dv for Tylo and Laythe lander.

[SSSPutnik]

I've built a lander for heading out to Jool for the first time.

Its a one kerbal lander can, fuel, docking port etc and 2 aerospike engines.

It can dock to the orbiter for refueling. Also a couple of parachutes which may come in handy.

Deltav stat is about 5300.

Is this enough to land and get back to orbit for Tylo and Laythe?

Edited November 28, 2013 by SSSPutnik

[Monkeh]

Add parachutes and it should be fine for landing and leaving Laythe. Landing on Tylo is a different matter that requires much more delta v. A good, efficient landing and you might well have enough.

Good luck.

[Commissioner Tadpole]

Is your dV stat from launch or from LKO? If the former, it won't even get to the Mun.

[SSSPutnik]

Its a lander only. I'll launch it to Kerbin orbit and dock to main craft to take it out to Jool. It has parachutes.

(In fact I am taking two with me so I have a spare in case of an uncontained crew event.).

Edited November 28, 2013 by SSSPutnik

[Commissioner Tadpole]

Oh. Alright. And, as Monkeh said, parachutes are indeed helpful in planets with atmospheres(namely Eve, Kerbin, Duna, Jool and Laythe), though on Tylo you'll need a lander that's able to counteract it's gravity and not run out of fuel while doing so, due to it's lack of atmosphere.

I recommend testing such a lander on Kerbin, due to their similar gravities(though Kerbin's gravity is slightly stronger than Tylo's and you have drag to take account on). A lander that can counteract Kerbin's gravity is a lander that can counteract Tylo's gravity(I think. Don't rely too much on this tip, so try using unmanned rockets to test this theory to prevent loss of Kerbals)

[SSSPutnik]

If it boosts straight up on Kerbin, dry tank max altitude is 120km.

Testing landing trickier due to atmosphere

I need to strut the chutes, at the moment they rip off when they fully deploy.

[SSSPutnik]

Pic.

https://moc-per.micromine.com/owncloud/public.php?service=files&t=987f9a3829e0af0d9773ef6ef41a588d

[Kasuha]

I don't recognize the part below the command pod but even if i assume it's full of fuel it still doesn't seem strong enough for Tylo. But I may be wrong. If you can get it to Kerbin orbit with third of its fuel then it might suffice.

Regarding chutes, put drogues on those struts and normal radial chutes on the tank. That will ensure much smoother landing. And no additional struts needed.

I'd suggest reducing the monopropellant by half.

[SSSPutnik]

I always run out of mono so 4 makes me secure. What bit below command pod? The big tank or ? Its a KW rocketry liquid fuel.

Drogues a good idea, but scared to add any more weight. I've tested the chutes on kerbin and they work after strutting them.

[kahlzun]

The dirt on Tylo:

Local gravity is 0.7 Kerbin, so you'll need to be higher than that to land safely.

The higher the TWR, the less you need, but it will take about 3000ms dV to land safely, and about the same to regain orbit.

Interestingly, if you put a parachute on the lander, you will have a craft that will land on any body in the game. Tylo is officially the hardest to land safely on.

[Umlüx]

4,4k dV wont be enough to land and take off from tylo again. last try i failed with 6k... now aiming for 7k

thrust seems good enough and will get higher the more fuel you burn.

[Kasuha]

I always run out of mono so 4 makes me secure.

I didn't put RCS on my Tylo lander at all. It is not necessary for landing and in orbit it's better to have small RCS tug mounted on the mothership. Less weight to carry down and back up again.

[Nao]

In theory with your TWR and perfect landing from very low Tylo orbit it could take ~2500m/s to land, then another 2400m/s for ascent.

So you do need more dV, and as Umlüx mentions, 6000m/s might be not enough when if you include reasonable starting orbit and landing corrections.

Also you could decouple the parachutes to save weight, if you land at Laythe first.

[SSSPutnik]

Yeah was thinking of doing Laythe first. Easy enough to add decouplers for chutes.

6000dv would mean a major redesign.

If I cheat and use mechjeb and drop off at lowest orbit was hoping to make it.

Guess there is one way to test....

[SSSPutnik]

I didn't put RCS on my Tylo lander at all. It is not necessary for landing and in orbit it's better to have small RCS tug mounted on the mothership. Less weight to carry down and back up again.

Good idea, I have room for a tug.

[numerobis]

Easy enough to add decouplers for chutes.

Then you don't have chutes when you get home to Kerbin. Also, chutes are fairly light, so you'd better have a lot of deltaV afterwards to make up for carrying the decouplers all the way to Laythe. Finally, I'd recommend wings over parachutes; makes it easier to land on land at Laythe, rather than taking a drink.

[Geschosskopf]

Landing on Tylo takes about 3100m/s, but pack 3500 just in case. Taking off again is a bit easier because it's airless so you can go horizontal as soon as you leave the ground, provided no mountains are downrange. If you're on high ground at or near the equator, you can get back to a very low orbit (10-15km) with about 2800m/s, so have 3000 or more just to be safe, more if you're not on the equator, not on high ground, or want a higher orbit.

TWR is very interesting. You'll have to burn pretty hard nearly all the way down. This means your ship loses a large fraction of its mass during descent, so your TWR will increase fairly significantly the lower you go. It's therefore possible to start with a 1.0 TWR and still land safely, relying on the TWR increasing.

HOWEVER, the single most critical thing about Tylo is the flight profile. Because Tylo landers need so much fuel, they usually don't have a TWR in the 1.5 range or so. This is NOT anywhere near enough for a stop-and-drop landing starting from a low orbit. The gravity will pull you into the ground LONG before you kill off your ~3000m/s horizontal speed. Thus, you need to start from high altitude and expect to burn almost all the way down, so you can keep your vertical velocity under control while you kill off your horizontal velocity. But this also allows time for your TWR to increase. Thus, I've found that if your original TWR is in the 1.0 to 1.5 range, you need to start landing from 175-200km altitude. But when taking off again, you only need 20-50km to allow some leeway above the mountains during the ensuing rendezvous to pick up the crew or refuel what's left of the lander.

Landing on Laythe is like landing on Kerbin--get in the atmosphere, slow down that way, and pop chutes. 50m/s and sufficient chutes is all you need. The only real trick there is that the only places to land are tiny islands so you have to be fairly good at landing within 1-2km at most of where you target. Taking off again requires about 3/4 the delta-V that the same payload would need at Kerbin.

[Kasuha]

HOWEVER, the single most critical thing about Tylo is the flight profile. Because Tylo landers need so much fuel, they usually don't have a TWR in the 1.5 range or so. This is NOT anywhere near enough for a stop-and-drop landing starting from a low orbit. The gravity will pull you into the ground LONG before you kill off your ~3000m/s horizontal speed. Thus, you need to start from high altitude and expect to burn almost all the way down, so you can keep your vertical velocity under control while you kill off your horizontal velocity. But this also allows time for your TWR to increase. Thus, I've found that if your original TWR is in the 1.0 to 1.5 range, you need to start landing from 175-200km altitude. But when taking off again, you only need 20-50km to allow some leeway above the mountains during the ensuing rendezvous to pick up the crew or refuel what's left of the lander.

That looks like potentially quite inefficient landing. I agree that suicide burn is about the most efficient landing, but setting it up so you just end it on the surface is very tricky - you have 50% chance you'll end too high above terrain and 50% chance you'll crash. If you get a safe margin, you always end too high.

The most effective landing I found for Tylo starts by lowering your periapsis to about 10 km. Then you start burning retrograde at that periapsis and as your height starts to decrease you change your pitch a bit and burn slightly above retrograde to keep your vertical speed low. From orbital view it looks like you're pulling apoapsis behind your ship. This way you can manage to kill your horizontal velocity while at low altitude above terrain. The thrust you spend on killing your vertical speed is negligible most of the time.

[Kerolyov]

The landing described by Kasuha is the way I do it, while it is possible to land with 3000dv (or even less) its best to pack at least 3300dv as any slight mistake would otherwise result in a failure (ie crash) by running out of fuel.

Here is a video by Kosmo-not on the landing method

For Tylo I'd set a periapsis of around 5-6km and check in map view you don't clip into the surface, then start burning retrograde at the periapsis, as you vertical speed starts to increase then pitch up to keep it under control (around -10m/s). Then keep doing that until your horizontal velocity is almost zero (so you're retrograde marker is near centre of blue part of navball) and then gently descend burning retrograde.

Once you have the technique sorted then you can start to play with it to improve efficiency.

Edited October 25, 2014 by Kerolyov

[Nao]

That looks like potentially quite inefficient landing. I agree that suicide burn is about the most efficient landing, but setting it up so you just end it on the surface is very tricky - you have 50% chance you'll end too high above terrain and 50% chance you'll crash. If you get a safe margin, you always end too high.

Has somebody actually tested the claim that suicide burn is more efficient? I don't have any numbers on it right now, but i'm pretty sure that standard low orbit retrograde burn would be more efficient for landers with TWR below ~5 TWR.

[Dun Kirk]

yerh laythe and tylo are tricky to land on... 5x the mun's gravity (kerbin is 6x).

[Geschosskopf]

That looks like potentially quite inefficient landing. I agree that suicide burn is about the most efficient landing, but setting it up so you just end it on the surface is very tricky - you have 50% chance you'll end too high above terrain and 50% chance you'll crash. If you get a safe margin, you always end too high.

I'm not claiming efficiency. In my example, the lander has sufficient delta-V but its TWR is closer to 1 than 2, which is fairly typical even after a lot of work. The closer your TWR is to 1, the higher you need to start your descent to have sufficient vertical room to kill off your horizontal speed before you run out of altitude. Killing 2000-3000m/s horizontal speed takes a long time with such a TWR, and you'll be gaining vertical velocity from gravity from the get-go. Because your TWR isn't huge, you can't afford to let your vertical speed get too big because you've got a long "stopping distance".

The most effective landing I found for Tylo starts by lowering your periapsis to about 10 km. Then you start burning retrograde at that periapsis and as your height starts to decrease you change your pitch a bit and burn slightly above retrograde to keep your vertical speed low. From orbital view it looks like you're pulling apoapsis behind your ship. This way you can manage to kill your horizontal velocity while at low altitude above terrain. The thrust you spend on killing your vertical speed is negligible most of the time.

I don't really find this more efficient. It costs about 3100m/s to land on Tylo no matter how you slice it. The lower you are, the more horizontal speed you have to kill off. The higher you are, the more you fight gravity all the way down. But it ends up more or less a wash in practice. I find it easier to land at or near a specific spot starting higher, but you've got a long time to worry about whether you're keeping your vertical speed under control. Starting low with an upwards vertical velocity takes away some of the anxiety about vertical speed but I find I have little if any control over where exactly I land.

[Kasuha]

The closer your TWR is to 1, the higher you need to start your descent

This kind of landing is possible even if you start with TWR less than 1. Of course it assumes your TWR will grow over 1 as you burn fuel, otherwise you'd crash.

Killing 2000-3000m/s horizontal speed takes a long time with such a TWR, and you'll be gaining vertical velocity from gravity from the get-go.

Not if you fight it. Trigonometric functions play in your favor - if your ship is inclined by 5 degrees, 99% of your thrust still goes to kill horizontal velocity, while 10% of your thrust already goes to kill gravity pull.

I don't really find this more efficient.

I also thought that. I had an argument with Kosmo-not about it and we eneded up in a kind of contest who can land a ship more effectively. Whatever I did, my most effective suicide burn (which ended literally a few meters above ground) ended a few units of fuel worse than his landing. And the most important part on it is that while you need either a lot of luck or a lot of retries for effective suicide burn, you can pull this "horizontal" landing almost anytime.

After all, they used the same landing approach for lunar modules, too. (check Braking Phase chapter on page 13 and Appendix on page 28).

Edited November 29, 2013 by Kasuha

[Geschosskopf]

I also thought that. I had an argument with Kosmo-not about it and we eneded up in a kind of contest who can land a ship more effectively. Whatever I did, my most effective suicide burn (which ended literally a few meters above ground) ended a few units of fuel worse than his landing. And the most important part on it is that while you need either a lot of luck or a lot of retries for effective suicide burn, you can pull this "horizontal" landing almost anytime.

After all, they used the same landing approach for lunar modules, too. (check Braking Phase chapter on page 13 and Appendix on page 28).

Geez, now I've got a lot of reading to do--I haven't read that paper yet. Thanks for the info. Still, "a few units of fuel", while technically more efficient, doesn't seem like a significant difference given the huge amount you need at Tylo anyway.

Designing Tylo landers is sort of a hobby of mine. I keep making new ones, HyperEditing them out there, and seeing how they work. With each new design, the testing process is to start from an orbit just above the mountains and see what happens. If it goes splat, I raise the orbit a bit and try again, repeat, until I can get it down safely. I have yet to succeed in landing from any starting altitude less than 175km and 200km seems to be the "sweet spot" for most designs.

However, this has always been from a circular orbit. I've never considered starting from the Pe of an eccentric orbit but now that I am, it seems to me this would require very careful planning to get any benefit. The greater your eccentricity, the faster you're going at Pe compared to a circular orbit at that altitude, so the more horizontal speed you have to kill off and the more fuel that requires. Thus, any benefit over a circular orbit must come in the vertical direction which would seem to be a function of eccentricity because that determines your trajectory's upwards angle after Pe. So it seems to me you'd have to calculate the ideal eccentricity and the orbit's Ap and Pe for the given planet and the thrust/fuel characteristics of the specific ship you're flying.

[Nao]

This kind of landing is possible even if you start with TWR less than 1. Of course it assumes your TWR will grow over 1 as you burn fuel, otherwise you'd crash.

Not if you fight it. Trigonometric functions play in your favor - if your ship is inclined by 5 degrees, 99% of your thrust still goes to kill horizontal velocity, while 10% of your thrust already goes to kill gravity pull.

I also thought that. I had an argument with Kosmo-not about it and we eneded up in a kind of contest who can land a ship more effectively. Whatever I did, my most effective suicide burn (which ended literally a few meters above ground) ended a few units of fuel worse than his landing. And the most important part on it is that while you need either a lot of luck or a lot of retries for effective suicide burn, you can pull this "horizontal" landing almost anytime.

After all, they used the same landing approach for lunar modules, too. (check Braking Phase chapter on page 13 and Appendix on page 28).

Agreed. Tavert has done charts for landing on Tylo for different engines and the lowest mass (best mass efficiency) for one of them (LV-N i think) was at starting TWR of ~0,9 or less.

Is the argument about suicide burn you had with Kosmo-not documented in posts here somewhere? I would like to have a look at it if possible.