Nao

Ohhh finally i get to design something before thread closes Since now we have career mode i think Kerbal X should be more of an inspiration and technology showcase craft for the sandbox rather than a learning tool. Thats why i decided on a more complicated craft that is "easy to get into but hard to master". I present you The HexaDragon launch system. (former KEX) Features! Triangular based design Around 8000m/s dV to play with Additional 1000m/s with optional 3 kerbal escape pod. Landing legs for landing on moons and smaller planets. Replayable (flexible) design, allowing the player to reach more distant targets through use of creativity and cleverness. (escape pod as a lander, use of drop tanks, special fuel management and manual decoupling) Nuclear free! Design: - 132 parts (82 for lander) including 12 struts only for launcher that serve mostly educational purpose. - Minimal clipping (present mostly in optional escape pod) - No asparagus (standard) launch system - Includes solid boosters for first stage - Drop tank system (lander) - Followed by asparagus (lander) - Optional use of RCS propulsion on escape pod. Usage: - Fully stable on launchpad without stability enhancers, no wobble in flight - High starting TWR for stunning liftoff - No calories, no overheats - No pollution! launch debris stay in atmosphere. - Design encourages better flight profiles (stable and sluggish at first, nimble at gravity turn, long burn time for changing to horizontal flight) - 6 landing legs giving stability and redundancy, 2 level landing area illumination. - Emergency "escape pod" in case of crash, lack of fuel, or other mishaps like loss of control, tipping over during landing etc. - Parachute system that gently rotates the ship into right position when deployed - Excitement increasing system! Creating harmless explosion at touchdown - Possible return in escape pod to Kerbin - Enough thrust for powered landings on Kerbin Educational/showcase - ascent efficiency highly dependent on flight profile, not hard to get to orbit, but allows for lot of improvement over several ascents. (refining bad habits) - drop tanks + asparagus staging, shows the difference in a less stressful environment (than ascent) - use of angled (rotated) parts, notably landing legs, boosters and fuel tanks. - RCS for small craft propulsion, idea of emergency systems. - encourages no debris left in orbit. HexaDragon craft file. More pictures will be uploaded if i have time . Oh and if anybody feels like ascent TWR is too low, i have reasoning for that but that's for another post/discussion (in short it makes the player think and let's him learn something).

I thought that for a long time, but now i think the opposite. The higher you go the lower the TWR should be, that's because right after starting gravity turn the importance of TWR diminishes quite fast, and if we have less engines (lower TWR) more of the fuel energy is transfered to payload itself, making the launcher more mass efficient. The thing is, while flying vertical at terminal velocity is the most fuel efficient method for given craft, after we get to some vertical speed (enough to coast out of thick atmosphere) gaining more will only net us losses. That's why we do gravity turn but then if we turn the ship at an big angle to velocity vector, we get big steering losses, and if we try to avoid that by starting it early we get increased drag losses. In the end the most efficient way is actually to "coast" at low thrust (flying below terminal velocity) until we fly more horizontally. Then comes the second part where thrust is important as we accelerate semi horizontally, but it ends quickly as we gain orbital velocity, lowering the gravity drag. And since we still have a lot of vertical speed stored accelerating fast in middle atmosphere only increases drag losses. At this point the difference between accelerating fast and slow doesn't bring us much improvement. And if we bring less engine mass up there, it means we have saved a lot of fuel (more than we would have gained from more efficient - high TWR flight profile).

Fuel flow, is shown in total fuel+oxidizer (or in case of jet engines, fuel+air) in tons, so for the kahlzun's image its 0,47kg/s. And since Thrust = Isp * g0 * fuel flow, (where g0 is a constant of 9,81 m/s^2) we have relation between the numbers shown there 0,00047 *9,81 * 391 = 1802N or 1,8kN In general, for ascents and landings on heavy bodies, weight is more important as engines take big part of total craft mass, but for orbital operations, transfers, insertion burns, corrections etc. high isp is more Important as you can get away with small number of engines making fuel the biggest part of ship's mass. In the end it all comes down to burn time of the particular engine (how much energy or dV it produces) if it's working for a long time, giving large amount's of dV it may be better to pick heavier more efficient engine. (rough estimate of "long time": 3-4 minutes) Hmm that said this have given me idea about a chart, maybe ill edit one in later.

Skipper achieves 320 ISP quite early in launch, but that is easy to test by yourself (I don't have KSP open right now) 350 is for vacuum although above 10km it is already pretty close to it ~345+ It also has 2 advantages over 3 LVT30's , less parts and gimbaling which can help a lot in controling the rocket. While ISP is important you shouldn't build rockets that engage more efficient engines as you reach higher altitudes to gain performance, as it will actually cost you some. The more engines fairing at launch the better, because any engine that waits for its turn is a dead weight that costs fuel to get to the point of ignition. In the end even LV-N engine with its isp at sea level of ?225 in many cases is better off burning at launch even thou it uses fuel less efficiently because it adds thrust. The mass cost of fuel burned inefficiently will still be smaller than additional mass (and fuel cost for that mass) of more engines required to reach same thrust to weigh ratio (TWR) without the LV-N burning. edit: @ blizzy78, uhh didn't think of that lol, sometimes veteran players think of stuff as granted >_< good hint.

@ PrivateFlip from the look at resource tab there seems to be no fuel imbalance of any significance. From the screenshot i do see that one of the legs is deep under sand, it's possible that it got stuck there, if the rockets flips violently right after launch it could be the case of stuck leg. Try retracting and extending your gear if that is the case.

I don't think the penalties are that severe in KSP, for example: 2 minutes burn 0,26 TWR vs 13 second burn 2,3 TWR, both 320m/s from 70km orbit the dV difference is only ~0,3m/s that's only 0,1% loss. In the case of bigger burn: 1561m/s with TWR 1,05 and 9,45 respectively (that's a burn to Moho from 70km Kerbin orbit) the difference is only around 0,68% (counted by energy change). With higher dV burns will be penalized more but over the 2minutes it shoudn't be more than 1% in most cases.

Unfortunately This only means that you are loosing dV to steering looses more when burning slowly (not burning at the velocity vector). And this is more of a change in steering error than difference in propulsion. More precise test would be with mechjeb locked to "prograde" and that would show almost no difference in speed change (periapsis). Unless the low TWR would be really low, and there would be losses to Oberth effect due to burning fuel at higher altitudes. And that can be mitigated by dividing the low TWR burn into several small burns close to Periapsis. edit: In other words, if you want to get the most from your fuel, never burn at the maneuver node, always pro/retro-grade. (just start around half to 1/3 of burn time before the node).

Woha, nice! "I'm so good at designing ships that i don't know how good I am" That is true, but Oberth would like to point out that we want to burn as low as possible, and coasting to apoapsis is a waste of energy. If you use 9 rockomaxes the TWR is always greater for them, and with FLT400+FLT200 they are lighter by 30kg while having around 3m/s less atmospheric dV and above 50m/s more vacuum dv. A simple test with one stage of 9x rockomax at 2,03 TWR got me maximum altitude of 3368m (617m/s dV expended), while RT-10 stage with 1,87 TWR got only 3169m (609m/s dV expended). So not only they save 30kg but give more dV. @Seanner great results congrats . The BACC is kind of bad thou, a simple LV-T30 with FLT800 give very similar performance. For example 2x BACC at 1,9 Twr can give ~1000m/s and for the same weight 3x LV-T30 (with FLT400+200+100 tanks) will have slightly better TWR and ~100m/s more dV

(going backwards on your post)Figuring out optimal ascent profile for that SSTO is interesting (and a good challenge by itself), but recently I've been favoring low TWR instead of efficient use of throttle, and that adds even more variables to the formula. Having more engine mass to accelerate seems to gut the efficiency of whole rocket. And the savings of that mass seems to be greater than the losses from suboptimal ascents. When doing gravity turn I feel like the most important variable is vertical speed, and how much i get it depends on burn time of later stages. In a way, I think of maximum vertical speed as a bank for accelerating sideways. Many different rockets and flight profiles that i tried (not including long burning, low TWR LV-N stage like the one posted here) i find that around 350-400m/s maximum vertical speed was giving me best results (500m/s for the LV-N). Maybe it would be possible to make some useful correlation with it. And idk about RT-10, I've loaded simple ship in KSP, and counting atmospheric dV they have pretty much the same performance at 2 TWR. (using 9x 48-7S +FLT400+FLT200 in place of RT10) but i may be wrong of course. I love the 0,2% improvements thou, such dedication. Now it needs a long launch legs to put CoM higher and get even more free Dv.

For a non LV-N entry 18,6% is really good, congrats. The TWR you got there also seem quite big, that must have been quite efficient flight path. That design looks crazy, Is there any other reason than looking great for the probe to be so high up? One thing of note, i think RT-10 *was* the best stage 1 propulsion, from my recent simple calculations 48-7S take the cake right now Also controlling flight path with thrust seems to be a great idea for any ship that has thrust to spare. It would be interesting actually to use decoupling of stages on the base of required TWR and not on the amount of fuel in tank. This could increase effective engine use.

Welp, there is no reason to use standard staging in KSP from efficiency standpoint, but i think it's easier to make good looking designs with it, as the center stage will have the most fuel and the first booster is quite small. And since good payload fraction comes from actual engine TWR efficiency (having all engines 100% thrust all the time while keeping speed and TWR within efficient flight profile), id doesn't matter much if we use fuel crossfeed or not, as the most important is when and how much engines are we decoupling. While designing this rocket I also tried to lower stage amount as much as i could, it turns out that getting the right TWR at launch (or just after accelerating to vertical ascent speed) can make the rocket TWR increase follow increased TWR demand from atmosphere changes. So even thou we know that having more stages means more dV, I can use the increasing TWR of long burning stage to lower dV required to orbit by flying more efficient profile. I think 18,5% would be possible with only 2 stage standard rocket. Nevertheless it's fun designing rockets in a new way. Give it a try edit: also i do it because tavert is a boss and i can't beat him and his mathematical simulations so i go for small victories

Please read the challenge requirements first Kourston . Jet engines are not accepted, and submissions require more data to be visible on screen. So unfortunately i don't think this is a valid submission Also idk if the info panel is enough for the OP but at least we need resource panel open on when in orbit. Please post your results after you make necessary adjustments, good luck

So, i took another bite at the "no asparagus idea", also lowering my previous stage count to only 3 stages. Payload: 7,4 t (this time it's fully 0.2 drag) Launch weight 39,45t Payload fraction: 18,76% Screenshots were merged to save on the imgur image limit. It was flown on MJ but it isn't mechjeb compliant since it needs flight path angle changes when staging and near the end of the burn. There is still room for improvement, and i think "no asparagus" has the potential to get above 19%.

Seconded, the career mode is currently in very early development, it just adds more confusion to the game. Go with sandbox and experiment until it works, or you can try recreate ships you see on the youtube. You can move items in stages as well as stages themselves. Modifying stage tree is also possible in flight!

Toastie_Buns, that craft could fly on its own on iniglide from control surfaces, you could get to the same alt without RCS probably. It would be nice if Simon added "no control surfaces exploitation to this challenge. And continuing my rampage with random images in this thread... extreme case of infiniglide in action (only 12 small control surfaces and 8km/s in atmosphere, all stock of course) (I will make an entry when i finish building my new monster PC thou.)

Slingshotting around Moon to change inclination was actually done in real life too, (i don't remember exactly) but i think some satellite was placed in reverse or polar orbit through moon flyby because they couldn't launch it from available sites into desired orbit. I think it was because of safety reasons as most launch centers have some kind of unpopulated area on the early ascent path (water usually) to the standard orbits, and launching in other direction meant flying over populated areas so direct launch was out of the question.

Can i do it in older patches ? (All stock, only rcs propulsion, you could get an orbit at sea level or get to Jool on one tank, good times. it was 0.16 or something)

Yeah i should stop talking today, not feeling well and it shows . It's just that when you mention LV-N and ION engines I've felt you were going off topic. Also unless its Eve i don't think using atmospheric ISP would be accurate, as after only 30s of ascent LV-N already have 500 ISP, and they have like 750 ISP on ground on Duna. (i usually use 3/4 of the ISP difference between atmo and vac for rough estimations for launches on kerbin) Oh and your turbojet TWR is wrong, it has 112,5 kN of thrust on launch so the TWR would be 9,55 (idk about the modded jet engines)

It's not fair comparing atmosphere ISP of engines designed to work in space >_<, also that way mainsail blows ION engine out of the water Also after some thought this calculation does really not give us anything useful. I mean at this point it is calculating engine efficiency at deltaV = 0 and that means that high twr engines almost always win. The only high ISP engine that could compete with the high TWR engines would be pre-nerf Aerospike engine i think.

and that times ISP is how much exactly ?

( 60000 / 9,81 / 2250) * 800 = 2174,6 How do you count TWR ? Oh and on a side note of completely pointless calculations, my favorite is: Thrust * burn time / mass, where mass = engine mass + full fuel tank mass. It roughly counts energy density of current stage, and allows for direct comparisons of engine systems for given TWR and deltav.

It's even worse, as when the 909 starts winning over 48-7S, LV-N is already better than both of them. <- and that was before the 20kN to 30kN thrust change! So in short aside from part count savings and aesthetics there is no point to 909 whatsoever now T_T. edit: Wait how is it less useful? TWR*ISP ION: 840 LVN: 2133 Mainsail: 8250 48-7S: 10500 We are multiplying some design value (TWR where by design higher = better) by engines efficiency (ISP where higher = better), so one would think the higher the value the better

Nice challenge . You could add some scoring penalty on the use of Jet engines. As they can bring most of the 320t to Kerbin orbit in several flights. Something like: Rocket scientist Complete the mission without using jet engines. I think something between +5 and +10 would be a good score number.

This awesome program has the graph you are looking for. Bi elliptic transfer starts being better from singe burn plane change from 38,94deg up to 60 where leaving SOI and returning with proper inclination would be better (at lest that's how i understand Bi-parabolic transfer in KSP ).

In stock game you can see most of the planets, Ive seen Eve and Jool from Kerbin ground, so Duna should be visible too. It's not visible at all times thou so you should to be as close as possible to it. (A little counter intuitive for an astronomer as in KSP we don't need the sunlight to reflect off the planet we are observing.) edit: yes, Duna is visible, it requires maximum zoom thou (max mousewheel zoom+middle mosue button) double clicking on window in IVA helps also a little. The only nice planet to observe is Eve thou as it's more than 2-3 pixels wide