Eve Ascender - Any Tips?

[Aegolius13]

Hey folks,

I'm working on my first manned Eve Landing.  This is my prototype Eve ascent module.

 

Getting to land on Eve without cheating is a work in progress, but it looks viable for the ascent stage.  It  was able to get to orbit from a 500m starting elevation, with about 300 delta-v left in the tank.  (This first run was also without a nosecone, due to an ill-fated attempt to put a heat shield on the front.  So it would probably perform better with the cone as shown).  

Overview of the craft:

Six asparagus-staged radial boosters, each consisting of two FL-T800 tanks, a Dart and a nosecone.  Three of the boosters have landing legs, and each has a parachute.

Core stage is two Vectors plus 4000 units of LF.

Second stage is one Dart plus 800 units of LF in a 2.5m to 1.25m adapter.

Third stage is a Terrier with 300 units of LF.  

Payload is one Mk 1 capsule, with battery and nosecone.  

 

TWR seems OK, at least by the usual standards.  It starts around 1.3 and builds from there.  One "problem" I've noticed is that the TWR really spikes (starting at > 3 at full throttle) when I've ditched all the radial boosters.  The Vectors are overpowered for this stage, and on top of that, this is the point where the air finally starts to thin out.  The only solution I've been able to come up with is to put only one Vector under this stage, and put two more on the final set of radial boosters.  But that adds more total weight, which I'm not excited about. 

I'm very new to Eve operations and would love any tips to improve performance and/or reduce weight. Should I try to keep TWR between 1.5-2 like on Kerbin, or is a higher or lower number better?  Also curious what people have found to be the most effective gravity turn.  I clung to "hold radial out" for dear life until 10-15km, and then tried it gradually from there, but I think I ended up climbing too steeply.  (The lack of thrust vectoring on the single Dart stage did not help either, but I'm reluctant to change the engine since it fits the TWR curve well).  

It would also be nice to make the whole thing shorter, to make it easier to keep behind a heat shield.  But I don't want to make it fatter, and hence draggier.  The obvious option is to make the radial boosters a little longer and the main stage a little shorter, but that will exacerbate the thrust spike of the two-Vector stage even more.  

Thanks!

[pTrevTrevs]

I believe Scott Manley dos a series in which he flew a crewed mission to Eve, but I think it was before the aero overhaul, so I'm not sure how many of his design choices are still relevant.

Also, why are there parachutes if it's meant to be the ascent stage? Are they for helping the craft descend or to preserve the boosters once they're jettisoned?

[Aegolius13]

1 minute ago, pTrevTrevs said:

Also, why are there parachutes if it's meant to be the ascent stage? Are they for helping the craft descend or to preserve the boosters once they're jettisoned?

Helping the craft descend.  I'm still not exactly sure how this thing is getting to the surface, but my first take was to put an inflatable heat shield on the front, and take just this module plus the heat shield to Eve reentry.  Did not go well. Much flipping, many explosions until I turned overheating off.  

My new idea is to include two fuel pylons with inflatable heat shields on the back end, which should be more stable.  I might try to put the chutes on those fuel pylons, land with them, and then discard for ascent.  

[TheDestroyer111]

24 minutes ago, Aegolius13 said:

Hey folks,

I'm working on my first manned Eve Landing.  This is my prototype Eve ascent module.

 

Getting to land on Eve without cheating is a work in progress, but it looks viable for the ascent stage.  It  was able to get to orbit from a 500m starting elevation, with about 300 delta-v left in the tank.  (This first run was also without a nosecone, due to an ill-fated attempt to put a heat shield on the front.  So it would probably perform better with the cone as shown).  

Overview of the craft:

Six asparagus-staged radial boosters, each consisting of two FL-T800 tanks, a Dart and a nosecone.  Three of the boosters have landing legs, and each has a parachute.

Core stage is two Vectors plus 4000 units of LF.

Second stage is one Dart plus 800 units of LF in a 2.5m to 1.25m adapter.

Third stage is a Terrier with 300 units of LF.  

Payload is one Mk 1 capsule, with battery and nosecone.  

 

TWR seems OK, at least by the usual standards.  It starts around 1.3 and builds from there.  One "problem" I've noticed is that the TWR really spikes (starting at > 3 at full throttle) when I've ditched all the radial boosters.  The Vectors are overpowered for this stage, and on top of that, this is the point where the air finally starts to thin out.  The only solution I've been able to come up with is to put only one Vector under this stage, and put two more on the final set of radial boosters.  But that adds more total weight, which I'm not excited about. 

I'm very new to Eve operations and would love any tips to improve performance and/or reduce weight. Should I try to keep TWR between 1.5-2 like on Kerbin, or is a higher or lower number better?  Also curious what people have found to be the most effective gravity turn.  I clung to "hold radial out" for dear life until 10-15km, and then tried it gradually from there, but I think I ended up climbing too steeply.  (The lack of thrust vectoring on the single Dart stage did not help either, but I'm reluctant to change the engine since it fits the TWR curve well).  

It would also be nice to make the whole thing shorter, to make it easier to keep behind a heat shield.  But I don't want to make it fatter, and hence draggier.  The obvious option is to make the radial boosters a little longer and the main stage a little shorter, but that will exacerbate the thrust spike of the two-Vector stage even more.  

Thanks!

But WHY use Vector engines in the middle with aerospikes on the outer asparagus boosters? The Vector has better atmospheric Isp by 5 seconds, while the aerospike has 25 seconds better vacuum Isp.

[pTrevTrevs]

Well if you can, I would recommend detaching those parachutes, along with every other piece of equipment that isn't absolutely necessary for the ascent, before liftoff. I've never tried launching from Eve, but I know enough to tell you that every gram counts.

If you weren't planning this already, make the ship that the Kerbal(s) return home on wait in orbit, so you make the ascent vehicle much smaller. If it doesn't have to carry all the fuel for the return trip it can be lighter and therefore easier to get into orbit.

Edited September 18, 2016 by pTrevTrevs
To autocorrect, the word "planning" is spelled "tol annoy"

[Aegolius13]

8 minutes ago, TheDestroyer111 said:

But WHY use Vector engines in the middle with aerospikes on the outer asparagus boosters? The Vector has better atmospheric Isp by 5 seconds, while the aerospike has 25 seconds better vacuum Isp.

My main reason was that my core stage needs more thrust.  But I might play around with something like a cluster of 2-3 Darts on the core, and two Vectors on the final set of boosters.  That might end up underpowered once the boosters detach, though.  Also, at my landing elevation, the Darts actually have better ISP than the Vectors (~230 vs. 200 according to the right-click menu).  I guess the Vectors catch up around 1 atmosphere (which is actually around when I loose the Darts), then the Dart picks up again at lower pressure (when I go to the one-Dart upper stage).  

 

15 minutes ago, pTrevTrevs said:

If you weren't tol annoy this already, make the ship that the Kerbal(s) return home on wait in orbit, so you make the ascent vehicle much smaller. If it doesn't have to carry all the fuel for the return trip it can be lighter and therefore easier to get into orbit.

There is no stage to return to Kerbin.  The existing ship is enough to get to EVE orbit with 300 delta-v left.  I am planning a rendezvous with an orbital shuttle to get home (hence the tiny docking port on the front of the pod).  

[mikerl]

One more thing to consider is wet landing vs dry and refine.  Either take fuel or mine and refine it on the surface.  Your current craft is 102 tons in the pic and about 80 tons worth of fuel in it, so consider bringing detachable ISRU equipment.  Detach anything not used in ascent, parachutes, ladders, and landing legs to name a few.  inflatable heat shield should help landing that, but is that enough parachutes?  To save parts on ladders, i have seen people use a pod near the base and then transfer the kerbal to the main pod, then detach the landing pod.

[Aegolius13]

10 hours ago, mikerl said:

One more thing to consider is wet landing vs dry and refine.  Either take fuel or mine and refine it on the surface.  Your current craft is 102 tons in the pic and about 80 tons worth of fuel in it, so consider bringing detachable ISRU equipment.  

Interesting idea - this would definitely save weight for launch, and go a little easier on Eve entry.  But also adds complexity and more parts to fit under that heat shielld.  

 

10 hours ago, mikerl said:

 Detach anything not used in ascent, parachutes, ladders, and landing legs to name a few.

Yep, my revised version put all that stuff on decouplers.

10 hours ago, mikerl said:

 inflatable heat shield should help landing that, but is that enough parachutes?

I ended up adding a lot more chutes (24 total).  The original version might have been enough for an engine-assisted landing, but that's a little fussy given the demands of Eve.  Definitely better to let the chutes do all the work.

 

10 hours ago, mikerl said:

To save parts on ladders, i have seen people use a pod near the base and then transfer the kerbal to the main pod, then detach the landing pod.

Seems like this would save a little mass on takeoff (when it's much more important to be light), but add again add complexity as well as mass for the reentry.  Personally I think ladders are light enough to stick with here.  I was more concerned about the lousy kerbal climbing skills not working, but they did, even on Eve.  

 

Anyhow, I got down to Eve and back to orbit with a slightly revised version of this design.  Other than the parachutes and decouplers mentioned above, the other major change was to swap out two of the Darts for Vectors, and go with just one Vector rather than two under the core stage.  Here's my mission log.  Thanks everyone for your input!

 

Edited September 23, 2016 by Aegolius13

[McQuacker]

8.4 km/s of delta-V might be a slight overkill. My own Eve sample return mission ( http://imgur.com/a/DLmc6 ) had about 7.7 km/s and managed to reach low Eve orbit from 1100 meters with about 150 m/s left.

For small craft a Dart might be preferable over a Vector even for atmospheric ascent because of its smaller mass, since then the mass of the engine takes up a significant portion of the craft's dry mass.

But it looks like a viable design nonetheless, I think it should easily fit behind the 10-m heatshield. Just make sure you have some big stabilizing fins on the top end to make sure it doesn't flip during the descent.

[Aegolius13]

1 hour ago, McQuacker said:

8.4 km/s of delta-V might be a slight overkill.

Yeah, it ended up having a lot left in my latest test, from around 500m altitude.  Maybe I could lose the outermost set of boosters, or a little bit from the core stage.  But leaving in a margin of error does not seem like a bad thing.

[septemberWaves]

I've found that the key with an Eve ascent vehicle is aerodynamics. Even if you need to use a fairing as an interstage, it's better to have that small amount of additional mass than to have a sharp transition between two diameters. I've made some pretty powerful Eve ascent vehicles in the past, and their good aerodynamic shapes are the only reason they flew at all.

Also, I would say to make sure that you have adequate roll/pitch/yaw control, but it seems that you probably do since I can see reaction wheels and Vector engines (although, I would really suggest limiting the gimbal range of those Vectors to between 20% and 30% so that you don't overcompensate and end up flipping, which can happen in Eve's atmosphere).

Edited September 23, 2016 by eloquentJane

[Spraki]

I recently did my first ever interplanetary encounter with Eve (talk about going straight to one of the big bosses of KSP lol). 

One thing I learned was that Eve's atmosphere will BURN the hell out of your ship. And even if you have a heatshield, multiple aerobrakes (not sure if that was the right term) will eat away ablator padding fast. You can still use them for entry but it will go away fast. Your entry is also roughly some 4km/s or so, IIRC. 

Or maybe you get get the entry with a part that can eat the heat and which you can ditch right after via staging. Dunno. 

I haven't sent Kerbals yet to Eve. My mission mod said to send unmanned there first. So I cannot help with ascend-stuff. 

I must remind though not to over-engineer on too many parachutes either. Last time I dropped something off on Eve, it took like almost an hour or something until it got to the ground. xD

I am no expert so don't take me that seriously lol. 

[Aegolius13]

40 minutes ago, eloquentJane said:

I've found that the key with an Eve ascent vehicle is aerodynamics. Even if you need to use a fairing as an interstage, it's better to have that small amount of additional mass than to have a sharp transition between two diameters. I've made some pretty powerful Eve ascent vehicles in the past, and their good aerodynamic shapes are the only reason they flew at all.

That's a good idea.  Maybe some day we will finally be able to do engine shrouds in other sizes.  Every Rockomax 8 tank + Terrier lander setup would work so much better on launch.  

 

14 minutes ago, Spraki said:

And even if you have a heatshield, multiple aerobrakes (not sure if that was the right term) will eat away ablator padding fast.

True for the ceramic heat shields, but the inflatable heatshield does not use ablator, so you can brake for as long as you want.  That thing is pretty OP, though I guess the flipping issues it can create help even it out a bit.  But I basically never use the ceramics anymore.  

[Spraki]

Doh. Didn't think about that with the inflatable one. Yes - You will have issues with flipping and stuff. I've had a few "rover-gliders" go up in fireworks because the entry velocity is just waaay to high. Wasn't the best of engineering btw. And just a tiny part at the wrong spot can send you spinning. ,_,

 

[Aegolius13]

2 minutes ago, Spraki said:

Yes - You will have issues with flipping and stuff.

Fortunately my lander was so bottom-heavy that flipping was not really an issue.  (It was catastrophic when I tried a top-mounted shield, though).  I did have some wobbling problems at first, but was able to keep it nice and straight with some beefier reaction wheels (to be detached with the heat shield) plus some airbrakes on top.