Lt_Duckweed

This right here x100. I did the math and at sea level at mach .9 (which is where backface drag peaks before starting to drop off again) you are losing something like 7% of a rapier's thrust to it's own backface drag.

Landed!

Managed to reach 1686.2m/s at 21.86km. Craft does NOT want to take off easily and I had less than half of a kn of spare thrust leaving the runway, but it could, so there is probably room for optimization by reducing wing area and taking off from the flats around the ksc rather than the runway itself. EDIT: Woops, forgot to land it, let me do that real quick.

I don't have the craft file of the edit available right now, but I do have the file for the ssto it is based on: https://kerbalx.com/Lt_Duckweed/Nuclear-Grace And here's an album about it: https://m.imgur.com/gallery/fTWS13F Keep in mind that it is NOT easy to fly if you aren't already a pretty skilled plane pilot. To upgrade it for 3.2x scale it needs about half the payload mass replaced with liquid fuel, and double the number of nervs. It's already at the limit of what can make it off the runway, so if you add any mass to it it needs to take off from the flats around the ksc instead (which there is plenty of at 3.2x scale)

I would highly recommend using the fan blades instead of props. They have higher top speed, more thrust, and are more compact. Also, this is Eve we are talking about. It is punishing. Unforgiving. Cruel. Forget the rover, forget the solar panels, forget the large isru, forget the docking port. Eve does not give you the luxury of having luxuries. The last time I made an Eve ssto it was 180 tons, and had a payload to low Eve orbit of 3 tons of liquid fuel. Eve is HARD, there are probably less than 2 dozen players who have made successful Eve ssto's

So I was curious, so I swapped to 1.9.1 and installed the needed mods for a 3.2 rescale. I then made a quick and dirty edit to my orange tank lifter. Namely, I added an extra pair of Nervs to the front of my existing nerv stack, then rotated half the stack so they faced backwards. Then I permitted pulling liquid fuel from the payload tank. Starting mass is 78.587 tons, mass in orbit is 45.617 tons. Payload mass is 21.950 tons (because I pulled fuel from the tank, I need to subtract the dry mass of the percentage of the tank I used to get the true payload) This gives me 32.97 tons of liquid fuel (well a smidgen of ox is mixed into that number because I forgot to set the rapiers to manual switching) burned to get 21.950 tons to orbit. This gives me about 240 funds per ton to orbit, only counting fuel costs. Obviously the overall cost will depend on how accurate you can get with runway landings. Payload fraction on this is 27.9%, so a bit better than I predicted, but this is a fairly optimal case, so I would expect a practical design using a fairing to land solidly in the middle of my predicted 20-25% range.

I would argue that this is a case where you would prefer the stock system over FAR, as you enjoy substantially higher high supersonic and hypersonic lift to drag ratios in stock. With a decent understanding of stock aero, it is easily possible to enjoy a 4+ lift to drag ratio from about mach 1.5 to well past mach 5, with a peak a bit past mach 2, without needing to resort to any weird aero exploits. When using weird aero exploits it is possible to push this to close to 5, possibly a bit past 5. As far as I am aware FAR planes do not enjoy anywhere near this l/d ratio at these high mach numbers. Conceptually, this isn't that hard to design for. You need about 2km/s more dv and probably something like double the twr in the nuclear phase of flight, and while there may need to be some design changes depending on the heat settings, not a whole lot else changes. Ballparking it here, but I would expect payload fraction would drop by a factor of 2.5 or so, so something like 20-25%.

The approach that I took was to get the explicit equation for an ellipse with one foci at (0, 0), then perform 3 integrals 1. The integral for the ellipse from c-a to n (where n is the x coordinate point we are interested in) 2. The line radiating out from the origin to the point in interest expressed with slope as a function of n, then integrated from 0 to n 3. The ellipse integrated from n to c+a. After much variable wrangling and simplification, I got to the equation n= a*sin((c/a)(1-((n-c)/a)^2)^(1/2))+c where n is the x coord of the point, a is the semimajor axis, and c is the distance from the foci to the center of the ellipse (in other words a*eccentricity). I'm sure you can see the issue here. while I have a nice clean n by itself on the left, I also have one buried deep within the sin term on the right.

Yeah, that's way better than the integrals I was doing in rectangular coordinates lol.

For funsies, I decided to take a stab at this and uhh, it's not pretty at all...

Right, duh, brain fart on my part.

Because I use a built in 5 degrees of incidence on virtually all my planes, I have this same behavior of a tendency to climb. However, rather than using elevators to inhibit rate of climb by utilizing negative lift me big dumb, I do so by decreasing angle on my canards, thereby decreasing positive canard lift.

I think this would be quite interesting, perhaps a challenge for lowest fuel/ton/km to various destinations (Island Runway, Desert, Circumnavigation, Multi Circumnavigation) with various weight classes?

In addition to kerbal wind tunnel (which is absolutely fantastic btw), correctCoL (correct center of lift) and rcs build aid are both extremely useful for spaceplane builders. CorrectCoL because it shows the true center of aerodynamic pressure on your ship, and has handy stability charts as well. RCS build aid because it can show wet and dry CoM at the same time, and show you how each fuel type on the craft contributes to CoM shift.

Just as an fyi, that isn't how aero clipping works. It doesn't matter where you originally placed the part, only weather or not the CoM of the part is physically in the bay and the bay is larger than the part it is shielding (ie you can't shield a nerv with a standard 1.25m bay). Same goes for fairings, where you originally placed the part is irrelevant, all that matters is that the CoM be within the fairing (and the aforementioned size restraints).

This album details some of the design and flight of an efficient cargo lifter: https://m.imgur.com/gallery/fTWS13F Though this is a cargo lifter, if the carried tank + docking ports was instead replaced with liquid fuel, it would have a smidge over 8000 dv. If I added a cockpit and mining equipment it would drop the overall delta v in orbit by about 1000, still leaving 7000 in orbit. Adding 2 nukes would drop it again to 5000. When it comes to the most extreme of craft, I have been able to get 11,000 m/s in orbit with pure liquid fuel by minmaxing to an extreme degree. 104 tons takeoff mass, 2 rapiers, 2 nukes. Big S strakes for wings (6:1 wet:dry vs big s wing 4:1) a kerbal in a payload bay, hundreds of the tiny mk0 tanks (they have a 11:1 wet:dry ratio vs the standard tanks 9:1) stuffed along with all the engines under a tiny fairing, etc.

The answers you get are going to very much depend on what you feel a "high" twr is. For me, a lko twr of .2 or higher is enough to count as "high". With this twr you can get up to about 8000m/s in orbit with a well optimized craft. If you double your nukes for a lko twr of about .4, you can still achieve something in the region of 6000m/s. This is for me quite the generous twr, and I would feel comfortable landing on anything duna or lighter. If you go up to .6 twr, you are edging close to the point at which nukes are no longer your best option, but you can still get something like 4500m/s It is worthwhile to note that these numbers do not account for passengers or isru. You would need to adjust the numbers down a bit in that case.

While it is certainly true that actual reuse like the op is talking about is nearly impossible without excessive levels of tedium, the economical argument for sstos is quite strong. A typical expendable rocket can expect to cost about 1000 funds per ton delivered to lko A cost optimized expendable rocket with srbs can expect to cost about 700 funds per ton to lko A cost optimized reusable rocket ssto can expect to cost about 300 funds per ton to lko A cost optimized reusable spaceplane ssto can expect to cost under 100 funds per ton to lko (I've gotten as low as 60 funds per ton)

Does this count?

I feel like both example payloads are too small. The smallest SSTO I fly is an orange tank lifter, with most of my designs clustered around 115-145 tons payload. I find that below 36 tons it's just not worth it to try and build to payload size as 36 tons of payload is already down at a 2+2 rapier/nerv config and going any lower runs into issues of either having way more trust than needed, or having to figure out how to balance the craft and still be able to deploy the payload easily when you have one of each engine.

Today I visited Kerbol in an SSTO and got the first (to my knowledge at least) Eva report from Kerbol's atmosphere:

Unfortunately I can't share the craft file, as that is reserved for Stratz's patreon. It would most definitely work on Duna thanks to the huge wing area and large number of props, (plus you could just directly zoom away on nerv power alone, it has right about 1 twr in rocket mode) except for the fact that it doesn't have wheels. You would need to land it vertically and then take off vertically, which would require very flat ground. As for eve, the nuke twr is far too low, so it wastes most of its fuel trying to get supersonic, then runs out well short of orbit. We haven't retested this craft in 1.9, but all my other Jool sstos broke so this one would too. If the goal is just to get to low Jool orbit from it's 0 altitude that is definitely still doable, the margins on that are way more forgiving than on this craft.

The only time I have seen the root part effect drag is when the root part is either a fairing or a cargo/payload bay. As long as your root part isn't one of those it's likely the issue is coming from somewhere else.

Third and final update of the night. By swapping my intake/liquid fuel storage setup from one precooler to a partially filled Mk0 tank and replacing two aerodynamic nosecones with circular intakes, and also getting rid of my roll control surfaces, I was able to trim another 215 kg off of the craft. Mass: 18,322 kg wet, 8,295 kg dry Lf/Ox mix: 10,000 kg full, 252.9‬ kg remaining in orbit Liquid fuel: 175 kg full, 23.8‬ kg remaining in orbit Dv left in orbit: 91 m/s

In a stunning turn of events, Mr Oneupsmanship 3 was revealed so quickly, that Mr Oneupsmansip 2 never even got a chance to launch. This craft improves on the original by shaving 1.2 tons of dry mass. Mass: 18,537 kg wet, 8,295 kg dry Lf/Ox mix: 10,000 kg full, 332.25 kg remaining in orbit Liquid fuel: 200 kg full, 39.65 kg remaining in orbit Dv left in orbit: 117 m/s Parts replaced/removed are: Mk1 Inline Cockpit + Aerodynamic Nosecone -> Mk1 Command Pod + Small Nosecone: 220 kg saved 2x Circular Intake -> 2x Aerodynamic Nosecone: 40 kg saved 2x Elevon 4 pitch surfaces -> 1x Elevon 4 pitch surface: 40 kg saved 2x Thud -> 1x Thud: 900 kg saved