Landing on Duna

[JBMCW2010]

I have sent a large mission to Duna of 7 Kerbals with a station and 2 landers. Each of the landers is similar to a basic Mun lander that you'd have launched on your first trip to the Mun or Minmus. I'm having a difficult time landing on Duna. My speed isn't an issue, each attempt I'm successful in the ship landing on its side...I'll hit the ground at 0.5-2 m/s. Then I'll bounce a bit usually manageable but then it simply keeps bouncing and each bounce gets worse due to the hilly terrain.

So my question I guess is 2 fold, should I adjust my landing gear to be more stiff? Or is it more my landing site location? Should I find another spot that might be more flat? I keep landing in the lowlands, midlands and highlands.

[18Watt]

I would adjust the landing legs.  If they are too 'springy', reduce the spring strength, and increase the dampening.  I would max out the dampening.

[Foxster]

Due to some strangeness introduced a few builds of KSP ago almost anything else makes better landing struts than the stock landing struts. 

[Guest]

I set all my landers legs to max spring and dampen in the advanced tweakable settings. So much better than the default. (Also if your lander is going wobbly you could try setting your SAS to Radial Out after you touch down. That should keep you stable until you feel like it will sit still.)

Edited July 9, 2019 by Guest

[Geschosskopf]

9 hours ago, JBMCW2010 said:

So my question I guess is 2 fold, should I adjust my landing gear to be more stiff? Or is it more my landing site location? Should I find another spot that might be more flat? I keep landing in the lowlands, midlands and highlands.

The stats for lander legs, landing gear, and rover wheel suspensions MUST be adjusted every time you build something due to the borked nature of the system.**  See below for some advice on how to do that.

As to landing sites, only about 10% of its surface (the various basins) is flat.  80% is rolling dune fields (highlands, midlands, and lowlands) and the rest is totally un-landable mountains.  So you have to be able to land out in the dune fields if you really want to see the place in all it's glory.  Of course, you can alternatively land in a basin and then go see the rest in a rover or airplane, but either way you still have to be able to deal with the dunes.  So I'd just adjust your lander legs to cope with the non-flat dunes

**For the record, this is NOT a KSP problem, it's a Unity issue.  I think it was Unity 5 that totally revised the way it does wheels (and lander legs are just wheels that don't turn).  Anyway, this new system was meant for more mainstream games where the vehicles are pre-built and all in the same environment (racing games, GTA-like things, etc.).  It doesn't work so well for KSP where the vehicles are all custom and operate on different planets.

4 hours ago, Dale Christopher said:

I set all my landers legs to max spring and dampen in the advanced tweakable settings. So much better than the default. (Also if your lander is going wobbly you could try setting your SAS to Radial Out after you touch down. That should keep you stable until you feel like it will sit still.)

Hmm.  I recommend doing things the other way.  I max damping and reduce springs to 0.50.  This seems to give good results for all types of "wheels" (including lander legs) on all planets.  High "spring" settings increase bounciness in my experience.  But if this works for you, then the system allows multiple solutions, which is good :).

Another thing I'd recommend (especially for lander legs) is to max out the friction.  This really helps reduce sliding down hills.  It's not that good an idea for wheels, though, unless you can't climb a hill any other way.

 

[Guest]

1 hour ago, Geschosskopf said:

Hmm.  I recommend doing things the other way.  I max damping and reduce springs to 0.50.  This seems to give good results for all types of "wheels" (including lander legs) on all planets.  High "spring" settings increase bounciness in my experience.  But if this works for you, then the system allows multiple solutions, which is good :).

Another thing I'd recommend (especially for lander legs) is to max out the friction.  This really helps reduce sliding down hills.  It's not that good an idea for wheels, though, unless you can't climb a hill any other way.

 

Hmm, I haven’t found when I increase both that it’s springy. It feels stiff, but I’m probably not putting a lot of weight on them either, my landers are generally pretty light. 

I didn’t think of increasing the friction tho, I’ll keep that in mind!

Edited July 9, 2019 by Guest

[Geschosskopf]

16 minutes ago, Dale Christopher said:

Hmm, I haven’t found when I increase both that it’s springy. It feels stiff, but I’m probably not putting a lot of weight on them either, my landers are generally pretty light. 

I didn’t think of increasing the friction tho, I’ll keep that in mind!

Do you use the same settings for airplane and rover wheels?  

As I think I understand what folks with more knowledge of the system have said, the "damping" really isn't a shock absorber.  Nobody really knows what it is.  In my experience, it seems to be just another spring, pointed in the opposite direction of the real spring, but is stiffer (has a lower oscillation frequency and smaller magnitude for the same force applied).  So having more damper than spring reduces bounciness by putting more "stiffness" in the suspension.  However, both also affect ride height.  The less spring you have, the lower the vehicle sits under its own weight, so the less total suspension travel you have.  If you reduce spring to zero, the suspension will be bottomed out by default, which is generally a bad thing.  Thus, I find max damper and 0.50 spring gives a stiff suspension with still some travel for bumps and terrain irregularities.

As to friction, this seems to work both laterally (parallel) and vertically (perpendicular) to the ground surface.  Thus, a rotating wheel must fight its own friction to turn because it has to pull the tread up off the ground.  This reduces speed and increase power consumption, so is not generally a good thing for rovers.  The best way to climb hills with rovers is to turn off traction control, which basically kills power to the wheels when going uphill.  But for lander legs, high friction is a good thing.

Edited July 9, 2019 by Geschosskopf

[Guest]

@Geschosskopf

naw, I generally find that I’m ok with rover wheels. The only thing I sometimes do is turn off the steering on some of them, generally the rear ones so my rovers aren’t tumbling flip machines >_<.

but yer I’ve had success with increasing both attributes getting rid of the weird increasing bounce thing. But at the same time I haven’t experimented too much with different settings either. Increasing dampen alone might be better. Tbh I don’t feel like starting another lot of testing >_< 

At least until I have to make another lander or something. 

[JBMCW2010]

Success!! Thank you all for the advice, stiffened the dampening and brought the springs down to 0.5, also used the radial out SAS and all combined I landed upright for the first time. Though I've not tried to get out with this lean.

 

[Foxster]

A tip for next time is to put the landing struts on the outer stacks. That would make the base size bigger and more stable. Plus you'd throw their mass away when you drop those stacks. 

[JBMCW2010]

Just now, Foxster said:

put the landing struts on the outer stacks.

With this being my first landing attempt onto Duna I was 100% unsure of the fuel requirements (I've seen the dV maps but those are ideal and not my lead foot inefficient landing skills.) so without knowing how much juice I'd need I actually assumed I'd drop those during the landing. I've also been playing with ideas of having a sort of 4 outer engines and then have the science collection all within a central stack and if I do I'll for sure put the struts outside.

[Geschosskopf]

12 minutes ago, JBMCW2010 said:

I've also been playing with ideas of having a sort of 4 outer engines and then have the science collection all within a central stack and if I do I'll for sure put the struts outside.

Making your landers as short and wide as possible usually gives better results at the objective than tall and skinny.  Problem is, short and wide means more atmospheric drag so launches and sometimes landings on atmospheric planets can be more of a bother.  This really isn't an issue on Duna, however, as the air is too thin to cause much of a problem.

My typical lander design is exactly what you describe here:  4 radial engines (and their tanks) on outriggers with the crew and science stuff in the center.  This also allows me to hang a rover under the center, which I now have more incentive to do since BG came out.  The rover is carried right-side up and is staged with a stack separator ring after landing, so it lands on its wheels and can drive out between the radial tanks.  And the separator ring soon falls off the top and explodes to provide some entertainment.

Edited July 9, 2019 by Geschosskopf

[Cavscout74]

51 minutes ago, JBMCW2010 said:

With this being my first landing attempt onto Duna I was 100% unsure of the fuel requirements (I've seen the dV maps but those are ideal and not my lead foot inefficient landing skills.) so without knowing how much juice I'd need I actually assumed I'd drop those during the landing. I've also been playing with ideas of having a sort of 4 outer engines and then have the science collection all within a central stack and if I do I'll for sure put the struts outside

I've done something like this with my reusable landers for everywhere but Eve, Laythe & Tylo.  I have a center 2.5m stack with crew cabin, batteries, science gear, etc on top of a center fuel tank, then 4 radially mounted 1.25m stacks with the engines & landing gear.  Makes a nice, wide, stable design for just about anywhere - I can switch out engines to adjust for planned conditions (Duna vs Ike), while keeping the same basic design.  I also use parachutes & airbrakes to assist on the Duna version.  Since this is a reusable design, the radial tanks are permanently mounted.  I've used this design - or some variation of it - on Moho, Duna, Ike, Dres, Val, Bop & Pol.   I could probably get it to handle Laythe with different engines and it should be able to land at Tylo but it would need refueling to get back to orbit.  I just haven't tried it.

I also have a heavy tourist lander for Mun/Minmus that mounts the gear on stageable tanks that get dumped prior to getting back into orbit.  I've been using it through multiple careers now, and the only landing accident I've had was due to me not paying attention while in physics warp at low altitude.  Even then, the pilot & passengers survived, just not the engine.

Reusable Duna lander:

Tourist lander:

 

[Tonka Crash]

@Cavscout74  On your Duna lander, what mod provides the curved parts that form the top of the radially attached 1.25m stacks? 

[Cavscout74]

35 minutes ago, Tonka Crash said:

@Cavscout74  On your Duna lander, what mod provides the curved parts that form the top of the radially attached 1.25m stacks? 

Dr Jet's Chop Shop.  There are 2 versions - a decoupling version (with built-in sepratron) & a structural version.

[JBMCW2010]

@Cavscout74 wow those look great. I've only ever installed the Kerbal Engineer and Alarm clock mods. Is Dr Jet's a "must have" or a really "nice to have" or is it something more towards the oh this is neat type thing?

[Cavscout74]

I'd say between "nice to have" & "oh this is neat" for most of it.  Besides the aerodynamic blisters, it adds single piece sky cranes with built in drone core & retracting engine nozzles in 1.25 & 2.5m sizes (which are great for landing rovers & small bases), a set of inline parachutes, a tiny electric prop engine, some Mk 2 parts, some single piece rover bodies (manned & unmanned).   Like a lot of mods I have, I've deleted the stuff I don't use, so I'm sure I'm forgetting stuff.  I think all I still have are the 'chutes, skycranes, blisters & the electric prop.