Is it even possible to make a <15t laythe roundtrip SSTO?

[panzer1b]

Anyways, im back from a break from KSP, and i still cant seem to make a stock craft that does a laythe roundtrip and is under 15, let alone my original requirement of 10t in mass. Im no math expert so i dont know if it can even be done, but if so, could some of the more experienced players here give me some tips on what i can use to make a truly super lightweight laythe roundtrip craft that doesnt jettision a single part during the whole trip, and doesnt have any less then a 0.2 TWR (i cant stand super long burns, as game doesnt have any real way to burn on rails stock at least).

All in all what im trying to make is a SSTO that has:

has above 3.5K space dV (id rather not have to deal with slingshots and all that stuff, should be able to direct hohman transfer to laythe and back, something ive done in the past multiple times with craft that had 3.7Kish)

weighs absolutely no more then 15t fully fueled

no cheats or exploits and 100% stock

Now if this is not possible, then i can live with that, but if so, could someone give me some ideas as to what sort of build would work here.

And ofc, unless proven otherwise, i consider all eeloo roundtrip SSTOs to be dead 100%, i dont think its even possible to get to eeloo, land, and return to kerbin without staging after 1.0 came around.....

Edited August 2, 2015 by panzer1b

[Dispatcher]

That's quite a challenge. Part of your strategy ought to be including enough air intakes to allow you to achieve low orbital apoapsis before jets flame out or Rapier is switched to vacuum mode. Ideally your rocket engine(s) will not be engaged until your air breather(s) run out of air; if you are not using the Rapier.

I think your design should incorporate chutes/ aerobrakes to land your craft without using (much) fuel; at both Laythe and Kerbin. Any chutes will need to be repacked at Laythe.

If you plan on resource extraction at Laythe, the equipment is gonna impose a mass penalty in itself.

Good luck and we want to see pics if you succeed.

Edited August 2, 2015 by Dispatcher

[panzer1b]

That's quite a challenge. Part of your strategy ought to be including enough air intakes to allow you to achieve low orbital apoapsis before jets flame out or Rapier is switched to vacuum mode. Ideally your rocket engine(s) will not be engaged until your air breather(s) run out of air; if you are not using the Rapier.

I think your design should incorporate chutes/ aerobrakes to land your craft without using (much) fuel; at both Laythe and Kerbin. Any chutes will need to be repacked at Laythe.

If you plan on resource extraction at Laythe, the equipment is gonna impose a mass penalty in itself.

Good luck and we want to see pics if you succeed.

you do know 1.0 and subsequent updates have made achieving above 1400m/s before switching to rockets basically impossible without spamming extreme TWR, which is going to be killer lateron, and speeds above 1600 are pretty much impossible on jets/rapiers alone, need rockets.

chutes or aerobrakes arent an issue, since i can angle the craft properly, slowing it down in teh process, allowing a unpowered glide to the surface, or at a bare minimum using little if any fuel to land.

resource extraction i have considered, but there is no way whatsoever to bring the stuff wiht a 15t hard limit on ship mass, it just aint happening nomatter how you try.

Anyways, ive already tried as much as i can, and im always running out of fuel before i can get back, the mostr ive managed to do sofar is a laythe one way trip with just about enough fuel to get into orbit, although ive yet to manage thism, perhaps with a more efficient hohman transfer i could pull it off, but even that, without using grav assists (which may or may not work, im not good enough nor patient enough to wait all that time ect), i just cdant seem to pull it off, its either too much mass is brought in rapiers, which makes the long interplanetary burns suffer, or there isnt enough rapiers and i end up using way more fuel then i have to to get into orbit.

Im starting to think this cant be done with a lightweight vessel, since the only way ive actually managed to get a laythe roundtrip is abusing clipped fuel tanks/ion engines, and cramming the entire assembly into a service bay that essentially disabled all drag for the gear. That and i edited the probe core on teh vessel to have like 5 million electric charge so i didnt need to drag 5t of batteries or massive solar panels up there, again, i cant consider this to be a legit attempt as its pretty much cheating. Still trying to mess with a single nuke single rapier combo, but i cant seem to get it high enough fast enough on that single puny rapier pushing 15t so that the nuke doesnt eat a boatload of fuel when its circularizing a suboptimal trajectory left behind by the rapier.

[Dispatcher]

I hear you. BTW, I wasn't sure what you meant by SSTO since that does not have to be a spaceplane, so my reply was based on a general approach. If you follow the link in my sig line to my engine test results graph (not the old chart), you'll see the practical mass I was able to lift with a single stacking engine or 3 and 2 radials. The test was using 40% "wet" mass, but I think its scalable up or down in a crude way, and multiple/ mixed engines add thrust (and mass). As you know, there are those pesky trade off's between thrust and iSP/ efficiency.

Oh, outside of Rapier use, the best SSTOs (spaceplane or not) I've made used a turbojet/ aerospike combination. Of course for reasonable mission times and fuel use, I've relied solely on LV-Ns for orbit to orbit flights in the past. I've not yet experimented with translunar/ interplanetary flights using the Nuke since before v. 1.0.

Edited August 2, 2015 by Dispatcher

[selfish_meme]

It has been done, see he ssto to Laythe challenge thread, 2 rapiers and an lv-n and just enough fuel, then you just need fantastic piloting

[GoSlash27]

It might be barely possible if you don't mind extreme clipping (I consider that cheating).

Otherwise, my back- of- the- envelope sez it ain't gonna happen. At least... not with a hohmann transfer and a kerbal in a cockpit.

A decent SSTO spaceplane will have a payload fraction of around 20% to LKO in small scale. 15 tonnes of spaceplane on the ramp will give you 3 tonnes in orbit, which includes the cockpit.

Not enough to carry a nuke and not enough fuel to feed the RAPIER for all that DV.

Ions could do the job (probably), but you're going to have issues with the solar panels at Laythe and you'll need lots of batteries (hence the clipping).

A vertical lift RAPIER design is liable to improve your payload fraction to orbit, and would therefore open up interesting possibilities.

*edit* yeah. A vertical lift RAPIER design could get you over 30% payload fraction in small scale. That would make nukes do-able.

Good luck!

-Slashy

Edited August 2, 2015 by GoSlash27

[selfish_meme]

It might be barely possible if you don't mind extreme clipping (I consider that cheating).

Otherwise, my back- of- the- envelope sez it ain't gonna happen. At least... not with a hohmann transfer and a kerbal in a cockpit.

A decent SSTO spaceplane will have a payload fraction of around 20% to LKO in small scale. 15 tonnes of spaceplane on the ramp will give you 3 tonnes in orbit, which includes the cockpit.

Not enough to carry a nuke and not enough fuel to feed the RAPIER for all that DV.

Ions could do the job (probably), but you're going to have issues with the solar panels at Laythe and you'll need lots of batteries (hence the clipping).

A vertical lift RAPIER design is liable to improve your payload fraction to orbit, and would therefore open up interesting possibilities.

Good luck!

-Slashy

Laythe and back 39 tons Red Iron Crown people have made it just to Laythe with much less, PLAD 7.7 tons, the difference is piloting these guys are using gravity assists across the whole solar system.

Edited August 2, 2015 by selfish_meme

[panzer1b]

It might be barely possible if you don't mind extreme clipping (I consider that cheating).

Otherwise, my back- of- the- envelope sez it ain't gonna happen. At least... not with a hohmann transfer and a kerbal in a cockpit.

A decent SSTO spaceplane will have a payload fraction of around 20% to LKO in small scale. 15 tonnes of spaceplane on the ramp will give you 3 tonnes in orbit, which includes the cockpit.

Not enough to carry a nuke and not enough fuel to feed the RAPIER for all that DV.

Ions could do the job (probably), but you're going to have issues with the solar panels at Laythe and you'll need lots of batteries (hence the clipping).

A vertical lift RAPIER design is liable to improve your payload fraction to orbit, and would therefore open up interesting possibilities.

Good luck!

-Slashy

Vertical lift rapier rockets are actually more efficjent then a classic spaceplane? That would at a minimum make landing especially if its not laythe (say i choose to go elsewhere) much easier as landing with wheels is hard unless you plan well ahead and take advantage or some flat areas that are hard to find (and ofc that might be able to land on water if done right).

Also, i dont have anything against clipping if its within reason, for example clipping a FLT-200 inside a MK1-MK2 adapter is ok as both have same fuel capacity and the adapter has roughly 2 times the volume of the flt with equal fuel inside, so based on sound logic, you could actually fit that much volume inside it, as for 2 FLTs, i stay away from any more then say 20-30% clipping unless im designing a purely for looks vessel in which case i usually dont care about fuel at all since pure for looks = Hedit or inf fuel to orbit anyways.

As for ion clipping batteries/fuiel tanks, ive already done a fully working laythe roundtrip SSTO that way, i basically shoved ~12 ions, all the batteries i need, ~30 of the .625m xenon tanks, and some RTGs inside a MK1 service bay. Im quite aware that abusing teh game makes laythe roundtrips doable (i managed a 13t laythe roundtrip in a super small fighter like craft before in 1.03), but the idea behind this thread is well, being able to pull this off with what id consider a rather non cheaty craft. Clipping i have nothing against fundamanetally, especially since alot (err 99% of) my designs are designed to some degree based on appearance, but the things i avoid are clipping engines, fuel tanks, wings, ect. Only exceptions to that general rule are: i need to get a particlar lok and need to clip a small control surface in nose or tail without it visible, or nukes as i hate how ugly they look fully exposed, usually clip them so only the rear shows and the rest is inside a fuselage or fuel tank or whatever. Aside from that, i stay away from anything id consider cheaty.

Also, do you know what the optimal wing area per ton is in 1.04, i know its far less then older versions of the game like 0.90 where wing spam was not a bad thing, but here it seems that i can get away with as little as a 2 delta deluxes and 2 small control surfaces for ~10t, which is imo rather low. Im no expert, but is it true that the less wings you use the better off you are in general?

Ohh, and apparently placing a circular intake behind a rapier and clipping it inside the rapier essentially disabled drag on teh rapier and gives you both intake air AND lowers drag. Ofc i do not consider this legit, but i also dont get why having exposed engines in the rear gives such a harsh drag penalty vs placing a nose cone or intake behind said engine makes you have LESS drag and free intake air (shock cones or circulars in front and behind every stack gives the least drag possible.

Edited August 2, 2015 by panzer1b

[Starhawk]

I must say I'm a but surprised that you're asking this.

I would have thought the SSTO to Laythe and Beyond challenge would have answered the question one way or the other by now.

My spaceplane that could do Laythe and return in 0.90 massed something like 25 tonnes on the runway, so doing it in under 15 under the current system seems very unlikely to me. Unless maybe using physics exploits or extreme clipping as Slashy suggests.

Good luck.

Happy landings!

[GoSlash27]

This vertical lifter weighs under 15t on the pad and has over 6200 m/sec DV in LKO; more than enough to do the deed including a launch to orbit at Laythe and return to Kerbin. <-- forgot to carry the one O_o Ignore that.

This one has 2500 m/sec in LKO, so probably still not enough.

Just a proof of concept. It has no chutes, solar panels, or batteries.

Best,

-Slashy

- - - Updated - - -

Selfish_meme,

They were over the weight limit of 15t and Plad used a probe. As you point out, they all used extreme slingshotting.

The question is if it can be done with a Kerbal in a cockpit, Hohmann both ways, and under 15t.

I say yes, but it'll have to be a vertical design or resort to extreme clipping.

Best,

-Slashy

Edited August 2, 2015 by GoSlash27

[panzer1b]

http://i52.photobucket.com/albums/g13/GoSlash27/LaytheSSTO_zpsnifcvf2p.jpg

This vertical lifter weighs under 15t on the pad and has over 6200 m/sec DV in LKO; more than enough to do the deed including a launch to orbit at Laythe and return to Kerbin.

Just a proof of concept. It has no chutes, solar panels, or batteries.

Best,

-Slashy

- - - Updated - - -

Selfish_meme,

They were over the weight limit of 15t and Plad used a probe. As you point out, they all used extreme slingshotting.

The question is if it can be done with a Kerbal in a pod, Hohmann both ways, and under 15t.

I say yes, but it'll have to be a vertical design or resort to extreme clipping.

Best,

-Slashy

Thx, you just solved my question of if its even possible, now to make something of this sort but using more efficient circular intakes and ofc adding other stuff i need onboard (around half the drag of your design).

How well does this handle reentry at interplanetary speeds?

[GoSlash27]

Thx, you just solved my question of if its even possible, now to make something of this sort but using more efficient circular intakes and ofc adding other stuff i need onboard (around half the drag of your design).

How well does this handle reentry at interplanetary speeds?

panzer1b,

Please check the correction on my earlier post. I screwed up the math and the DV estimate was way wrong. It was based on the erroneous assumption that jet fuel weighs twice as much as it actually does.

As for how it handles reentry heating at interplanetary speeds, I wouldn't know. I'd imagine pretty poorly.

Best,

-Slashy

Edited August 2, 2015 by GoSlash27

[Dispatcher]

panzer1b, I even have my doubts about a 1-way mission being attained with your target parameters. At least with my skills it would not likely happen. I do think its cool that you are trying, though. I'm in the multistage camp when it comes to interplanetary missions (and back). But I also am a fan of SSTO planes, the true definition given by the acronym. As I wrote earlier; let us know what you achieve and post those pics or videos!

[GoSlash27]

Dispatcher,

Same here.... Sorta. I break my missions into legs and have vehicles optimized to their part of the mission. I use ssto spaceplanes to interface between KSC and LKO, then hand the job off to interplanetary ferries. I use specialized landers to interface between the ferry and the surface at the other end.

While I personally wouldn't use an SSTO to get from Kerbin to Laythe surface and back*, I won't discourage anyone else from doing it. They may come up with improvements that I might find helpful.

Best,

-Slashy

*did it once in .25 just to prove a point. I used this highly-cheaty SSTO to visit Eve, Laythe, and Duna all in the same trip. Long live infigliders and Kraken drives!

Edited August 2, 2015 by GoSlash27

[Red Iron Crown]

To Laythe's surface and back in a single stage is definitely possible using Hohmann transfers without cheating, that's how I did the mission selfish_meme linked earlier (though I did use assists to capture at Jool). It was much more than 15t though, more like 40 for the Rapier/LV-N design I used. I don't think an LV-N will be viable for a 15t version, but a Rapier/Ion design might be able to do it.

[panzer1b]

panzer1b, I even have my doubts about a 1-way mission being attained with your target parameters. At least with my skills it would not likely happen. I do think its cool that you are trying, though. I'm in the multistage camp when it comes to interplanetary missions (and back). But I also am a fan of SSTO planes, the true definition given by the acronym. As I wrote earlier; let us know what you achieve and post those pics or videos!

Javascript is disabled. View full album

Possible heck yes, one ways ive been doing for ages. This particular vessel is ~16t though, 1 more then what i want but it had more then enough fuel.

one way under 15t is 100% doable, what im having issues with though is 2 way trips. With a grav assist im confident this could do a roundtrip, but i want 4K dV so i dont have to do this.

Still, im not giving up, i feel it MAY be done legit and the vertical launch seems to be a little better then aircraft like builds when it comes to payload and the fact theyre lighter with no wings ect.

[Michaelo90]

I just quickly slapped together a plane that reached a 77*77 km orbit with just over 3000 m/s of delta-v left with just under 15t on the runway. That could be able to do it, but I'll try to improve the design and my piloting a bit first to try to get a bit more delta-v in orbit.

Edit: No delta-v improvement, but some other small improvements to the plane. I'll try to get it to Laythe tomorrow.

Edited August 2, 2015 by Michaelo90

[Val]

I got close.

View full album

Complete craft with 1 Kerbal pilot and RTG for power (clipped into nose cone for aesthetics)

CoL is pretty close to Dry-CoM, so you could run into unrecoverable stalls, if you go too far off prograde when low on fuel in atmosphere.

I'm working on an improved design now.

[Val]

Woohoo. I made one with more than 3.5 km/s that weighs less than 15 t.

View full album

No oxidizer. Pure Airbreating Rapier and Nuke. Tried with Turbo Ramjet, but not enough speed.

No fuel line, need to manually transfer fuel from lower tank once Rapier is out of air.

Not much room for science kit, though.

[Starhawk]

Woohoo. I made one with more than 3.5 km/s that weighs less than 15 t.

Amazing! Nicely done.

I didn't think it was actually possible with that configuration.

Happy landings!

[Dispatcher]

Woohoo. I made one with more than 3.5 km/s that weighs less than 15 t.

No oxidizer. Pure Airbreating Rapier and Nuke. Tried with Turbo Ramjet, but not enough speed.

No fuel line, need to manually transfer fuel from lower tank once Rapier is out of air.

Not much room for science kit, though.

Also an interesting craft. I'm so habitual in terms of symmetry of design that I never would have thought of it.

- - - Updated - - -

Possible heck yes, one ways ive been doing for ages. This particular vessel is ~16t though, 1 more then what i want but it had more then enough fuel.

one way under 15t is 100% doable, what im having issues with though is 2 way trips. With a grav assist im confident this could do a roundtrip, but i want 4K dV so i dont have to do this.

Still, im not giving up, i feel it MAY be done legit and the vertical launch seems to be a little better then aircraft like builds when it comes to payload and the fact theyre lighter with no wings ect.

Nice design. Keep up with your goals on this. I'm sure a vertical launch design will be more effective.

[PLAD]

The 2nd part of the OP mentioned an Eeloo SSTO round trip. I think a single-stage flight to Eeloo landing and back to Kerbin is clearly possible using some of the ships from the SST-Laythe challenge. It is possible to go from LKO to Eeloo's surface and back to Kerbin for 3050m/s. I did it here using the old aerodynamics for 2897m/s, modern aerodynamics would prevent that 142m/s braking pass through Jool's atmosphere but doing it just outside the atmosphere would work for 150m/s. This uses the K-Mu-E-K-K-J path to get to Jool, if you wanted to use a simpler K-E-K-J path you could do it for only 300m/s more, so 3350m/s. Or you could go straight to Jool and fly on to Eeloo with the greatly reduced arrival speed that Jool allows for 4000m/ round trip total. (And as always using a Jool flyby on the return to Kerbin.) With no flybys at all it takes about 2100 (LKO to Eeloo)+1400(brake into orbit)+620(land)+620(takeoff)+1100(LEO to Kerbin)=5840m/s, which I agree would be roughly impossible for an SSTO.

Regarding the SS-to Laythe and return, with no flybys I think it's flatly impossible for anything under 15 tons with more than 1 LV-N and 1 Rapier ("1L/1R"), and barely impossible for even that. With flybys it should be possible for the 1L/1R design. I'm not counting ion ships, the ultra-low TWR for a Rapier-ion only ship would be too brutal to contemplate. Now I have to prove it...

[Michaelo90]

Woohoo. I made one with more than 3.5 km/s that weighs less than 15 t.

http://imgur.com/a/SP0it

No oxidizer. Pure Airbreating Rapier and Nuke. Tried with Turbo Ramjet, but not enough speed.

No fuel line, need to manually transfer fuel from lower tank once Rapier is out of air.

Not much room for science kit, though.

Nice!

My attempt is similar with one nuke and one rapier but I abused clipping to make it really compact and have the thrust in line.

The four fuel tanks are clipped almost completely together, the nuke is clipped into the rapier, and the RTG is clipped into the nuke Also, because of all the clipping, the CoM doesn't really move at all, the dry CoM marker is actually activated in that screenshot

Seems like you're much better than me at piloting a low-TWR spaceplane since I only got just over 3k delta-v left in orbit even though I had more fuel. Here is my craft file if anyone wants to try it, someone might get more out of it than me Use action group 5 to dump the nuke fairing.

Edited August 6, 2015 by Michaelo90

[Nich]

any wings you bring to space are going to hurt your dv in space. I suggest you look at Nao's entry for the stock payload fraction entry. Trim some fat and give it a retractable landing gear so it is a true SSTO and reduce the lift and it might be viable.

http://forum.kerbalspaceprogram.com/threads/116729-Stock-Payload-Fraction-Challenge-1-0-4-Edition?p=2041263&viewfull=1#post2041263

[Val]

Nice!

My attempt is similar with one nuke and one rapier but I abused clipping to make it really compact and have the thrust in line.

http://i.imgur.com/F4HJDCJ.png

The four fuel tanks are clipped almost completely together, the nuke is clipped into the rapier, and the RTG is clipped into the nuke Also, because of all the clipping, the CoM doesn't really move at all, the dry CoM marker is actually activated in that screenshot

Seems like you're much better than me at piloting a low-TWR spaceplane since I only got just over 3k delta-v left in orbit even though I had more fuel. Here is my craft file if anyone wants to try it, someone might get more out of it than me Use action group 5 to dump the nuke fairing.

Thank you

My thrust is mostly in-line, at least for the nuke. The Rapier not so much, but it doesn't matter since it's only used where control surfaces can compensate. The reaction wheel combined with moving fuel around is enough to keep it stable in vacuum.

I think the reason you get less dV is because you have more drag, so you use more fuel getting to orbit.

Like in real life, KSP wings only produce lift when they're at an angle to the Airflow. If you mount your wings parallel to the rest of the craft, then the whole craft has to be angled for the wings for lift. This is bad for drag.

To get around that, your wings need to be angled, in relation to the fuselage, so the leading edge is higher than the trailing edge (Angle of Incidence). Because it's better to have only the wings, at an angle to the air flow, than the whole craft.

I angle wings 5 degrees on my designs. USE Shift + W, A, S, D, Q, or E, as appropriate before mounting, or one tick with the Rotation Gizmo, while holding Shift in angle snap mode.

When that is done, you can probably reduce the wing size, too. You only need about 1 lift rating per 10 ton (not counting Control surfaces).

Mine has 2 Small Deltas (2x 0.5), 2 Structural Wing Type D (2x 0.25) = 1.5 Lift rating for 15 tons.

Control surfaces are also twice as heavy compared to the Lift rating they provide. With a few exceptions*, wings weigh 100 kg per Lift rating and control Surfaces ~200 kg per Lift rating. So try if you can do with less.

*) Swept Wings are too heavy at 257 kg for 1.37 Lift. FAT-455 Aeroplane Tail Fin, Big-S Spaceplane Tail Fin and Deluxe Winglet are lighter than other control surfaces, maybe because they are considered wing and control surface combined.