Eve SSTO possibility?

[Jod]

I am determined to make a single stage lander-lifter for Eve, and looking for possible configurations. I've gone over the math for 11500 delta-v required and it seems that only Ion engines and nuclears( >600 Isp when above 20 000m) can lift a single stage from Eve surface. At a ridiculously sluggish pace as you can imagine. Aerospikes are not even close to the needed Isp, falling short by a third or so.

Has anyone tried to make this kind of craft? I would imagine a lot of nuclear engines, even more ionic ones, and a single aerospike(to at least somehow boost the craft) can pull that stunt off with 1-2 tons of cargo(some kerbals at least... i dunno, in seats?), though I have my doubts about this setup, especially if the drag eats up the really slow acceleration it provides.

Edited October 11, 2014 by Jod

[ApocSurvivor713]

You may be able to pull it off if you use seats. I really have no idea how to help aside from that, but do try to keep it light. You may also want to use drop tanks for fuel. That way, you actually drop weight as you go up. Good luck!

[kahlzun]

If you're not too caught up on being all stock, the Hooligan airship mod will make your life much easier...

...also, the ion engine isn't able to lift itself on Kerbin, let alone Eve.

Bringing those along will just increase the weight of the craft.

[Sephta]

I remember some eve landers posted here in the forum, but a SSTO? I don't recall one (at least not stock)

I think your best chance is a spaceplane - you can basically glide down all the way and you don't need a TWR over 1 to go back, so nukes ans Ions get a possibility. As the max dV for a nerva is around 17000m/s it should (theoretically) be possible to build a ssto spaceplane go from LEO to surface and back.

Hints:

Eve also has a plateau, that's quite high. Most people use this as landing destination.

You could use the Kethane mod to refuel on Eve, the Kethane-Jets don't need oxygen to work.

[HoY]

I second the Spaceplane SSTO method. lower than 1 TWR is your best bet

[Nao]

I don't think it's possible, even with a Spaceplane.

Aerospike engines have a maximum Dv of around 7600m/s on one stage with payload being only 1% of ship's mass. So even if we take the perfect plane (Dv requirement same with rocket ascent, but with much lower thrust avilable) it's still not enough energy to ascent and accelerate out of Eve's atmosphere. And any other engine has less Dv in atmosphere...

Except the PB-ION, although its already extremely hard to to Kerbin SSTO just on electric power. Eve would be even harder.

edit: i'm talking mostly stock here, airship mod could help a ton here.

[tavert]

The LV-N has better Isp than the aerospike above altitude 13670m on Eve, but it's quite heavy to lift up to that altitude. Theoretically you would need aerospikes and maybe some SRB's to get you off the ground, and one or more LV-N's to finish the ascent (route the fuel so it runs out for the aerospikes first). I never got very far in trying this, the TWR and delta-V of the LV-N "pseudo-stage" are pretty lousy if you have to carry all the empty tanks and out-of-fuel aerospikes the whole way to orbit. I'm not sure whether you would need the extra thrust of the LV-N(s) enough that it would be better to turn them on even at the low inefficient altitudes, or if it would be better to keep them off until their efficiency increases.

Without using balloons from a mod, this would be exceptionally difficult, presumably impossible until we see someone pull it off.

[Jod]

...also, the ion engine isn't able to lift itself on Kerbin, let alone Eve.

Lol I forgot to mention I am making a glider. I'm making everything in the aerospace hangar as I haven't even touched the vehicle assembly building once.

Drop tanks are out of the question, it won't be an SSTO with them. And without drop tanks, for liquid fuel the dry mass is at least 1/9 of the full mass, which rules out any engine with an Isp less than 600.

Ion engines have really, really low TWR, but flying with them is not a problem, the problem is accelerating within reasonable amounts of time. So if they can get a fuel tank+nuclear engine to 20 000m in less than 30 minutes I think it is possible to pull off. I will try this on Kerbin and see how it goes.

[tavert]

The unfortunate thing about ion planes is with stock aerodynamics, you'll be getting much more thrust from infiniglide than the ion engine(s), assuming you have any control surfaces and touch the controls at all. Maybe people have had success with ion planes using FAR, dunno.

[Nao]

Also, there is one more way i try to get to work from time to time (always with catastrophic results ).

It could work in theory!

With drag model as it is in KSP every ton of fuel/engines will contribute to drag, why not let only wings go fast, and make the heavy fuel slowly ascent through the dense atmosphere.

[kahlzun]

that's a question: how well does infiniglide work on Eve? You should be able to get a stock SSTO using that...

[tavert]

Probably quite well. I don't know if the glitchy ladder physics was fixed in 0.20, but the FTL egg worked perfectly on Eve in 0.18 and/or 0.19. I think an SSTO that relies on glitchy physics is less of an accomplishment in most KSP players' opinions.

[Mihara]

It's very unlikely to be feasible with stock parts. It would be feasible if Eve had oxygen, but -- pure rocket planes don't SSTO very well even on Kerbin, on Eve the task is magnitudes harder.

With mods, Hooligan Airships are known to be capable of SSTO on Eve with parts otherwise stock, and you might have a chance with the kethane turbine. Both would probably be even better.

[Richy teh space man]

If you do manage to make a stock Eve SSTO, feel free to post it in this thread: http://forum.kerbalspaceprogram.com/showthread.php/33352-Mods-Reusable-Eve-SSTO I think it'd win the competition.

There's also a couple of designs in there that might inspire you, but I seriously doubt it can be done with stock, unless you exploit game glitches.

[Jod]

Unfortunately, my PC can't handle more than 400 small solar panels(ones that don't break in atmosphere) and the PB-NUK are too heavy, so looks like the ions are not an option for me. Trying with an aerospike and LV-Ns. Math says it's gonna be close.

[Rune]

If you manage to make a working Eve SSTO with a stock KSP install, and without abusing bugs like infiniglide (though how you would make an infiniglider with fuel and rockets is another "interesting" proposition), I promise to eat the hat of your choice. Seriously.

Rune. Every once in a while someone will get the urge to try this. So far, nothing to show for it.

[Anglave]

I assume you'll be starting your ascent from the highest point on Eve (that your plane can take off from)?

I've been working on a (decidedly NOT single stage) Eve Lander that can lift a single "lander can" from sea level to orbit. It's a 280t lander, 14 stages of Aerospikes. I'm with Rune, if you can SSTO this [stock] and without significant infiniglide contribution, I'll eat a hat.

[Jod]

Currently testing a low TWR 7000 delta-v(calculated with an average 500 Isp) aerospike/LV-N combination on Kerbin. It can get to space, but atmospheric drag eats a LOT of delta v, which is my prime concern. Does anyone know how terminal velocities work? How much does meeting terminal velocities improve burn efficiency? Low TWR planes don't look very promising at this point.

[Anglave]

The longer your ascent takes, the more ÃŽâ€v you'll lose to drag. You'll want to go really slow low in Eve's atmosphere, it's like peanut butter. This article might help you.

I'm convinced that due to the way KSP models drag, the most efficient ascent path is a traditional vertical launch. A spaceplane trades engine and fuel mass (since you can use less thrust) for additional wing mass and losses to drag. The big benefit in KSP is that jet engines are more reasonable for space planes than rockets. But jet engines are not going to work on Eve.

That said, efficiency and low mass don't need to be your goals. If you can make an ascent using a plane with many acres of wing area, pushed by many ion engines - perhaps using much more ÃŽâ€v than a traditional ascent, you might still make it.

Earlier in this thread I saw the concept of "maximum ÃŽâ€v" tossed around. I'm unfamiliar with the concept. Does it relate to SSTO limitation, or planetary launch limitations? (I could see an engine having a max ÃŽâ€v because it can't lift more than X amount of fuel). How is this "max ÃŽâ€v" calculated, how does using a plane style ascent rather than a vertical ascent affect the calculation?

Edit: more thinking on maximum ÃŽâ€v. In interplanetary space, and with a willingness to stage away spent fuel containers, no engine has a maximum ÃŽâ€v (well, except as dictated by part count or a craft's maximum size, arbitrary game engine limitations).

On direct planetary ascent, an engine has a maximum effective ÃŽâ€v because it can't lift more than a certain amount of fuel and maintain a TWR > 1.

This consideration is affected by doing a spaceplane ascent; you can have TWR much less than 1 and still go up. However, there's still a maximum amount of fuel a given engine can lift.

I'm still not seeing the "single stage" limitation on my own, though. Even if you start with 100 orange fuel cans and a single mainsail, assuming it can go "up" at all, the mass of the craft will only go down as you continue to thrust. Sure, it's inefficient to carry all that dead weight, but 101 orange cans will still have more ÃŽâ€v, right? 102 cans has more than that... Or is that not true?

Adding more fuel mass reduces the effect of thrust, which reduces the ÃŽâ€v of all the fuel you're already carrying. If you have to spend most of your flight also carrying the dead weight of the spent fuel container, is there a point of diminishing return?

Edited June 6, 2013 by Anglave

[tavert]

There are several concepts of "max delta-V," all of which are only strictly valid for a single stage with a single type of engine. One of these concepts just considers the mass ratio of the stock fuel tanks, which is 9 for all bipropellant tanks except the tiny ones. So for bipropellant engines, even in the limit of infinitely many fuel tanks per engine you can never get better than Isp*9.81*ln(9) delta-V.

The other concept also considers mass of the engines, and is the max delta-V to achieve a given acceleration (or TWR for some given planet/moon). You take the thrust of an engine, divide by the required acceleration to get initial rocket mass, subtract the engine mass (and any payload) then multiply by 8/9 to determine how much fuel mass you can carry to achieve the required acceleration for a given engine. So that gives you the max delta-V you can carry for a given engine to, for example, achieve TWR=1 on Kerbin or Eve, which is the minimum you'd need at least for a vertical ascent. Lower TWR is possible with planes, giving a higher max delta-V but requiring a less efficient ascent trajectory.

Both of these concepts can be slightly worked around by what I call "pseudo-staging" (my own completely made up term, take with grain of salt), by which I mean using different combinations of engines at different times of the ascent. It's like a stage since the Isp changes and you can slightly get around the above concepts of "max delta-V" by changing engine types, but not by too much since you still have to carry the empty weight of your initial tanks and disabled engines.

[MR4Y]

It's very unlikely to be feasible with stock parts. It would be feasible if Eve had oxygen, but -- pure rocket planes don't SSTO very well even on Kerbin, on Eve the task is magnitudes harder.

With mods, Hooligan Airships are known to be capable of SSTO on Eve with parts otherwise stock, and you might have a chance with the kethane turbine. Both would probably be even better.

And SasquatchM's Pulse Detonation Engine as well.

[Nao]

Currently testing a low TWR 7000 delta-v(calculated with an average 500 Isp) aerospike/LV-N combination on Kerbin. It can get to space, but atmospheric drag eats a LOT of delta v, which is my prime concern. Does anyone know how terminal velocities work? How much does meeting terminal velocities improve burn efficiency? Low TWR planes don't look very promising at this point.

There are some great knowledge bombs above me but i would add that while going at terminal velocity is the most fuel effective way to ascent, due to engine weight (especially high on Eve) it might be better to ascent a little more slowly (around 1,8 TWR) burning more fuel but having less engine weight, that in the end could mean lower empty mass for when you switch to LV-N, giving it more Dv. This mostly works for staged craft's that can keep their TWR near constant.

For SSTO i think it's only important to not overspeed above terminal velocity (mechjeb or KER can show it in flight) and have launch TWR not lower than ~1,3-1,4 as more fuel only marginally increase performance (the added Dv of more fuel is lost in increased inefficiency of launch profile)

Also another thing to consider is the use of SRB's , they have only 225 ISP but their engine mass is *really* low and their (idk how to call it) energy efficiency per mass is great even in atmosphere. I have used them successfully in getting 50t craft with mk1 pod from ground to Eve orbit.

[M5000]

The only real way to do an Eve SSTO is to do an ion-powered spaceplane. The thicker atmosphere should help, but it's going to take a LOT of parts. (There also needs to be a higher thrust stage for that awkward time in the not-quite-space upper atmosphere. Maybe a NERVA and one of the longer fuel tanks. Ion engines as main propulsion, shave off ANY weight you can. Maybe even get rid of RCS and when it's time to return the Kerbal to the mothership, just have him EVA. And definitely use seats, just remember to shield the pilot on the way in

[animalcross]

I doubt this is possible, may give it a shot at one point though. I think your best bet might have to result in dropping at least one stage.

[Jod]

Unfortunately, I don't think there is a way of refueling SRBs...

As for liquid fuel - I'm getting immence drag due to huge fuel tanks required, which pretty much rules out aerospikes as an initial ascending engine. So the real problem right now is getting to at least 15 000m height, after which LV-Ns work semi-well.

Can anyone post links of good Eve ion planes? I am still considering that option.