Erm... I decided to test launch an under-development Eve lander, and Kraken decided my kerbals could not stay on kerbin

[TanDeeJay]

(Mod list: KER, KAC, DPAI, Dock Rotate, Transfer Window Planner)

I have been developing a ship capable of flying to Eve, landing, taking off and then returning safely to Kerbin.

So I've been working backwards, and started with the "return to kerbin" module which is a small craft with a Nerv engine and enough seating for 7 kerbals and enough DV for a good transfer window (determined by Transfer Window Planner) (un-tested - assuming I have enough DV based on Transfer Window Planner).

Next I have been working on the ship that can land on Eve, and then take off again and dock with the return craft.  This one I have been doing extensive testing by using the set orbit cheat.

Now, it is not quite there, and last night I was going to do another test, but by the time I got to the computer, I figured I didn't have enough time to do a full Eve landing test, so thought "what the heck, I'll just launch it from kerbin"

Well...that didn't go too well, after several failed launches where I returned to the VAB to add more struts, and update the auto strut, I go to launch .

As I have configured the staging for the Eve landing and launcing, the Mammoth engines are not staged for a kerbin launch so I had to manually activate the mammoth engines, then activate SAS, and then increase the throttle to about 50%

well, again the ship breaks up, but this time I watch what happens to the grizzily conclusion, but then things started going strange.  so tonight I tried again and videoed it... the really interesting things start to occur around 2:41.  Ths reminds me of some videos I've seen of early versions of KSP

 

[VoidSquid]

I've had exactly the same with my heavy Eve lander of 5800 tons start mass, gave up after almost a week of tweaking. Well the smaller lander for two Kerbals does the job anyway.  

[TanDeeJay]

It got big trying to get enough DV for eve liftoff. Only 3 kerbals can go down. I initially started off landing with empty tanks and taking some mining equipment to fill the tanks, but then found I didn't have enough dv to get to orbit, so changed to this design where I carry all my fuel down. How do you make a smaller eve lander? 

Edited January 12, 2021 by TanDeeJay
Typo

[VoidSquid]

I'm using a mod pod, 1.25 m, 2 Kerbals. 

Vessel can bring those 2 Kerbals from Kerbin launch pad to Eve and back to low Eve orbit (where they will be picked up by a taxi).

Built in 1.7.3, updated in 1.10.1. 3126 tons start mass.

Let me know if you're interested in more details, don't want to bother you now with my "oh-so-great-construction" (it isn't, but it does the job)  

[TanDeeJay]

Actually I would be interested. If my behemoth with only the Eve lander invites kracken to the launch, whats going to happen once I start trying to launch it for real? My son suggested I might need to break it up and launch in bits and put it together in orbit. 

[VoidSquid]

The Eve lander uses several mod parts from:

Don't know if you're fine with this, I uploaded the craft file here:

https://easyupload.io/i6pac9

I also found this tutorial pretty good, used a couple of ideas from this:

 

[TanDeeJay]

Thanks. Will have a look tonight.

[king of nowhere]

your launch vehicle looks a lot like mine, and mine did work well enough (though it was suffering from some aerodinamic instability from the last stage)

the difference in launch vehicles make me think that the problem in your case could be the use of overly long trusses. short trusses hold weight magnifically, but make them too long and they collapse easily. your thermal shields don't need to be hundreds of meters above the vehicle.

also, for kerbin i used a launch vehicle with low twr, to minimize turbulence.

 

then again, your case was clealry a kraken, with speed suddenly shooting up. but it's likely a kraken started by some mechanical failure

 

[TanDeeJay]

F3 showed that the first failure was when the connection between two of the girders failed. I had the top heat shields so high because I kept having stability issues while enterimg Eve's atmosphere.

I like your idea with the stability fins. I had the top heats hields so high due to stability issues. Your way would mean no need to put the top heatshields so high. I also had problems when jettisoning the lower heatshields, they'd always destroy something critical if I got rid of them before the parachutes had fully deployed, and then if I jettisoned them after the descent speed had dropped below 10m/s they would often fall straight down and end up getting in the way of landing, so I had to add 12 sepratrons for each heatshield to get them out of the way.

And how did you get away with so few parachutes? Mine kept getting destroyed by aerodynamic forces until I added a whole bunch of drogue chutes as well.

What I've got works for landing on Eve, but I've yet to prove it can then get back into orbit.... 

[VoidSquid]

17 minutes ago, TanDeeJay said:

I had the top heats hields so high due to stability issues

Regarding the 10 m heat shields, this my little cheap trick for the landing part during the atmospheric decent

No need for any fins  

[TanDeeJay]

Better still. My original design I needed 3 kerbals because I was taking down a bunch of mining gear to fill the tanks. Wanted pilot, engineer to increase efficiency of mining and scientist to reset some science, was even trying to get the engineer to build a rover but found parts were too heavy to use. Didnt think to cut down on the number of kerbals after I abandoned the miming idea.

Edited January 14, 2021 by TanDeeJay

[king of nowhere]

3 hours ago, TanDeeJay said:

F3 showed that the first failure was when the connection between two of the girders failed. I had the top heat shields so high because I kept having stability issues while enterimg Eve's atmosphere.

I like your idea with the stability fins. I had the top heats hields so high due to stability issues.

Stability fins made for a smooth descent. Be wary, though, that they are horrible when launching from kerbin. I had a lot of stability issues there. so much, in fact, that if i were to do it again i would launch those top fins as a separate craft, in a payload fairing, and dock them to the main lander.

anyway, once you are at eve, they definitely beat a dozen trusses. though in some cases the lander would still flip.

Quote

Your way would mean no need to put the top heatshields so high. I also had problems when jettisoning the lower heatshields, they'd always destroy something critical if I got rid of them before the parachutes had fully deployed, and then if I jettisoned them after the descent speed had dropped below 10m/s they would often fall straight down and end up getting in the way of landing, so I had to add 12 sepratrons for each heatshield to get them out of the way. And how did you get away with so few parachutes? Mine kept getting destroyed by aerodynamic forces until I added a whole bunch of drogue chutes as well.

the problem is not the heat shields, the problem is eve. I found entering jool at 6 km/s and reaching low atmosphere is easier than landing on eve. Anyway, through trial and error (meaning, lots of reloads) I devised a sequence working for my craft:

- enter eve orbit with rockets, intercept speed is too high

- with a periapsis of 75 km, gradually aerobrake until you are in a low orbit(this bleeds 1300 m/s of extra speed)

- final atmosphere reentry. hold still until the part with the flames has finished. when reaching 50 km altitude, deactivate time warp (in time warp, the lander flips). Do NOT activate chutes, as they would deploy too early and then get destroied

- the atmosphere will be enough to slow you to less than 200 m/s. when your speed starts to stabilize, only then get rid of the upper heat shields and deploy the chutes (i moved those commands in the same stage)

- set the parabrakes to deploy at 5000 m of altitude, to have plenty of time to slow. actually i set 4 of them to deploy at 5000 and the rest to deploy in sequence a bit later, to make deceleration less brutal

- set the main parachutes to deploy at 3000 m

- after speed stabilizes to around 20 m/s, only then can i get rid of the lower thermal shields. and dropping them from this high means they disperse far from the landing site. But that's not required (see later)

- at this point, i'm falling at 20 m/s. when I am close to the ground (less than 100 meters), i activate the engines to slow down to a safe landing. this only takes a tiny bit of deltaV. the vehicle reaches orbit with over 500 m/s left, there's plenty spare.

 

however, i later found out i did not need to actually drop the lower heat shields. Instead, falling at 20 m/s, I could simply let myself fall, the shields would hit first and explode, but they would slow me down and protect the rest of the ship. and the mammoths have excellent impact resistance anyway. So, the last 20 m/s i actually lithobrake, and it works.

 

I made a couple mistakes in that lander, though. First, i attached the chutes to the main body; i should have put them on a separate staging with the shields, so i could jettison them before reentry too. Second, my last stage, the one actually reaching orbit, is overengineered. that's because i use it to land on laythe too, but it would have been better to make another ship entirely; as it is, it is too draggy and too heavy. i could get away with a smaller rocket if i had used a smaller thing with a terrier engine. So, I have stability issues going up.

Most important, though, I made a classic model with lateral boosters, and that turned out to be a problem; upon first stage separation, the wind pushed at least one of the boosters against the main body, destroying the ship. If I had to make it again, i would have a first stage detach entirely from the bottom, to avoid the problem. as it was, i learned to shut down the first stage engine, decelerate to 100 m/s, and only then detach the boosters. and wait until they separate and go their own way before turning on the engine again. this, of course, is inefficient, but luckily i packed extra deltaV.

the first stage goes up straight, at a speed of 250 m/s (above that, it's flipping time and horrible death). the second stage accelerates to 7-800 m/s (it could go faster, but drag heating would then destroy the last stage. I really hate eve) and to 50-60 km of altitude. It also starts turning after crossing 15 km altitude. the last stage is now in a barely suborbital trajectory, but it has 3500 m/s of vacuum deltaV, enough to circularize with some spare.

 

All in all, it was a grueling ordeal, and i exploded dozens of times before finding the correct sequence of actions to avoid all the horrible deaths. so, don't worry if it happens to you too.

Edited January 15, 2021 by king of nowhere

[TanDeeJay]

On 1/15/2021 at 10:06 AM, king of nowhere said:

All in all, it was a grueling ordeal, and i exploded dozens of times before finding the correct sequence of actions to avoid all the horrible deaths. so, don't worry if it happens to you too.

Oh yeah! already had lots of explody test failures   My ship that invites kraken to a kerbin launch has some special order of action required for entry...   As it was the landing component of an eve mission I was testing, I was starting by setting orbit to 110k Eve orbit... (getting to eve would have been the next level of designing after proving I could take off...)  so once in orbit, I would first decouple from the 'return to kerbin' stage, use a small amount of RCS to move the 'return to kerbin' stage out from amongst all the struts, girders and heat shields, then rotate the lander to retrograde, and fire the poodle to lower the PE to 72500m.  this would burn a bit over half the DV in the deorbit stage.  then decouple the poodle stage, and activate the parachute stage.  next, deploy the heat shields with action group 1.   then wait....  (safe to warp until altitude is 95k, then you have enough time for the SAS to re-orient to retrograde), then wait... everything starts to heat up....  altitude will continue to drop as the heatshields get hotter... around 35k,  one of the mamoths starts to display a heat bar, but that only displays for a few seconds, as by this time, speed is starting to drop significantly, continue to wait until the drogue chutes deploy.  at this point activate action group2 to decouple the top heat shields.  (Do not wait until horizontal movement has been eliminated, as the heatshields will come crashing back through the ship with destructive force when the chutes open and slow the ship right down... discovered this one the hard way... for some reason, after decoupling the upper heat shields when horizontal velocity is eliminated, the heat shields continue to fall in a very stable formation, so that when the main ship slows right down, they return with avengeance...)  Now it is just a waiting game... the main chutes will deploy at about 5000m.  Continue to wait... the drogue chutes will then fully deploy at 2500m, and then the main chutes at 1000m at which time speed will drop to around 6.5m/s now it is safe to activate action group 3 which will decouple the lower heatshields, and the structural members holding them in place, and they will fall straight down.  you can watch them fall and they should all explode to non-existance when they hit the ground... if they don't they might get in the way of landing... but so far in all my tests, they have been successfully destroyed.  then don't forget to activate the landing gear, and the landing lights if you are landing on the dark side of Eve.  Rotate the ship so that the north/south axis on the navball is horizontal so that when you take off, you only need to worry about 1 axis...  as long as the ground isn't too steep, you should be good...

I have yet to achieve a successful take off test from eve with this ship, however with all the excellent advice received in this thread, I will be re-designing...  

 

 

[king of nowhere]

5 hours ago, TanDeeJay said:

 (Do not wait until horizontal movement has been eliminated, as the heatshields will come crashing back through the ship with destructive force when the chutes open and slow the ship right down... discovered this one the hard way... for some reason, after decoupling the upper heat shields when horizontal velocity is eliminated, the heat shields continue to fall in a very stable formation, so that when the main ship slows right down, they return with avengeance...)  N

  you can watch them fall and they should all explode to non-existance when they hit the ground...

 

that's very curious, it didn't happen to me. the top heat shields, many of them collided with each other and exploded. the rest took irregular trajectories and eventually reached the ground in scattered formation.

and while some thermal shields broke on the impact, most survived. at least, when they didn't have a 400 ton lander drop on top of them.

i wonder why the difference.