Sea level Eve landers post 1.0

[KerikBalm]

There, that clickbait title should get the Eve experts looking here...

I got my lander to LKO in a SSTO spaceplane, fully fueled, ready to have a tug take it to Eve...

I still think there is a lot of optimization to be done though, I ws hoping to have the lander come in well under the 90 or so tons that I ended up with.

Can any one help me design a more efficient Eve lander post 1.0?

This weekend I decided to take on Eve for the first time post 1.0

Here were my requirements:

* Must be able to lift 1 kerbal inside a lander cabin/pod... No external command seats.

* Must be able to launch from pretty much any solid surface on Eve... ie sea level launches.

* Obviously, must be able to de-orbit an land in one piece.

However... 90 tons seems... really heavy to me. I was using aerospikes as my lift engines - I know the mammoth has better Isp and TWR stats, but its 15 tons, and when I started trying to build these landers, they were coming in in the 50's... making the engine simply too heavy to be worth it its not good when your first stage engine is 30% of the craft's total weight).

Can anyone share advice for Eve sea level ascents?

When to start a gravity turn, design tips, TWRs that shouldn't be exceeded (a stage as it becomes light may exceed terminal velocity?)

As for my designs... It took me three design iterations to get to orbit:

I text-edited (should I get hyper edit? ) my way to Eve orbit, and succesfully deorbited the Mk1... after a few attempts where I came down in liquid, or lost parts during re-entry.

Landing at just over 9 m/s resulted in partial unplanned disassembly... more parachutes or a retroburn would be needed... to be solved later...

So I text edited the craft to the surface of Eve in one piece... and tried to get to orbit... an ion powered upper stage (while it looked superior to the Ant-engine upper stage I was also considering) proved to be woefully underpowered.

The Mk1 got to space, and failed to achieve orbit, the Mk2 got a higher apoapsis, but still didn't give nearly enough time to circularize with the ion engine.

The Mk3 used a 38-7s last stage, and also added some more fuel to earlier staged - adding about 20 tons total ot the craft.

It got to orbit.

In this design, I had even sacrificed a docking port, as I didn't want to deal with the drag... 350 m/s should be enough for a rendevous... but it willneed to be clawed, or he'll need to jetpack over (clawing could get me science for a vessel return).

But... orbit... thats a good thing...

On to solve the re-entry heating issues, and more importantly, the disassembly issues.... the Mk4

Step 1: additional drop tanks to allow a propulsive landing without cutting into the fuel for ascent.... easy enough to add.

Step 2: Relocate airbrakes to the drop tanks (should help a little on ascent),

Step 3: More parachutes + airbrakes + heat shields for said items to help re-entry heating

Step 4: More struts

I tested the Mk4,

Re-entry heating wasn't too bad, only 1 strut was in need of repair after the propulsive landing, got back to orbit with a little more fuel than the mk3 (but it also started ~200 meters higher... so...)

A minor change after the test was to add fuel lines from the drop tanks, that had been omitted, so they could even help ascent a little.

Then a minor tweak to fins and heat shield orientation to get it to fit in my SSTO cargo bay (I tried SSTOing it under its own power, it wouldn't make it)

The fairing as always gave me trouble and the game was already running slow with all the parts, so I made the fairing first, then stuck in the payload...

I normally avoid part clipping, but the fairing UI is so hard to use, I make exceptions for fairings.

Looks like my eve mission is on its way... now to design a sciene payload with wings to land nearby the eve lander... because the only concession to science on board the lander is a single antenae for transmiting eva reports and such (not sure it even has enough power generation for that 4x ox stats on the lander cabin... maybe I should have added some power generation/storage equipment on the drop tanks)

Edited August 17, 2015 by KerikBalm

[Sharpy]

bad, bad clickbait.

[Red Iron Crown]

I'm not wholly convinced that an Eve SSTO is still impossible, especially if you start from that 6km high mountaintop. I think a Mammoth might be better suited to it than the aerospike. It might be that wings are worthwhile, too, now that drag is much lower than in the pre-10 aero. *rubs chin thoughtfully* Maybe I should try to put something together.

And yes, get HyperEdit, it's essential for this sort of testing.

Edited August 17, 2015 by Red Iron Crown

[QuesoExplosivo]

An Eve SSTO is definitely possible with a Kraken drive. It only needs enough fuel to get up to ~800 m/s.

[xtoro]

Would have helped, but not for the intentional clickbait...

[Kelderek]

There's really only two engines worth using at sea level on Eve: the Mammoth and the Aerospike. After those two there is a dropoff of more than 30 ISP for the next best engines (twin boar, mainsail). The Mammoth is around 198 ISP at sea level and still gives about 2500 thrust, while the Aerospike is roughly 189 ISP and only 100 thrust. The Mammoth also is handy with its 20m/s crash tolerance which makes for decent landing gear. Engine efficiency improves quickly with altitude on Eve, so it's only super important for your first stage engines if you are starting near sea level. I think that 10.6 km altitude on Eve is equivalent to sea level on Kerbin for ISP and thrust purposes.

[Agost]

Am I the only one to think that sea level Isp of the Aerospike has been nerfed too much? IRL Aerospikes have much better SL Isp compared to bell nozzles, so 300-320 would make more sense to me. Moreover they have gimbals ( again, IRL )

[KerikBalm]

awww fine, clickbait removed....

I recall seeing another thread recently about the possibility of a SSTO from above 7km...

Most eve landing threads end up talking about launching from high altitudes...

I want to launch from low altitudes, to get the full challenge, to be able to launch from anywhere on eve (though building one to survive a water(?) landing is also interesting... hmmm, I haven't tested mine on water).

I'm still not sure about the mammoth... if I was doing a 2 kerbal mission, I'd probably take them.

I know the mammoth's TWR and atmospheric Isp are preferable (surprisingly, LV-T30s produce less thrust than aerospikes, despite being the high thrust, low altitude performance 1.25m engine) to the aerospike for most of the eve ascent...

However, 1.25m aerospikes can have more staging events... asparagus staging is still pretty good.

While they "fixed" the aerospike TWR, I think it should have been given more thrust, not less mass, an aerospike can't lift a very tall stack.

The mammoth probably suffers less from drag for most of the ascent...

My problem is the mass of the mammoths.

Suppose I want to stage the mammoths in a crossfeed design... 2 outer stacks feeding to a central stack, all mammoth engines...

That is 45 tons of engines already... half the mass of my lifter in engines alone!!!

To come in under 90 tons, that leaves only 45 tons for other stuff, even if its all fuel tank, thats 40 tons of fuel maximum... and that is less than 2,000 vacuum dV...

A 3x mammoth crossfeed design is out.

Maybe 2x mammoths feeding to an aerospike center?

A single mammoth with drop tanks and a LV-909 upper?

Does anyone know how much sea-level thrust a mammoth has at eve?

Using the 1 atm thrust, a single mammoth could lift 112 tons at a 2:1 TWR under Eve's gravity, but it won't be at 1 atm. I don't know what the curve is, but a linear approximation suggests it would have a 1.82 TWR at 5 atmospheres for a 90 ton payload

Thats plenty good TWR... leaving 75 tons for other stuff to come in at the same weight or lighter.

Lets assume I leave 15 tons for the next stages... 60 tons for the first stage, subtract... I don't know, 5 tons for landing legs, chutes, airbrakes, decouplers, all that stuff

55 tons for fuel+ tanks... that leaves 48.9 tons of fuel for the first stage, assuming 260 Isp averaged (I don't know, is this right?), leaving <2000 m/s dV.

It consumes 1.3 tons of fuel/second, so assuming travel at terminal velocity (it will do worse), it burns for 37.6 seconds, losing at least1,256 m/s to aero and gravity drag

Thus reaching about 750 m/s straight up, it won't even reach 15km... will a 15 km start be enough for the 15 ton upper stage to make it?

I don't know... it seems dubious to me that it will result in a smaller lander than the aerospikes, I'd love to see some working examples of sea level eve ascent vehicles that come in under 90 tons.

I had a look at:

http://garycourt.github.io/korc/

But I'm not sure of the required dV I should enter, and i'm pretty sure it uses the atmo stats at 1atm in the calculator, not eve's 5 atm.

[Red Iron Crown]

IRL Aerospikes have much better SL Isp compared to bell nozzles

They do not. A real life aerospike is always worse than a bell nozzle at that bell's optimum pressure; a bell optimized for sea level pressure will beat any aerospike. The aerospike's advantage lies in less variance with changing atmospheric pressure.

[Laie]

Near sea level, aerospikes are the best engines even in terms of TWR. The Mammoth is hardly worse, though, and makes for a much more bearable part count. At a 6km mountaintop, mammoths or mainsails should be the way to go.

As to SSTO, I don't think it's doable yet. Can you pack 6km/s into a single vessel of sufficient TWR? The atmosphere also is rather odd. The problem of not burning up forces a pretty steep ascent at any rate, and then I found that there was very significant drag as high as 80-90km... ultimatley my launch approached the "straight up then turn left" paradigm with circularisation burns on the order of 2km/s, because any attempt at speed-building while in atmosphere turned out to be too costly.

The perceived amount of drag at 90km(Eve) equalled about 35km(Kerbin). I didn't measure it or look at numbers, but this is how it felt like.

Edited August 17, 2015 by Laie

[KerikBalm]

Near sea level, aerospikes are the best engines even in terms of TWR.

You mean Eve-sea level? They are the best 1.25m or 0.625m engine, undoubtedly.

The Mammoth is hardly worse, though, and makes for a much more bearable part count. At a 6km mountaintop, mammoths or mainsails should be the way to go.

I had a look in the VAB with KER, and using the stats it says...

At sea level(eve) the Aerospike gets 230 Isp, The mammoth gets 193.2

9.8:1 TWR at Eve sea level for the mammoth, the Aerospike, only 7.3...

I seem to recall a recent patch changed the thrust/Isp curve for aerospikes, that must be the reason for the discrepency with Kelderik's numbers

The mammoth suffers more than I thought... I thought it would do better as its Isp at 1 atm is better than the aerospike.

Looking at the stats KER shows for eve sea level... the mammoth looks terrible... It doesn't equal the Aerospikes Isp until 5.3 km, then it has a better Isp than the aerospike until 14.3km, at which point the aerospike overtakes it again... but ascending those first 5.3km takes a lot...........

As Red mentioned, an aerospikes advantage is being near optimal across a wide pressure range, but at each pressure you should be able to design a bell nozzle that is better.

The problem is that the mammoth, should be optimized for somewhere above 1 atm, and have significant underexpansion on Eve.

As to SSTO, I don't think it's doable yet. Can you pack 6km/s into a single vessel of sufficient TWR? The atmosphere also is rather odd. The problem of not burning up forces a pretty steep ascent at any rate, and then I found that there was very significant drag as high as 80-90km... ultimatley my launch approached the "straight up then turn left" paradigm with circularisation burns on the order of 2km/s, because any attempt at speed-building while in atmosphere turned out to be too costly.

Well, my gravity turn started slowly after passing 20km... I'm not sure if that was best, but it worked, I don't think I was really pitched over much until about 60km.

Edited August 17, 2015 by KerikBalm

[Kelderek]

I had a look in the VAB with KER, and using the stats it says...

At sea level(eve) the Aerospike gets 230 Isp, The mammoth gets 193.2

9.8:1 TWR at Eve sea level for the mammoth, the Aerospike, only 7.3...

I seem to recall a recent patch changed the thrust/Isp curve for aerospikes, that must be the reason for the discrepency with Kelderik's numbers

I apologize, you're right, they must have changed the aerospike in a more recent version. My numbers came from an earlier 1.0.x release.

I failed miserably when I tried an Eve ascent in my first post-1.0 career game. I had no trouble getting to orbit from sea level on Eve, my trouble was with landing safely on Eve - I always had trouble with re-entry tearing up my large ships. But my launches worked fine if I hyperedited the ship to the surface. I was also trying to get all 4 of my orange suit kerbals there and back too, so that necessitated a bigger design. This has always been such a great challenge in this game that it always seems to suck me back in from time to time to try it over and over again.