mk1980

i agree with @Snark. the last time i sent something to moho, i adjusted the periaps during the plane change burn. afaik it gets more expensive the closer you already are, so if you can tweak it to where you want to have it while you are still very far away, it costs a lot less. i used a terrible transfer and the original capture burn would have cost >5000 m/s. with a 200m/s adjustment i lowered the PE to ~15 km (i think) and the capture burn went down to ~4000m/s. same principle applies (in a much smaller scale) to something as simple as a transfer to mun. if you first capture into a high orbit and then lower it, it costs more than spending like 10 m/s on a correction burn early on to get the PE as low as you dare and do the capture burn at the lower PE:

to be honest my ascent profiles tend to be a little chaotic. depends a lot on the number of engines i put on the plane. my first design used only 8 rapiers with a mass of ~240 tons, so it had fairly low TWR at takeoff. in that case, i stay in horizontal flight to pick up some more thrust and see if i can go supersonic before climbing. if that works, i fly horiztontal until ~ 400-450 m/s, then pull up to climb reasonably quickly into the higher layers of the atmosphere. with a higher TWR (like my most recent addition - 12 rapier & ~180tons mass), i pull up immediately to avoid the extra drag in the low atmo. once i get to higher altitudes, it gets chaotic. sometimes i lower my ascent a lot to squeeze out more horizontal velocity. basically a horizontal "speedrun" somewhere between 15-20km. i push the plane to >1500 m/s and then pull up and try to get the projected AP to a decent altitude before i have to switch over to closed cycle. in other attempts i also do a "speedrun" but don't pull up a lot and keep going in a shallow climb in rocket mode. in this case i actually reach orbital speeds and *almost* cicularize within the atmo (like AP at 40km, PE at 20km). adding more horiztontal speed at that point automatically raises the AP out of the atmo, but it will be somewhere on the other side of the planet so that profile involves a very long "coasting" phase through the upper atmo with phyiscs warp. i usually try to avoid that since it takes a lot of extra time for (probably) very little gain. and sometimes i just climb at a somewhat constant angle and just switch over when the rapiers get too weak to provide useful acceleration. i think that profile is a bit wasteful because i often end up switching over at subpar horizontal speeds (1300 m/s or something). that profile is my preferred method for the somewhat overengineered craft i use in career, for the simple reason that it takes a lot less time and effort (gets to orbit almost as fast as a rocket). i don't think it is competitive if fuel efficiency matters, but IMO saving a few thousand extra funds isn't really worth spending a few extra minutes of real time (except for the purpose of a challenge where funds == score). no matter what ascent i pick, i always have the feeling that i'm doing something wrong i guess it can't be completely wrong, though, otherwise my contraptions wouldn't end up with roughly the same fuel spent as the other craft that were presented (?)

new attempt. after some redesign of my previous craft, i got it a bit more stable. still flies like a cow and i had to use like a dozen struts to make it not explode during takeoff. and i found a clever (*cough*) solution to the nosecone problem. hope it qualifies. technically we decouple the nosecone, but only for a minute or so, then we dock it onto the (now free) docking port that previously held the fuel tank. the docking was needlesssly complicated since i'm an idiot and put the engines so close together that the cone almost didn't fit through it. but that way at least the RCS ports were not entirely useless LF: 8450 - 30.30 = 8419.7 Oxi: 3190 MP: 120 -101 = 19 score: LF 8419.7 * 0.8 = 6735.76 Oxi 3190 * 0.18 = 574.2 MP: 19 * 1.2 = 22.8 sum: 7332.76

ISRU seems a bit over the top. i'm not really sure if it's *unrealistic* since i have no clue how real ISRU is supposed to work, but i guess the converters would be a lot less efficient and heavier? (i may be totally wrong here). also, the nuke engines seem a bit unrealistic to me. as far as i know, they were never actually used in real life, so having working nuke engines in the game seems a bit weird, especially since they are placed on a fairly cheap research node. i could see them as some sort of "near future" tech similar to the rapier engines, but then they'd have to be on a 1000 tech node and require the fully upgraded R&D to unlock. but maybe that's just me.

what about fairings? the "open end" craft i was playing around with also has a nosecone (on the back end of the tank) for aerodynamics. it would probably also work with no back end at all, but the blunt end will create lots of drag. i guess i could just wrap the tank into a fairing, though. technically the craft doesn't lose parts when the base of the fairing is on the plane and not the cargo.

generally speaking, RCS is always a loss of deltaV. even if you don't need the monoprop for maneuvering and use it up for acceleration/deceleration, it's a net loss because RCS thrusters have very bad specific impulse (fuel efficiency) which is one of the main components of the deltaV equation. every single rocket engine has better Isp. think twice if you really need RCS and at all. if it's a large ship, it may be convenient for docking, but a small lander should be quite easy to dock without RCS.

tried a new design, based on something i posted eralier, just a lot smaller (original design was built for heavier cargo) worked surprsingly well, except for the reentry. aerodynamically unstable should have moved the engines further forward... not in the mood to continue right now. maybe tomorrow... if i get it to work, it should score pretty good. not as good as Nefrum's stingray but almost in the same ballpark. uses about 8000 LF & 3000 Ox. i think i would fit well into the "station builder" category. unlike the mk3 cargo bay, that "open end" design allows for some fairly bulky cargo stuffed inside a fairing for aerodynamics. most station modules etc. mass a lot less then fuel, so if it can lift a double orange tank, it should be able to lift pretty much everything that fits inside a 2.5 meter fairing. in theory one might even replace the mk3-2.5m adapter with an mk3-3.75m adapter and use a 3.75m fairing for even bulkier cargo. might have to use longer landing gears for the ground clearance, though.

don't want to be the "party pooper", but does the "stingray" actually qualify? don't get me wrong - it's a very impressive design, but it doesn't seem to fulfil the "must have functional RCS and a usable docking port" requirement. i don't see any RCS thrusters or vernors on the screenshots.

- large 2.5 meter SRB - a 2.5 meter version of the rapier engine for big spaceplanes (basically the same as 4 "normal" rapiers merged into one) - a 2.5 meter version of the nuclear engine (4 merged into 1) - a set of 1.25m to 0.625m multi adapters (bi/tri/quad coupler - same layout as as the 2.5 to 1.25m bi/tri/quad coupler, but on a smaller scale) - a 2.5m diameter LF only tank

- you can adjust the "thrust limiter" of rocket engines during flight. this can be very useful for doing small burns that require high precision (like correction burns to adjust your periapsis location in the target SOI). with some practice, you can use the same technique (combined with a lot of reaction wheel torque) for rendezvous and docking maneuvers without RCS thrusters. - one of the aircraft tech nodes contains the "small hardpoint". this part is essentially the same as a radial decoupler, but costs only 60 funds rather than 600. this is especially useful for small-ish rockets. using the cheap, small "hammer" or "thumper" boosters is a lot more economic when the decoupler to mount the booster isn't more expensive (or almost as expensive) as the booster itself. - structural pylons or girder segments can be used as very sturdy "static" landing gear for spacecraft. this avoids the problems with the relative fragility of retractable landing legs. note that they are also quite a bit heavier than the landing struts, so it's not recommended to use them on small-ish craft like a one seat mun lander. they are better suited for larger craft like mining rigs or science outposts. - structural aircraft wings can be used to widen the "base" of landers without adding a lot of extra weight (especially the long and thin structural wing type C). it's a bit of a hassle to get such craft to space, though, as the additional drag near the top of the rocket makes it much more likely to flip over.

your craft doesn't seem to have a docking port. if that's the case, you should add one (it's one of the rules of the callenge) also, i think it would make sense to keep the rapiers burning until you run out of oxidiser. hauling around unused oxidiser is a waste of deltaV, especially considering the low value of oxidiser for the score. and don't forget the reentry burn - that will also take some fuel.

not sure about the comment on the scoring system. i doubt mainsails will be used - their vacuum Isp is garbage, so you might as well just use the rapiers and not add an extra engine. i actually couldn't get my original plane to the target orbit with just rapiers, so i added a pair of nukes and switched an LF/O tank to pure LF. that worked. to get the same amount of deltaV out of the rapiers in closed cycle, a lot more fuel would have been required. and then additional engines to carry that weight. and then more wings to lift the whole thing up. so the whole things gets bigger and bigger. i guess i'll give it a try - instead of a nuke, i'll try to do it with just rapiers and see if i can get it to work. i think the score system is not bad. the 300km orbit makes nukes for orbit the obvious choice. but with the adjusted score, we might actually see some creative solutions other than "enough rapiers to get to space + 1-2 nukes to get to the 300km orbit and back". also, isn't that the price (in kerbal currency) of the fuels in game?

those images look like you are reentering from a retrograde transfer orbit. your capsule is pointing at 270° on the navball). if that's the case, then that's also the solution. make sure your transfer back gets you into a prograde orbit. if you come in from the wrong direction, you move ~400 m/s faster (relative to the atmosphere). that's a big difference and can easily kill a capsule that would easily survive a prograde reentry. EDIT: ignore that. i've been playing with spaceplanes too much lately and completely forgot that a capsule points retrograde in the reentry

i don't think the challenge requires that specifically. i guess it would be within the spirit of the challenge to build something that can (technically) also lift bulky cargo that doesn't fit into a cargo bay but can be packed inside a fairing that is attached to the lifter plane somehow. i made something along that line a while back. in this case i used a bunch of ore tanks as the "placeholder" cargo (~120 tons), but the plane was designed with other payloads in mind that would be inside a fairing docked at the port behind the cockpit section. i went with a more "traditional" design for the challenge because i don't think that an "open cargo format" plane design can compete (too much drag). would be interesting to see something like that specifically tailored to the requirements of the challenge, though.

it's more of a "brute force instead of efficiency" craft. the payload is basically the mk3 cabin (6.5 tons) and about 3 (?) tons worth of mining equipment in the cargo bay. there are more elegant ways to get such a payload to minmus, but brute force also works i tend to use the medium sized landing gears on mk2 planes and either the large or extra large (for heavy cargo) on mk3 planes. i think this plane actually uses the medium gear since it's *relatively* light for an mk3 SSTO (< 100 tons fully fuelled) in my duna SSTO, i also used medium sized gear, but i didn't land it like a plane, so i guess that doesn't really count. regarding the pitching up: when in doubt, you can always put a few reaction wheels somehwere in the tank stacks or in a cargo bay. they don't have a lot of mass, make orbital maneuvers less tedious and help (a bit) with maintaining attitude during reentry. alternatively, you can put a few RCS ports or vernor engines (basically more powerful RCS ports that use LF/Ox instead of monopropellant) on the belly somewhere in the foreward half of the plane and toggle RCS for the takeoff (so they assist when you pitch up). guess that should be enough.

another attempt with a heavily modified plane. as i suspected, it worked a bit better with more rapiers (12 instead of 8). this time i only used one nuke. looks a bit silly since it s basically just tacked on the back end on the fuselage. other than that, i kinda like the aestehtics of the craft with the mk2 engine nacelles embedded in the wings. wings are more in the back this time. looks better (imo), but it's harder to keep under control in atmospheric flight (after reentry) now for the fuel numbers: LF: 13410 - 528 (left after landing) = 12882 Ox: 7590 score: LF: 12882 *0.8 = 10305.6 Ox: 7590 * 0.18 = 1366.2 sum: 11671,8 conclusion: a few more engines and a bit less fuel seem to work better; wings at the back work "ok", but wings+engines centered around the mid section (ie. skylon style) are more stable in flight with empty tanks.

in general i agree with Rune , but there is also a point where minimizing engine count seems to be counter productive. it's probably more of an edge case and not very relevant for long range SSTOs, but if you don't pack enough punch to get out of the atmosphere reasonabyl fast, you may end up losing more deltaV in the ascent than you would gain from having a few tons less (unused) engine mass in space. well, at least that was my experience when experimenting with minimum engine count planes. there's currently a challenge in the subforum about getting a 72 ton payload (2 orange tanks) to a 300km orbit and my design used only 8 rapiers. in that case, i think some additional engines would actually have improved the performance. though in the long run, the reduced engine mass will probably trump the additional fuel you burned in the ascent - empty tanks are less dead weight than unused jet engines.

i did a bit of testing regarding the ISRU. made a "quick and dirty" tourbus-style spaceplane with an mk3 passenger cabin in sandbox and just enough deltaV to get to minmus to refuel. the cargo bay contains a small converter, a large drill (i'd always go for a large drill if you land "blindly" with no knowledge of ore deposits - the small one requires a minimum of 2.5% and if your landing spot has less, you're screwed). 1 big solar panel (might need more for outer planets- solar power output scales with proximity to the sun) and 1 small radiator. plus a big battery as buffer (would need more than 1 if it's supposed to cover the whole night). and a surface ore scanner (not really necessary if you're not going to drive/hop around in search for better spots) the tanks were almost empty when i landed and it took about 50 "in game" days to fill up ~7000 LF and ~4500 Oxidiser. there are multiple engineers on the craft, but i honestly don't know if only the highest level counts or if multiple engineers stack. obviously, with more drills or the big ISRU, it could have been much faster, but chances are that you'll have to wait a few months or years for the launch window back home anyway if you fly to duna or further out/in, so it doesn't really matter that much if you need 5 days to fully refuel or 100. the landing spot had a moderate ore concentration (4.5%) if you rely on ISRU, it's probably a good idea to have a named save (ALT+F5) while still in orbit so you can redo the landing and pick another spot if you happen to land on a really terrible ore concentration.

1. what dou you mean exactly by "land with no problem"? i don't think i noticed any problems with the nukes. when you make "traditional" (non-plane) spaceships with nukes and reenter retrograde, nukes can blow up, but on a plane that's very unlikely. usually the stuff at the nose gets hot first. you'd probably blow up the node of the plane before the nukes even display a heat bar. if that's not what you mean, please clarify 2. the rapiers will need both oxidiser andliquid fuel to work, so the moment you run out of oxidiser, they stop working (in "closed cycle mode"/"rocket mode"). that's not a bad thing. if you have multiple fuel types on a ship, you generally want to burn the least efficient fuel first to maximize the deltaV you can get out of the ship 3. on a windows PC, you hold down the alt key ( i think mac and linux sysems have different "modifier" keys) and click (or was it right click?) 2 (or more) tanks. then the game shows "in" and "out" labels on the contect menu of the tanks and you can transfer fuel from one tank to another. the system works best when you drain multiple tanks into one target tank (click the "in" button on the target tank) or refill multiple target tanks from one source (click the "out" button on the source tank). if you click the "out" button on multiple tanks, the logic gets confusing and the tanks will seemingly randomly push/pull fuel also note- if you want to do that in career mode, the function requires a building upgrade (i think the R&D must be upgraded) - not relevant in this case i guess. also a word of caution regarding mining: if you don't have a survey scanner in orbit that gives you an idea where the higher ore concentrations are, it is a bit of a gamble. you may end up with a poor location and it will take a long time to refuel. you should bring an engineer with a high level (level is the rirrelvant in sandbox/science mode-- all kerbals are level 5 by default). engineers speed up the mining dramatically (i think a level 5 engineer speeds it up by a factor of *20 or something). and you need neough power and cooling for the drill(s) and converter to work properly. also, you must have at least one small ore tank (the converter can only convert ore to fuel and the ore must be "buffered" in an ore tank - can't directly convert freshly mined ore to fuel without an ore tank)

hmm doesn't look too bad. some general notes: -instead of the inverted mk->1.25m bicoupler adapters with the ramp intakes, you could use the normal (or the double length) mk2->1.25m adapter with one chock cone. 4 shock cones in total should be enough to feed the 8 jet engines. i think that would also reduce drag somewhat (?) - instead of the skipper, you can use an mk2-> 1.25m tri or quad coupler and stick aerospikes on it. 3 aerospikes produce a bit less thrust than a skipper, but they have better fuel efficiency. not a big deal though. an alternative might be to not use rapiers at all and put a rhino engine at the back. it's heavy, but it has huge thrust and is (almost) as efficient as the terrier & poodle vacuum engines. probably overkill for that plane (don't need that much thrust), but worth a thought if you try to make something even bigger some day. i'll load up the craft file in KSP and take a closer look. maybe i can give you a tip regarding the wings if i see them in action. EDIT: i think the angled wing geometry (outer sections of the wings) messes up the lift. i removed the outer sections and just added a delta wing and a structural wing and it seemed to work quite well. probably should have stopped at that point, but then i continued and changed more stuff. removed the RCS thrusters and the MP tank and added vernor engines instead. i think they have lower drag (?) and better heat resistance and they are more powerful (and they consume LF/Ox fuel instead of MP) i also removed the whiplash and skipper engines and ran the plane with 8 rapiers (sorry, couldn't resist) a small (useful!) change would be to move the solar panels into the cargo bay. you can also set the "toggle cargo bay" in the same action group as the "toggle panels", so it's still just 1 key press. they are better protected in the bay and (i think) produce less thrust. then i also changed the "X" shaped tail fins to a more coventional setup (2 planar fins moved a bit upwards so they don't occlude the engines) and i replaced the winglets (canards) with 2 sets of the .. i think they are called "high performance canards" (?). i angled them slightly upwards (with the rotate tool +SHIFT key for finer rotation . i think it rotates in 5° steps) so they produce some automatic pitch without pressing the key and then your plane didn't reall look like your plane any more some images of the plane "in action". it's not exactly what you were asking for, but i got carried away a bit. i hope the proposed change to the wing geometry will at least be useful

you don't need fuel lines for the rapier engines - they pull fuel from all tanks equally even when you switch them to closed cycle mode. the nukes pull fuel like standard rocket engines (most distant tank first, drain empty, then move to the next). fuel lines add drag and nukes burn slowly, so it may be more efficient to just transfer liquid fuel manually to the tank that is directly attached to the nuke. unless you are lazy (like me )- in that case you'll want at least some fuel lines that feed into the tanks of the nukes. they do add drag, so it's not smart to use them on a plane if you can avoid it.

after some more messign around, my design made it. didn't change much. just replaced one Mk3 LF/O tank with a pure LF tank and added a pair of nukes for orbit here's the album. hope i captured all the required footage. i forgot to ask if kerbal engineering is allowed. let me know if not. doesn't make much of a difference, tbh. i guess i could re-do the whole flight without the mod if necessary (and without the stupid cloud mod that almost killed me in the final landing approach...) fuel spent: 14610 LF total (ignoring the 5760 units in the cargo tanks) - 518 remaining after landing 8030 oxidizer 13 Monoprop (120 - 107 remaining). wasn't necessary but i fired the thrusters for a few seconds to get away from the cargo tank after dropping it off) score: 14092 * 0.8 = 11273.6 (LF) + 8030 * 0.18 = 1445.4 (Ox) +7 * 1.2 = 8.4 (MP) => 12727.4 total conclusion: not worth it to try and minimize engine count too much. getting a ~72 ton payload to a 300 km orbit with just 8 rapiers and 2 nukes is possible, but you waste too much fuel to the low thrust to weight ratio (taking off at a TWR of 0.32 is painful). also takes way too long to get to orbit that way.

yeah i suppose it might be possible to to a half size version of the same thing. but that plane had almost no payload to begin with (really just the passenger cabin for 4 kerbals, not even a cargo bay with science instruments or similar). and some of the elements in the design are sort of "fixed" weight - you'll need at least 3 landing gears and i don't trust in the small ones, so the "half size" plane would have to carry the same weight of landing gears. don't know if that would break the design completely. won't make things easier, though. instead of the 4 person cabin, i could use the mk1 cabin for 2 passengers, or an inline cockpit (which is about the same weight). those items have terrible heat resistance, though. reentry from an interplanetary transfer is no joke. an it's not fun to fly all the way to duna and back just to blow up when you finally get home i don't consider that type of spaceplane very practical, tbh. i only made it for the challenge, but if i were to use something like that in a career game, i think i'd cut the fuel down dramatically and just pack a mining drill and small converter. or more likely - i'd just send up another plane and refuel the expedition plane in kerbin orbit before i send it off.

i did a roundtrip to duna surface and back for some forum challenge a while back. it's not an easy task. you need A LOT of fuel to pull that off without mining equipment to make fuel in situ. that plane wasn't pretty. it was basically a lot of fuel tanks with some engines at the back and a passenger cabin at the front. from experience, you'll need something like 3500 m/s in kerbin orbit to get to the surface of duna and back. my plane had a bit more and had like 200 m/s left after aerobraking into kerbin orbit -which i spent on a plane change to try and line up with the equator for a KSC landing (didn't work, that beast was uncontrollable with empty tanks) i basically had to "cheat" with the landing on duna (there are parachutes stowed in the service bays on the inner tank stack). getting back to orbit was painful with just 2 nukes. not going to do that again ever. bottom line is - it's a lot of effort to squeeze in enough fuel for the transfers and the return from duna surface to orbit. and it's quite a hassle to get a plane with so much excess fuel to kerbin orbit in the first place.

i guess that skylon-like setup will be a common sight. the plane i've been playing around with looks quite similar to yours. a bit shorter and with less engines, but i haven't gotten it to the target orbit yet, so i may also have to slap on some extra engines and longer tanks to acutally make it work.