How do you fight Lander Tipping Disorder (LTD)?

[Brainlord Mesomorph]

No fundamental problem, it can be made to work; you may find it impractical, however.

Tylo has a relatively high gravity (0.8 Kerbin-Gs); an LV-N can lift only about 7.5 tons, and 2.25 tons of that is the LV-N itself. Add in the fuel for landing and takeoff, and it may well be that you can't even add a MK1 Lander Can. Certainly not much more than that: no legs, no science.

#^$^*%#!

I was so busy designing for delta V I forgot about TWR!

(jeeze this is like rocket science!)

I just checked a TWR calculator - - sigh - back to the VAB!

[Jouni]

A Tylo lander with one nuclear engine and the equivalent of 10 FL-T100 fuel tanks can carry around 1.2 tonnes of payload, for a total mass of around 9.075 tonnes. The TWR starts at below 1 but gets high enough before you touch the surface. Landing is quite hard, because if you make mistakes during the early parts of descent, you can't fix them later.

I've done it with 4 engines, 40 fuel tanks, and 4.68 tonnes of payload. My approach had three phases:

1. Kill most of horizontal speed and lose as much altitude as you dare while keeping the descent rate under control (probably at around 100 m/s).
   
2. Let the lander fall freely for a while.
   
3. Do an almost perfect suicide burn with no more than a couple of seconds of hovering.
   

You can make the landing easier by carrying some high-TWR engines (such as the 48-7S and the 24-77) and using them for extra thrust during the final moments of the suicide burn. This obviously reduces the payload capacity.

[michaelhester07]

How I fight it:

1. Flat landing spot. Less than 8 degrees slope, with Kerbal Engineer reading the slope out.

2. Barring 1: Wide base with girders to spread the legs out. My landers have special constraints for base construction (that is they have launch pads on the bottom end of girders with extraplanetary launchpads) so the legs get spread out anyway. I had to rescue a Duna lander in my latest career after a sudden unplanned orientation change upon landing. The wider the base the easier to land. 3x1 girders can maximize the area.

3. Lots of torque. If my lander has to be narrow, then lots of torque. This especially goes for probes and mk2 lander can landers. Stack 2-3 SAS modules on top of it and I can stay upright on a 40 degree slope with a narrow leg profile. Probes can even fix themselves after an unplanned orientation shift.

4. I don't fix it. The duna lander above was a base deployment vehicle that was tall enough to turn over. I had to launch 2 ships, one with drills, the other with garages, to get the base operational. Needless to say I learned how to do a precision landing on Duna, both recovery ships landed within KAS pipe range of the downed lander.

[Vallius]

Thank you all for the good advice. I don't do mods, other than Astronaut Visual Pack and Chatter (which are immersive, rather than gameplay changing).

So it looks like the best advice I've seen is.

1. Wide lander with a low center of mass.

2.a Come in low and orbit once or twice to grab the right landing site. It also lets you spot large inclines on airless bodies.

2.b Kill horizontal velocity before touchdown. (I'm usually pretty good at this, unless I panic at the last minute--see 4.)

3. Extra torque and RCS for the landing stage. (I can't believe I never thought of that before! I'll have to try it.)

4. Don't Panic! (My big mistake on my last Mun landing, other than insufficient torque).

[bdito]

Thank you all for the good advice. I don't do mods, other than Astronaut Visual Pack and Chatter (which are immersive, rather than gameplay changing).

So it looks like the best advice I've seen is.

1. Wide lander with a low center of mass.

2.a Come in low and orbit once or twice to grab the right landing site. It also lets you spot large inclines on airless bodies.

2.b Kill horizontal velocity before touchdown. (I'm usually pretty good at this, unless I panic at the last minute--see 4.)

3. Extra torque and RCS for the landing stage. (I can't believe I never thought of that before! I'll have to try it.)

4. Don't Panic! (My big mistake on my last Mun landing, other than insufficient torque).

If you install Kerbal Engineer, it only provides stats, nothing more, then it has a readout of the degree of slope directly below you.

[Slam_Jones]

Just for the record, with practice and precision you can land on slopes on low gravity moons.

Stable Landing on Minmus

But for other cases, well, they already told you.

Good luck!

[Vallius]

If you install Kerbal Engineer, it only provides stats, nothing more, then it has a readout of the degree of slope directly below you.

Knowledge is power--especially in Kerbal Space Program. That seems like something that should really be in the base game

After all, landers have a distance-to-surface radar. Why not a slope indicator?

I guess I'm hoping against hope that squad will add this functionality to landers in the future.

Tell you what, if there's no better way when 1.0 finally comes out, I'll happily adopt Kerbal Engineer.

Edited October 31, 2014 by Vallius
Typos...

[michaelhester07]

Kerbal Engineer is kind of a game changing mod even. It does the calculation part of the rocket science for you. What you were doing in excel it shows as you build the rocket.

[Guest]

My old moon lander, on slope: (clickable)

A rather big lander ship, now re-purposed as emergency response ship: (clickable)

(you might notice an old stock flag in the corner, I do not use it anymore)

Edited October 31, 2014 by Guest

[Pecan]

Reconnaissance (and another mod - SCANSat)

That is (map the surface with satellites first then) land a pilotless drone to see what the surface is really like. If it's safe use the drone as a target.

[Master Tao]

Since I was asked, the part on top of the lander can in this post is a 2.5m Universal Docking Port from Kip Engineering.

[Laie]

#^$^*%#!

I was so busy designing for delta V I forgot about TWR!

Well, good that you asked.

Also, what starman said: a very low TWR will devour lots of delta-V. High-powered engines for the hot phase of the landing and take-off will not only make your life a lot easier, they may well lead to a more lightweight vessel overall. Especially if you're willing to stage away the strong thrusters as soon as they're no longer needed, together with some empty tanks.

[GoSlash27]

Everybody's covered the high points already; wide aspect ratio, low center of gravity, and arresting lateral velocity.

It also helps if you make your landers no heavier than they need to be. A lot of players either over-engineer their DV budget or crutch an inadequate design with "moar boosters". In both cases, it's a bigger vehicle and more prone to tipping.

Crunch the numbers first and design it to not tip, and you shouldn't have a problem.

Best,

-Slashy

[Jouni]

Also, what starman said: a very low TWR will devour lots of delta-V. High-powered engines for the hot phase of the landing and take-off will not only make your life a lot easier, they may well lead to a more lightweight vessel overall. Especially if you're willing to stage away the strong thrusters as soon as they're no longer needed, together with some empty tanks.

An efficient high-TWR Tylo landing requires around 5000 m/s of delta-v. It's a bit more than what it takes to reach LKO, but without any atmosphere interfering, so highly optimized multi-stage landers should have payload fractions around 15-20%.

Things get interesting when we consider reusable single-stage landers. With chemical rockets, the optimal initial TWR seems to be around 1.5, according to tavert's charts. Going above that saves at most 200 m/s of delta-v, while fuel usage increases due to significantly higher dry mass. With nuclear engines, we get reasonable results with initial TWR 0.85 and 6000 m/s of delta-v. In the following, mass ratio is based on 105% of the delta-v target, fuel tank and engine masses are fractions of dry mass, and payload and wet masses are for landers with a single engine.

[table]

[tr]

[td]Engine[/td]

[td]Mass ratio[/td]

[td]Fuel tank mass[/td]

[td]Engine mass[/td]

[td]Payload fraction[/td]

[td]Payload[/td]

[td]Wet mass[/td]

[/tr]

[tr]

[td]LV-N[/td]

[td]2.23[/td]

[td]0.154[/td]

[td]0.558[/td]

[td]12.9%[/td]

[td]1.16 tonnes[/td]

[td]8.99 tonnes[/td]

[/tr]

[tr]

[td]Aerospike[/td]

[td]3.94[/td]

[td]0.367[/td]

[td]0.397[/td]

[td]5.97%[/td]

[td]0.888 tonnes[/td]

[td]14.9 tonnes[/td]

[/tr]

[tr]

[td]KR-2L[/td]

[td]4.08[/td]

[td]0.385[/td]

[td]0.125[/td]

[td]12.0%[/td]

[td]25.5 tonnes[/td]

[td]212 tonnes[/td]

[/tr]

[tr]

[td]Skipper[/td]

[td]4.24[/td]

[td]0.405[/td]

[td]0.230[/td]

[td]8.59%[/td]

[td]4.74 tonnes[/td]

[td]55.2 tonnes[/td]

[/tr]

[tr]

[td]LV-T30[/td]

[td]4.24[/td]

[td]0.405[/td]

[td]0.290[/td]

[td]7.18%[/td]

[td]1.311 tonnes[/td]

[td]18.3 tonnes[/td]

[/tr]

[tr]

[td]48-7S[/td]

[td]4.61[/td]

[td]0.451[/td]

[td]0.181[/td]

[td]8.00%[/td]

[td]0.204 tonnes[/td]

[td]2.55 tonnes[/td]

[/tr]

[/table]

For small payloads, the 48-7S is obviously the best lander engine. The LV-N has the best overall payload fraction, but it's harder to use. The LV-T30 can be a useful replacement for a pile of 48-7S engines. For large landers, the Skipper is slightly more efficient than the 48-7S. And if you have a huge payload, the KR-2L can be almost as efficient as the LV-N.

Things get more complicated, if we consider the delta-v requirements for reaching Tylo and returning back to Kerbin. With a reusable nuclear lander, we only need some docking ports and fuel tanks for that, as the lander engines can be used for efficient transfers.

Edited November 1, 2014 by Jouni

[NFUN]

If you are quick enough, turn on SAS before you land. Just as you hit the ground you can see which way you need to apply force on the bottom right meters, so it is easier to realize how the rocket must be turned to stay up. This is somehwat stronger and more effective than pure automated SAS.

[How2FoldSoup]

There is always the mix of KOS and Infernal Robotics...see this video which is just awesome

Skip to about 2:40 to see the demonstration..

That however requires some mods, but at least it is nearly foolproof and very cool!

[Vallius]

I'm rather flattered. How often does a question-answer thread get an extra page of answers and 400 more looks after it's been marked as answered?

[Ruedii]

There are two ways to reduce lander tipping. I recommend using both:

1. Make your lander wider: A lander that has a wider base is going to have the center of gravity over the base for a wider angle. A good way to do this is to attach a side stage that is discarded on launch.

2. Land vertically: I can't stress this enough. Sideways momentum will tip your lander. Seriously, your lander is not an airplane, and unless it has wheels pointed in the direction of horizontal momentum, landing sideways will make it tip!

3. You can always use wheels: Wheels aren't just for space planes and rovers, and making your lander double as a rover is great. Rover wheels do absorb a lot of shock, and if you don't mind repairing them they tolerate even more shock! Keep your brakes off and you can roll on landing, and this will allow you to have more horizontal velocity without tipping!

[AlexinTokyo]

I'm rather flattered. How often does a question-answer thread get an extra page of answers and 400 more looks after it's been marked as answered?

Around here? Pretty often, in my experience. It's one of the things I love about this place.

[LethalDose]

A note on using RCS in landers: I will sometimes use the translational controls to kill any remaining lateral velocity after I've slowed to landing speeds (< 20 m/s).

[Skorpychan]

Lander design:

Wide base, low CoM, short engines if possible.

No heavy objects at the top.

SAS.

Enough fuel to not need lithobraking.

Piloting:

Land as slow as possible.

As near zero horizontal as possible.

If you can't do that, angle the lander so a leg is pointing in your direction of travel to act as a shock absorber.

Got monopropellant for docking? Don't be afraid to use it to help stabilise a lander.

DON'T LAND ON A SLOPE. Seriously. Flatter is better.

Recovery:

Reaction wheels. Try and tip it back up.

Toggle the landing gear. Gear up, wiggle upright, gear down.

Monopropellant. No good having it if you can't get back up there.

EMERGENCY ONLY: Roll to point down the slope. Gear up, throttle up, then pull upwards sharply. Kill horizontal velocity, and land more carefully this time.