RCS jets are in-line with the center-of-mass:

KxrvJbI.png

Edited by PTNLemay

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Moving to Making History Discussion.

1 hour ago, PTNLemay said:

I'm wondering if there are things about the part that I'm missing.

You appear not to have noticed the second connector node underneath.  :wink:

My impression is that it's a hyper-specialized part that's meant to be a kerbalized version of the Apollo lander.  With that in mind, it makes a bit more sense:

The built-in fuel supply is supposed to be for the ascent stage.  It wants to to put some tiny little engine, like a Spark, on the upper connector node underneath-- not the one that activates the "collar", but the one above that.  Then what you do is you attach a 1.875m stack decoupler to the big node (activating the "collar), and put the landing stage under that (fuel tank, landing legs).

So that results in a two-stage lander.  Whole shebang goes down, lands with the legs on the lower stage.  Only the top part climbs back to orbit, a la Apollo.

The RCS thrusters are meant to rotate the ship, which is why it has no reaction wheels and an extra-big monoprop capacity.

All in all... it's certainly a cool looking part, but frankly I find myself not using the pod for anything, at all, ever.  It's just too specialized.  If what you want to do is to build a Mun lander that looks and acts as much as possible just like the Apollo lander, then it's great at that-- but it's kinda clunky and not very useful for anything else I've found.

And since I'm in the business of playing KSP to make my own creations, rather than trying to reconstruct historical stuff, I find myself without any use for the part at all.  That's in contrast to the other parts that Making History adds, which have useful gameplay roles as well as imitating history.  For example, those conical Soyuz fuel tanks are awesome, I love those things.  I've never once been even slightly inclined to build an actual Soyuz replica, but the tanks serve as useful "Lego" parts for a variety of lifters, so I use them all the time.  And so forth.

I'm kinda sad about the MEM.  It's so cool looking, it's just that I feel it sacrificed too much "playability" in the name of over-specializing and trying to mimic history at the cost of usefulness.

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4 hours ago, Snark said:

I'm kinda sad about the MEM.  It's so cool looking, it's just that I feel it sacrificed too much "playability" in the name of over-specializing and trying to mimic history at the cost of usefulness.

Yup, agreed. They should just have given us a few parts that would have helped make a vaguely LEM-like craft possible, not provided a whole not-Kerbal-like craft that's not really very good. 

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I don't know how accurate this is, but I feel like this is a case of listening to outside input. If you guys remember all the weeklies, every time they showed a new part, it would be taken apart and discussed at great length. On any "historical" parts, there was always much discussion (including pictures) of how this particular part didn't look like its real world equivalent. I thought that was a good thing, because I prefer to build my own, very Kerbal, rockets. I'm not into replicas, and I don't wanna build rockets that look like everyone else's. That seemed to be a minority opinion in the weeklies though. So I wonder if that helped to shape the LEM? I don't know for sure, so I could certainly be wrong. I just know I'm already missing the Mk1 Lander Can. Which is saying something.

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You have to drag the parts from above to use the real engine node. The MEM is a mess. The CM is wrong, so the RCS doesn't work (and adding RCS entirely defeats the purpose of it being built in).

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The main problem with the MEM RCS is that the part's Center of Mass is at the base, rather than up in between the RCS thruster quads where it is supposed to be.  

3c8g94k.png

This is with only a Docking Port Jr. and Spark engine attached, which seems to be the intended typical usage for ascending from the Mun.

A secondary problem is that the thruster quads themselves are attached asymmetrically, on both the vertical and longitudinal axes... which makes it effectively impossible to perfectly balance the craft without fixing the thruster positions in the part model.

uewvQB0.png

I did some experimenting with offsetting the MEM part center of mass and found a reasonable compromise with torque around all three translation axes in the hundredths of a kN.

The values I settled on are:  CoMOffset = 0, 0.6998, 0.029  (the order of axes being lateral, vertical, then longitudinal)  

The torque from horizontal translation is reduced to about 4% of that caused by the default CoM position.  Horizontal thrust torque could be reduced to near zero, but that unfortunately leaves the pitch torque caused from fore/aft thrust untouched and it becomes very noticeable when horizontal thrust problems are fixed.

You can download here a ModuleManager script that applies these values to (mostly) fix the MEM RCS balance. 

 

14 hours ago, Snark said:

The RCS thrusters are meant to rotate the ship

That doesn't mean they shouldn't be balanced.  

In the real-world Apollo LM ascent module, the thrusters were balanced along all axes in case the LM needed to perform the docking with the CSM.  While the CSM was intended to perform the docking (and did on all flown missions), the LM was specifically design to also have this capability as a backup in case of a system failure or other emergency aboard the CSM.

The balanced thrusters can still rotate the craft just fine, as also seen on the Apollo CSM.

Not balancing them in this part simply makes it less useful and, since the default CoM position is simply the model origin, it looks very much like this was just one more oversight in the MH part config files.

Hopefully, Squad will at least move the CoM... which addresses most of the problem.  Fixing it completely would also require a change to the part model, which I do not expect.

Edited by RoboRay

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It will be interesting to see if this was intended design, or if it is like some of the other parts and simply has typos or other mistakes which result it in being the way it is at release of the dlc.  Looking forward to the MH patch.

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21 minutes ago, klesh said:

It will be interesting to see if this was intended design, or if it is like some of the other parts and simply has typos or other mistakes which result it in being the way it is at release of the dlc.

Yep.  I could imagine it going either way.  For example, it might be deliberate because landers always want a low, low CoM so they don't tip over.  Clearly this is a part that was very specifically designed to be on a lander and nothing but a lander, ever, so I could imagine someone making the design decision to give it an unusually-placed CoM to assist with that-- similar to the way the jet engines have a CoM that's displaced radically forwards.

I'm not saying anyone did do that (because I'm not privy to their design decisions)... just that I could imagine a plausible scenario in which it might be.  And it wouldn't be so much of an issue if they'd just given the lander can a bit of reaction torque, which they didn't (another design decision that makes the part less attractive to me-- I'm sure they had their reasons, but it doesn't suit how I play KSP).

4 hours ago, Cpt Kerbalkrunch said:

I just know I'm already missing the Mk1 Lander Can.

What do you mean, "missing"?  It's still there.  :)

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15 hours ago, Snark said:

You appear not to have noticed the second connector node underneath.  :wink:

... Yes, thank you.

It was very well hidden I tell you!

15 hours ago, Snark said:

My impression is that it's a hyper-specialized part that's meant to be a kerbalized version of the Apollo lander.  With that in mind, it makes a bit more sense:

Yeah, but even so I'm determined to make this thing work.  In the past I've had a lot of fun using the 1-man lander can as an RCS-powered transport used to skip between space stations.  The game's RCS is powerful enough that such a transport-pod can get really good delta-V.  The new MEM is begging to be made into a 2-seat version of that.  It's a heavy part, but in terms of volume it's cute and tiny.

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16 minutes ago, Snark said:

What do you mean, "missing"?  It's still there.  :)

Is it? Wow. Been on the Mission Builder since the release. I could've sworn it was gone. That actually makes me happy. Now if they would just bring back the Mk1-2. :)

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4 hours ago, tater said:

You have to drag the parts from above to use the real engine node. The MEM is a mess. The CM is wrong, so the RCS doesn't work (and adding RCS entirely defeats the purpose of it being built in).

What you can also do instead of trying to move it in from above is hold the 'ALT' key, which forces node snap. I found that's the best way to get stuff onto the right node. Since I found out 'ALT' does this its been my most used key within the VAB. :)

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3 hours ago, klesh said:

It will be interesting to see if this was intended design...  Looking forward to the MH patch.

 

 

It appears to be unchanged in 1.4.2

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On 3/28/2018 at 1:10 PM, klesh said:

It appears to be unchanged in 1.4.2

True... but that doesn't indicate one way or the other whether it was intended design.  It might mean it's intended... or it also might mean that they haven't got around to fixing it yet, like the off-center CoM of the Soyuz tanks.

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To be sure.  Just stating a fact in case someone were to visit after that patch.

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Well, I just got making history, and I like this little piece. Even if I'm making a 1 stage lander, its better than the old 2 kerbal crew cabin. I've found that no use of the offset tool is needed if you want to add a small reaction wheel to the "intended engine node" and then put a spark underneath that, and then a 1.875m decoupler at the node that activates the collar.

the RCS and fuel tank included is nice, and helps reduce part count, its a shame that a reaction wheel is needed, as that increases part count again. I've found that the internal fuel tank is right on the border of big enough for an ascent on a 3x rescaled Mun, so for extra margin for error, I add 2 of those spherical LFO tanks to it

I'm more concerned by the other parts which IMO need a stat adjustment, so today I made a MM config for that.

Spoiler

@PART[LiquidEngineKE-1]
    { 
        @mass = 6.5
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 1460
            !atmosphereCurve
            atmosphereCurve
            {
                key = 0 295
                key = 1 285
                key = 20 0.001
            }
        }
    }
@PART[LiquidEngineLV-T91]
    { 
        @mass = 1.15
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 145
        }
    }
@PART[LiquidEngineRE-I2]
    { 
        @mass = 3.5
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 760
        }
    }
@PART[LiquidEngineRE-J10]
    { 
        @mass = 2
        @MODULE[ModuleEngines]
        { 
        @maxThrust = 260
            !atmosphereCurve
            atmosphereCurve
            {
                key = 0 360
                key = 1 70
                key = 6 0.001
            }
        }
    }
@PART[engineLargeSkipper]
    { 
        @mass = 3.75
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 865
        }
    }

 

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On 4/4/2018 at 12:59 PM, KerikBalm said:

the RCS and fuel tank included is nice, and helps reduce part count, its a shame that a reaction wheel is needed, as that increases part count again.

  Reveal hidden contents

@PART[LiquidEngineKE-1]
    { 
        @mass = 6.5
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 1460
            !atmosphereCurve
            atmosphereCurve
            {
                key = 0 295
                key = 1 285
                key = 20 0.001
            }
        }
    }
@PART[LiquidEngineLV-T91]
    { 
        @mass = 1.15
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 145
        }
    }
@PART[LiquidEngineRE-I2]
    { 
        @mass = 3.5
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 760
        }
    }
@PART[LiquidEngineRE-J10]
    { 
        @mass = 2
        @MODULE[ModuleEngines]
        { 
        @maxThrust = 260
            !atmosphereCurve
            atmosphereCurve
            {
                key = 0 360
                key = 1 70
                key = 6 0.001
            }
        }
    }
@PART[engineLargeSkipper]
    { 
        @mass = 3.75
        @MODULE[ModuleEngines]
        { 
            @maxThrust = 865
        }
    }

 

Ummm, Chief, i think its not supposed to have reaction wheels. A) KSP makes them WAYYYYYYYYYYYYYY OP and the most they can do is barely keep the ISS pointed the right way with 3. B) The LM didn't have Reaction wheels because it would be a waste of space so it Uses RCS. While i wish it has Wheels, i dont like using them cause it seems unrealistic to clip them in, or just have them at all.

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Yes, it didn't really have reaction wheels, but the same is true of many other parts based on real things

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On 12/10/2019 at 2:54 PM, kerbalk said:

Ummm, Chief, i think its not supposed to have reaction wheels. A) KSP makes them WAYYYYYYYYYYYYYY OP and the most they can do is barely keep the ISS pointed the right way with 3. B) The LM didn't have Reaction wheels because it would be a waste of space so it Uses RCS. While i wish it has Wheels, i dont like using them cause it seems unrealistic to clip them in, or just have them at all.

Except the MEM Ascent Module has been broken since release, and the CM is off, so RCS doesn't work.

 

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On 3/28/2018 at 5:26 AM, Snark said:

I'm kinda sad about the MEM.  It's so cool looking, it's just that I feel it sacrificed too much "playability" in the name of over-specializing and trying to mimic history at the cost of usefulness.

I agree. It's also doing too many things in one part -- fuel, RCS, crew, the works. I love the spherical command pods but I think they would have been "more Kerbal" without the built-in decouplers, as cool as they look -- for example, I quite often use them as crew modules in landers where the decoupler isn't needed at all. 

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Those are also handy as worker pods for rearranging station modules.

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On 3/4/2020 at 2:15 PM, Brikoleur said:

I agree. It's also doing too many things in one part -- fuel, RCS, crew, the works. I love the spherical command pods but I think they would have been "more Kerbal" without the built-in decouplers, as cool as they look -- for example, I quite often use them as crew modules in landers where the decoupler isn't needed at all. 

I don't know about 1.9+ but in previous versions the "disable staging" option doesn't even work on the pods - just fixing that would make a huge difference.  I've had to launch rescue missions after a staging accident left a lander crew sitting in their pod on the surface next to the rest of the lander.

oMBR5a2.png?3

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