Eve One - Soliciting advice for an Eve Ascent Vehicle

[Red Iron Crown]

Think of it like a chain, it'll break at the weakest link. Mine has 2/3 legs on a girder attached directly to a tank, yours looks like it has 6 legs on girders attached to a radial decoupler. Radial decouplers are very weak, especially against shear forces. And no amount of struts can replace strong connections. (In my last image of my new ship, the top wobbled like crazy no matter how many struts I added. Then I added 6 docking ports on girders around the outside and no more problems.)

I knew the decoupler was weak so I strutted the girders directly to the tanks. The weird thing is it's not the girder rolling out of place that causes the squat, it's the attachment points between legs and girder.

I reworked it, now I've got six girders attached to radial decouplers in a starlike arrangement, with six legs on each girder for 36 total. Same number of legs, but this is way stronger, can take a 10m/s landing without anything breaking. Odd that the orientation makes such a difference.

[StrandedonEarth]

Finally landed and returned to orbit from Eve. I didn't aim for any particular spot aside from a dry one, and ended up about 950m ASL at a latitude of 42deg. It took a few quickload launches to sort out the details, like making sure my stages would fire at the same time they decoupled (I had so many stages to sort out when I stacked it on my launcher in the VAB, I gave up and decided to sort out the lander's stages once I made Eve orbit), as well as constantly throttling back to stay within 5% of terminal velocity then firewalling it at staging. The final 'Ah-ha!' was remembering that the most efficient ascent would pitchover onto a heading that was the same as my latitude, which is the best I could do since I didn't land at the equator (now that I think of it I may have been lucky that I started near 45deg, maybe I needed to pitchover to 90deg minus latitude. Hmmm).

All in all, I ended up in a 250km x 125km orbit with 750m/s to spare. My orbiting tug had to burn over 3km/s to match orbits, but that's no big deal, it had 11km/s available.

Ok, I cheated slightly by just using a Ext Command Seat. The lander massed 153 tons fully assembled, about 140 tons after dropping the landing gear and 'chute trusses. That doesn't include the drop tank that let me fire a few engines while the drogues opened, I then transferred fuel before dropping it. I ended up making a 28-point landing on top of the engine fairing at a leisurely 7m/s, luckily that didn't damage anything. I had 8 asparagused twin-'spike SOB's on a Mainsail core, with an LVT-45 second stage and 48-7s top stage that had 1/3 of my total dV. No reaction wheels meant I had little control authority, especially when throttled down. It flew like a lawn dart; trajectory changes were gradual. Altogether I was at 740 parts on the launchpad, 280 of it the lander. The transfer tug launched separately.

That was my second mission to Eve, the first one failed horribly. But all it needed was MOAR STRUTS! Now I just have the routine task of returning to Kerbin with the science that I really have no need for. I also realized the drawback of doing the landing and ascent from a command seat: I could only do one EVA report and no crew reports. I suppose I could have put a lander can (2 for balance) on the landing trusses to stash reports in. It also would have helped if I remembered to add an antenna.

Now I may try to build a bigger one. With a lander can instead of a seat!

[Red Iron Crown]

*Snip*

All in all, I ended up in a 250km x 125km orbit with 750m/s to spare.

Ye gods, how much dV did your ascent stage have altogether?

Impressive design, I like the variety of engines used. I don't see a lot in the way of fuel lines in the pic, did you use onion staging rather than asparagus?

[WhiteKnuckle]

Looking at all these gigantic designs makes me so glad I went with a Kethane powered plane.

[StrandedonEarth]

Ye gods, how much dV did your ascent stage have altogether?

Impressive design, I like the variety of engines used. I don't see a lot in the way of fuel lines in the pic, did you use onion staging rather than asparagus?

Thanks! This pic is at a better angle to show fuel plumbing. KER is showing Eve atmospheric stats. The top stage gains about 700m/s dV in vacuum, to bring it to the 12km/s recommended for Eve. It helped launching from 900m ASL; I wonder how much dV that saved me. The outer SOB's feed the inner ones, which are asparagus-fed into the core. When the first outer pair drop, the second pair is a quarter full. With a test launch from Kerbin depending on direction it can go either interstellar or sunspot sampling, which I guess is the mark of an Eve-capable ascent vehicle.

[Red Iron Crown]

I think I solved my landing gear woes. I gave up on retractable landing gear altogether and just built my own out of truss parts. Only 7 parts per leg times 6 legs means it only adds 42 parts to the total, and each leg weighs only a bit over a half ton which is significantly lighter than the beams plus retractable legs I was using before. Pretty resilient during testing, too.

VAB pic:

Seems like a lot of ground clearance, but the legs are fairly flexible and allow the body of the lander to plunge a fair bit on impact.

Testing:

A 9m/s landing at near maximum deformation, surprisingly the feet don't break off. Just bounces a few times before reverting to shape and settling. At 10m/s the connection to the decoupler fails and everything goes boom. I'm a bit leery of strutting it any further, the flex in it seems to be what provides the missing "suspension".

Next step is chutes.

[ScottyDoesKnow]

I think I solved my landing gear woes. I gave up on retractable landing gear altogether and just built my own out of truss parts. Only 7 parts per leg times 6 legs means it only adds 42 parts to the total, and each leg weighs only a bit over a half ton which is significantly lighter than the beams plus retractable legs I was using before. Pretty resilient during testing, too.

Be careful with that. I haven't tried those parts, but on previous craft I used 18 upright girders as the landing legs. Yours may work better due to the flex, but what I noticed with mine was it landed fine but some of the girders were angled and it swayed a bit. And when I landed on a hard slope it actually slid down with all the girders skipping around, though that was a pretty heavy slope you shouldn't be landing on.

Edit: so in the end it did work, it just bothered me that it would sway around while landed. Yours may do better because of the flex.

[Red Iron Crown]

Scotty, I tried single long trusses pointed straight downward first and experienced something like what you are describing. Angled long trusses worked better but offended my aesthetic sensibilities as they didn't look realistic at all. The current design oscillates vertically for a while after a hard landing but eventually settles down, at least in testing at KSC.

That's a good point about sloping landing sites. I'm not sure I can test that very well on Kerbin given the top heavy nature of the lander when loaded to simulate its weight on Eve. Guess I'll have to avoid sloping landing sites as best I can. I think I'll add some lightweight scout rovers to the transfer stage like you did on your recent Eve mission, seems like a simple precaution to take.

[Navy2k]

Try strutting the legs not directly to the tanks but use some Cubic Octagonal Struts.

Struts can't strech and will break off parts to give them room. The Cubic Octagonal Strut can receive this forces and can load them off into internal flexing. (That's how it was told me).

Greetings

Ben

[Red Iron Crown]

I've heard that advice, too. I'm not sure it's really necessary in this case, though, as the legs seem up to the task of cushioning a heavy landing without breaking. I don't plan to land at 9 or 10 m/s, I was just testing to see how far it could be pushed. For science, of course.

[capi3101]

Well...lessee......if you know how the craft was behaving with standard legs, take the highest speed that you were landing at safely on Kerbin, multiply it by 1.7, and see if you can land safely at that speed. Say....20 m/s or so. I think the impact tolerance of the girder segments and adapters is 80 m/s, so they should survive; the question is one of how well the rest of your ship survives the impact.

[WhiteKnuckle]

Well...lessee......if you know how the craft was behaving with standard legs, take the highest speed that you were landing at safely on Kerbin, multiply it by 1.7, and see if you can land safely at that speed. Say....20 m/s or so. I think the impact tolerance of the girder segments and adapters is 80 m/s, so they should survive; the question is one of how well the rest of your ship survives the impact.

Remember, chutes are also more effective on Eve so he should be landing well under 10m/s.

[Red Iron Crown]

capi3101, I think I owe you an apology for hijacking your thread. How did you do with your mission?

[capi3101]

No apologies necessary; if a discussion of the topic can help out prospective Eve explorers, I'm all for it.

Haven't made the attempt yet, to be honest. I've been focused on my career game of late (finally finished that up last week) and then this week I've been busy taking care of my wife post-surgery, so I haven't had much time to play. I did get a chance to fiddle around with a ladder system and KAS is going to let me do what I hoped it would (i.e. have Jeb pluck them off the side of the ship as he ascends back to the capsule), so there's that at least. I also still need to finish setting up the refuel and return portion of the mission - the transfer stage for the hardware is up; I need to finish getting all the fuel canisters up and then attach the return stage. So still a fair amount to do before I make the attempt. Ship's going to be roughly 1000 parts, so it's going to take some time to finish no matter what.

[cerberusti]

That first ship I posted (landing on girders instead of legs) can set down at about 15 m/s on the pad without breaking, even at 1 m/s it cannot handle landing on eve (one girder eventually starts shaking, then flies off... and it is downhill from there.)

I think the impact tolerance is just that the part will not immediately blow up if it hits at under the listed speed, not that it will necessarily stay attached to your craft.

[Red Iron Crown]

Haven't made the attempt yet, to be honest. I've been focused on my career game of late (finally finished that up last week) and then this week I've been busy taking care of my wife post-surgery, so I haven't had much time to play. I did get a chance to fiddle around with a ladder system and KAS is going to let me do what I hoped it would (i.e. have Jeb pluck them off the side of the ship as he ascends back to the capsule), so there's that at least. I also still need to finish setting up the refuel and return portion of the mission - the transfer stage for the hardware is up; I need to finish getting all the fuel canisters up and then attach the return stage. So still a fair amount to do before I make the attempt. Ship's going to be roughly 1000 parts, so it's going to take some time to finish no matter what.

I'm a parent of two young kids, so I can sympathize with family responsibilities coming first. I'd love to be able to do the multi-hour marathon KSP sessions that some of the posters here can do, but I seem to only be able to get an hour in here or there.

I hope your wife has a full and speedy recovery.

[Red Iron Crown]

I've been working on my parachute configuration, and I think I'm almost there with 6 drogues and 48 radial chutes. The parachute calculator gives a terminal speed of about 5m/s at sea level on Eve.

I discovered something interesting during testing: I can mount 2.5m parts under the "feet" of my landing legs without them getting damaged by the aerospikes' exhaust. I think I'm going to mount the transfer tankage there and use the lander engines for the transfer. Saves on the part count by avoiding transfer engines, even if I have to give up the LV-N's efficiency. Not much of a sacrifice as the aerospikes are quite efficient in vacuum, too.

I've also been testing getting the lander into LKO, turns out TAC Fuel Balancer makes this almost trivially easy. Just set all tanks to balance fuel and oxidizer and it makes orbit easily on just the lander fuel with all aerospikes burning. MechJeb seems to get a bit confused by not dropping stages though, I had to do the circularization burn manually. My plan is to get it up there and refuel in orbit; it would be more elegant to do a single launch but the part count is already getting pretty high for my Core 2 Duo.

[StrandedonEarth]

Ah yes, the parachutes. You may not need that many if your gear can handle a faster landing, and removing 'chutes doesn't up your terminal speed much. My landing at 900m ASL was at 6.9m/s with 4 drogues, 4 Mk25s, and 28 radials. The trick for me was getting those drogues open without ripping the ship apart, that slowed it down enough so that opening the rest of the 'chutes was not an issue. I had to set 2 drogues to fully deploy before before the other 2 along with a brief engine firing or the drogues would just rip the girder they were mounted to right off. Eve's air is so much thicker than Kerbin's that while I had no problem testing the chutes on Kerbin, everything tore apart when I first got to Eve.

[Red Iron Crown]

My goal is to do a completely unpowered descent (other than the deorbit burn) as I'm pretty marginal on dV if I happen to land near sea level and would like to avoid drop tanks if possible. Maybe I can keep a little fuel in the transfer tanks and bring them down with me, jettisoning them before I pop chutes. That'll avoid leaving any debris around, too. StrandedonEarth, I think your lander was in the same weight class as mine at around 150t, yes? Just for clarity, you had 4 drogues, 4 large chutes, and 28 radials?

That's a good point about the atmospheric density, I've only been testing on Kerbin where I could open all 6 drogues with impunity and the g force from the radials opening was only about 6Gs or so. They're pretty sturdily attached to the lander in a manner similar to the landing legs so I hope it doesn't tear it apart. Not really sure how to test it without HyperEditing to Eve, which is a bit too cheaty for me.

[StrandedonEarth]

Correct on the 'chute loadout and weight class. The drop tank I used was only ever attached in the first place so my lander would clear a tall pair of asparagus stages on the launcher that got it off Kerbin, but it came in useful. I fired 4 of the 16 'spikes on my lander about 500m before the first pair of drogues fully deployed at 5000m to slow it a little more. Then I topped up the tanks those spikes used and dropped the tank before the main 'chutes deployed. I could have put some radial engines directly on the drop tank for that purpose and not had to top-up. Maybe a bunch of sepratrons would work too. Once those first 2 drogues opened it slowed everything enough that there were no other problems.

The main reason I had a mainsail (a skipper probably would have worked but it wouldn't have shot off the surface as quickly) was to be able to mount it on my launcher. If I used a landercan instead of a seat (or maybe side-mounted seats) I suppose I could have mounted it upside-down.

Imagine my surprise when everything worked perfectly while testing on Kerbin, but everything ripped apart on my first mission to Eve. The second mission, after adding more struts, worked better but I still lost the drogues until I quickloaded and did that small burn. I think at one point it pulled 9Gs according to KER but didn't notice if that was during landing or ascent, that's just what the max showed. I definitely suggest opening just 2 drogues before the rest

Edited March 29, 2014 by StrandedonEarth

[cerberusti]

I set mine in the VAB to open in pairs a few hundred meters apart for drogues, and 50 meters apart for the radials (which means no symmetry when adding parachutes.)

The side girders extending up from the landing gear in the ones I posted are mostly to attach the parachutes, as that way only one part of the craft needs to be able to take a significant jolt. Both of the craft I posted can enable the parachutes in orbit and allow them to open as the ship falls without anything ripping off.

The heavier one is a little over 300 tons with 18 drogues and 72 radial. The lighter one is 90 tons, with 8 drogues and 24 radial.

A I did a small burn at landing to reduce the impact speed with the larger craft, but the rest of the decent was unpowered (entirely unpowered for the small one.)

[Red Iron Crown]

which means no symmetry when adding parachutes.

Just FYI, you can break symmetry groups in staging, both in the VAB and in flight. Click once to expand the group, click individual items to select them.

Edit to add:

Chutes and Ladders in the VAB:

I used the bigger decouplers to give clearance for the trusses to drop when they're staged away. Currently they're staged with all the drogues deploying together first, then all the radials together, though I'm starting to think that won't work well on Eve based on the advice in this thread. I'm hopeful that the strut and truss arrangement will absorb some of the shock in a similar manner to my landing gear.

The ladder system was a bit fiddly to set up where it crosses the top of the tank, but it's working well now. I'm hoping this isn't one of those things that seems fine on Kerbin but fails on Eve.

Edited March 29, 2014 by Red Iron Crown
Now with more content.

[gilflo]

Here is the ascent ship I built to gather science on the top of the highest Eve mountain. Asparagus stage design

Landing at 267T with 186 MK2 chutes plus 18 MK25 to lower speed at 2500m. You need them otherwise the speed drop at 500m is too important and brokes the ship

All the sensor and science stuff is very near from ground so that Jeremiah can gather all science, then embark and take off, leaving gears, chutes and all sciences stuff.

Take off weight is 220T and you got 8600DV. I made it taking off from 7500m. There only aerospace engines and 3 Vesta VR1 from KWRocketry. TWR is around 1.55 on take off to 1.7 after, all the way up.

Here is my second Eve return lander. it's a rescue lander. 180T on landing, same chutes system with 186 MK2+6 lighter MK1 and 12 MK25. All 60 gears and all chutes ejectable before take off. Asparagus stages also

Landing 179T only with chutes at 4,7m/s. I landed a lighter one at 4,5m/s on Eve without damage.

Take off at 135T and I got 10500DV, so we can land as low as 4500m, that's the rescue goal.

This time I only used Vesta VR1 engines, cluster of 3 on larger tanks. 3 Vesta VR1 are lighter and more powerful than 1 aerospace engine, less ISP on ground 350 against 388, but better in Vac 400 against 390. Design is lighter and TWR is around 1.55 on take off. Don't go below that. I definitely will use this engines for lander on atmospheric planet. And it's easier to design as you can use decoupler and adapter on these engine, and they got gimbal.

Here on the top of the ascent vehicle

[StrandedonEarth]

Holy spiderweb Batman!

I tried tweaking my design to a lander can, but it's just too much extra weight and I can't get the dV back up. It would have to be a clean sheet redesign. So I gave up and tried to build a spaceplane and the game froze.

[ScottyDoesKnow]

My goal is to do a completely unpowered descent (other than the deorbit burn) as I'm pretty marginal on dV if I happen to land near sea level and would like to avoid drop tanks if possible. Maybe I can keep a little fuel in the transfer tanks and bring them down with me, jettisoning them before I pop chutes. That'll avoid leaving any debris around, too.

I would recommend against this. I mean it's up to you, but my experience was the amount of parachutes and landing legs (though you have custom ones) required for a consistent unpowered descent was too much. In the end I found it much easier to just spend a bit of fuel on landing (my 300t lander has 12 drogues and 12 radial parachutes). I could land at 3 m/s, so the parachutes would put me to around 10 and then under 50m I'd use the engines for a safe landing. Only costs about 100 dV, could even just throw a couple drop tanks on the sides for the landing fuel and drop them when you launch, though that does mean debris.