is an Eve SSTO rocket possible?

[KerikBalm]

13 hours ago, GoSlash27 said:

I would argue that there isn't *any* way to success on this project. The math says that using a Mammoth (even with zero drag) will yield *at best* 6,790 m/sec DV. That's with an infinite number of fuel tanks, no mass that's not fuel tanks, and vacuum ISP.

It's nowhere near enough.

If he has any chance at all of making orbit from sea level in a single stage, he'll have to use nukes or ions in the process.

Best,
-Slashy

And design after design has tried to have something with a high Isp that doesn't get lit until its higher in the atmosphere... all failed miserably because the LV-N, even in vacuum conditions, never had enough TWR to generate the requirted dV in the required time.

Pack on enough nukes to have a decent vacuum TWR, and you can no longer lift it with the lower stages to near vacuum conditions. To even get a 0.5 TWR on Eve, your craft mass must be 42.5% LV-Ns by mass.

Down low you need vector/aerospike/mammoth engines... up high their Isp isn't so great. To even lift off with the fuel needed to get to vacuum conditions means a lot of LFO engine mass, which kills the LV-N TWR, and you don't make it.

If you had just 1 mammoth engine(15 tons) and empty Kerbodyne s3-1440 tank (9tons empty), to get the 0.5 TWR with nukes, you'd need 17.7 tons of LV-Ns to get a 0.5:1 TWR when the LFO runs out... 6 of them... except thats not budgeting any fuel for them (and you want a coule/few thousand m/s with them). You'd need the LV-Ns+ fuel to be 54.9% of the mass to have 2km/sec at a 0.5TWR on eve... so 29 tons of LV-N + fuel... 22.6 tons of LV-N. SO now we're asking a mammoth to lift itself (15 tons), a full kerbodyne tank (81 tons), and 29 tons of LV-Ns and fuel, 125 tons total. At 5km on Eve, the mammoth produces 225 kN/Ton, giving it a 13.5:1 TWR, and a 1.6:1 TWR for the craft.... Ok... but how much dV does that first stage have? Not enough that it + 2000 m/s from the LV-Ns gets you to orbit.

Add more tankage to get you to lets say a minimum 1.2 TWR for eve ascent? add more LV-Ns... run into tyranny of rocket equation... nope

We need a better engine to do it. No combination of stock parts does it.

Even reasonably balanced modded parts make it very difficult. For instance... I made air augmented engines/turborockets based on stock jet engines but with lower TWR(same thrust, a bit higher mass) and half the Isp (well 0.9/2 so slightly less than half the Isp). They are just fine for use on Kerbin SSTOs since the airbreathing fuel consumption is minimal, and its relatively easy to add more engines for enough TWR.

Eve SSTOs with them were really really hard to make (I forget if I ever succeeded) because the craft would over heat in the lower atmosphere, or when high enough that OHing wasn't such a problem, the airbreathers produced little thrust and were mostly dead weight preventing reaching orbit... or when more LFO was packed on for rocket mode... they didn't have enough TWR in airbreathing mode because of eves high gravity.... they'd suck through lots of fuel in the lower atmosphere.

As before, LV-Ns don't help them because of TWR, and they need to go from ~1,400 m/s to about  ~3,100 m/s (1,600 more after airbreathing cutoff) vs a kerbin airbreathing ssto of about 1,500 m/s (orbital) to ~2,300 m/s (a mere 800 m/s more).

 

Eve is really hard... its not just the dV that gets you, its often the TWR.

Edited August 19, 2016 by KerikBalm

[GoSlash27]

4 minutes ago, foamyesque said:

Well, no, not from sea level, not in one shot. It might be possible to cart an integral ISRU unit to space so you can do a chain of sea-level -> mountaintop -> space, but you'd need a truly monstrous rocket to make it happen. The deltaV from a 6500m+ mountaintop is, IIRC, 5500m/s or so, which is just within a Mammoth's reach.

foamyesque,

 All true, but I got the impression that he wants to do it from sea level. I could be mistaken...

Best,
-Slashy

[Sharpy]

11 hours ago, GoSlash27 said:

Sharpy,

Well... *sorta*. Fuel is consumed at a lower rate with lower thrust, but over a longer period of time due to the reduced acceleration. You wind up spending a lot more time in atmosphere and suffer more DV loss to drag than you would otherwise.

 

 

Work = Force * distance.

The energy lost to drag is the work it performs on braking your vehicle.

Atmospheric drag is quadratically proportional to airspeed. Distance is linearly proportional to airspeed.So drag losses (the work) per unit of time is proportional to third power of airspeed!

Sure you'll cover the distance faster, but that's again, only one order reduction - you still have a square of airspeed in losses per given distance.

By going slower, you both reduce the drag force and the distance you cover over unit of time, so actually fuel consumption due to atmospheric drag, per unit of time, drops with the third power of speed.

This is of course disregarding gravitational drag, and the potential energy due to climbing. But the loss due to potential energy is fixed per change of altitude regardless of other factors, and with wings gravity loss becomes quite negligible - it's all atmospheric drag then - if you have enough lift. Without lift, gravity loss is your loss (and lift is also a square of airspeed).

Of course, with lower density lift will drop, and you will need high speed to overcome gravity drag. But then the air drag becomes negligible too. We're talking about souposphere for now.

In short: try to reach the thin air altitude over shortest possible distance that can be covered by wing lift instead of vertical thrust, and try to cover this distance as slowly as possible. If you go too slow, without enough lift your distance will grow as you'll be climbing slower. But if you go faster than necessary, you'll be losing to drag.

I wonder what kind of craft could do it. I think it would need wings fixed at a positive angle of attack.

---

On wet wings:

They provide a very lousy dry:wet mass ratio, and they are big and heavy overall, with a plenty of drag.

I'm not saying they aren't worth their weight in lift they provide, nor that their drag is excessive relative to that lift - but as I said before, in the souposphere you don't need much wing surface (or speed) at all to produce a lot of lift - so unless your SSTO is a huge monster, that despite the souposphere stil requires that much lift to climb, you may be better off with much smaller dry wings.

 

[GoSlash27]

Sharpy,

 I understand where you're coming from, but it doesn't actually work that way. At least... not in KSP. If your hypothesis were true, it would apply equally on Kerbin, and that's a relatively simple test.

Build a space plane that just barely gets through Mach one in level flight and see how much fuel it uses to get to the transition point. Then add a couple engines and repeat. Speaking as a guy who's been all over this territory countless times, I can tell you that the most efficient t/w is not at the bare minimum.

Best,
-Slashy

[Kergarin]

I have tried a lot of different designs.

-High and low twr

-More wings, less wings, tilted wings, no wings

-Vertical and horizontal launch

-Fast and slow ascend

-Vectors, spikes, mammoth in every thinkable combination

 

The best I did until now was 3.080m/s at ap 90km started from 5.800m.

It's nice to have all this theory here, but this is how the game works: the low twr slow ascend works worst.

Edited August 19, 2016 by Kergarin

[Red Iron Crown]

On 8/18/2016 at 5:19 AM, Warzouz said:

The whole purpose of a SSTO (whatever design it has is reusability. Other than that, there is no real meaning for SSTO. When you use a Tylo SSTO lander, as I did back in 0.9, it's because you want to use it multiple times (or recover funds for most of it).

You're generalizing your own reasons for doing things to everyone, and redefining an established term to suit.

As near as I can tell, people don't try to make Eve SSTOs to have a reusable craft they can use to support Eve operations at reduced cost, they don't care about cost or reusability. They do it because it is a big challenge that is barely possible (if it still is at all). It's a stunt, and stunts can be fun.

Reusability is a separate concept from SSTO, you can have 100% reusable craft with multiple stages, and you can have single stage craft that are not reusable. While it is certainly true that SSTO makes reusability simpler, that doesn't mean that an SSTO has to be reusable.

[magnemoe]

1 hour ago, GoSlash27 said:

Sharpy,

 I understand where you're coming from, but it doesn't actually work that way. At least... not in KSP. If your hypothesis were true, it would apply equally on Kerbin, and that's a relatively simple test.

Build a space plane that just barely gets through Mach one in level flight and see how much fuel it uses to get to the transition point. Then add a couple engines and repeat. Speaking as a guy who's been all over this territory countless times, I can tell you that the most efficient t/w is not at the bare minimum.

Best,
-Slashy

The benefit of an winged accent stage is that you can manage with lower TWR as the wings takes much of the gravity loss, the penalty is drag, the drag really come back and bite you as you move faster.
Look at designs for real world winged spaceplanes. 
On kerbin the rules are a bit different as we can use the very efficient jet engines. 
 

[Kergarin]

1 minute ago, magnemoe said:

The benefit of an winged accent stage is that you can manage with lower TWR as the wings takes much of the gravity loss, the penalty is drag, the drag really come back and bite you as you move faster.
Look at designs for real world winged spaceplanes. 
On kerbin the rules are a bit different as we can use the very efficient jet engines. 
 

 

Have you tried it?

I did several times.

It just does not work on eve.

[magnemoe]

1 hour ago, Kergarin said:

 

Have you tried it?

I did several times.

It just does not work on eve.

No not tried it, watched the Eve SSTO video and the one with an full reusable Eve mission with tug to circulate, both used an winged rocket. 
I'm a rocket guy myself and not an good pilot, but it looks to me that you would not get an standard rocket of Eve as ssto as the twr get to low.

 

[Kergarin]

27 minutes ago, magnemoe said:

No not tried it, watched the Eve SSTO video and the one with an full reusable Eve mission with tug to circulate, both used an winged rocket. 
I'm a rocket guy myself and not an good pilot, but it looks to me that you would not get an standard rocket of Eve as ssto as the twr get to low.

 

I think the question is: how do you define low twr and slow ascend? Until now, I was thinking you are talking about something, that's much slower than the planes in those two videos.

 

My best eve planes have a takeoff speed of around 150m/s and i'm trying to keep it at 200m/s on full throttle at around 45degree angle until I'm out of the soup.

Is this what you mean by slow, or are you talking about even less?

Edited August 19, 2016 by Kergarin

[magnemoe]

19 minutes ago, Kergarin said:

I think the question is: how do you define low twr and slow ascend? Until now, I was thinking you are talking about something, that's much slower than the planes in those two videos.

My best eve planes have a takeoff speed of around 150m/s and i'm trying to keep it at 200m/s on full throttle at around 45degree angle until I'm out of the soup.

Is this what you mean by slow, or are you talking about even less?

I referred to the videos as I have not done it myself, I never talked about staying slow, just an takeoff and low attitude TWR who is less than that would work on an rocket. 

It might even be an idea to increase climb rate as in becoming an rocket once your TWR start to become reasonable for an rocket to reduce drag an heating then pull nose down for the gravity turn. 

[Kergarin]

3 hours ago, magnemoe said:

I referred to the videos as I have not done it myself, I never talked about staying slow, just an takeoff and low attitude TWR who is less than that would work on an rocket. 
 

Ok, then I got you wrong, sorry. I thought you were talking about something like "just a few aerospikes" 

 

3 hours ago, magnemoe said:

It might even be an idea to increase climb rate as in becoming an rocket once your TWR start to become reasonable for an rocket to reduce drag an heating then pull nose down for the gravity turn. 

 

That's exactly how I did it in my first attempts.

But it seems more efficient, to climb in a straight line until you go into a gravity turn.

At the moment when twr is high enough to increase climb rate, the atmosphere is already so thin, that you can fly more efficient straigt throug it.

Edited August 19, 2016 by Kergarin

[KerikBalm]

At a given point in time, wings allow you to trade losses due to gravity drag for smaller losses due to aerodynamic drag, proportional to the L/D that the wings/raft can get.

Then you have to figure out how much extra time is added to your ascent due to the lower climb rate, and yo ucan find a break even point.

Even in those winged designs, they were still climbing at pretty steep angles. With a super high L/D, in a climb of 45 degrees, one could make due with roughly 70% the TWR of an unwinged design if my thought process is right

[foamyesque]

The point of the winged designs is to cut down the engine mass you need for the first few kilometres of climbing, which means you're carting less dead weight through your 2000m/s+ lateral burn. I have an Eve sea-level lifter -- not SSTO, for various reasons, but same principle -- that has a liftoff TWR of 0.35. The investment of five tonnes of wing repays itself in not requiring an extra thirty tons of engine.

[Kergarin]

Did it!!!

(at least unmanned SSTO from EVE, landing is another part )

 

The video and details will follow soon!

 

[Kergarin]

So here it is.

It's the total oposite of what i was thinking about when i started working on an Eve SSTO...

No wings, no drag. Just get out of the soup as fast as possible.

 

Im working on an upscaled manned version with ISRU. But that only reaches 3.080m/s at 90km AP by now. Seems possilbe!

 

 

 

[GoSlash27]

Makes sense for a high altitude SSTO.

Best,
-Slashy

[Brainlord Mesomorph]

9 hours ago, Kergarin said:

No wings, no drag. Just get out of the soup as fast as possible.

That's what I was thinking, but you guys seemed so sure of the opposite.

The tough part is going to be reliably landing that thing upright. 

good work!

Edited August 20, 2016 by Brainlord Mesomorph

[GoSlash27]

8 minutes ago, Brainlord Mesomorph said:

That's what I was thinking, but you guys seemed so sure of the opposite.

The tough part is going to be reliably landing that thing upright. 

good work!

I am certain that it is the opposite *from sea level*. Assuming it's possible at all from down there... which I don't. The math precludes the possibility of a vertical SSTO from down there.

Best,
-Slashy

Edited August 20, 2016 by GoSlash27

[Brainlord Mesomorph]

Just now, GoSlash27 said:

I am certain that it is the opposite *from sea level*. Assuming it's possible at all from down there... which I don't.

LOL

I NEVER SAID SEA LEVEL!

someone did in the thread (I think it was you) but that was the easiest mission parameterto through out the window.  I'm still negotiable on "Orbit" as long as we get to suborbital rendezvous I think we've done it.

[magnemoe]

9 hours ago, Kergarin said:

So here it is.

It's the total oposite of what i was thinking about when i started working on an Eve SSTO...

No wings, no drag. Just get out of the soup as fast as possible.

 

Im working on an upscaled manned version with ISRU. But that only reaches 3.080m/s at 90km AP by now. Seems possilbe!

Congratulation well done.
Payload here is an 100 kg probe core, is it an shielded docking port in front? That is 100 kg more, as I can see no power or reaction wheels or fins. 
An Mk1 pod will be 0.84 ton and should be doable.

ISRU is another issue, the small isru have so low efficiency it will use many months filling the huge rocket. My Tylo ssto use a week and only hold around an orange tank of fuel.
It also had two of the large drills. bringing the total weight up to 1.25*2+125 its also award to place without generate lots of drag, As I used the SSTO on Laythe too I put drills and isru into MK2 cargo bays with MK2 probes as bottom and aerospike as engine, this too has plenty with drag, 


 

[GoSlash27]

On 8/13/2016 at 5:02 PM, Brainlord Mesomorph said:

its supposed to take 8km/s of dV,

^ These were your words, correct? This value is for sea level, not the mountains.

SSTO from the mountains is a much easier prospect. Definitely not the "ultimate KSP rocket". Perhaps in the future you should sort out exactly what you're after so we're all on the same page.

 

Edited August 20, 2016 by GoSlash27

[Brainlord Mesomorph]

36 minutes ago, GoSlash27 said:

SSTO from the mountains is a much easier prospect. Definitely not the "ultimate KSP rocket". Perhaps in the future you should sort out exactly what you're after so we're all on the same page

If your topping out TWR and dV at same time and accomplishing the NEARLY unaccomplishable then that's ultimate in my book.

/ in the OP I was asking "what's possible" 
//do any of us really ever know exactly what were after?

/// slashies for Slashy

39 minutes ago, magnemoe said:

ISRU is another issue, the small isru have so low efficiency it will use many months filling the huge rocket.

I still think you'll need a sistership/tug to get that beast to LEO and from LEO back to Gilly. And you put big ISRU on that.

Also suggestions for names:

Since this would be the most powerful lander in KSP I would call it the Hercules Lander, and the sistership is obviously The Athena (who helped Hercules on is labors, she was also the Goddess of manufacturing, i.e. ISRU)

Edited August 20, 2016 by Brainlord Mesomorph

[Kergarin]

1 hour ago, GoSlash27 said:

Makes sense for a high altitude SSTO.

Best,
-Slashy

I think high altitude is the only altitude that works.  Even from 1.000m less it seems impossible.

Every letter and number of the model name C9H8 stands for a new type, model and version that I have tested. And that's not a straight line, there a dozens parallel to that. Nothing else worked.

1 hour ago, Brainlord Mesomorph said:

That's what I was thinking, but you guys seemed so sure of the opposite.

The tough part is going to be reliably landing that thing upright. 

good work!

Thanks 

I think my upscaled version can land, and its so wide that it won't flip. But it's still 120m/s short on ascend...

47 minutes ago, magnemoe said:

Congratulation well done.
Payload here is an 100 kg probe core, is it an shielded docking port in front? That is 100 kg more, as I can see no power or reaction wheels or fins. 
An Mk1 pod will be 0.84 ton and should be doable.

ISRU is another issue, the small isru have so low efficiency it will use many months filling the huge rocket. My Tylo ssto use a week and only hold around an orange tank of fuel.
It also had two of the large drills. bringing the total weight up to 1.25*2+125 its also award to place without generate lots of drag, As I used the SSTO on Laythe too I put drills and isru into MK2 cargo bays with MK2 probes as bottom and aerospike as engine, this too has plenty with drag, 


 

Thanks 

The shielded docking port is the only part that I found to be heat resistant enough. If I go up any slower, I don't reach orbit, even not with the reduced weight or drag of the other nosecones that I have tested.

The only reaction wheels are the ones inside the probe core. That's just enoug to keep it straight before reaching orbit. The rest is done by engine gimbal.

The problem by using the mk1 Pod isn't weight, it's heat again. I just can't get fast enough, without exploding the pod. (if it's top mounted) Also a really usable top mounted pod would need ladders. And ladders are enough to change the the CoM so badly, that the rocket will flip.

I have tried a bottom mounted lander can, but you can't get back inside it, because it's not possible to walk between the engines of the mammoth. (collision box does not match the real model) 

An ISRU refuel will take month, if not years.

But there is a much bigger problem: there is no ore at my launch site 

[Brainlord Mesomorph]

10 minutes ago, Kergarin said:

The problem by using the mk1 Pod isn't weight, it's heat again.

The MK1 inline has a higher max temp. Could it be mounted radially on the bottom (Millenium Falcon style?)

you could offset the weight and drag w/ a fuel tank on the other side?

Also how about Disposable Replaceable Heat Shields?

with that shielded docking port on the nose, you could mount an Inflatable heat shield on a docking port and dock them in orbit, enter Eve atmosphere, and then toss the thing right before parachute deployment.

The sistership could carry 3 or 4 spares.

Edited August 20, 2016 by Brainlord Mesomorph