Nao

Thanks for the chart SaturnV. Could you try one more profile? With the rocket keeping 45deg attitude continuously through the burn. I think it will go even further, or at least the same as the gravity turn one. Also since we are doing over 100m/s2 acceleration this is almost like an artillery shot (5s burn time), it would be more interesting to do much longer burn. Doing a simple test with your numbers, with engine throttled down to 20% thrust, range with keeping velocity vector roughly 45deg is 18,82km (attitude of 65->62deg) and with keeping constant attitude of 45deg is 21,52km

Sorry to nitpick, but Im trying to understand this clearly. So if gravity losses aren't permanent (i understand why) then what are the looses during vertical ascent ? I mean is there other term for that? Ive never read about gravity drag as a part of energy exchange, it was always about loss of Dv during finite TWR thrust.

Hmm in orbital motion we have transfers from potential energy to kinetic and vice versa, the word losses does not fit the above description. For me gravity loss, would result in irreversible loss of energy, like for example ship hovering over ground, expends chemical energy without gaining both potential nor kinetic one. Also at the bottom of this page i've found a following definition (...) For a finite thrusting period perpendicular to the position vector of the spacecraft no gravity losses occur. (...) I assume this includes moment when the craft's velocity vector is not at right angle to gravity vector.

@Alistone yup thats what i meant For me gravity and steering losses are pretty similar and both base around the idea of thrust vector that isn't in line with current velocity vector.From what i understand right now If we are not at Ap or Pe when burning prograde/retrograde we won't be burning toward horizon, and both steering and and gravity losses will be zero. The lack of efficiency of such burn would come from Oberth effect and not from gravity losses. edit: im actually not sure what is Hohmann effect, i know about Hohmann transfer and Oberth effect... can you link a wiki article or something about Hohmann effect, cant find it on google.

So first thing first, Ive already concluded in my previous post (the one with data) that the lowest Dv required to travel a small distance is by burning 45deg attitude no matter the TWR, that also results in horizontal flight at 1,41 TWR, and for many low TWR crafts the trajectory is pretty shallow. I tried some different profiles on the Mun in actual game and the results were similar. If you don't believe me, you can check it in game with some low twr lander. Second, burning at maneuver node is what actually generates steering losses when TWR is lower than infinity. Imagine a burn with Ion powered probe that takes half the orbit to complete, the node marker would point retrograde at the end of that burn. I can't really explain this in english but being in gravity well means that we cant just add vectors like that, since our velocity vector changes constantly due to gravity.

Wait wait. Firstly the idea i'm having is that we keep 45deg attitude in relation to the horizon, and after 10 seconds it still will be 45deg. Secondly (for standard orbital operations) i thought burning directly at maneuver node is less efficient than burning prograde. I mean we are in a gravity well, so the path the craft takes is a part of an ellipse. Yes the ship will rotate in relation to fixed reference point in space but the angles will remain the same in relation to gravity vector (and surface).

I may be dumb here, but i'm not seeing how would the vectors go to make optimal attitude more vertical than 45deg. I think it would be the opposite, with more horizontal burn at longer distances due to centrifugal acceleration lowering gravity drag. Also TWR does not seem to change anything at all really, unless it's less than 1,41 so the ship cannot keep 45 deg attitude without crashing.

Thanks for the links Jarnis! After skimming some data, I've found that FH boosters will have propellant mass fraction of 0.966+ Which is crazy if you think about it. It's like a big fuel truck that can transport 40000L (30,8ton) of fuel while weighting as much as a small city car... with a power of a train... that can go to space! This would make singe stage flight really efficient, although I forgot that Merlins have quite low ISP (compared to numbers on SSME or KSP) so I guess thats one of the reasons to use cross-feed on Falcons (they run closer to Dv limit so the Dv increase from staging is more significant).

Adding to the many good comments here. The reason for asparagus staging is so good in KSP is that both engines and fuel tanks themselves are much heavier in KSP. Just by making simple 3 stack one stage configuration into 2-1 two stage asparagus increases the Dv by around 24%. Comparably, real world engines are ~6x lighter and fuel tanks are ~4x lighter, that Dv increase would be less than 5%. And thats not counting additional pumps and fuel line mass (that would probably bring the Dv increase to a whooping ~4%). The additional costs for the complicated fuel pumping system isn't just worth the saving. Also from what i've read "asparagus" staging on falcon V heavy is only going to be used to lift the most heavy payload. The asparagus system is just a way of maximizing payload at a considerable cost that is still lower than making competently new design. Edit: @Jarnis do you have any sources on the comparison of different versions of Falcon V? I'm somewhat out of the loop on this.

The steering and gravity looses balance is a really nice way to show why 45 deg works. Thanks . That'll help making next set of equations that include orbital motion. edit: to post above. I would say that trajectory (path that craft takes) is what is changing with TWR, what is constant is attitude in relation to horizon. And I think that's what caused (at least for me) some confusion.

For the instant horizontal burn and coast on power, it feels like we are making big steering losses with burning twice at 90deg angle to each other. I would be surprised if it was equal or better to the ballistic path. Science continues.

Unfortunately i don't know if there is a support thread, but since the problem persists through many version, it would be good to have one. Also are you changing default patched conics settings? If yes it would be good to include that information in the thread. I use CONIC_PATCH_DRAW_MODE = 2 and CONIC_PATCH_LIMIT = 4 or 5 and have the problem described from time to time (didn't see it in current version but I've not flew any complicated missions in it yet).

More science complete! Math was done under assumption of a flat surface (no centripetal force and no initial surface motion). While this is pretty big generalization, horizontal speeds of 155m/s reduces gravitational pull by ~7,5% so i think trends shown by the data are meaningful. In real flights Dv numbers at higher max speeds will be somewhat lower. Constant altitude burn Mun g 1,61 m/s2 Distance 4 km Hacc - horizontal acceleration H Vmax - maximum speed, at the half distance point. angle TWR Hacc H Vmax Dv m/s 5 11,5 18,4 271,3 544,7 15 3,9 6,0 155,0 321,0 25 2,4 3,5 117,5 259,3 35 1,7 2,3 95,9 234,2 45 1,4 1,6 80,2 227,0 55 1,2 1,1 67,2 234,2 65 1,1 0,8 54,8 259,3 75 1,0 0,4 41,5 321,0 85 1,0 0,1 23,7 544,7 Constant angle burn with coast Mun g 1,61 m/s2 Distance 4 km angle 45 deg Hacc - horizontal acceleration Co-ang - starting coast angle Vmax - speed at the beginning of coast phase TWR Hacc Co-ang Vmax Dv m/s 11,5 13,1 41,2 76,0 161,7 3,9 4,4 32,4 71,2 170,1 2,4 2,7 21,9 70,6 185,4 1,7 2,0 10,7 74,0 205,7 1,4 1,6 0,0 80,2 227,0 Ballistic calculation (TWR = infinity), 45 deg angle. Dv needed = 160,5 m/s As always I'm not 100% sure about those since i tend to make mistakes, but the results are quite realistic. What surprised me actually was that if we insist on flying at constant altitude then accelerating constantly and turning around at half the distance, is worse than just burning at 45deg with lower throttle. Because of that I think the constant altitude flight could be made more efficient by first accelerating at full throttle and then coasting for a little while just burning upwards. (Although earlier tests indicated otherwise). So not counting orbital mechanics, just burning at 45deg full throttle, coasting and burning opposite direction at 45deg is the most efficient way to travel short distances with limited TWR.

Yeah, rotation of the body is a can of worms to include in the maths, fortunately for most bodies its quite low compared to surface orbital velocity. But i did a simple test on Mun at 1,8 start (mun) TWR. First flight: constant altitude, using 755m/s Dv gave distance of 37km, then using constant attitude of 45deg result was 57km. And the first flight even had a little hoop as i needed to clear a hill so it was launched at 30deg attitude. You must construct additional Pylo... Science! edit: yep did a bunch more test in 200m/s Dv range and 1,8 TWR ... longest range was with constant 45deg burn then small coast and another 45deg landing burn (~4km of distance). Other tries included: constant altitude flight (at constant throttle), staying close to velocity vector (quite bad) and a constant altitude burn with a mid section of upward burn (similar to constant alt burn).

After some thoughts on the infinite TWR craft, i wonder if the right path to take would be a part of minimal energy orbit (assuming point mass at the center) that that intersects the surface at start and finish. In the extreme of going to the other side of the moon/planet, it would just be half of the circular orbit at ground level. And on the other end (short distance) probably it would be very close to ballistic patch (with 45deg angles at start/end) with the Pe of said orbit would be very close to the point mass in center. edit2: after messing around in KSP orbit mechanic it looks like the orbit approach can work but not for "minimal energy" but rather minimal speed at ground intersects. Using kerbin as base (not counting atmosphere) 20km distance has minimal launch velocity of 439m/s at 45deg. And 628km distance has minimal launch velocity of around 1980m/s at 28deg. Also 1256km needs around 2338m/s at only 14deg.

Thats quite interesting question! I would have thought that ships with high TWR would want to burn at 45deg for several seconds at launch and then the same in reverse just before landing, just like artillery shot. With bigger distances the speed will be closer to orbital velocity so probably lower launch angle would be better. But for a low TWR craft doing what Asimov mentioned, could actually be the right thing to do! This needs more science!

Thank's regex!. Much appreciated I've not played with Yargnit's loader yet so i can't comment on that but i did test playing with science base and cap values equal and it's pretty nice. Just for reference if somebody wants to try playing with only one 100% transmission giving science per event without spoiling himself with text in the file. Here is the file i'm using on my current save. The science values are half "cap" values with only exception for surface sample that has base divided by 3 and cap left original.

Welp i was just about to post mine , Is 1/8 of stock actually playable? edit... wait the 1/8 file crew raport has 2.5 base and 4 cap ... that's 1/2 not 1/8 somethings not right edit: sigh i somehow deleted the original file, and looks like KSP can't recreate it on launch (like settings). If it wouldn't be a big problem, could somebody post the default one? If not i'll reinstall the thing later. edit2 sigh2 ok downloaded the wrong file, its working ok 1/8 is 1/8

The new SAS is an improvement, but for me it's way too slow. Most of the time i keep it off during burns. It would be awesome if we could get a way to set how strong it tries to control the craft. Or at least have 2-3 parts that have different settings with them.

WHAAAAAAAAATT? This game is work in progress but still ... some semblance of balance would be nice as we go along.

I like the usage of basic engines for first stage every bit of edge helps. Using my ship from 4minute challenge and switching boosters for more fuel (somewhere around 48000-49000 total) I've beat my previous record by 10%. 48-7S is so much better than other engines its not funny anymore 7241 is no small feat thou gj!

BACC's are much much heavier without significant thrust increase over RT-10 so the overall performance is quite a bit worse for this challenge, much bigger empty mass does not help either. From what i tested, when straight up compared in 30s of burn time RT-10 are better than mainsail stack but at this particular TWR (~6) the difference is quite small, and when we add the ability for mainsail to be staged twice (15s burns) or more, they give almost the same performance. And on topic of drag, yes the RT-10 have 50% more, and terrible sea level ISP but they still are the best first stage for most crafts since their engine and tank weight is so small (including Eve ascent module). I imagine they are made of paper, and explosives . Oh and I've found a fuel bug in my craft on the mainsail stage, repositioning one fuel line increased Dv by 8m/s and burn time to 240s haha .

It turns out SRB's are quite on the edge for this. I thought they would give better performance but numerous problems with them cancel it out. Tavert done a great job making 13 stages out of 300parts. With the SRB idea and not so efficient design i could only fit 9. Still its above 15km/s so i'm happy. Numbers: VAB Dv: 15096m/s, VAB mass 399,90t, 299parts, 239s burn time. In flight Dv: 15117m/s, mass 399,82t.

I was waiting for this , its ON!

To get things going 10720m/s in 3m 58s 19 parts and 57,6t in 3 stages of simplicity. Funny thing that launch stage ended up with <20 m/s Dv after reaching 100x100 orbit (41l of fuel left).