Looking for tips for efficient ssto design

[panzer1b]

As the title says, im trying to design some sstos that are EXTREMELY long range, as in at a minimum capable of going to lathe, landing, taking off, and returning home in one piece (provided ofc i dont crash land it ). Now i have alot of experience with ssto builds when it comes to basics, so i dont need to know stuff like how to balance its cog, ect, but id really like some advanced tips on making my sstos able to maximize their range and preformance. Things like how many intakes/engine to get the best out of my jets befor eorbit, how much rocket fuel to jet fuel proportions, how many jets/total mass of ssto, ect. Any help is appreciated, and while i do not mind pictures and stuff, i do not want to just copy someone's ssto, i prefer to make it myself, i just would liek to know how to make it as optimized as possible (without making it look like utter crap with intakes all over it). Also, i am fine with clipping and intake stacking, heck all my current designs use clipping to a massive extent, i just choose to place those things internally so they dont take away from the looks.

Edited November 18, 2014 by panzer1b

[Raptor9]

An atmospheric SSTO and a long-range interplanetary ship capable of going that far is a tall order since those two requirements are damn near polar opposites in engineering requirements. Especially if you don't want it looking ridiculous. At a minimum, I would say an orbitial fuel depot around Kerbin would be a minimum (maybe even pre-stage a fuel tank cluster at Laythe ahead of the SSTO), and putting LV-N's on it would be a serious consideration, if not a requirement.

[Pecan]

So you're ok with your spaceplane design and, of course, Laythe is an ideal destination for a spaceplance since you can use jets there. 8 intakes per engine is, apparently, the optimum but presumably you know that.

For space-travel efficiency you want as low a TWR in space as your patience can cope with. Ions are best there, but LV-Ns the usual choice, one LV-N should be enough for anything but the heaviest spaceplane, you might prefer two ions. Coat the whole thing in OX-STAT panels if you're using ions and just use KER/MJ/VOID to tell you how much fuel you need.

Naturally, for anywhere except Laythe there's no point in optimising a single-stage much, as it's far, far, more efficient to undock the space part from the SSTO stage once in Kerbin orbit. Just re-dock before landing when you come back.

[panzer1b]

So you're ok with your spaceplane design and, of course, Laythe is an ideal destination for a spaceplance since you can use jets there. 8 intakes per engine is, apparently, the optimum but presumably you know that.

For space-travel efficiency you want as low a TWR in space as your patience can cope with. Ions are best there, but LV-Ns the usual choice, one LV-N should be enough for anything but the heaviest spaceplane, you might prefer two ions. Coat the whole thing in OX-STAT panels if you're using ions and just use KER/MJ/VOID to tell you how much fuel you need.

Naturally, for anywhere except Laythe there's no point in optimising a single-stage much, as it's far, far, more efficient to undock the space part from the SSTO stage once in Kerbin orbit. Just re-dock before landing when you come back.

So if i can make a ssto thats light enough (probably single jet with just 1 tank of jet fuel), and put 2-3 ions on that as well as solar array, would that be the best method to get somewhere far out? Since the micro solars and landing gear are apparently physics less now, it lets me put as much on as needed.

Also, one more question that i never managed to figure out, for maximum preformance, what is the optimal lift/mass ratio? My most successful ssto is more or less a rocket with some wings and triple jets, and its by no means long range as the best i can do with it is get to anywhere within kerbin area (mun/minmus) and return/land. Then again, under 2000dV isnt gonna do me much good. Any idea how much dV i actually need to have to reach lathe and return, only refueling near kerbin (i have plenty of capital ships in orbit, i can just pirate some fuel from one of those)

[Overfloater]

If your SSTO is a plane, put 1 jet for every 13 tons of your craft. If it has very good lift rating, you can get away with 1 jet per 15 tons.

The more intakes it has, the more fuel efficient it is. 10 intakes per 13 tons should get your ship to orbit on jet fuel alone, more intakes than that aren't necessary.

If your target is laythe, drain 1/3 of the oxidizer from your fuel tanks. This way 2/3 of the fuel is rocket mix, 1/3 of the fuel is jet fuel.

- when ascending from Kerbin, be sure you have 1/4 of that jet fuel left with you, that's all you'll need for Laythe.

[GoSlash27]

As of right now here's the best tip I can give you:

Use the strakes as wings and use the bare minimum to get you to 28KM up at 2KM/ sec in level flight under jet power.

Other helpful but less-critical info:

-For intakes, I've had good luck with the ram air intakes and shock cones (1 per engine) or radial intakes (4 per engine).

-Don't bother adding RCS propellant. You have plenty in the cockpit.

-1 RAPIER is adequate for 12 tons of aircraft, including the Rapier itself and it's fuel.

-Fuel/ oxidizer ratio (not counting whatever you're using after orbit) is about 1.23 KG of fuel for every KG of oxidizer.

Best,

-Slashy

[Pecan]

So if i can make a ssto thats light enough (probably single jet with just 1 tank of jet fuel), and put 2-3 ions on that as well as solar array, would that be the best method to get somewhere far out? Since the micro solars and landing gear are apparently physics less now, it lets me put as much on as needed.

You got it. OX-STATS are massless (landing gear isn't any more) and ions are even more fuel-efficient than jets so you won't need a huge mass of Xenon fuel. For a one-jet SSTO stage 2 ions should be plenty, but again, you can even get away with one if your patience can stand the really low TWR.

Also, one more question that i never managed to figure out, for maximum preformance, what is the optimal lift/mass ratio? My most successful ssto is more or less a rocket with some wings and triple jets, and its by no means long range as the best i can do with it is get to anywhere within kerbin area (mun/minmus) and return/land. Then again, under 2000dV isnt gonna do me much good. Any idea how much dV i actually need to have to reach lathe and return, only refueling near kerbin

Depends what aerodynamic model you're using, but in stock KSP wings are simply a waste of mass on the way up; you're better-off just using a VTVL jet ascent-path without them (that is, straight up for the first 1-2km then pitch down, instead of horizontal (runway) and pitch up). Since you want the wings for coming back down and landing though you then have to think of tail-landers versus horizontal and all that. I can't really help you there since I wouldn't want to make an interplanetary single-stage. Space is space though, whatever sort of vehicle you do it with; the basic figure for Laythe is 4,360m/s each way, including orbital insertion but aerobraking can reduce that a lot and the good news is there are plenty of options for aerobraking in the Jool system as well as around Kerbin.

I tend to design for worst-case and would probably go for a (space) requirement of at least 8km/s but wouldn't be surprised if those that go to Laythe more often suggested a figure half that.

[Wyre311]

http://forum.kerbalspaceprogram.com/threads/96406-The-Arcadia-series-and-the-Zeus-Ships?highlight=Arcadia

Mine can make it to duna after a refuel in orbit. After that just refuel them at duna and i think they can do it. Look them over

[panzer1b]

Thanks for all the tips, prolly gonn go with a super small jet thing, and then just spam xenon fuel, or is there a point where you start to have issues with fuel, say if i bring like 5000+ xenon fuel?

As of right now here's the best tip I can give you:

Use the strakes as wings and use the bare minimum to get you to 28KM up at 2KM/ sec in level flight under jet power.

Other helpful but less-critical info:

-For intakes, I've had good luck with the ram air intakes and shock cones (1 per engine) or radial intakes (4 per engine).

-Don't bother adding RCS propellant. You have plenty in the cockpit.

-1 RAPIER is adequate for 12 tons of aircraft, including the Rapier itself and it's fuel.

-Fuel/ oxidizer ratio (not counting whatever you're using after orbit) is about 1.23 KG of fuel for every KG of oxidizer.

Best,

-Slashy

Arent rapiers HORRIBLY inefficient period?

The only viable interplanetary engines in space according to my knowledge are nukes and ions, since anything below 800 isp is useless for long range.

http://forum.kerbalspaceprogram.com/threads/96406-The-Arcadia-series-and-the-Zeus-Ships?highlight=Arcadia

Mine can make it to duna after a refuel in orbit. After that just refuel them at duna and i think they can do it. Look them over

I generally avoid B9 as it has massive loading times, kindof stick to as much barebones as im able to, its not like the last update didnt add alot of cool new MK2 stuff i can finally use for sstos.

Edited November 16, 2014 by panzer1b

[Pecan]

Thanks for all the tips, prolly gonn go with a super small jet thing, and then just spam xenon fuel, or is there a point where you start to have issues with fuel, say if i bring like 5000+ xenon fuel?...

Starting small is always a good move. There certainly is a point where you start to have fuel issues; 5,000 Xenon masses quite a bit so it'll be that much harder to take-off in the first place, let alone land with it.

Perhaps you'd like to try it with your first design - to prove it's possible (which it very much is) - and then issue a challenge to see what other people can come up with.

[numerobis]

So, I just posted this thing.

It's an evolution of a design from quite a while ago. I've long been wanting to fly to Laythe and back while giving the Kerbals room to move around. I'd say my plane is utterly minimal for that: the two Kerbals have a lab and two cockpits. I'd feel better giving them at least a crew cabin each. This build has just barely enough for Laythe; I haven't tested it yet to there, but I've made trips to Minmus and Mun.

The absolute best wing per area is the delta-deluxe now (used to be the small control surface). That's because control surfaces act very weird when it comes to the stock aerodynamics model. My 40t plane has just 14 delta-deluxes and lifts off at about 50 m/s. Landing speed at the end of the mission is under 20 m/s.

The best intake is the ram intake, but radials are pretty good too, and easier to place. Since I was dumping most of my intakes, I used a *lot* of radials (96 to be precise), which gets me to a 160x40km orbit off jets alone. This isn't the most efficient when you have to fly to Laythe and back; use fewer intakes than I did.

Using ion engines requires a lot of patience. The LV-N will get you much faster burn times.

[bitslizer]

I have a vtvl ssto design based off of cupcake's drop ship series that can goto Dunas + ike land on both and return to kerbin but I don't think it got enough delta V for transit to laythe and back, it's 4 turbo jet with 2 lvn 8x intakes air hogging per jet post a pic when I get home

[Laie]

So if i can make a ssto thats light enough (probably single jet with just 1 tank of jet fuel), and put 2-3 ions on that as well as solar array, would that be the best method to get somewhere far out? Since the micro solars and landing gear are apparently physics less now, it lets me put as much on as needed.

I suggest you look at the featherweight department of the Jool-5 Challenge. That can be built really small and lightweight, to the degree that you'll need only one ion engine and a handful of tanks. You're very constrained in your design decisions, though -- there's little room for being original about it.

If money is also a concern: xenon is quite expensive. For simple straightforward probes, the point where nukes become cheaper than ion drives (despite being a whole lot heavier) is somewhere around 2t or so. For a plane with wings and everything, the calculation is possibly not quite as simple.

You definitely want 4000m/s of rocket mileage in order to get to Laythe and back. This assumes that you're familiar with transfer windows and aerobrake on either end.

[Redshift OTF]

If you are looking for inspiration or what is possible then you can have a look at these creations I came up with:

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This is for one Kerbal, no re-fuelling needed. Has 6 jets and 2 nukes, (I find a 1/3 ratio works well for SSTO's to Laythe).

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Or this if you want to take 3 Kerbals. Harder to land though.

It's all about the payload, (or cabin weight). The less weight you use to transport the Kerbals the easier, (or at least less difficult), it gets.