AeroGav

I'd take a bit from @Brikoleur and @bewing I'd launch like an airplane from Kerbin, refuel in Kerbin SOI, but i would put nukes on the thing, in fact i'd make it oxidizer-free because if you're building around low drag mark 1 parts you can very easily get to orbit from Laythe with Panthers and nukes only. Nuke only works best with a nuke TWR of 0.3 to 0.6 to 1 - this works fine so long as you can build an airplane that actually flies like one, with more lift than drag. Too many Kerbal airplanes look like airplanes but are really rockets, they have more drag than lift and only fly because KSP jet engines are overpowered and give you TWR of 2 to 1 or better. The seaplane aspect makes things harder, you need a good TWR to break free of the surface or you need to get lucky with hydrofoil design - perhaps you're best off with Panthers as your jet engines for this reason (highest twr at sea level and low speed). If you're going with the refuelling approach, use an inline clamp o tron instead of a shielded docking port (much less drag). On the other hand, all that docking and refuelling is going to be a PITA, especially in the Laythe system. You could refuel in Laythe orbit, doing so on the surface is really hard and annoying (ever tried ground docking two vehicles that are being influenced by gravity, terrain and landing gear legs ? very hit or miss) So you could just put a small IRSU on the airplane, 4 RTGs to power it, one small drill, one small deployable radiator , the smallest ore tank, and bring an engineer with you (should come in under 1.5t for that stuff, put the drill and ore tank and RTGs inside the 1.25m fairing on your nose) If this contraption lacks the umph to get to Minmus from Kerbin, consider fitting droppable booster engines on pods under the wings like this thing https://kerbalx.com/AeroGav/Kranker or this I also wrote a guide on Panther NERV ssto for career mode, though as you're not stuck to tier 7 techs i'd swap all the Modular wing parts for Big S wings and Big S Stakes, this will enable you to get rid of most of the cylindrical tanks ( big s wings have better capacity to drag ratio than cylindrical tanks, should always be used where possible on a spaceplane)

Yeah I wouldn't fret over this too much. This is already a very useful mod - CorrectCoL has the stability analysis if you want that (actually, almost everyone does, they just don't realise it). Though if you ever get this to work it will save me having to install 3 other mods - CorrectCoL, and it's dependencies Toolbarcontroller and Clickthrough blocker

Something i made about a year ago. It's a bit unwieldy, https://kerbalx.com/AeroGav/stol But then again, it does go to orbit. Actually with over 2800dV to spare. @Matt Lowne challenge mode - can you land an ssto horizontally on the roof of the VAB, then take off from that roof and land on Eeloo, without refuelling ?

The inline cockpits are better for heat. Inline mk1 is better than pointy mk2 , because it is protected by whatever nose cone, intake, service bay etc. goes in front of it. My "Sparrow" speedbuild SSTO uses liquid fuel only, no oxidizer. Drag is so low that a single Whiplash provides all the air breathing thrust you need, the twin nervs provide ample power to continue cruising upwards when the jets quit. https://kerbalx.com/AeroGav/Sparrow If you follow the KerbalX link there's a video of the build . 3 seats, 1800 dv in orbit, inline clamp o tron. I'd recommend two mods at this point. CorrectCoL Shows a nice "Static Analysis" graph in the SPH, with aerodynamic torque vs angle of attack. On a stable airplane, the more pitched up you are the stronger the nose down torque gets. But you can also see at which angle of attack the aero torque drops to zero, which is the angle of attack the plane will go to with no control input from you or from SAS. So you take a basic, stable airplane, then tweak the elevons slightly with fine rotate tool to a slight nose up trim, until static analysis indicates the line crossing the horizontal axis at an AoA of 3 or 4 degrees or so. Do a quick test flight (no need to get more than a few hundred metres up) to verify this is indeed the case. You'll find you get a natural AoA of 3 or 4 degrees with SAS off, and about 1.4 degrees with SAS set to Prograde hold . If you want to foce the plane to level off completely for the speedrun or to accelerate through mach 1, use prograde hold with Navball in Orbit mode, which makes the nose pitch to the horizon. This eliminates the horrible jerkiness and sideslip you get from flying with SAS in default "stability assist" mode, which just holds the nose at a fixed angle relative to the sun, not taking account the curvature of the planet. If you are a couple degrees off course , rather than roll the wings and actually turn the plane to 90 degrees magnetic, it just uses rudder to sideslip the nose and keep it pointing at the same angle relative to the sun, without changing the flight path (sideslip) Also , i'd like to point you to Kerbal Wind Tunnel, which shows a flight envelope plot of "excess thrust" vs speed and altitude https://forum.kerbalspaceprogram.com/index.php?/topic/177302-1415-kerbal-wind-tunnel-120/& Above is 3 plots from one of my dual stage panther/nerv spaceplanes. Left plot is panther only, middle one is panthers and nervs running, right plot is nervs only after jettisoning the panther nacelles. Work out the best engine combo to fill out any holes in the ascent path without even leaving the SPH!

Try to reduce the mk2 parts to a minimum - if you really need a multi purpose cargo bay, have that part only be mk2, and immediately transition down to mk1 size with an adapter before and aft. Use an inline mk1 cockpit and crew parts. Any rocket fuel you need above what is stored in the mk1 to mk2 adapter short x 2, put in mk1 tanks. You could try combining rapiers and panthers for better low speed punch to get over mach 1. I can't see how you're ending the main fuselage stack from either picture shared, that could also be a drag issue. I presume you have a lot of liquid fuel storage for laythe transfer ? Keep your liquid fuel in big S wings and strakes. They have lowest drag per unit of volume of any tank. Strakes orientated vertically make good tail fins/vertical stabilizers. Finally, it appears you not only have drag from angle of attack, but also from sideslip, because you are using SAS stability hold mode. Every 2 degrees off prograde doubles drag. Better way to control the airplane is to use fine adjust tool on the elevons so it naturally gives the right angle of attack to make lift with low drag when on prograde hold mode or with sas off altogether. This will reduce drag from sideslip.

One slightly unrelated point to add as a fifth tip - CRASH TEST. Your airplane should have a combo of resilience, crumple zone and low landing speed such that you can fly your SSTO at stalling speed into the side of the VAB. The building should collapse but everyone on the SSTO should walk away. If this is the case, your little guys are in with a shout.. A 5 leg landing gear design, an extra vernier thruster or some braking chutes would have made this thing easier to put down...

This is the truncated version of the 6.5 ton payload craft, minus extra fuel tanks. Cockpit gets hot, would be cooler with a lighter payload. You could just turn this into a drone i suppose, you only need the prograde hold feature when flying to space not when returning, even then it just helps to maximise your delta v. Of course, the reduction in dry mass up front means pushing the wing mounted nukes further forward. Perhaps reduce the chord of the wing to a single wing part, and push the whole front wing forward

I'll take a look at your craft in a minute, but if you want a rolling horizontal landing on Duna you're going to need to employ at least two of the following methods. Three is better, and all four is best of all MOAR WING. Duna's thin atmosphere means landing speeds are just over double what they are on Kerbin, despite the low gravity. Your spaceplane needs to be able to land on Kerbin at less than 35m/s even if you're using brake chutes and lift thrusters. I did have a super STOL SSTO that had very strong landing gear and a stall speed of 20 m/s on Kerbin that was able to set down down on Duna without using thrusters or parachutes, but 30-35 is a more realistic goal. Note, the extra wing area can make it harder to milk top speed out of your air breathing engines, because it will generate so much lift it wants to zoom to such high altitudes they can't produce thrust, before the jet engines hit their design top speed. OTOH, those extra wings make good fuel tanks for NERV engines and will give a really high lift/drag ratio in the upper atmosphere once the jets quit. So, spam big S wing parts, don't use any fuselage liquid fuel tanks, keep all your fuel in the massive wings. The only oxidizer you bring should be for the Vernor thrusters. VERNOR THRUSTERS. One downward firing Vernor per 10 tons of weight is enough to halve your landing speed on Duna, thanks to the low grav. If you have a lot of vernors, it might be worth putting them in a service bay so they don't cause drag on the climb out of Kerbin. MOAR LEGZ. The basic tricycle landing gear setup is not very stable. Craft self disassembly usually results from the plane getting sideways then rolling, or the nose, wingtip or tail striking the ground. Consider a 5 leg setup. Office chairs in the EU have to have 5 legs for a reason ! One nose gear for steering. Fit a pair on the main wing not far behind the Center of Mass but as far out towards the wing tips as possible (prevent wing tip dig in). Finally, mount a pair on the rear fuselage close together to prevent tail strike. The rear pair should have friction control turned way up , the nose gear have friction way down. Why two rear legs when they are so close together, and why tweak friction ? For the same reason that (most) cars are engineered for understeer , the back end should have much more grip than the front, that way it wants to plough straight on rather than spin out or get sideways. DRAG Chutes. Popping a drag chute on touchdown makes a successful landing more likely for two reasons. The main one is that all this drag at the back end keeps the plane going prograde and makes it less likely to skid sideways and flip if a wheel hits a bump. The minor reason is that it stops you quicker, so you are less likely to encounter a bump in the first place.

@dire Haha ouch, with engines at the back weight and balance gets tricky when returning with no fuel and payload. BTW it looks like you're mounting the panthers with tri couplers that are designed for 1.25m rocket stacks. These 1.25m bicoupler and tricoupler parts are incredibly draggy , and will be more so because you are mounting them on the back of 2.5m fuel tanks. Use the 2.5m trcoupler - the one that has a 2.5m parent node and three 1.25m engine mounts on the bottom, it is the most drag efficient engine mount in game, and you are saving drag from the mismatched attach surfaces (back of tank to front of adapter) as well. Have a look a this design perhaps - payload in the middle, engines split front to back so neutral CG shift, and very low drag https://www.dropbox.com/s/v0g8bz5wu1xkp68/Fat Fairy.craft?dl=0 Also, have you had a look at my Panther/NERV SSTO tutorial ?

With regard to drag - you are looking in the wrong places. Fuselage parts create vastly , vastly more drag than wing parts in KSP. Never use a liquid fuel fuselage part if possible - store ALL of your liquid fuel in the wings if you can. Weight and balance issues sometimes prevent following that 100%, but that is the ideal. Also, never sacrifice stability/controllability in the name of weight saving or drag saving. See above. The tiny amount of weight/drag saved by the fin will be lost many times over by the fuselage creating extra drag because you are no longer able to hold it at the right angle to the airflow. On my designs, I find that having the nose pointing an extra 2 degrees off prograde doubles drag. As regards to the general approach - An SSTO consists of 3 major components - fuel, engine, and payload. Getting a decent payload fraction to orbit means keeping engine mass down, which in turn requires good / lift drag ratio to avoid excessive "gravity losses" (that's a rocket term really, the spaceplane equivalent doesn't have a name but is complicated by the fact they have wings) For a pure chemical SSTO I'd say the optimum number of engines might be 1 panther and 1 rapier for every 40 tons of takeoff weight. So, if you got a 150 ton ship, i'd say you might want to try 3 rapiers and 3 panthers, or 4 R / 4 P, or 3P and 4R. You could try switching the inner pair of rapiers to close cycle while the outboards stay airbreathing as long as possible. For a nuke/liquid fuel cargo ssto Airbreathing engines i'd still say fit panthers and rapiers in a 1 to 1 ratio. You can probably push that out to 50 tons per rapier and panther, because you'll be able to turn the nukes on to help bust you through the sound barrier. Nukes have very weak TWR so you will need one nuke per 15 to 20 tons of takeoff weight. On the upside, they are so efficient you can get to space with only a 25%-30% fuel mass fraction. However, due to the low TWR you need a really good lift/drag ratio to be able to fly in the upper atmosphere, after the jets quit. As regards that second design you linked, it has tiny wings for its weight (might be ok on a pure chemical ssto) and large and very draggy fuel tanks (not something you want on nuke). Also, beware of that space shuttle style engine mount. It has a central 2.5m engine attachment node which you aren't using, and unused nodes create huge "flat plate" drag - the game basically treats it as a missing nose cone on a 2.5m rocket stack. So put a 2.5m cone on the back of this mount (clip it inside for cosmetic reasons if you like) or put a 2.5m triple mount on this point. Re: Weight and Balance If you have not done so already, get RCS build aid. It shows a red ball in the VAB / SPH which is your centre of mass when empty. Huge CoM shifts are a problem in cargo sstos especially. To get your dry CoM further forward , put your lightest engines at the back (panthers, 1.2ton each ) , rapiers further forward (2tons) and shove the nukes as far forward as you can (3 tons ) I'm not saying you should emulate this, as this design uses every trick i can think of to make a good payload fraction pure liquid fuelled cargo ssto. The space shuttle engine mount actually has all 3 1.25m nodes occupied as well as a triple 1.25m mount on the big central mount, i've used offset tool to give a different cosmetic appearance. Also you will notice there's three types of engine hanging off the back there, i had to attach them individually and offset them till RCS build aid said zero torque. https://kerbalx.com/AeroGav/Andromeda

I've just hit a bug with the CG-04 short mk2 airplane cargo bay. People often attach several of these together back to back to accommodate larger cargo, but it may result in the part not being shielded from drag if any individual piece of the cargo is longer than the individual bay sections. Worse, when you go into the debug menu and enable the option to show aero data in the right click menus, all of the cargo pieces still show zero drag, and nose of the CG--04 cargo bay sections show the extra drag either. You'll just find that your airplane suddenly won't perform and the total craft drag, as shown by the Aero Data GUI , doubled. This airplane has three CG-04 short bays, here it is loaded with an FT800 tank and an FT400 on the back - lift/drag ratio is down to 2 or so As a panther/nerv oxidizer free ssto, this extra drag consumes most of our available thrust and it's difficult to reach orbit with three ft400 tanks in the payload bay instead, lift to drag ratio almost doubles, and it reaches orbit with 1300dv remaining. I understand determining if cargo is shielded from drag or not is hard to do and problems with this have come and gone with successive updates, but the game should at least draw your attention to the fact that a part is not being shielded, i wasted over 12 hours redesigning is this aircraft over and over, only to find the cargo itself was the problem. The fact that the aero data menus lie to you is the kicker, i've always taken what they report as fact. At the very least, a warning about this needs to be sticked at the top of the gameplay questions and FAQs section of the forum.

Alright, my last image was from an empty flight. This time i changed the cargo to a stack of 3 ft400 tanks. This does not appear to trigger the bug, maybe it only appears if individual pieces are longer than the cargo bay. Because the extra drag is not shown in the aero data gui for the cargo bay or payload, you have no way of knowing if this is happening or not, short of making full test flights which is very time consuming :-( As you can see, the lift to drag ratio is the same when flying empty. There is more weight so we are lower in the atmosphere at the same velocity, so we have more lift and more drag - but the ratio is the same. Due to the extra drag, excess thrust is a bit less which combines with the extra mass to give us a slightly shallower climb angle and slower acceleration. So it turns out the craft is actually massively overbuilt, after subtracting the LF in the payload we still had 1036 LF remaining so we could eliminate a pair of mk1 fuselage tanks for sure. I may in fact be able to get rid of that engine nacelle in front of the cockpit , (makes the nose too long and spoils the look imho) and replace one pair of the tanks either side of the cargo bay with a nacelle (or even go to a circular intake, yours appeared to survive the flight to orbit without melting) as well as eliminating one of the mk1 tanks So the side tank stacks would now consist of an engine nacelle and a mk1 tank with an ncs on the front and on the back

Ah yes, it's making a difference - 1.1 output 1.2 shows this

Your plane has a small decrease in L/D ratio but nothing major. I was getting 3.8 to 1 instead of 4.1 to 1 in the supersonic regime Sorry about the extreme cropping but i'm still having issues with image uploading , this was the only way to get the file size small enough to upload And I have finally discovered what is wrong with Firefox, and its derivatives. IT WAS THE TEST PAYLOAD. I never flew that airplane empty or changed the cargo bay contents. I right clicked on the payload, with "show aero data in action menus" enabled, and when it showed zero drag, I believed it. Yet my craft's total drag was higher than i could account for by adding up the drag of its individual parts. The issue appears to be I'd used an FT 800 tank and an FT400 tank as a test payload for my three small cargo bays. It appears that having the FT800 tank span two short cargo bays does not work, the game thinks it is outside the bay and applies drag accordingly, but it does not appear on the action menu. With it gone, we are now rocking 4.2 to one L/D ! What a horrible glitch though.

Why do people tease us by asking something potentially interesting, but don't give us complete information and (often) never post back in the thread they created... or if they do, not for days? That rocket is stunning, i presume he is trying to replicate some sci-fi ship ? I presume it also has to SSTO off some body or another.. Kerbin.. anywhere else? More delta V, not allowed to reduce TWR (can't add fuel) , can't use different engines. Probably not much scope for reducing payload fraction either.. can anyone do the math re: emtpy weight and full weight? Options not looking great. I'm thinking a) change the Swivels for Aerospikes, slightly better ISP SL and VAC, they are a little pointy but probably not pointy enough for the OP. Or clip them inside an NCS adapter for same effect b) Make a Kerbin/Laythe SSTO by swapping that centreline bottom facing shielded docking port for a RAPIER. Swap the three outboard engines for Reliants. Use them to get it off the deck and up to a velocity where the RAPIER is going to go nuts... it will then boost you to 1300 m/s or so, finish the job with your chem engines. I presume the docking port is another "non negotiable" thogh

OK I got your airplane to orbit first try with 80 m/s to spare. I have a screenshot but IMGUR been playing funny buggers all week and the pictures are failing to upload. I made a version with as many parts as possible swapped over to mk1 size, 4 terriers and 2 panthers. I angled the wings up where they attach to the fuselage so you can fly on prograde hold for less drag. It weight 6 tons less and makes it to orbit with less pucker factor on the fuel gauge. However, I had to reroot the ship to change the cockpit, and that seemed to make RCS build aid loose it's $##4 , it kept telling me my dry CoM was too far aft, i put forward swept wings on, moved the panthers out to the tips and ended up sliding them so far forward they were alongside the cockpit, before realizing it was broken and stopped listening to it. So, you could probably have done this with a planform that looks more like your original. RCS action group deploys this nose down trim flap which i installed to try stop it climbing above 14km before hitting mach 2.5. Even with that, on the test flight, i overshot this slightly, ended up coasting to 29km (!) then it does 5g pullout, bottoming out at 830 m/s and 9.5km. Started the Terriers at 13km and just stayed on Prograde hold. Edit - this 77kb image took 10 minutes to process by IMGUR apparently. Nothing else will upload at all. Need to send Dilbert i think. https://www.dropbox.com/s/krtigx263gr5wnv/kLUDGER 1_3.craft?dl=0

Yeah mk2 rocket fuel fuselage long holds 800 units of lfo, but has over twice the drag of the ft-800. So yes, you are better off with two mk1 stacks instead of a bicoupler usually at least on the side stacks if not on the main fuselage (since you got to have a mk2 there anyway for the cargo bay). I can make small tweaks to the design that will reduce drag a bit, but i suppose due to the high thrust of the Swivel engine drag might not be the main problem. The main issue with panther / chemical rocket ssto is that the air breathing top speed is only 1800 vs orbit velocity of 2200 which requires a lot of rocket fuel to bridge. With a panther/nerv the large amount of rocket delta v is not such a problem nut you have to keep drag down, so you're better off with fairings or just bilding passenger/interplanetary craft only and forgetting about cargo. BTW nervs are 300 tech but that can still be researched on the tier 2 R&D building. Whiplash and rapuer are 500 and 1000 science points, both of which require the tier 3 building which is hugely expensive. Also, the poodle engine and the procedural fairing are 90 tech parts. I'v never gotten much more than 5% payload fraction out of a panther / terrier design on a mk2 cargo bay, but i'll see if your ship can be optimised at all.

Would be better if you could upload the craft file itself on KerbalX or just give us a dropbox link as we've only got screenshots to go on. I presume this is the pic you wanted to share ? Mk2 parts are horrifically draggy , even more so in 1.5. That is probably why you need so many panther engines. Panther thrust falls off a cliff above 750 m/s, so a less draggy airplane would not need so many. Admittedly they are light for jet engines, but your delta V margin to reach orbital velocity on chem engines from a 750 m/s starting point is slim to start with. I understand you want a cargo bay though. You got two choices a) try to make the mk2 stuff as minimal aa possible. In front and behind the cargo bay, taper down to mk1 size using the mk1 adapter (small). Use an inline mk1 cockpit with a nose cone or intake ahead to absorb re-entry heat. Swao all the other fuel tanks to mk1 size b) ditch the mk2 cargo bay altogether, use 2.5m parts and a fairing. - this is not my video but it's total genius, 2.5m tanks have the best drag/capacity ratio of all. So keep all your rocket fuel in those. I'd recommend a Poodle engine, it has good ISP in vacuum and high altitude. One poodle and two panthers should easily be enough on a low drag ship. Here is a thread showing the trouble i had converting a mk1 passenger spaceplane into a cargo.

I encountered this, I found that if you attach the nuclear engine early in the craft's construction it doesn't happen, I wondered if it was affected by frame rate in some way, if the colliders don't finish their calculations in time the part fails to attach to the node. So if i'm building a craft with NERVs i attach the NERV nacelle very early on eg. to the root part, then move and copy this nacelle later on as needed (eg. if you've mounted the nerv to an engine precooler, you can alt click and copy or move that part with its attached nerv no issues). I think i've seen this problem when after deleting the CorrectCoL folder so it isn't necessarily this mod at fault . As regards low frame rate, the frame rate tanks after i open the static stability display for the first time, I can work around that by checking the checkbox "use stock centre of lift marker" in the top left corner of the static analysis GUI. The stock CoL marker is good enough for roughly planning the layout of the craft, i update the static analysis plot when fine tuning.

Is it in the latest build yet? I really would love to see this feature, sounds less complicated to implement than a "best ascent profile planner" thing. I built this two stage career space plane with droppable Panthers https://kerbalx.com/AeroGav/KrankerSpoiler = picture of the "booster" stage ) Here are the reported flight envelopes - to the left is Panther stage, middle pic is NERVs and Panthers, right pic is with NERVs running after separation of the Panther nacelles. That appears to be without centripetal force, MECO occurs at about 38-40km with 2100 m/s and the AP going above 70km, when you fly the thing by just setting Prograde hold (the wings are angled up at 5 degrees to the fuselage) . Judging by this pic, the service ceiling is probably Eeloo. As regards optimum ascent profiles, I use this mod to help me to it manually, by breaking the flight down into 3 stages 1. Airbreathing climb - follow the yellow stuff, try to be at whichever altitude gives max excess thrust for your velocity 2, Speedrun - level off at the altitude that gives the best combo of top speed speed combined with height, with speed being more valuable than altitude. In the example of the above aircraft, the very highest speed occurs at 8km, but it achieves a top speed about a dozen or so less than that at just under 14km, so that's what i do. Above 14km Vmax falls off rapidly , not worth losing 70 m/s velocity in order to get up to 15km. Once in the speedrun, when do you accept the airbreathers have given you all they reasonably can ? Let's say your jet engines are Whiplash, with 4000 ISP, and your rocket engines are NERVs, with 800. The air breathers are 5x as fuel efficient as the rockets, so stay air breathing until drag is at 80% of your thrust - at that point, their fuel efficiency advantage has gone, even if you're still accelerating, so it's time to stage. 3. Once in rocket mode, I just follow the yellow/red as per 1. In practice, this means holding the wings at 5 degree angle of attack with the body hopefully at zero It's not perfect, but "close enough for government work", as they say.

BTW, I'm noticing you've got Mechjeb installed. It might not be an issue if you're using an autopilot, but it doesn't look like the plane has very much yaw stability. That fin has a fairly small lift rating and is fairly close to the centre of mass (when fully fuelled). If you find it keeps wandering off heading, you can attach a wing strake to the upper surface of the wing, rotate it so it becomes a vertical fin, then slide it backwards so it extends past the trailing edge. This will have more lift rating and a longer lever arm to work with and will provide a lot of passive yaw damping. You don't really need an active control surface on the fin, but if you do want that ability you can clip the tiny mk4 elevons to the back of these. Here's an example of passive strake/fins (note, they are attached to outboard engines here, but can be mounted direct to the wing on a design like yours)

@Cloakedwand72 Your pic didn't appear in my browser so i've edited the link in case other people can't see it as well. The Red ball means he is using RCS build aid. The red dot shows where centre of mass will be when the fuel tanks are empty. You can see it's marginally stable on full tanks (like a P51D Mustang ) but very stable when empty (borderline lawn dart ish). He is using a mod for CoL - that double graph symbol down on the toolbar is CorrectCoL. Two thumbs up for having these mods installed, makes aircraft design much easier. BTW, that is an absolute metric F-ton of fuel. He's got a super efficient Wheesley engine, that would circumnavigate many times over at a decent cruising altitude, maybe not if he just goes full throttle on the deck.

If I have good reason to stop at Minmus before making the interplanetary journey - for example, refuelling on there with ISRU - then I do so, but I don't concern myself with fancy assist maneuvers in that case (after refuelling, delta v is hardly likely to be an issue in any case. I just get back into orbit of Minmus from the surface, then do a Minmus escape burn (for what its worth, i try to time this so that we escape prograde to Kerbin orbit, so this contributes to the escape from Kerbin SOI. Once in orbit around Kerbin, you're looking at an under 100 m/s burn to escape into orbit around the Sun. And from there, plan the interplanetary journey as a straight Hohmann transfer, though if you want you could get fancy by assisting off other planets to get to the final destination from that point. Minmus itself has such low gravity I don't think there's much Oberth effect to be worth the trouble it is to exploit.

@Pecan A thing i've found in my career games, when i've been limited to the smallest retractable gear for a while, is that 5 small gears is much more stable than 3 medium. One on the nose for steering , like on conventional tricycle, friction control set to low (we want understeer rather than oversteer - it's not a drift car). Two attached to the wing close to the centre of mass, as close to the wing tips as possible so it can't tip over onto either wing. Then two towards the rear to prevent tail strikes, maybe attached to tailplane and with friction control set to max (again, to promote understeer). Landing gear don't add much drag when retracted so fit more if this is a consideratoin. Ground clearance can be an issue with the small ones, that is the only problem. Also you'll want to offset the rear ones upwards as much as possible so it sits on the ground with a slightly nose high attitude, or takeoff speeds can be increased (unless you've got a really strong pair of canards or vernor engines that can lift the nose off the ground - the rear anti tailstrike wheels will prevent you pushing the tail down to get the nose up on rotation otherwise)

Nice design BTW, I see you're using the prograde lock method as well :- Something weird is going on here. Are you on the current 1.5,1 version of the game? Flight profile shouldn't come into it. Once you're past the transonic high drag region, lift/drag ratio is pretty constant all the way to orbital velocity. The only other factor is angle of attack, which we're both similar on as we're both flying prograde. Your craft is getting a Lift / Drag ratio of 4.1 , my mk2 cargo bay ship was getting 2.2 - the only difference can be the craft itself. In supersonic flight, at optimal angle of attack, wing parts have a L/D of over 15 to 1, but fuselage parts with negligible lift and higher drag pull the average for the whole craft down. For your airplane to be doing better than mine on total L/D ratio it must either have more wing relative to the fuselage or more of the fuselage must comprise lower drag mk1 parts vs mk2 parts. Neither of these things appear ot be the case. So, something must be glitching out with my craft file... i did build the interplanetary ship a few weeks ago, before the latest hotfix and the cargo derivatives were all made yesterday. Perhaps grafting this stuff on to an older ship caused a problem? Or I've done something really dumb, like attach one of the rear cargo bays to the payload instead of the cargo bay in front of it, etc. I checked the obvious bt enabling the "show aero data in action menu" option and clicking each new part in turn, and couldn't really account for the doubling of overall airplane drag. Can you share the craft file of the pictured vessel, and i'll see if it gets 4.1 Lift/Drag on my KSP install, and would you mind taking "Rainbird" for a spin and seeing if it only gets 2 to 1 max on yours?