Eve One - Soliciting advice for an Eve Ascent Vehicle

[Virtualgenius]

Have you consider keeping some small SRBS in reserve to give you that initial kick and velocity

[Jouni]

Hmmm, I would have though that by the time I got to the Lv-909 stage, TWR wouldn't be so important, and I'd be in the upper atmo soing my gravity turn.

I did that mistake with my Eve landing. The pilot had to abandon the ship and circularize with his jetpack.

The velocity at a low Eve orbit is around 3150 m/s, or something like 40% more than around Kerbin. Consider now an efficient ascent from Kerbin - how much delta-v can be from a stage with low TWR? As a rough approximation, that number can be 40% higher on Eve, but the rest of the delta-v must come from stages with high TWR.

[KerikBalm]

Well, I just made the attempt...

I added av-8r fins to the outer asparagus ring, big mistake.

I landed on a hillside, barely didn't tip over. ~1,300 m altitude.. saves me about 500 m/s I guess - still wasn't far from the liquid.

Lift off was very difficult because the fins kept trying to bring my attitude to be in line with my velocity vector, which starts out more horizontal than I'd like due to the tilt of my landing site. Also, I had arranged it so that my outer asparagus stage was asparagused with the booster stage to get the lander into orbit, and I didn't action group my liftoff engines, so the engines fired as I was increasing the throttle, rather than set it to full and then firing the engines.

I had to get creative with retracting certain landing legs, and locking/unlocking some suspensions, but I was able to finally launch without flying horizontally to my doom.

Once the fins were gone, it flew much better, the single lv-t45 provided enough control.

My lower asparagus ring had not quite enough TWR, so the ascent was a bit inefficient.

The core of the lower asparagus had not enough TWR, but I had it asparagused with the twin FL-T200s+ 48-7s above it, which helped its TWR, and the TWR of the LV-909 stage.

At one point around 30-40km I think I actually started overspeeding, but then again found myself under terminal velocity (although you don't want to travel at terminal velocity as you get more horizontal in the gravity turn.

My ascent profile wasn't very efficient, I ened up with an apoapsis of 136km, and a perapsis of 36 km.... :/

It required less than 80 m/s to bring the perapsis above 100km.

With a bit of optimization, I think it could get my 2 kerbals into orbit without using their jetpacks.

Certainly, if I had just landed at a higher location, it would have been fine (while with that ascent profile, if I had landed at sea level, even jetpacking... they may not have made it into a stable orbit).

*edit* just ran it again from the quick save, a more optimal ascent path got me into a 105 x 120 km orbit, with about 3.2 units of liquid fuel left in the top stage (sufficient for over 300 m/s of dV)

I declare the lander a success... the only problem... ones gets science for bringing a ship/vessel back from Eve, no?

I may need to design a lander where I can recover a part of it, to get maximum science...

Edited March 16, 2014 by KerikBalm

[capi3101]

^^^

My first instinct is to suggest KAS - I'll have to look to see if docking ports are among the pieces that can be stored in containers. If so, you could rendezvous your return craft with the bit that was left, stick a docking port (and maybe a chute) on it, and fly it back to Kerbin.

If docking ports can be stowed, that might be an adjustment I want to make to my own design. In any case, congrats on making the ascent; I hope to be able to report success myself in the near future.

[KerikBalm]

Yea, I'm doing full stock, so I'm just sticking a small docking port on there, and an extra oscar-B fuel tank, hopefully the docking port weight doesn't affect my dV that much, and the oscar B doesn't kill my TWR.

I also modified the launcher - which has a core of 2 stacked orange tanks with a mainsail - so I can ditch the mainsail and refuel the core as an InterPlatentary (IP) stage, maybe even dock my lab-rover to the bottom (putting a large docking port, and then a mainsail which detaches), but now my launcher seems to break on the launchpad...

I still haven't actually sent kerbals (just the lander with a probe core and empty seats), or a return vessel. I also haven't bothered with refueling the launcher core for the IP journey, and just burn my lander's engines for the IP burn, land, and then edit the save file to give it full fuel for the ascent trial.

Still working on getting the whole mission together... the lander launch, the sciene package, the refuel for the IP burn, and the return craft... (should be pretty standard stuff)

However, I can at least cross off the ascent stage and ascent launcher - even though I'm now tweaking it with the docking port additions

[von Ziegendorf]

Hmmm... Maybe I'm wrong but you seem to enjoy the fun of designing the 'right' ship. If not, you would have read tutorial on wiki

I don't want to sound like a 'KSP oracle' but I think those craft's are oversized. My first and only Eve ascent (in 0.18.1) lifted 0.95t (Mk1+SAS+Jr. port) from 555m above sea level in 150 tons. I didn't know about 'drogue' chutes at this time so went without. Lander had 6 Mk16-XL and 6 regular Mk16. A small burn prior to first chutes opened and opening next in pairs one by one took me safely to the ground.

[capi3101]

Lander legs are starting to give me headaches - I've finally got the chute sequencing down to where they won't rip off, but landing at 3.5 m/s and still breaking stuff is getting on my nerves. Anybody got any suggestions for how handle that? My design oughta weigh somewhere in the neighborhood of five hundred tonnes when it reaches the surface unless I'm mistaken - I should pay attention to that in the next set of tests.

[Accelerando]

No suggestions on parachutes. Suggestion on the ship: Command pods are unnecessary mass.

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Design needs wings for stabilization, steering. ~100+ parts, mass ~56 tons. I can't add more because my computer keeps choking on it, but parachuting this to Eve will be less stressful than 500 tons.

[capi3101]

Well...I'm going with a Lander Can, so that's not particularly helpful, but thank you anyway.

[Ice30]

I would definitely look at reducing your mass capi3101. The reason things are breaking off is the engine is struggling to simulate that amount of parts and mass. A lander for eve should also have a **** tonne of landing legs to act like suspension to cushion the landing. Consider decoupling all these legs (and parachutes) before take off. I'm not keen on using the command seats for spacecraft as they are unrealistic and kind of feels a bit cheap and not in the spirit of KSP, but having said that you could consider this too.

[Red Iron Crown]

Count me in the "don't use command seat for atmospheric craft" camp, I avoid them for aesthetic and roleplay reasons.

Though oddly, I have no such compunction about leaving a kerbal in a one man pod for years.

[Ice30]

Though oddly, I have no such compunction about leaving a kerbal in a one man pod for years.

Haha this. It's no wonder some kerbals (especially jeb) laugh like maniacs throughout an entire mission lol

[capi3101]

I would definitely look at reducing your mass capi3101. The reason things are breaking off is the engine is struggling to simulate that amount of parts and mass. A lander for eve should also have a **** tonne of landing legs to act like suspension to cushion the landing. Consider decoupling all these legs (and parachutes) before take off. I'm not keen on using the command seats for spacecraft as they are unrealistic and kind of feels a bit cheap and not in the spirit of KSP, but having said that you could consider this too.

I figured the problem was not enough lander legs, though I was hopeful when the craft came up on the launchpad and the legs I had on it held up the ship without it breaking anything. Decoupling the chutes and legs is definitely part of the plan, along with anything else I don't absolutely absolutely hafta hafta need for the ascent.

Since I use KAS, the notion occurred to me to just have Jeb grab the ladders and drop them off the ship as he went back up. I know he can do that with the smaller extendable ladder; don't know about the big one off the top of my head. Was disappointed to find docking ports not included in things that could be stowed in KAS containers.

500 tonne figure...the ascender is something like 395 tonnes or so and I've got twelve of those ejectable parachute packs I'm using on there; those come in at seven tonnes a pop, thus around 85 tonnes of parachuting equipment. I dunno how much the lander leg system is going to add to the mass of the ship yet; right now it's sitting at 24 LT-2 lander legs on the end of long I-Beams. I also have six of the long unboxed solar panels sitting on TT-38K decouplers for the flight from Kerbin to Eve; I should be able to ditch those during the descent. 500 tonnes is an estimate, but a close one.

500 tonnes on 24 legs...that works out to just short of 21 tonnes per leg. Seems a bit much, doesn't it? Maybe I oughta look into doubling it to 48 legs. Distribution will also be important, I imagine.

Edited March 17, 2014 by capi3101

[cerberusti]

the water is much easier to land in if you have the dv and your ship is stable in the water.

I did my eve return yesterday with a lander at about 300 tons (100 of which was landing gear, parachutes, and extra fuel to soften the landing.) Even touching down at 0.1 m/s the uneven terrain was causing me issues on land, but I managed an ocean landing with no trouble (other than an atmospheric sensor which was too low in the water to click.)

I had about 14000 dv at liftoff, and had over 1000 left once I made orbit.

[Red Iron Crown]

the water is much easier to land in if you have the dv and your ship is stable in the water.

I did my eve return yesterday with a lander at about 300 tons (100 of which was landing gear, parachutes, and extra fuel to soften the landing.) Even touching down at 0.1 m/s the uneven terrain was causing me issues on land, but I managed an ocean landing with no trouble (other than an atmospheric sensor which was too low in the water to click.)

I had about 14000 dv at liftoff, and had over 1000 left once I made orbit.

Got a pic of your craft? I find it very challenging to exceed 12km/s of dV. Did you use a command seat?

[cerberusti]

I used a lander can.

Let me see if I can get a screenshot up.

VAB side:

http://steamcommunity.com/sharedfiles/filedetails/?id=239369829

VAB top:

http://steamcommunity.com/sharedfiles/filedetails/?id=239369826

This one is in flight, so you can see the DV:

http://steamcommunity.com/sharedfiles/filedetails/?id=239369833

Edited March 17, 2014 by cerberusti

[capi3101]

The water, eh? Didn't consider that...definitely something for tonight's tests. Might make it a bit difficult to plant a flag...

[Red Iron Crown]

I used a lander can.

Let me see if I can get a screenshot up.

*snip*

I can see how that would be difficult to get landed on the ground without breaking up. Nice design, BTW.

[cerberusti]

Yeah, no flag on the water... although you could choose a landing site within swimming distance of the shore. I had actually intended this to be able to touch down on land or water, but under eve gravity it shook itself apart within 30 seconds or so of touching down if not in the water (I probably need more landing gear, or a very flat site).

I put an 800 ton base down in a hard landing (over 10 m/s) in a previous patch with a crumple zone of trusses, that works somewhat well for the super heavy structures compared to the huge number of landing legs you would otherwise need.

Also, low TWR is ok for upper stages. My main orbital stage was at .89 or so in eve gravity for a while (1.49 normal), and managed to keep a good rate of climb and acceleration.

[Jouni]

Also, low TWR is ok for upper stages. My main orbital stage was at .89 or so in eve gravity for a while (1.49 normal), and managed to keep a good rate of climb and acceleration.

In your case it was ok, because you had a lot of delta-v to spare. Still, you managed to use almost 13000 m/s for the ascent, meaning that you lost something like 1500 m/s due to an inefficient ascent profile.

[cerberusti]

At that point the rocket was light enough that adding another decoupler was probably not worth it. My point was that once you are at altitude it is not strictly necessary to have a 1.0 surface TWR (although it is the most efficient point to have one, as drag is no longer an issue.)

I probably should have started my gravity turn earlier than I did, and I used some of the DV on a slow ascent out of the water.

I did this as my last mission of career mode before installing mechjeb, part of the reason for the high DV is that I eyeballed it. This was the first run for the rocket (with one round of testing on kerbin, and a few quickloads after crashing on eve) so I thought it turned out fairly well.

EDIT:

If you go for a water landing, make sure it is a very soft landing. A wide rocket and girders on the bottom are very effective in water to keep your stability, although I did not notice any bounce in the sea on eve. I am not sure if this is how eve works, or if my rocket is just very stable in water.

Edited March 17, 2014 by cerberusti

[Jouni]

At that point the rocket was light enough that adding another decoupler was probably not worth it. My point was that once you are at altitude it is not strictly necessary to have a 1.0 surface TWR (although it is the most efficient point to have one, as drag is no longer an issue.)

It's not strictly necessary, if you can waste 1500 m/s for inefficient ascent, and still have over 1000 m/s left when you reach orbit. For most Eve landers I have seen, the margin of error is much, much lower, maybe something like 500-1000 m/s. With designs like that, you can only afford having a low TWR for the last 1000 m/s or so.

The orbital velocity at a low Eve orbit is around 3150 m/s, while you need something like 11300 m/s of delta-v to reach the orbit from sea level. During the ascent, at least 8150 m/s is spent fighting drag and gravity. On Kerbin, the numbers are 2250 m/s, 4550 m/s, and 2300 m/s, respectively, so you can afford getting a much higher fraction of the delta-v from low TWR stages than in Eve ascents.

[cerberusti]

If you fly it up with a perfect gravity turn it would matter, I did not actually expect to reach orbit on the first try (my DV estimate was lower than the total mechjeb is giving.) In my case the ascent was less than perfect anyway, so I had some time to put on orbital velocity (and would simply have cut my engines longer while waiting for my ap burn at a higher TWR.)

Playing without mods I tended to over engineer quite a bit.

EDIT:

The number of landing legs you need to put a 500 ton vehicle down on eve is large, probably well over 100. Once you strut them and count other structure you will need, it starts to eat into the part budget. At that point you need girders and trusses (which also increases your part count by quite a bit.)

The water landing is probably best (add a few pylons which increase your width if it is not stable, and make the girders two deep at the bottom, as one is not really enough to clear most of the ocean.)

Edited March 18, 2014 by cerberusti

[Jouni]

If you fly it up with a perfect gravity turn it would matter, I did not actually expect to reach orbit on the first try (my DV estimate was lower than the total mechjeb is giving.) In my case the ascent was less than perfect anyway, so I had some time to put on orbital velocity (and would simply have cut my engines longer while waiting for my ap burn at a higher TWR.)

People make mistakes all the time, but usually that 500-1000 m/s margin of error is enough. Small deviations from the optimal ascent path don't really matter that much - it's like approximating a curve with line segments.

Those last few thousand m/s of delta-v of an Eve ascent are like the upper atmosphere part of a Kerbin ascent. Drag is still quite significant, but as the terminal velocity starts rising rapidly, you need high thrust to keep up with it. You can keep accelerating and pushing your apoapsis higher even with low thrust, but what you really want to do is to keep the climb rate high enough while gaining horizontal speed, so that time to apoapsis keeps increasing.

In an efficient Eve ascent, you should be close to orbital velocities before reaching 60 km, while drag remains significant until about 80 km. Climbing those 20 km takes a lot of time, and every second you spend below 80 km costs you delta-v due to drag and gravity. I'm not sure what's the optimal climb rate at those altitudes, but it's certainly better to climb 200 m/s too fast than 200 m/s too slow.

[capi3101]

Alright - tonight I tried a test water landing on Kerbin. Chute deployment went well and I had a nice, cushioned landing at 3 m/s. No parts fell off at splashdown. Chute ejection went as normal. On take off, however, the rocket promptly did a couple of loops and went right into the drink. It was almost like I had lost an engine somewhere along the line.

The new tweaks may have given me the delta-V I need, but I notice that it's now nearly impossible to steer. Common problem with the Aerospike, I know. Anybody have a suggestion on how to correct it?