Eve lander design tips anyone?

[Firemetal]

So I have done round trips to all of the planets in the Kerbol system. Jool V, Moho, Eeloo, all of them. Except Eve. A while back, I did a career mode save and landed a small base on Eve to complete a contract. Now I am taking on a round trip.

Now I have built many landers before. I've tested them all and only one or two of them made it to orbit. The best engine to use when ascending from Eve is the Aerospike. It has the best ISP and has a relatively high thrust. However it has no gimbal. If I were to make all of my engines Aerospikes and be able to control myself during ascent. I'd have no problem designing a small enough lander to push to Eve. But... Everytime I build one like this, it flips over 5 seconds after launch. I need a less efficient engine like the vector in the middle to help control going up. Less efficient means less DV means more fuel which means more mass which means it will be much harder to get the lander to Eve in the first place.

Now is there a way to make it controllable on the way up? E.G winglets, torque?

Secondly, Hyperedit got implemented into the debug menu in the latest update. Sort of. With this revamped debug menu, is there a way for me to land my lander on Eve without having to edit into orbit and land manually?

Thanks in advance.

Fire

[IncongruousGoat]

From what I remember, the Vector actually has the same sea level ISP as the aerospike (290 seconds). In my experience, the aerospike is not the ideal choice of engine. Its TWR is too low to be functional on a high-gravity planet like Eve, and of course there's the gimballing issue. Although, of course, this all depends on where you're lander is landing. If you're starting from the surface, the Vector is probably the best choice. If, on the other hand, you're choosing to precision land on a tall mountain, the aerospike would be the better choice, simply due to being lighter. If your heart is still set on aerospikes, though, my advice to keep from flipping is A: lots of reaction wheels and B: fins on the bottom, to make the vehicle aerodynamically stable.

On the subject of the debug menu, no, there isn't a way to cheat your vehicle to the surface, not as far as I know. Although, it might be a better idea to start from orbit in the first place. Eve re-entry (as I'm sure you already know) is fiery death unless you prepare for it. Your lander has to be able to reach the surface in one piece, even before you start testing launching.

[Firemetal]

33 minutes ago, IncongruousGoat said:

From what I remember, the Vector actually has the same sea level ISP as the aerospike (290 seconds). In my experience, the aerospike is not the ideal choice of engine. Its TWR is too low to be functional on a high-gravity planet like Eve, and of course there's the gimballing issue. Although, of course, this all depends on where you're lander is landing. If you're starting from the surface, the Vector is probably the best choice. If, on the other hand, you're choosing to precision land on a tall mountain, the aerospike would be the better choice, simply due to being lighter. If your heart is still set on aerospikes, though, my advice to keep from flipping is A: lots of reaction wheels and B: fins on the bottom, to make the vehicle aerodynamically stable.

On the subject of the debug menu, no, there isn't a way to cheat your vehicle to the surface, not as far as I know. Although, it might be a better idea to start from orbit in the first place. Eve re-entry (as I'm sure you already know) is fiery death unless you prepare for it. Your lander has to be able to reach the surface in one piece, even before you start testing launching.

Ok. I'll try both. Vectors first though since it does sound a little better although I still think the Aerospike is more efficient.

Secondly, I'm talking about after surviving re-entry if I need to tweak the lander because it failed ascent, I do not want to have to go through re-entry again, just to test ascent.

Thanks for the help.

Fire

[bewing]

1 hour ago, Firemetal said:

Secondly, I'm talking about after surviving re-entry if I need to tweak the lander because it failed ascent, I do not want to have to go through re-entry again, just to test ascent.

Quicksave when you are on the ground? And flipping generally happens on Eve from going too fast, too low. Either land higher, or resist the impulse to mash Z.

[Firemetal]

1 hour ago, bewing said:

Quicksave when you are on the ground? And flipping generally happens on Eve from going too fast, too low. Either land higher, or resist the impulse to mash Z.

So if you quicksave, go back to VAB and make a change and then quickload, the change stays?

 

[bewing]

1 minute ago, Firemetal said:

So if you quicksave, go back to VAB and make a change and then quickload, the change stays?

 

Ah. No. Thought you just meant a context menu tweak, or a launch profile tweak. An actual editor change needs either Hyperedit, or a full scale reentry from Eve orbit -- which is the closest that SetOrbit can get you.

[Foxster]

I have found aerospikes to be the best engine. If you go for vectors then the mass balloons. 

The lack of gimbal doesn't matter. Add some control fins on the centre stack and they will be effective most of the way up but can be ditched for the final stage that you can steer with the capsule's reaction wheel. 

You want the craft very aerodynamic or you will lose lots of dV to drag. Several size 1 stacks is better than a few fat ones. 

Mk1 capsule is the best choice. Low drag and mass. The lander can is just too draggy. 

You can get it down with an inflatable heat shield on the leading edge and a lot (maybe 8-12 for a larger craft) of air brakes at the back. Don't forget plenty of chutes too. 

Put chutes, ladders, air brakes, landing gear/struts, science gear, etc on decouplers and dump them before lifting.  

[Firemetal]

1 hour ago, Foxster said:

I have found aerospikes to be the best engine. If you go for vectors then the mass balloons. 

The lack of gimbal doesn't matter. Add some control fins on the centre stack and they will be effective most of the way up but can be ditched for the final stage that you can steer with the capsule's reaction wheel. 

You want the craft very aerodynamic or you will lose lots of dV to drag. Several size 1 stacks is better than a few fat ones. 

Mk1 capsule is the best choice. Low drag and mass. The lander can is just too draggy. 

You can get it down with an inflatable heat shield on the leading edge and a lot (maybe 8-12 for a larger craft) of air brakes at the back. Don't forget plenty of chutes too. 

Put chutes, ladders, air brakes, landing gear/struts, science gear, etc on decouplers and dump them before lifting.  

Thanks the tips, but aerospikes just aren't easy to fly with. I put six of them with a vector in the middle and it still, even with 10 degrees of gimbal, had trouble turning. On Kerbin!

But anyway, I put together a lander with a Mk1 capsule and parachute, landing gear all decoupled. And this lander is overkill as heck.

How is an Eve lander overkill? Well...

OK here are the last two stages of the lander. Sorry the pictures is dark and I have a habit of turning off the interface to take pictures. But the lower stage, 2.5m powered by a vector, has 1/3rd of its fuel left. In low Eve orbit. The upperstage which hasn't been used yet which is 1.25m powered by a terrier. This upperstage has about 2.7m/s of DV in it. So if I added a heat shield and parachute and decoupler to this, it would have enough to escape Eve's SOI and return to Kerbin without a return ship in Low Eve Orbit. I designed it to have one yet this lander has over 10k m/s of DV.

The only downside is, it weighs about 200 tons. So now I have to decide whether to figure out a monster ship to get it there or take it there dry and either add mining tools to it or bring a separate vehicle that refuels it with a claw. I also need to tweak it a bit but not too much.

Thanks for all your tips and help guys, Much appreciated,  

Fire

 

[Foxster]

Well, yes, at 200t it is going to be tricky to turn. My Eve landers tend to be <45t. 

[foamyesque]

Vectors are nice, but the engine you really want is the Mammoth if you're landing anything of substantial size, and double especially if you're going deep into the atmosphere. Atmospheric TWR is king on Eve.

Airbrakes and parachutes are for chumps; land it on wings. Gives you more control over your entry, and if you land horizontally you don't have to deal with the tipping issues of a vertical rocket; it's also easier for your Kerbs to get in and out of your machine. It also enables a TWR < 1 liftoff, which saves you on your engine count; mount your wings on drop tanks, with whatever engine(s) you want on your center stack. Cruise up to an altitude where your engines start working properly on the wings and drop tanks, pitch around to vertical, and ditch them to fly the rest of the ascent like an ordinary rocket. Works a treat.

 

Also, there's a lot of misconceptions concerning drag out there. @Foxster is incorrect, or, at least, incomplete, about 1.25m stacks being better than larger ones. For the same amount of fuel, arranged in the same length, larger diameter tanks are more drag efficient and by a very large margin. 1.25m stacks are only advantageous if you're either a. staging them away in a big hurry (e.g. asparagusing it up, which runs into its own design issues) or b. have used them to make your craft very long and skinny. Long, skinny craft have a great many other problems and given the amount of fuel needed to actually get off Eve I would not recommend trying to reconfigure 3.25m tanks into 1.25m stacks. Ship's already going to be plenty tall.

 

[Foxster]

7 hours ago, foamyesque said:

Also, there's a lot of misconceptions concerning drag out there. @Foxster is incorrect, or, at least, incomplete, about 1.25m stacks being better than larger ones. For the same amount of fuel, arranged in the same length, larger diameter tanks are more drag efficient and by a very large margin. 1.25m stacks are only advantageous if you're either a. staging them away in a big hurry (e.g. asparagusing it up, which runs into its own design issues) or b. have used them to make your craft very long and skinny. Long, skinny craft have a great many other problems and given the amount of fuel needed to actually get off Eve I would not recommend trying to reconfigure 3.25m tanks into 1.25m stacks. Ship's already going to be plenty tall.

 

I guess that, again, it depends on the size of the craft. Asparagus helps enormously in reducing mass, especially with the new fuel flow system, as does having several stages. These craft only getting tall if you use more powerful (and massive) engines.

I tend to make practical missions that can get to Eve surface and back in a single launch. I see some great craft for landing on Eve but they are so large that it looks to me like they only get to Eve thanks to HyperEdit or a lot of complicated multiple flights and assembly. 

[foamyesque]

Well, the thing about going wide in an asparagus design is that you lose the drag advantage and you can end up flopsy, and if you go long and skinny you're structurally fragile. Also, I object to asparagus staging on principle

[Foxster]

6 hours ago, foamyesque said:

 Also, I object to asparagus staging on principle

Fair enough but I'm curious why? As far as I'm aware it is a physically practical thing. 

[foamyesque]

4 hours ago, Foxster said:

Fair enough but I'm curious why? As far as I'm aware it is a physically practical thing. 

 

Not the way some people do it. Drop tanks, or something like a ring boosters crossfeeding a core stage, okay, I'll buy that; they exist or are proposed. Space magic that lets forty engines all draw from two tanks hundreds of feet away in a giant spiral, not so much.

[Foxster]

I've not seen so many craft like that since the more realistic atmos drag was introduced a while ago. Craft like that now tend to be too draggy to be useful. 

I'm with you in that I do tend to have one stack in the middle and a ring of drop stages around it for Eve lifters. 

[juanml82]

Speaking of Eve landers, how do you prevent them from tipping over during reentry. Do I need moar vernors?

Here's a couple of pics of the lander I'm designing (and failing to land)

[foamyesque]

Fighting aerodynamic instability with RCS engines on Eve is always a losing game. If you're insistent on dropping a big thing like that behind an inflatable heatshield, you're going to want disposable fins and/or more airbrakes and/or a second heat shield at the top, the purpose of any of which is to get your center of drag behind your CoM.

 

But me, like I said, I'd abandon a vertical landing/launch idea entirely and build a plane with jettisonable wings.

Edited December 8, 2016 by foamyesque

[juanml82]

42 minutes ago, foamyesque said:

Fighting aerodynamic instability with RCS engines on Eve is always a losing game. If you're insistent on dropping a big thing like that behind an inflatable heatshield, you're going to want disposable fins and/or more airbrakes and/or a second heat shield at the top, the purpose of any of which is to get your center of drag behind your CoM.

 

But me, like I said, I'd abandon a vertical landing/launch idea entirely and build a plane with jettisonable wings.

I'll try a spaceplane, but wouldn't it spend more time inside Eve's thick atmosphere?

[foamyesque]

10 minutes ago, juanml82 said:

I'll try a spaceplane, but wouldn't it spend more time inside Eve's thick atmosphere?

 

It depends. You can launch with an Eve TWR of < 1. You use your wings to fly a gliding landing (easy on Eve, even for heavy machines) and to let you cruise to a decent rocket operation altitude (8km+, where you're at around Kerbin sea-level atmospheric pressure-wise), at which point you pitch to vertical, ditch the wings and drop tanks, and fly a rocket ascent from there on out.

 

If you have a high TWR rocket (or land on a mountain) you need not even do the cruise-climb; you can simply do a horizontal run up to your takeoff velocity, pitch vertical as soon as you're clear of the terrain, then jettison the wings and fly a rocket ascent.

 

Either works; unlike on Kerbin, you can't use airbreathing engines, so there's no benefit to a long flat climb while they push your horizontal speed up. A rocket plane wants to transition to a rocket ascent as soon as it has the TWR to do so and to jettison its wings as soon as it no longer needs them to provide lift. You start out horizontal, ride your TWR to 80 degrees+, pitch the wings, then fly an ordinary gravity turn from there out.

Edited December 9, 2016 by foamyesque

[Aegolius13]

I did a 100 ton-ish Eve lander recently and found the Vector to be the most useful engine overall.  Yeah, the Mammoth has marginally better TWR, but it's more thrust than you might need, and you can't stage away half of it like you can with multiple Vectors.  Also being unable to build underneath the Mammoth can raise design problems for getting the thing to Eve.  Aerospikes, while not the best pick for a main engine (you really need that gimbal) can be useful to add some extra thrust to your drop tanks.  Staging away the aerospikes can help keep your thrust somewhat even, compared to staging away Vectors at long intervals.  

Interestingly, I found that the aerospikes had the superior ISP below 1000m elevation.  Then, as you climb toward 1 Kerbin atmosphere, the Vector's ISP slightly surpasses the aerospike.  Then, once the atmosphere keeps thinning, the aerospike retakes the lead with its superior vacuum ISP.  So this too argues in favor of putting aerospikes on your radial boosters.  

On Eve entry with an inflatable heat shield, I was able to keep my ship straight with a combination of a low COM (all those Vectors help with this), a bunch of airbrakes at the top, and a couple of large reaction wheels set to jettison along with the heat shield.,  

Mission report here:

Album:

http://imgur.com/a/tqh5M

 

 

 

[Foxster]

8 hours ago, juanml82 said:

Speaking of Eve landers, how do you prevent them from tipping over during reentry. Do I need moar vernors?

Here's a couple of pics of the lander I'm designing (and failing to land)

There's a couple of things...

You'll need a lot more air brakes. The 1/2 doz you have won't cut it, you need maybe 3 times that number. Try stacking them on top of each other. Luckily they are light. 

Those fins on the bottom of the craft will be fighting you. They will tend to undo the effect of the air brakes. See if you can reduce their number/size and still keep it vertical on lifting. 

Also...

Put your air brakes and chutes on decouplers to dump them before lifting. 

Put the science suit on the bottom of the craft and dump that too. 

Do you really need all those batteries and reaction wheels? If they are only for landing then attach something inside the heat shield instead and dump them together before landing. 

You can get the same performance out of one vector in the middle and a ring of aerospikes around it. Reducing the fuel and engine mass considerably. 

Don't carry that used fairing all the way down to Eve and back up. I'm not sure what it is doing for the craft anyway. 

Rather than physical struts, use auto-strutting. Rather than fuel ducts use fuel priority. Both are heavy and very draggy. 

Don't use RCS and take the monopropellant out of the capsule. The RCS fuel is wasted mass and the jets are very draggy. 

Basically...Strip the mass to the bare minimal, especially the last stage that goes into orbit. Then you won't need all the extra engines and fuel. Then you won't need all the RCS/fins/reaction wheels. Then the air brakes will work better. 

Edited December 9, 2016 by Foxster

[juanml82]

7 hours ago, Foxster said:

There's a couple of things...

You'll need a lot more air brakes. The 1/2 doz you have won't cut it, you need maybe 3 times that number. Try stacking them on top of each other. Luckily they are light.

I've multiplied the amount of airbrakes by 6. Still tilting over, though.

Quote

Those fins on the bottom of the craft will be fighting you. They will tend to undo the effect of the air brakes. See if you can reduce their number/size and still keep it vertical on lifting. 

I'll just remove them

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Put your air brakes and chutes on decouplers to dump them before lifting. 

Already are in decouplers

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Put the science suit on the bottom of the craft and dump that too. 

 

I'll check the dV savings. By keeping them in the top stage, I can still harvest any science I've missed during the descend while ascending. The service bay also contains a pair of rtgs, which are a few dozen kilograms heavier than solar panels, but they continue to generate power during the descend, which is needed for the reaction wheels

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Do you really need all those batteries and reaction wheels? If they are only for landing then attach something inside the heat shield instead and dump them together before landing. 

I need the reaction wheels to turn that thing within a reasonable timeframe. The amount of batteries is overkill, but there are no lighter inline batteries. I can see about putting one or two in the central stack.

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You can get the same performance out of one vector in the middle and a ring of aerospikes around it. Reducing the fuel and engine mass considerably. 

 

I'll try that and see what dV and TWR I get

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Don't carry that used fairing all the way down to Eve and back up. I'm not sure what it is doing for the craft anyway. 

 

I'm using the internal truss to mount a docking port on top of the fly-by-the-wire cone. That's an easy spot to dock for refueling and also works if I decide to use a nuclear tug to carry it around. Alternatively, I could radially mount a pair of docking ports on decouplers. Or mount one at the bottom of the heat shield (and decouple it before reentry)

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Rather than physical struts, use auto-strutting. Rather than fuel ducts use fuel priority. Both are heavy and very draggy. 

I tried only auto-strutting but the bottom fuel tanks end up moving (wildly) anyway. IIRC fuel priority can't be used for asparagus staging

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Don't use RCS and take the monopropellant out of the capsule. The RCS fuel is wasted mass and the jets are very draggy. 

I'm not using RCS, I had forgotten about removing the monoprop, but it's on the bottom capsule anyway, and that one remains on Eve

[juanml82]

Ok, I've finally made it, with something like this

(This one is the corrected version. The original had only aerospikes in the outer ring and the TWR was too low, so I've swapped a pair of darts for vectors)

 

I did try a spaceplane, but it tilted over during ascend

[Nicias]

I've been having trouble with own lander, and had some questions.

How did you dock that thing to the transfer craft? I have been using shielded ports on the nose for that, but that forces me to use a lander-can or an inline mk1 cockpit. I'm having trouble with my designs flipping, so I've been trying to cut down on nose drag. The best I can think of is either a shielded port with mk1 inline (if thats better dragwise than a landercan) or mk1-0 pod with a naked top. (jettisoning a port)

Is the reported dV at Eve SLT? Did you have extra dV when you made it to orbit?

In terms of testing, I've been hacking gravity on Kerbin to 1.7 is that reasonable to test for filppiness?

 

[Foxster]

You don't have to re-dock with the transfer craft when back in orbit. Just EVA over the crewman from the lander and set it adrift. 

dV is hard to specify for Eve. Drag is a huge factor there. You can get a really aerodynamic craft to Eve orbit from sea level with as little as 6000dV with a well flown lift. Or it can take another 4000+dV if your craft is lumpy.

Just hacking the gravity doesn't model Eve well at all. Drag and increased atmosphere height need to be taken into account.