Eve SSTO is impossible!

[GoSlash27]

Just so I'm absolutely clear here, because I've been fooling around on Kerbin with interesting results:

- slap a skipper onto an orange tank (plus the minimum other stuff) and you have something with 5300 dV and plenty of thrust to reach orbit

- slap a pair of LV'Ns onto an orange tank and you have something with 12000 dV and enough thrust to slightly cushion the blow as you fall from the launch clamps to the pad

- slap all 3 on, and let them all run, and you run out of fuel before reaching orbit (if you just activate the LV-Ns you have 9740 dV but again not remotely enough thrust to go anywhere but down into the irradiated ground)

- however: slap all 3 on and manually reduce the skipper's thrust as you head up, so that you maximize the amount of contribution by the 800 ISP LV-Ns, and you wind up in orbit with a pile of dV left

By continuously shifting downwards the contribution of the less efficient engines to the ascent, and ultimately running from just LV-Ns (a much larger setup than the above would be required), could you pull it off? From a practical point of view I have no idea how you would throttle down a pile of engines one by one without spinning out of control...

Or is this approach negated by the pure math discussion above?

Unfortunately, yeah. The DV isn't additive like that.

Best,

-Slashy

[TheScareCake!]

Everything's good, but lv-n has different isp while in atmosphere. I think you can reach it using 5m parts from kw rocketry, those have enough thrust to... Blow the kraken away. *badumtss*

[James_Eh]

Hmph. So - can I extrapolate this discussion to figure out what the max dV available at 100x100 LKO would be for a purely liquid-fuelled vessel? (No air-breathers, no ions.) I had always figured that making orbit with a ship like this was nearly impossible, then the 23.5 parts came along, and now I am sitting as above at 3.5km/s dV. But I am beginning to believe that to boost that up to, say, 5.5, is impossible, despite the wings I have started to add and the fooling around with my ascent profile. My spreadsheet resolutely refuses to help me figure out whether the wings are hurting or helping, I am resorting to empirical testing...

[James_Eh]

Everything's good, but lv-n has different isp while in atmosphere. I think you can reach it using 5m parts from kw rocketry, those have enough thrust to... Blow the kraken away. *badumtss*

Yah, but by the time you reach a few thousand meters it is already out-ISPing everything else, just it is way too heavy to use as a primary lifter due to its thrust limitation.

[thereaverofdarkness]

Or is this approach negated by the pure math discussion above?

It's negated by the atmospheric Isp curve. The LV-N doesn't even become as efficient as a Skipper until something like half an atmosphere or lower.

[GoSlash27]

Hmph. So - can I extrapolate this discussion to figure out what the max dV available at 100x100 LKO would be for a purely liquid-fuelled vessel? (No air-breathers, no ions.) I had always figured that making orbit with a ship like this was nearly impossible, then the 23.5 parts came along, and now I am sitting as above at 3.5km/s dV. But I am beginning to believe that to boost that up to, say, 5.5, is impossible, despite the wings I have started to add and the fooling around with my ascent profile. My spreadsheet resolutely refuses to help me figure out whether the wings are hurting or helping, I am resorting to empirical testing...

Well... the rocket equation still holds. An infinitely large liquid rocket will never exceed 9:1 Md/Mw due to the tanks themselves. This translates to 21.6 * whatever Isp you throw at it. 17,244 M/sec at the absolute limit. Assuming that you hold the LV-N to .5G at Eve (injection and circularization), you're looking at 7.2MT total mass. 4.5T of this is the LV-Ns themselves, so setting aside your skipper, payload, and the fact that you're carrying largely-empty tanks, that leaves 2.7T of fuel. This yields (and I must stress that the actual value would be a lot less than this) 3,689 M/sec DV. Now remember that your Skipper is 3 tons, which means that as a practical matter you couldn't inject a skipper into orbit using 2 LV-Ns even with no fuel tanks whatsoever and infinite fuel turned on. But for the sake of argument, we'll let that go.

You still have to make 4,800 m/sec from your Skipper to get the LV-Ns to the point where they can finish the job. Skipper's 3 tons. The LV-Ns are another 4.5 tons. Crunching the numbers yields 4.61 mass ratio. 42 tons of fuel, not counting the tanks themselves. This is well- over the mass a Skipper is capable of lifting at even 1G from Eve.

So even taking all those liberties, this doesn't work from either end. It's too heavy to get off the ground, doesn't account for the mass of the tanks, and if it did get far enough to kick in the LV-Ns, there'd be no fuel left and the LV-Ns would be too weak to inject it into orbit anyway. This isn't counting the payload.

But still... you might stumble across something we've missed and the math *could* be wrong on this. KSP, after all, isn't a perfect model for real life.

Sorry to be the bearer of bad news!

-Slashy

[thereaverofdarkness]

GoSlash27 what do you think of my proposition at the end of page 15?

I made a ship to demonstrate the principle...

...but it barely got into LKO so this particular design probably won't work for EVE ascent.

Edited August 3, 2014 by thereaverofdarkness

[GoSlash27]

Really, your best bet (assuming you're using wings) is to use engines that have the best Isp in atmosphere coupled with the best Isp in vacuum at the top end. Happily, these are both the same engine; ion thrusters. They beat the stuffing out of everything else in the game for pure Isp. Which is a good thing, 'cuz using wings means that your Isp requirement is going to be much higher than a pure rocket due to the drag losses.

Of course... nobody has (as of yet) created an Ion SSTO from Kerbin, let alone Eve. At least not one that doesn't infini-glide...

[GoSlash27]

Reaver,

Hydrogen balloons would probably be ideal for this job... if they existed.

As for the rest of it, it would negate the entire point of SSTO. The idea is to create a vehicle that could make round trips to the surface of Eve and back to orbit without needing anything other than fuel. Staged landers/ ascent vehicles aren't a challenge. We've already figured out how to do that.

The entire point of this challenge is to attempt to answer *definitively* whether an Eve SSTO is possible with stock parts and without resorting to cheats.

Best,

-Slashy

[James_Eh]

But still... you might stumble across something we've missed and the math *could* be wrong on this. KSP, after all, isn't a perfect model for real life.

-Slashy

Taking the liberty of paraphrasing - "Let's see how many rockets this dunderhead strews into the purple sands of death!"

Challenge accepted!

(Mmph, first challenge is I have never used HyperEdit before... Why is this thing near Eeloo? I clicked Eve dammit...)

[thereaverofdarkness]

Well I'm pretty sure it's impossible with currently existing parts. But it seems more fun (to me) to make the challenge marginally possible or at least if it is impossible, to be almost possible. Making an ion SSTO from Kerbin would be almost possible if not possible because the engines can almost carry their own weight at the surface. With lightweight wings and solar panels, one might be able to carry itself high enough in the atmosphere to become light enough to send off after the air stops providing lift.

Also, I should have checked how much more dV was left in that rocket I posted above, because my rudimentary calculations suggest 1541 m/s. Maybe it is powerful enough to get from a high mountain on EVE to orbit, only by dropping the engines.

[James_Eh]

Oh and BTW, the first example I gave was just the first thing I slapped together. No more skippers in the design, just those 3.75m single engines plus LV'N's plus wings. Lots and lots of wings. (Absolutely no control surfaces though, don't need 'em and don't want to muddy the purple water more than I already will when I careen into the Evian ocean.)

[GoSlash27]

Taking the liberty of paraphrasing - "Let's see how many rockets this dunderhead strews into the purple sands of death!"

Challenge accepted!

(Mmph, first challenge is I have never used HyperEdit before... Why is this thing near Eeloo? I clicked Eve dammit...)

Certainly not calling you that! I really want somebody to succeed at this, and whoever does will have a rightful place in KSP Valhalla.

Best of luck!

-Slashy

[GoSlash27]

Well I'm pretty sure it's impossible with currently existing parts. But it seems more fun (to me) to make the challenge marginally possible or at least if it is impossible, to be almost possible. Making an ion SSTO from Kerbin would be almost possible if not possible because the engines can almost carry their own weight at the surface. With lightweight wings and solar panels, one might be able to carry itself high enough in the atmosphere to become light enough to send off after the air stops providing lift.

Also, I should have checked how much more dV was left in that rocket I posted above, because my rudimentary calculations suggest 1541 m/s. Maybe it is powerful enough to get from a high mountain on EVE to orbit, only by dropping the engines.

I'm also pretty sure it's impossible using stock parts without cheating. And I also agree that it's not all that much fun to bang your head against a challenge that doesn't look even close to doable. But this challenge is about answering a question, not having fun.

As for the Kerbin Ion glider, I have posted a challenge for that. http://forum.kerbalspaceprogram.com/threads/85728-Ion-glider-collier-trophy! That one is maddeningly close to possible, but hasn't been beaten yet. It's fun, but burns you out...

Try your hand at it

-Slashy

[RuBisCO]

Yep it is impossible, with stock parts. You can try launching from the highest point on Eve, I tried 6500 m, still needed 8000 m/s of delta-v to make it. Without stock parts it can be done easy, and reusable with kethane. I can use balloons to float up to 30 km and then its needs only ~4500 m/s to get to 110 km circular orbit.

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[TheKutKu]

One question: has anyone tried to do an ion-powered plane and take it off eve? Ion Powered planes work on kerbin, maybe they can work on eve.

[GoSlash27]

One question: has anyone tried to do an ion-powered plane and take it off eve? Ion Powered planes work on kerbin, maybe they can work on eve.

Ion planes are the one method that has kept us from declaring this outright impossible. They can work in theory... but in practice so far we have yet to make Kerbin orbit with one that doesn't infiniglide.

But perhaps an ion glider coupled with something else? *shrug*

Best,

-Slashy

[TheKutKu]

So, an eve ssto is impossible without wings/control surface.

Maybe ion for taking off and climbing up and nuclear for speeding up and going to space?

But it would need many Ion engines and wings.

hmmm...

I'm sure it can be done!

[thereaverofdarkness]

does loss of parts due to overheating or air resistance count as staging if they were placed on the rocket in a reasonable way and it truly looks accidental that they broke off?

Of course that denies re-usability, but perhaps a craft that was previously re-usable can make it to space through a series of "accidents" and accidentally get part of the thing into orbit.

Edited August 4, 2014 by thereaverofdarkness

[zarakon]

So, an eve ssto is impossible without wings/control surface.

Maybe ion for taking off and climbing up and nuclear for speeding up and going to space?

But it would need many Ion engines and wings.

hmmm...

I'm sure it can be done!

Try it on Kerbin. I don't expect you'll get far.

If it doesn't at least work on Kerbin, it definitely won't work on Eve.

[GoSlash27]

does loss of parts due to overheating or air resistance count as staging if they were placed on the rocket in a reasonable way and it truly looks accidental that they broke off?

Of course that denies re-usability, but perhaps a craft that was previously re-usable can make it to space through a series of "accidents" and accidentally get part of the thing into orbit.

Yes. Everything that is attached to it on the surface must remain attached all the way to orbit.

[catas4trophy]

This is an interesting one. I have a couple of ideas that I can try. (I just need to move my RSS ksp somewhere and get a fresh install....)

[Kobymaru]

does loss of parts due to overheating or air resistance count as staging if they were placed on the rocket in a reasonable way and it truly looks accidental that they broke off?

I'm pretty sure that counts as staging. I saw a Scott Manley video once where he built a rocket using solid boosters only that he staged using precise engine activation timing.

[RuBisCO]

Has anyone tried to Ion glide lately: I think they fixed it so that it is grossly inefficient and weak.

No it simply can't be done with stock parts, end of story.

Propellers to 30 km could do it but there are not propellers in stock. They would need to be powered electrically.

An air-breathing nuclear engine could do it, but that is certainly not stock.

Balloons can do it, most definitely as a two stage IRL though, but the Hooligan mod parts work well in a single stage.

Edited August 5, 2014 by RuBisCO

[thereaverofdarkness]

I'm pretty sure that counts as staging. I saw a Scott Manley video once where he built a rocket using solid boosters only that he staged using precise engine activation timing.

But that was obviously designed to blow the boosters off. If they hadn't exploded, the ones above them wouldn't have even functioned.

So, an eve ssto is impossible without wings/control surface.

Maybe ion for taking off and climbing up and nuclear for speeding up and going to space?

But it would need many Ion engines and wings.

hmmm...

I'm sure it can be done!

You might think that Eve's thicker atmosphere opens new doors, but you have to consider that by the time the atmosphere has thinned as low as Kerbin's at sea level, you've still got more gravity to contend with.

Edited August 5, 2014 by thereaverofdarkness