Some questions about SSTOs.

[panzer1b]

Well im working on a new SSTO to replace some aging designs, and im wondering if my new design requirements are even attaineable? the new SSTO is planned to replace my rather overkill heavy carrier based interceptors (20t for a interceptor is really pushing it when the carrier carrying it weighs under 100t, so basically bringing just 3 of these is more then half the carrier's weight).

I would like my SSTO to satisfy these constraints:

100% stock.

Under 100 parts.

At most 10t (without payload, and no less then 5t).

At least 4000 vacuum dV after attaining orbit with no refueling (i want this to get to laythe, land, and return without refueling).

0.5t payload (small deployable drone thing).

No more then a 15 minute burn for a jool ejection.

At least a 1.1 TWR in atmospheric jet mode (it has to be able to go straight up of needed).

Now i keep trying various iterations of designs, and i cant seem to pull this off. Are these requirements just not attainable with stock ksp? Or am i just not using the proper part selection? Ive tried all sorts of things, and the closest ive come up with is basically ion drive ship, but its going above my maximum part limit, not to mention its bloody PAINFUL to fly as the thrust is just anemic. Basically the major issue ive come up against is engine choice, as ions are way too part intensive and have way too little thrust unless i bring at least 10 of them, and using a nuke brings my weight up by over 2t just for the engine, not to mention it actually needs more fuel to pull off the desired dV.

Anyways, id like some input from the (obviously better then me) community of spaceplane/SSTO designers, and im primarily in need of suggestions for an optimal engine layout, as that sems to be my major killer problem right now, nomatter the combination of engines i choose, im almost either unable to do anything in jet mode, or im unable to get the needed thrust/dV in space.

Finally, if what im trying to build is impossible, then just say so, id rather just move on to another project if this is indeed unattainable, but if it is plausible/already done by someone out there, id love some input as to how to make such a SSTO.

Edited April 16, 2015 by panzer1b

[JTpopcorn]

With the delta v weight and twr requirement this looks like it may be hard to pull off. Just a question why not use the carrier to transport it?

[Alshain]

That is a pretty tall order for a plane. 4000 dV in orbit, plus cargo, and under 100 parts. I don't know that I could build that, at least not without Mk3 wings.

[panzer1b]

With the delta v weight and twr requirement this looks like it may be hard to pull off. Just a question why not use the carrier to transport it?

But can it even be done? Im willing to sacrifice here and there, but it has to be laythe capable at the bare minimum (that includes landing on laythe and returning to kerbin). As for why im not using carriers for transport, im looking for a "long-range" ssto build. I already have plenty of other craft, some micro-fighters that are like 4t heavy, and are space only short range carrier fighters, and i also have plenty of super long range laythe and beyond craft, but all of them are WAY to heavy to be practical on a carrier. Yes i know the carrier can carry fighters to target, but im just looking for a super long range interceptor thats carrier capable (as in has a docking port and can be supplied with ammunition/payload in space) but not specifically intended to be a purely carrier based fighter.

That is a pretty tall order for a plane. 4000 dV in orbit, plus cargo, and under 100 parts. I don't know that I could build that, at least not without Mk3 wings.

payload is the one thing i wouldnt calculate the dV with. Its just so that its technically capable of carrying it to orbit but at the cost of dV (i do not need it to be laythe capable with the added payload, all it really needs is a jr docking port somewhere to accomodate it if needed and to double up as a attachment point for the carrier mounting, new carrier thats being developed uses jr ports instead of the medium ones ive used in the past). The cargo is either a small probe drone thing (that doubles up as a kinetic missile when needed), or a unguided kinetic Ibeam missile (no explanation needed for that one). This is intended to be armed in space once reaching a ammunition supply ship i have stationed in the jool system (which ill probably replace as its running out of ammo).

Also, i am ok to bend the requirements a bit, but the few things i absolutely need the craft to do is be laythe roundtrip capable (landing too), have a TWR that is above 1.0 on kerbin sea level, be under 10t, and be under 100 parts. And ofc it has to be stock as i do not use any part mods (i use EVE, planetshine, ect, but nothing that actually adds parts or edits gameplay). id also really prefer a reasonable space TWR, as im not quite patient enough for 30 minute burns, but a 15-20min burn would be acceptable if there is no other way.

if this cant be done, then i guess its off to some other project.

Also, thinking about the engines, what engines should i use? Im almost positive teh atmospheric thing will be a single turbojet, as its the best in terms of thrust, mass, ect, but what enbgine is best for space useage? I know that nukes and ions are pretty much the only viable long range engines for a SSTO, but perhaps some smaller lighter engines will also work (no idea if the 48-7s is a good idea with such a craft but who knows).

Edit:

just did some more calculations, and ive pretty much narrowed it down to ions being the ONLY plausible engine with my requirements. Basically if i want 4000 dV, and my craft weighs at most 10t, i need 4 tons of this to be lfo when using a nuke. With a nuke/turbojet, the engines weigh a total of 3.5t, that makes my total to 7.5t already used for JUST the space fuel and the engines. The command pod (lets just say i use the mk1 command pod at 0.8t thats already 8.3t of mass, then ill most likely need around a ton of jet fuel, making it 9.3 tons! This makes it borderline impossible to pull off due to being left with under 1t for landing gear, air intakes, wings, reaction wheels, ect.

Ions, with all their problems, are sadly the only way to go, as while a nuke craft may be doable, its going to be extremely limited in every other way, as there is little if any room to put anything (im assuming at least .2-.3 tons of wings, and then even if i dump the reaction wheels requirement by making it super balanced, i need to add enough intakes to actually blast above the atmosphere with mostly jets.

So unless someone proves my math wrong, i think ions are the ONLY practical way to make a lightweight super long range SSTO. now i just need to find a way to counter the part count problem that comes with ion anything, you need ALOT of fuel tanks, at least 10 engines to get any sort of thrust out of it (which are actually quite heavy in that amount), and then ofc there is the issue of batteries/solar panels/RTGs (althoug with these weight requirementys i think ill stick to 1 RTG when i need it instead of the usual 2-3 i normally use on craft.

Edit:

I managed to pull off a ion craft that barely satisfies requirements. I used ions, as from some equations i found them to be the ONLY useable engine. The craft is 11t (not quite what i wanted but its still close enough), has 12 ion engines (i managed to make a rather good looking engine cluster surprisingly, i think ill name it the "Hex-Fighter" with the designation HK-106, owing to the ion cluster's appearance (6 engines externally visible, 6 clipped a bit internally to teh craft. It still takes forever to burn somewhere, but its what id call acceptable even if not exactly ideal.

If anyone can make something better (or even better rocket powered as ions take forver and require alot of massless batteries to actually work), id love to see ideas for some high dV small and light SSTO fighters.

Edited April 16, 2015 by panzer1b

[Starhawk]

The smallest Laythe surface return vehicle I've pulled off is 84 parts, but 28.6 tonnes. It carries a single Kerbal in a Mk1 Inline Cockpit.

It gets all the delta-v from a single nuke, but needs enough fuel for that nuke that it takes two turbojets to bring it up to orbit.

If you're willing to go unmanned, you might just be able to pull it off.

Happy landings!

[panzer1b]

The smallest Laythe surface return vehicle I've pulled off is 84 parts, but 28.6 tonnes. It carries a single Kerbal in a Mk1 Inline Cockpit.

It gets all the delta-v from a single nuke, but needs enough fuel for that nuke that it takes two turbojets to bring it up to orbit.

If you're willing to go unmanned, you might just be able to pull it off.

Happy landings!

My older HK-133 "Tri-Fighter III" is laythe capable (with weapons removed) and is under 80 parts armed, and weighs 18ish tons (nuke powered). The new thing is HOPEFULLY going to be able to pull off within the restrictions i want will be much smaller and hopefully have better range.

The current craft i have is 11t ish (i could drop it to 10 is i swapped the Mk1 inline for a probe core), has 5500dV fully fueled, 6000 if im out of jet fuel. I think for a 11t craft this isnt THAT bad......only major pain is energy consumption, which is rather annoying levels of high as i can at most add 2 solar arrays due to lack of spots to mount them without turning teh craft into terrible ugly, and im not about to ruin the appearance either, especially when it doesnt quite look as nice as i was going for. really the only MAJOR problem right now is that im limited to roughly 500dV at a time (forcing me to make much less efficient burns). Im basically running out of batteries non stop as i already have like 30 batteries (a bloody 1/3 of the craft is batteries), and even that doesnt give me too much dV before i need to sit back and recharge them.

After some more testing, i MADE IT TO LAYTHE AND BACK!

Ofc the burn was PAINFUL......i had to basically raise my orbit to 1000km, which then (while not as efficiently) let me burn to jool in one shot.

This PUNY thing weighs roughly 10t, and has 6000 dV in space, not to mention it is fully SSTO capable.

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Despite the painfully bad burn times, im quite happy with it.

24kN thrust, 97 parts (not counting any weapons), 6000 dV in space, laythe roundtrip tested with landing (although i got dangerously low on jet fuel and didnt quite land exactly where i wanted on the return trip), and its actually capable of landing on many lower gravity planets owning to just enough TWR, especially if you dump the jet fuel before landing on atmo-less planets. Its also capable of carrying up to 2t of ordinance (i managed to arm it with 2 tripedo-S guided missiles, or a nose cone of 3 625mm rockets. Its just a pain to take off with any weapons mounted.

Now although many people dislike this, i cant wait for the round-8 to be repurposed into a xenon tank, might cut down some of the excessive tank spam (i got 18 fuel tanks inside my craft)

Edited April 16, 2015 by panzer1b