The biggest challenge is returning crew from the surfaces of Eve & Tylo. Help and advice, please?

[Jouni]

So Tylo is easy to make a lander for, but difficult to fly it, actually. You have to time your deorbit burns just right. But that's what quicksave and quickload are for, right?

Precise timing is only needed, if you want to make the landing artificially difficult by trying to be efficient. Build a lander with 6 km/s or even 6.5 km/s of delta-v, and everything becomes much easier. The final moments before the touchdown are the hardest part, as you have to know how to handle the lander.

EVE, OTOH is far more difficult. You need like 11,500+ delta-V to make it to orbit from sea level, AND a TWR of around 2 for all the lower stages- and that's an EVE TWR of 2, so like 32, 33 m/s acceleration.

Eve TWR 2 sounds inefficient, because those engines are heavy.

Let's say that the first 30 km of the ascent take 200 seconds at terminal velocity (the figure should be roughly correct). With an average TWR of 1.6, you can already reach over 75% of terminal velocity, so the first 30 km will take around a minute longer. At terminal velocity, gravity and drag losses would be almost 6.7 km/s, while the lander ascending at 75% of terminal velocity would lose a bit over 7.1 km/s, or less than 500 m/s more. In the remaining part of an optimal ascent, the total losses will be less than 1.5 km/s, so a lander with average TWR 1.6 should only require 500-600 m/s more than an optimal lander.

An Eve lander is essentially a huge pile of engines and fuel tanks carrying a negligible around of payload. If you launch with Eve TWR 1.5 (which should make the average TWR 1.6, if you use asparagus staging), 21.5% of lander mass must be engines. Raising the initial TWR to 2 increases the engine fraction to 28.6%. Add 1.5% for payload, structural parts, and upper stage engines, and 1/9 of the rest for fuel tank dry mass, and we're talking about mass ratios 3.17 vs. 2.64. That's a major difference in delta-v.

[-Velocity-]

Precise timing is only needed, if you want to make the landing artificially difficult by trying to be efficient. Build a lander with 6 km/s or even 6.5 km/s of delta-v, and everything becomes much easier. The final moments before the touchdown are the hardest part, as you have to know how to handle the lander.

Well, when you make your Tylo lander a single stage design that can be refueled and reused many times on the same mission, it becomes much more difficult to exceed 6000 m/s dV and still carry a science payload. Oh it's possible, but you have to make the craft really big to squeeze out that last few hundred m/s.

Now, if you make your lander single-use, it's different.

Eve TWR 2 sounds inefficient, because those engines are heavy.

Let's say that the first 30 km of the ascent take 200 seconds at terminal velocity (the figure should be roughly correct). With an average TWR of 1.6, you can already reach over 75% of terminal velocity, so the first 30 km will take around a minute longer. At terminal velocity, gravity and drag losses would be almost 6.7 km/s, while the lander ascending at 75% of terminal velocity would lose a bit over 7.1 km/s, or less than 500 m/s more. In the remaining part of an optimal ascent, the total losses will be less than 1.5 km/s, so a lander with average TWR 1.6 should only require 500-600 m/s more than an optimal lander.

An Eve lander is essentially a huge pile of engines and fuel tanks carrying a negligible around of payload. If you launch with Eve TWR 1.5 (which should make the average TWR 1.6, if you use asparagus staging), 21.5% of lander mass must be engines. Raising the initial TWR to 2 increases the engine fraction to 28.6%. Add 1.5% for payload, structural parts, and upper stage engines, and 1/9 of the rest for fuel tank dry mass, and we're talking about mass ratios 3.17 vs. 2.64. That's a major difference in delta-v.

Thanks for the tip! You've got a good point, those aerospike engines are heavy. And you know what, I'm violating my own design rules for Kerbin launches. I always make my Kerbin launchers have a starting TWR of like 1.6 or 1.7, precisely to minimize engine mass. I haven't done the math to validate this though, but it seems logical.

So you think maybe I should rework my Eve lander I posted above? It would be fairly easy to modify it into a TWR of like 1.6 and increase the dV by what- 500 m/s? Even if you're right (and I think you are), I really don't think there would be any need though to modify the upper asparagus stacking though, because 48-7S engines have such a ridiculously high TWR.

- - - Updated - - -

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(quote this post to see how I did it if this isn't clear)

Thank you so much! I'll immediately fix my posts above so that people only have to see my screenshot spam if they click the spoilers!

[Jouni]

Well, when you make your Tylo lander a single stage design that can be refueled and reused many times on the same mission, it becomes much more difficult to exceed 6000 m/s dV and still carry a science payload. Oh it's possible, but you have to make the craft really big to squeeze out that last few hundred m/s.

It's still like saying that landing on the Mun is hard, because ion-powered landers with a decent payload have a low TWR. (Landing on the Mun with ions is similar to landing on Tylo with nukes.) Landing on Tylo is mostly a fast-paced piloting exercise, unless you deliberately choose to make it harder.

So you think maybe I should rework my Eve lander I posted above? It would be fairly easy to modify it into a TWR of like 1.6 and increase the dV by what- 500 m/s? Even if you're right (and I think you are), I really don't think there would be any need though to modify the upper asparagus stacking though, because 48-7S engines have such a ridiculously high TWR.

I've only done one successful Eve ascent mission. My lander had around 11.8 km/s of delta-v (an approximation based on mixed atmospheric/vacuum Isp) with initial TWR 1.5. Once all layers of boosters were gone, the TWR dropped below 1.2, and the lander actually slowed down for a while. I landed at around 2100 m and reached orbit with over 1 km/s remaining. The wiki says that it takes over 10 km/s to reach orbit from 2 km, so I couldn't have wasted more than 800 m/s.

[Renegrade]

It's still like saying that landing on the Mun is hard, because ion-powered landers with a decent payload have a low TWR. (Landing on the Mun with ions is similar to landing on Tylo with nukes.)

Yes, yes it is. Might not be a bad way of practicing too (although I still like just flying around the launchpad, there are some aspects of high gravity worlds that can't be simulated, such as the faster drop and the limitations of the throttle setting for keyboard users).

[Laie]

Eve TWR 2 sounds inefficient, because those engines are heavy.

Let's say that the first 30 km of the ascent take 200 seconds at terminal velocity

Time to go from sea level to 20km:

TWR=2    190 seconds
TWR=1.8  210
TWR=1.6  240
TWR=1.4  290

For the first 20km, dV is pretty much meaningless. Better to look at your TWR and add up the burn times of your stages. From 20km onward, 5500m/s will do. But by all means provide TWR>1.5 until almost to the very end.

@Velocity: your lander might be good for a takeoff from 4000-5000m altitude, but that last stage's low TWR bothers me. It will probably stall at 60km, pointing almost straight up just to maintain a positive climb rate. If it works at all, it will require a very refined ascent profile (that is, many attempts until you get it right).

For the very first stage, I like to have a higher TWR. It gets me up to speed quickly, while the following stages only have to maintain it. For the sake of part count, one may consider to drive the first stages with mainsails, quad clusters or even LFBs. The overall mass increase isn't that bad, and one mainsail equals eight aerospikes. Factor in decouplers and struts, and you have a 1:20 decrease in part count.

I've grown quite fond of LFBs, actually. I barely run them, most of the fuel is burnt in other engines during transfer. But they make sturdy landing gear, and briefly provide high TWR at liftoff.

Edited February 24, 2015 by Laie

[-Velocity-]

@Velocity: your lander might be good for a takeoff from 4000-5000m altitude, but that last stage's low TWR bothers me. It will probably stall at 60km, pointing almost straight up just to maintain a positive climb rate. If it works at all, it will require a very refined ascent profile (that is, many attempts until you get it right).

Wrong, it does not "stall", and it has a reasonable surplus of delta-V when it reaches orbit even when launched from sea level, in fact. As I said before, a previous version that was almost identical to this one flew successfully with a huge margin for error from about 50 meters ASL from Eve's surface in 0.24. And when I say "almost identical", I am not exaggerating. TWRs, engines, fuel tank sizes, were all identical. The only difference was that the final payload to orbit was slightly more in the older version, so this version actually performs better. So you're wrong, unless you're accusing me of lying. If I remember correctly, the previous version of this craft, launched from sea level, put me into something like a 600 km X 600 km orbit around Eve. I think that number is correct, but even if not, I do remember that I had a rather large margin for "error", and reaching orbit was rather easy. And again, I launched it from sea level.

While you are vastly overestimating the problem of the starting TWR of the last stage, you are correct in that it's lower than I'd like. I'd really like it to be about 1.2, but I can't add fractional numbers of 48-7S engines, I have to chose 1 or 2, and if I go with 2, it's vast overkill and hugely decreases my delta-V.

The reason you're wrong is because by the time that the time the last stage kicks in, the craft is into the gravity turn- even when launched from sea level. This means that the need for high TWR is already mostly removed, because you're mostly above the atmosphere, and the craft is mostly thrusting perpendicular to gravity.

Anyway, if I remember correctly, the only effect of the low TWR is that at the beginning of the final stage's burn, I have to keep the craft's nose maybe 25 or 35 degrees higher than I'd otherwise like to have it- so maybe the "efficiency" is decreased to 80% of normal. It's no big deal because that problem rapidly goes away as fuel is burned anyway.

Edited February 24, 2015 by |Velocity|

[Laie]

unless you're accusing me of lying.

Holster them guns, cowboy!

I was looking at the screenshot where TWRs are given relative to Kerbin, and translated that (wrongly) to about 1.8 on Eve.

[-Velocity-]

Holster them guns, cowboy!

I was looking at the screenshot where TWRs are given relative to Kerbin, and translated that (wrongly) to about 1.8 on Eve.

Ok good, I hate fighting. The final stage's starting TWR on Eve is 0.93 according to Mechjeb, but it's actually going be like 0.9 when carrying two Kerbals. As I said, you were correct in pointing out this as a flaw, you were just incorrect in the severity. I'd like to think of ways to fix it, but the craft works well enough that it might not really be worth my time. Didn't the Space Shuttle also have a point in its flight were the TWR was lower than they would have liked (right after jettisoning the SRBs, maybe?) And sometimes the benefits of carrying less engine mass can outweigh the negative effects of having a lower TWR than you'd really like, as Jouni points out too.

[Scorptrio]

Your favorite search engine should have helped you.

There's the Eve Rocks Challenge; only very few video submissions, but mostly very detailed picture galleries, and many have provided their craft files for download.

I've examined most of the videos and screenshots from those who have completed the "Eve Rocks Challenge" and none that I have seen meet the criteria of

my original scenario. To wit:

"I haven't been able to find any videos of anyone who has landed on the surface of Eve, planted a flag, and returned the crew to Eve orbit in the *stock* game. I've seen people use mods that make it easier, outright cheat, or use over powered sci-fi type parts, but never in the *stock* game. ‣ A video of someone in a recent version of KSP, using stock parts and *no flight consequential mods,* showing a mission that plants a flag on Eve or Tylo, and returns to orbit."

All the Eve Rocks Challenge finishers that I've examined, rely heavily on flight consequential mods to essentially fly the craft (play the game) for them. If there are examples of an Eve surface (plant flag) return with no trainer mods and no aim-bot mods, I've still yet to see it, despite use of my favorite search engine.

Thanks for all the advice on Tylo, I'm still working with a fully stock game to complete this for both destinations, but I've learned a lot from the postings on this thread, especially that smaller can be a lot better than bigger. Thanks again.

[Scorptrio]

Velocity and Jouni, thank you very much, those are some great posts with a lot of good information and examples. It's much appreciated.

[Mister Dilsby]

All the Eve Rocks Challenge finishers that I've examined, rely heavily on flight consequential mods to essentially fly the craft (play the game) for them. If there are examples of an Eve surface (plant flag) return with no trainer mods and no aim-bot mods, I've still yet to see it, despite use of my favorite search engine.

You must have missed mine then 100% stock and no helper mods other than Kerbal Engineer which does no piloting. Sorry there was no video, but you should be able to get a pretty good idea how I did it from the screenshots. Really there is nothing happening between frames of the ascent shots other than the ship flying in a parabolic line from point N to point N+1.

[Red Iron Crown]

If there are examples of an Eve surface (plant flag) return with no trainer mods and no aim-bot mods, I've still yet to see it, despite use of my favorite search engine.

Here is one.

[MarvinKitFox]

If a Mun landing and return is a 1 on the scale, and Duna is a 2

Then Tylo is about 5

And eve is about 732

[Scorptrio]

Thanks guys, and well done. I've finally been able to see how someone planted a flag on Eve and came back, without using cheating mods. I really like your vehicle configurations, Kuzzter, they look slick.