Return from Eve by Spaceplane

[Crush]

I would soon like to try the holy grail of Kerbal Space Program: A manned Eve return mission. Considering that Eve has such a thick atmosphere, I wondered if it would maybe be better to use it instead of fighting it and design my lander not as a rocket but rather as a spaceplane and have it land and start horizontal, aided by atmospheric lift.

The plane will be detached from an interplanetary transfer stage and only used for getting from Eve orbit to Eve surface and back to Eve orbit. Building the lander single-stage is not a must-requirement.

Do you think that this is a viable plan compared to a horizontal lander? Which and how many engines should I use (I know I can't use jet engines) and how much fuel would I need?

Edited July 29, 2013 by Crush

[El wonso]

I think using spaceplane would require more dV. I'd go for rocket.

Looks like aerospike is your new friend

[Immashift]

The problem with your design is that rocket ISP in chicken noodle soup atmosphere is roughly on the bad side of ATROCIOUS.

The more time you spend in the "I can drink this" thickness, the more fuel you burn fighting to get through it. My own return ship used piles of TWR to get through the thick crap ASAP. My ascent profile was something like straight up to 80km then gain horizontal velocity.

The lift of your wings is never going to make up for the wading through the atmosphere your engine is forced to do. Not unless you can use jets. Problem is jets don't like running on purple soup.

My current one floating in orbit uses Hooligan Labs airship envelopes to float up past most of it. You may or may not consider that cheat-y.

Edited July 29, 2013 by Immashift

[SnappingTurtle]

If you get the kethane mod you can use the kethane jet engine in atmospheres without oxygen, though you might also consider this cheat-y.

[numerobis]

You'll need a very large plane -- pa1983 style. And jets don't work, meaning you'll need to use rockets and build a plane that drops stages. So, take pictures when you fly this thing!

[kahlzun]

If you don't mind exploiting the physics, you can try to use control surfaces to infiniglide from Eve's surface. If you did it right, you can (potentially) get suborbital with no fuel burnt [citation needed]

[Immashift]

I may give it a stock, serious attempt at some point, but I was happy designing a big blimp with rockets. It's actually moderately difficult even with mods to do.

[dlmarti]

Eve's two greatest problems are the high gravity, and the thick atmo.

Trying to use one to your advantage is not a bad idea.

I am just not sure if the game mechanics have progressed enough to exploit it.

It has been well documented that launching rockets from airships is a viable and cheaper way to go, at least in real life.

[Crush]

Blimp mod... Kethane mod...

Nope, I won't cheat. Only stock accomplishments are real accomplishments.

The problem with your design is that rocket ISP in chicken noodle soup atmosphere is roughly on the bad side of ATROCIOUS.

It shouldn't be that bad with Aerospikes. And atmospheric drag depends on speed, so going slowly should me more efficient, and the only way to go slowly without losing too much delta-V to gravity is by having plenty of wings generating plenty of lift. At least that's my theory.

Edited July 29, 2013 by Crush

[astropapi1]

The advantage of planes on Kerbin and Laythe is the jet engines, which are extremely efficent, but on Eve, you'd be doing nothing but carrying the extra dead weight of the wings and following a super steep ascent trajectory.

[Alfondoo]

I literally just posted this in another thread about getting off eve in the general discussion.

It can get to a 150km orbit around Kerbin without firing the jets up at all (dropping them before takeoff). With the jets it takes me all the way out to that distance with 2km of delta/v left in the command pod/winglet stage.

EDIT: Just in case of "pics or it didn't happen"

Just after decoupling and about to finish up -

Edited July 29, 2013 by Alfondoo

[tavert]

Stochasty has done this, but it needed 3 stages (2x aerospikes, asparagused into 1x T45, then 1x LV-909 IIRC) and was designed for use with FAR. Spaceplanes are tricky to land, especially at the high-altitude sites that you really need to reduce delta-V cost for Eve ascent.

A single-stage aerospike-powered rocket just can't have both the delta-V and TWR that Eve requires. If you build something extremely large, you may be able to get away with aerospikes initially then LV-N's to finish the ascent, but I have yet to see this work in practice.

So this requires multiple stages, and making a multi-stage spaceplane that is properly balanced and structurally sound is a very difficult task. There is some benefit in that you can have a lower TWR with a spaceplane style ascent than a conventional rocket so more of your craft mass is devoted to fuel, but it seems to me that the more-horizontal trajectory you need outweighs any delta-V capacity advantage the spaceplane may have.

Edited July 29, 2013 by tavert

[Crush]

making a multi-stage spaceplane that is properly balanced and structurally sound is a very difficult task.

A week ago I would have agreed with you, but the new SAS makes it much easier to control a plane where the center of lift isn't exactly on the center of mass. Edited July 29, 2013 by Crush

[numerobis]

Nao's best rocket was over 40t in 0.19.x (lost in the forum database crash): 2x RT-10, 4x aerospikes, 1x LV-909, and 3x 24-77s; the Mk1 capsule, and pretty much no other fluff, just fuel. It could, with Nao's flying skills, just barely make orbit starting from the highest peak in that release; my best attempt got within 100m/s of making it, but I never quite succeeded in replicating the feat.

Your plane would need to be about that size. You might not need quite as much TWR on launch, but any mass you save in engines you'll pay in fuel.

[KerbMav]

Is it possible to mod propellers running on electricity to whirl up a bit first?

[numerobis]

Firespitter is your mod.

[Stochasty]

Stochasty has done this, but it needed 3 stages (2x aerospikes, asparagused into 1x T45, then 1x LV-909 IIRC) and was designed for use with FAR. Spaceplanes are tricky to land, especially at the high-altitude sites that you really need to reduce delta-V cost for Eve ascent.

A single-stage aerospike-powered rocket just can't have both the delta-V and TWR that Eve requires. If you build something extremely large, you may be able to get away with aerospikes initially then LV-N's to finish the ascent, but I have yet to see this work in practice.

So this requires multiple stages, and making a multi-stage spaceplane that is properly balanced and structurally sound is a very difficult task. There is some benefit in that you can have a lower TWR with a spaceplane style ascent than a conventional rocket so more of your craft mass is devoted to fuel, but it seems to me that the more-horizontal trajectory you need outweighs any delta-V capacity advantage the spaceplane may have.

I have a working stock version now, also - well; partially working. She's ten stages, asparagus staged, total of around 12km/s delta-v, and will make it to orbit in stock from any landing site above 4km altitude. The core is essentially the same as my FAR version, but with added drop tanks and a few more engines for thrust. Unfortunately, she's not capable of launching herself from Kerbin without staging, and landing is a pain to say the least, so I haven't yet succeeded in flying the mission for real. I'll post a video of it as soon as I manage it.

As an interesting note, the ascent from sea level up to 4km altitude costs over 4km/s delta-v, so I'd need to more than double her size to pull off a sea-level return.

Regarding mass and delta-v requirements for spaceplanes versus rockets: much testing on Eve makes it clear - there is /no/ advantage to wings. You are better off with a rocket. Yes, you can get off the ground with a sub-1 TWR, letting you carry twice as much fuel per stage as an optimal rocket, but you are much less fuel efficient during ascent out of the thick atmosphere since you end up flying a shallow trajectory. There may be a slight efficiency gain during the gravity turn, since you start picking up horizontal velocity much sooner than a standard rocket (AKA, you are trading worse efficiency as regards drag losses for better efficiency as regards gravity losses), but it is vastly outweighed by efficiency losses during the early climb.

On Kerbin, this is barely noticable (I've mentioned before that I've put spaceplanes into orbit for roughly the same delta-v requirements as rockets); however, on Eve, you spend so much more time in the thick atmosphere, and drag losses are so much higher compared with gravity losses, that the loss in efficiency is extremely noticable. That said, spaceplanes are fun; hence why I've been working on my Eve plane. Just, don't expect building a plane to make the mission easier.

Edited August 2, 2013 by Stochasty

[numerobis]

One proposal for a sea-level return is to drive up from sea level to a high peak, and launch from there.

[Stochasty]

That would probably take hours of tedium.

That said, I've serously considered it, which should indicate how difficult sea level return really is.

[Kulebron]

I checked parts weights, and see the wings weigh about 70 kg each, making less than 500kg, and I need only one aerospike engine to get reasonable speed, unlike a rocket in which I need many engines to lift... many engines and fuel for them.

As I tried making a return rocket (only to get into Eve orbit, the return ship will wait there), I got a 2 layers of asparagus staging around LV-T30 and FL-T800 . With rocket engine I needed much less fuel, less staging. I tested a plane with 1 aerospike and another stage with LV909 . I still have no skill in landing, but this looks promising to me.

[Stochasty]

Kulebron, I don't want to discourage anyone from trying this, but you should be aware (and if not you'll find out quickly as you start making attempts) that wings are not a magic answer to getting out of Eve. While they let you fly wth relatively low thrust, there's a big difference between just getting off the ground and into orbit; the problem is that you spend a lot more time in the low atmosphere fighting drag than you would with a comparably sized rocket, so any savings gained on reduced engine weight is lost due to the requirement for correspondingly more fuel.

This should give you an idea of what it actually takes to pull off spaceplane-style Eve ascent.

[Sirine]

Nope, I won't cheat. Only stock accomplishments are real accomplishments.

It shouldn't be that bad with Aerospikes. And atmospheric drag depends on speed, so going slowly should me more efficient, and the only way to go slowly without losing too much delta-V to gravity is by having plenty of wings generating plenty of lift. At least that's my theory.

If without mod, Jet and Turbo Jet Engine can't run at Eve, cause Eve does not have Oxygen.

So, you will have to use "Liquid Fuel Engine" with Wings...Just try it out at Kerbin. You need about bringing 1 full orange tank of fuel left to Kerbin orbit, before you try out Eve.

[MrPopcup]

Actually, THIS is the craziest thing i've ever faced! Getting out with the rocket is almost Impossible ( though I did return from eve..)

But imagine this;

A rocket starts going vertical, and climbs FASTER than your spaceplane, then the rocket will turn at a high altitude and start gaining more horizontal velocity, that being said, the rocket is more efficient than a spaceplane, you would need more than 15k delta-v to successfully reach orbit ( rocket needs 12k from Sea level ), also, if there was oxygen in the atmosphere so you could use the normal jet engines ( they wont work, cause there is no oxygen on eve )THAT would be much easier than a rocket!

So: if you so this with a spaceplane and all stock, I can assure you, you would be the most known guy in the forums!

Edited October 12, 2013 by MrPopcup

[Stochasty]

Check the post I linked, MrPopcup. I've done it. All stock. It was a pain; by far the hardest thing I've ever done.

You are off on your delta-V calculations. From 2km altitude, I managed to reach orbit with a total delta-V budget of about 12km/s. Still not easy, but much, much easier than the 15km/s you were guessing. (15km/s from sea level might be about right; those first few km of altitude are killer.)

Edited October 12, 2013 by Stochasty

[thescientist]

It shouldn't be that bad with Aerospikes. And atmospheric drag depends on speed, so going slowly should me more efficient, and the only way to go slowly without losing too much delta-V to gravity is by having plenty of wings generating plenty of lift. At least that's my theory.

Remember that 5 atmos mean LOT of lift with reduced wing-problems start to appear when you're higher.

Landing on an high mountain may reduce dV requirement but is quite problematic: the gruond ISN'T flat, so this may cause problem. Another thing: a big plane with an exteme dV has probably an elevate landing and (even worse) take-off speed even with a dense atmosphere (Ok, apologize, you need many wings). Also in real life planes have a "max landing weight" and must drop some fuel (-SPLAAAS-ooops, sorry Bob:mad:) to land safely if they exceed that limit.