Landing on Tylo

[seyss]

Hello,

I got on a 100km orbit around Tylo as shown below, but I'm having a hard time landing on it. Mechjeb's "Landing Guidance" crashes me hard on the surface.

Please note the craft status, fuel situation, and engines (2 atomic + 1 poodle).

Any ideas on how to land this?

Thanks.

Edited April 13, 2015 by seyss

[Deutherius]

Have you tried landing it manually? You should have enough deltaV to perform a landing.

I would just lower periapsis to ~7k, wait until a few minutes before Pe, use nukes to kill most of the velocity (by trying to keep the prograde marker at 0° vertical - if it goes below the horizon, turn your nose up a bit) and then touchdown with the help of the poodle.

[Mister Dilsby]

Have you tried landing it manually?

Hear hear.. "Turn off your targeting computer!"

And yeah, that's a very high orbit to come down from, you are giving Tylo lots of time to accelerate you. Mechjeb might have an easier time landing you from a lower orbit, say 20km or so--but I really do encourage you to try it manually. You might burn a bit more fuel than the autopilot would, but you'll be a better pilot afterwards.

[Empiro]

Also watch out for your TWR -- according to the KER display, it's at 0.5 on the surface. I'm not sure what your descent strategy is, but unless you get rid of those atomic engines, you're probably not going to be able to land.

[Mister Dilsby]

Also watch out for your TWR -- according to the KER display, it's at 0.5 on the surface. I'm not sure what your descent strategy is, but unless you get rid of those atomic engines, you're probably not going to be able to land.

He doesn't have the Poodle staged in (display shows 120kN available from the two LV-Ns). Hopefully that's on an action group or he can stage it in, then he'll have 340kN available. Hm. Hey OP, when you descended on Mechjeb was the Poodle online?

[seyss]

I'm following all those tips and still can't land.. starting my burn at ~7km altitude.

1- after dropping the 2 atomic engines TWR (surface) gets better. Please see:

2- I can drop the atomic engines but not poodle.

3- I tested Mechjeb without Poodle online.. going to test with all 3 online, then only Poodle. Edit: Mechjeb won't work in any configuration...

Hard!!

Edited April 5, 2015 by seyss

[Tex_NL]

Tylo requires roughly 3000 m/s dV. With the nukes you should have enough but you're never going to make it. As pointed out before the TWR is way too low. It can only lift half your craft.

Without the nukes your TWR should be able to stop your descent albeit barely. About 5/6th of your thrust is needed to lift your craft. Only 1/6th is used to slow you down. You'll be making an inefficient burn pretty much all the way down. Too bad the poodle's ISP is a lot lower than the nuke, you're 650 m/s short.

[Mister Dilsby]

^Was just going to say the same thing. Sorry, but this one isn't going to make it... Tylo is a real challenge, you need 6000m/s dV to get up and back, and a high enough thrust as well. I like to have 1.2-1.5 TWR myself: see http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet for a map giving delta V requirements to and from everywhere.

Good luck! This mission isn't a total loss, you're a better designer and pilot now for having tried this a few different ways.

[Tex_NL]

Indeed, this is not a complete loss yet. It can be salvaged. All you need is more fuel. At the moment your tanks are 62% full with 2354 ms dV (after you've dropped the nukes). Topping off your tanks would add roughly 1000 m/s bringing your total in the area of the 3000 m/s you'll need.

Don't worry if your lander doesn't have a docking port. You can transfer fuel to it after grabbing it with a claw.

[Empiro]

I don't know exactly how your staging works, but if you're just dropping the atomic engines, then you shouldn't do it -- they still have a TWR of better than 1 on Tylo, but if you also drop a lot of heavy tanks along with it, then it's worth it.

In either case, both the Poodle and LV-N are not great choices for Tylo because of their poor TWR. In the future, you'll probably want to use the small Rockomax engine.

[seyss]

Yeah I'm redesigning the craft.. gonna try again.

Thanks for all the info.

This is the last body (besides Moho) I haven't landed yet.

[Jouni]

That lander can definitely land on Tylo, but it's not going to be easy. Here are some things to consider:

1. It's cheaper to descend from a low orbit. I usually start the descent from just above 30 km.
   
2. Use the nukes to kill as much horizontal speed as possible. They're much more efficient than the Poodle.
   
3. Manage your descent rate. If it gets much above 100 m/s, you may not be able to slow down before hitting the surface.
   
4. Manage your angle of attack. If you need to point too far from horizontal to keep the descent rate under control, you're wasting a lot of delta-v to fight gravity. I would probably ignite the Poodle when the ship is pointing at 40-45 degrees (and turn closer to horizontal afterwards).
   
5. You'll probably have more delta-v and a higher TWR, if you don't drop the nuclear engines when igniting the Poodle.
   
6. If you're low on fuel, you may want to use the thrust limiter on the Poodle initially, and then increase the thrust when you're approaching the surface.
   
7. The last 1 km of the descent won't be your finest hour. You'll probably need a few attempts to get it right.
   

[John FX]

You can orbit Tylo as low as 10km. If your TWR is relatively low then you will not want to descend at a quick rate (<20m/s)

As Jouni says, once you are burning at a high angle, ignite the poodle.

Remember F5...

Try to do a landing like this (but quicker)

[Pecan]

Moho is hardest to get to.

Tylo is hardest to land on.

Eve is hardest to re-orbit from.

As others have said, TWR is the main problem here.

Stick with it; it's very possible, but don't feel bad about it not seeming easy - it isn't!

[TheXRuler]

Edit: John FX found the video I was looking for, oh well, I'll still leave this here.

As Deutherius says, maybe you should try landing manually, mechjeb does a rather inefficient landing because it lets you fall toward the surface after killing orbital velocity from far up. On eg. the mun that isn't as much of a problem since the gravity is so much lower that freefalling for ~7km won't completely ruin your descent. On tylo however the gravity is so strong that it will acellerate you very quickly, meaning you will not only have to kill orbital velocity, but also kill your vertical speed from falling the ~7 km.

This is horifically inefficient. You might want to try something a little more tricky but also safer. Get a grazing orbit that takes you down to less than 2 km above the surface. Use the LV-N's to kill most of you orbital velocity. Then land on the triple set.

The way you want to do this is aim fully retrograde, start burning and when you come to within less than 1km of the ground (use KER's radar altitude for this) you start pitching up to slow your vertical descent. When you reach about 45° on the navball you start toggling the poodle on and off to keep from smashing yourself into the surface. Keep your vertical velocity to something like 10-20m/s depending on the terrain (if it starts coming up towards you quickly you should reduce your vertical speed). When you have gotten rid of almost all your orbital speed you should be realy really close to the ground, within say 300m all you need to do is the standard descent (or let mechjeb do this part if you dont feel comfortable [forewarning mechjeb can make bad decisions when landing from a sub orbital trajectory]).

By landing with this profile you will maximize the burn time on your LV-N's which have a much better ISP and you will be making maximum use of the Oberth Effect. Also you will reduce gravity losses to a minimum by not freefalling from 7km

Might still not work, I do not know for sure, but it is definetly more efficient than what mechjeb does.

Edited April 6, 2015 by TheXRuler

[moogoob]

One workaround with Mechjeb (won't help in your situation without refueling but worth noting) is that while its landing autopilot is inefficient, you can trick it into more efficient flight paths. What I do is to do a manual (with maneuver nodes and 'landing prediction' turned on), shallow deorbit from a comfortably low height. Then, click "Land Anywhere" and MJ will take over from there with your new, shallow flight path.

Edited April 6, 2015 by moogoob
"Oh, if you want to be possessive, it's just I T S, but if you want to be a contraction, it's I T apostrophe S. Scalawag."

[Warzouz]

I'm also in a middle of a Jool exploration. I've built 2 lander for Tylo.

The first one is a 15T SSTO with 6000dV and 2 LV-N (no additionnal engines). The TWR is nearly 1.0 fully loaded with fuel. I hope to slow down horizontal velocity THEN (as TWR rise) go to the ground. I hope tyhat will do (and the pilot too)

The second one is a lightweight staged vehicle. 1 tank of fuel and 4 rockamax 48S. The landing stage (with science) stays on ground and the pilot lift off on a "flying chair" pushed by another rockamax 48S. I don't recall the TWR, but it's higher.

Each ship is trucked by a tug at low Tylo orbit. I'll make the attempt soon.

[TheXRuler]

Having a TWR that low is not a bad idea as such, you just need to be a lot more careful to keep you vertical velocity nice and low.

[tseitsei]

Yeah the best you can do with that amount of fuel left is:

1. Burn retrograde with your atomic engines as long as you can keep your descent speed at reasonable level (I would say 150m/s but that's just a guess you'll need to experiment with that.

2. After that ditch the atomics and burn retrograde with the poodle engine and hope you have enough fuel

Experimenting with the starting orbit height and when to ditch the atomic engines can help so try several combinations. I don't know if you still have enough dv to land and am too lazy to calculate it right now...

- - - Updated - - -

EDIT: on another thought maybe you shouldn't ditch atomics but just activate the poodle also and burn with everything. But again I should just do the maths to see which one is better option...

[Warzouz]

Ok, I succeeded with my light weight lander. I started at 40km and followed the retrograde then kill lateral velocity first and keeping vertical under control. At less than 600m, I activated MechJeb for landing (anywhere) because I was a bit overwhelmed. It misses a bit of fuel and hit the ground at nearly 30m/s. The medium landing struts did well. Nothing broken. Hopefully the area was very flat !.

Without fuel the landing ship is 1000kg. The TWR is 2 and it had 3500dv. The escape pod is 300Kg without fuel (with an overkill 9.8 TWR and 2800dv).

I did 10 experiments.

Edited April 8, 2015 by Warzouz

[Yakky]

I'm following all those tips and still can't land.. starting my burn at ~7km altitude.

1- after dropping the 2 atomic engines TWR (surface) gets better. Please see:

http://i.imgur.com/ETIUYRR.png

Hard!!

Even with staged dropping of the LV-N's, your final TWR is still so low that you're going to burn a lot of delta-V just fighting gravity losses during the later stage of your descent. If your TWR is only 1.18, then once your horizontal velocity gets significantly below orbital speed, you end up using 1.00/1.18 = 85% of your delta-V just to fight off gravity. That doesn't leave much for positive control of the spacecraft. It also means that once you're in terminal vertical descent, you can only slow down at 0.18 of a G.

Although I don't know exactly how the MechJeb landing algorithm works, MechJeb is probably crashing because the spacecraft just won't slow down as much as MechJeb needs it to.

This is also why you're running out of fuel even though you theoretically have enough delta-V for a Tylo landing. Even if you use the approach articulated by others here (come in shallow and then slowly transition from horizontal to vertical burn as you lose speed), there is no getting around the fact that it will take you a long time to slow down and you're losing a ton of delta-V to gravity losses along the way.

Edit: see this post for a quantitative look at the delta-V penalty incurred by landing with low TWR.

Your gravity losses are, roughly speaking, proportional to the time spent in powered flight at speeds significantly below orbital velocity. If you have a massively high TWR that can slow you from orbital speed to a dead stop in the final few seconds, you will lose almost nothing to gravity losses. For this reason it may be worth lugging a huge engine to Tylo despite the extra mass.

Edited April 9, 2015 by Yakky

[Warzouz]

This link is very intersting. It seems I did a loosy job when being short of fuel with my 3500dv light lander... hopfully at only few meters of the ground. My ship survived the 30m/s lithobraking.

[-Velocity-]

LV-Ns and Poodles are terrible engines for a lander in a high-gravity environment, with the LV-N being especially bad due to its extremely low TWR. Under high gravity, you need engines with a very high TWR, such as the 48-7S. The 48-7S is by far the best engine to use for Tylo, use a bunch of them unless you're landing something REALLY big, in which case, the KR-2L is better. But very few people are ever going to land something on Tylo so big that the KR-2L is the best engine to use. Just use a big group of 48-7S. 8X 48-7S is a common engine configuration to use for my single stage Tylo lander and ascent vehicles.

Just don't take the wrong lesson from how bad the LV-N is under high gravity. The LV-N is the best lander engine to use for very low gravity bodies, and there's a number of those in KSP. Obviously, the TWR of the LV-N is much higher on low gravity bodies, so that's why it works well there. But it's HORRIBLE on Tylo.

[Warzouz]

I did it with a double LVN. Start from 40000m, reducing horizontal from 2000 to 500m/s while keeping vertical speed under -100m/s then retrograde for a little time. At 6000m, switching to MJ auto landing. It did perfectly.

With little practice this can be fully manually. I burnt 3800m/s but I think I could start lower and keep vertical speed around -300m/s. It would save fuel.

[Deutherius]

I did it with a double LVN. Start from 40000m, reducing horizontal from 2000 to 500m/s while keeping vertical speed under -100m/s then retrograde for a little time. At 6000m, switching to MJ auto landing. It did perfectly.

With little practice this can be fully manually. I burnt 3800m/s but I think I could start lower and keep vertical speed around -300m/s. It would save fuel.

You could (and should) probably start a lot lower, depending on your TWR (and therefore the time it takes to kill the horizontal velocity). Best case scenario (which is hard to get, but oh so satisfying when you do) is to finish killing horizontal velocity just as you are about to land (a few tens of meters above ground max). I only managed a landing like that once, but it was the best.