Search the Community

I read your optimization simulations and its very interesting, thank you for sharing :). Though, one Question, did you tried that also in practice or only on formulas ? It would be interesting to know that formulas, if they are 100% correct, than i could know, why i fail to get to these values. I am testing since 2 or 3 days whenever i have the time, to get to the most effective Design&Ascent-Way which is only possible to minimize dV to LKO. In my last attempt i had a TW for about 1.90 and got to LKO with 3072 dV ( Im sort of proud after so many testing flights ) BUT: you showed a gravity loss of 669, i got to 835, you showed a Drag loss of 210, i got to 119 = total 945m/s ( well plus 25 m/s steering loss, so total-totaly = 970m/s loss ) And that is after dozens of dozens of tests. A few things got in my head after a few test: 1.) I thought all the time that in new KSP Atmosphere we should stick to a max-Q ( and I just took the advice from MJ for about 20.000pa) That is not true when the most important thing for you is most less dV to Orbit. You should stick with max-Q if you dont have a very well drag-optimized design to minimize stress on the rocket, thats also the way like they do it in Real Life, because an exploding rocket is fun in KSP, but it isn´t in Real Life. 2.) Further on beeing under Terminal Velocity is very important, you should not go over or you are waisting loss to drag. though in 1.05 its very hard for me to go over the TV limit. 3.) It seems that if you have a very well aero designed rocket, that the most important factor is not drag loss anymore, the most important factor is gravity loss, if you stick with max q limit to 20.000pa you will always have a too high gravity loss and if your rocket is stable you are not gaining anything. ( in a gamesim like KSP ) 4.) If you are trying to get the best optimized ascent, you can´t use Mechjeb Autopilot Ascent, you have to do it manually ! Though i was using MJ functions like maxQ, Terminal Velocity limit ect. for testing purposes. Also to get a perfect circularizing maneuver, the MJ Smatblabla function is useful to stay in prograde at Apoapsis. I found out that you can safe dV if you make the circularization manually and without a maneuver node, just stay 10 seconds behind time-to-ap and then burn exactly so that you dont go over or under the 10 seconds to ap, you will make perfect circularization maneuver. 5.) I cant make a totally handsoff Gravity Turn, the gravity turn is always starting to early or if starting at a good point, will end to early and I have to correct the pitch by myselve, thats a thing which grind my bears, because I wanted to make a gravity turn with so less drag and steering loss as only possible. And also I read that in Real life they are also trying to make a One-Steer only Gravity Turn ( the beginning pitch over ) though i also read that sometimes even in real life they have to use gimballed help to correct steer but at a minimal level ) I tried to give my rockets more weight to the top through tanks which i dont really need/use, so that I thought more weight on the top will result in faster gravity turn, but it looks like that is not true, further testing from my site is needed though. 6.) Im not sure about that thing, but it seems that a rocket with more width has also less drag in KSP and i think it should be the other way. Im testing this further on. I can only say that with similiar Ascent behavior, my first rocket with 1.25m did always had much higher drag loss than the rockomax parts rocket. 7.) Round about you should stick with that Degrees to Ascent: Pitch Over at : 100 m/s ( which is with a good TWR Vessel always something between 600m high and 1400m high, you should look only at m/s, because under 100m/s will return in too fast gravity turn and too much over 100m/s will return in a too straight gravity turn with much steering corrections and loss ) You are at 10Km = ca. 45° degrees Your AP is at ca. 40KM = turn down to 20° degrees Your AP is ca. 55-60KM= turn down to something about 0° degrees, you need velocity now It would be nice to go to 0° at 30Km but the heat will melt the cone and wings and may even melt more of the rocket. 3072 dV to LKO Rocket: Start Ascent at 28KM Ascent at 47KM after Burn Final Orbit If someone can show me that Im not right with some or even all facts, i would like to hear that ! Update 1 hour later i got to under 3000dV :=) Pic

With infinite thrust and perfect piloting, there is no difference between constant descent trajectory, reverse gravity turn or what you called a suicide burn: we just kill all the velocity instantly at the impact point, where or trajectory is tangent to the surface, with a horizontal burn. Assuming a finite thrust is what make the distinction relevant, instead of a comparison of gravity turn without turn VS a constant descent without descent. Likewise the fact a bi-elliptic transfer is more efficient than Hohmann transfer in some cases will be a Moot point if that cases don't happens because a previous intercept optimization. About what the terms means "to most people": we need to know what are we talking about, so let's make it clear what we mean when using those terms. We are already in the same page in regard to constant descent. And in divergence about suicide burn. But I think we can avoid it because we agree that (a) doing a manuever to reduce energy is better at lower altitudes because Oberth and (b) the maneuver you described as suicide burn is inefficient. The definition I know (and use) of gravity turn is: a ascent or descent* trajectory where the thrust is not used to steer the rocket but rather the rocket is steered by the gravity. ** *the descent version being the reverse gravity turn where the distinction is important. **if an atmosphere is present aerodynamic forces will also act on the craft affecting the turn. However what define a gravity turn is how gravity and thrust are acting on the vessel. Which pre-determined parking orbit? In the first reply to this thread is suggested to aim for a periapsis as low as you can get it without smacking into terrain. As far as I'm concerned we are assuming a parking orbit of radius R. Your demonstration that magic happens if the initial orbit is 12R only show that magic don't happens in the situation we are talking about. Again: your math seems correct. But is not applicable to the practical case at hand. Talking about 1,2R is already a stretch, leave alone 12R. If by "start out more similar suicide burn" you mean "kill some horizontal velocity first" that is a cirfularization burn and before the actual landing maneuver. If you start right away or several orbits ahead will not affect the efficiency. Also if that is the ideal height to start the landing (with finite thrust and safety margin) you should had aimed to that heigh at the intercept.

So, it's been a while since I've played this, and I've gotten back into it. And I am running into the same problem that a lot of new players have: How the frak do I get to Mun and back? I know I have issues with design, and I know I have issues with dV. But I've done this before...and now I can't. No matter what I do, I end up without enough dV to get to the Mun and back. Here's some shots from a recent attempt. First, the tech tree: That's not all that impressive, but very do-able. I know there are people who have done far more with far less in this game. Now, the Lander: Sitting in the VAB, she's got 2978 dV. If she were in LKO, according to the charts and maps and videos I've seen, that should be more than enough to get her to the Mun and back. And now the entire rocket. That's 5539 dV sitting on the launchpad. I know that when I launch, the 2978 shown for the lander goes up due to reduced weight of the craft, less pull from gravity the higher up you go, and less air resistance as the air gets thinner. However, once I do the transfer to the Mun, this puppy has less than 2000 dV remaining, which is about 1000 less than I need to get there and back. So, what am I doing wrong? I don't know, which is why I'm out here asking. I am not the greatest at gravity turns, and in the case of this thing, if I start turning at 75.0 m/s, she wobbles way off course and then eventually passes Ap and starts heading down towards the surface. So I have taken to not starting the turn east until I hit 10,000 meters, at which point I hit 45 degrees at about 23,000 meters. And that's stable enough to get me to LKO. I am quite certain that part of the answer here is "Pick up Flight Control and throw a reaction wheel on this thing somewhere"...but I can't. I am attempting to take on the Kerpollo Challenge, primarily because I've never been beyond Minmus before. I want to push myself, and right now I can't even get one foot out the door. I know that there are design issues here, but I don't know how to correct them. I hate that the lander is far too vertical, which is probably part of the problem. But I'm not sure how to flatten it out to and keep the dV I have. I also am aware of the "moar boosters" method, which I'm not opposed to...but again still unsure how to effectively make it work. Whenever I add weight, whether through engines or fuel or whatever, the dV goes down (which I fully expect; more weight = more thrust needed to reach the same speed and all). I hope I've stated all of this properly. My issue, at least through my own lens, is design. But I can't seem to crack the code on what to do to become more effective at this. Anybody got some pointers to throw my way to help me out here? I know I've done this before; I'm just not sure how I did it, or how to do it again.

All right. You've said that you don't really understand what an orbit is, so I suppose I should try to explain what an orbit is from first principles. I'll try to lay off the math as much as possible. Just as a disclaimer, I'm ignoring the atmosphere for much of of this explanation. The presence of air makes things needlessly complicated. First off, gravity. All things with mass pull at each other, with the pull getting stronger as the objects get closer. For most of the stuff you interact with on a day-to-day basis, this force is so weak as to be completely insignificant, but when you deal with objects as big as planets, moons, and stars, the force of gravity starts to matter. Something important to note is that when a very large object pulls on a very small object, the small object is going to speed up towards the large object at the same rate, regardless of how much mass the small object has, specifically. So, for example, a 10-pound bowling ball will fall at the same rate as a 15-pound bowling ball. If you're standing on Earth and you throw a ball straight up into the air, gravity will pull it back down. If you throw the ball at an angle, its trajectory (the path it follows as it moves) will form an arch shape (a parabola) - which means the ball flies along a curve. Now, this is the really important bit: the Earth is round. Gravity doesn't pull you down towards the ground, it pulls you in towards the center of the Earth. This means that, if you take your ball and throw it really, really hard, it'll fly so far that the direction gravity is pulling it will change as it travels. This is because the ball is moving with respect to the center of the Earth, so from the perspective of the ball the center of the Earth (and the source of all that gravity) is changing position. If you throw the ball in just the right direction, at just the right height, and at just the right speed, the rate at which gravity pulls it down will match the rate at which the center of the Earth changes position from the perspective of the ball. The ball will then be stuck, "falling" in a circle around the Earth. This is called an orbit. If you were to throw the ball at a slightly slower speed, gravity would pull it down faster than it could move around the Earth, and the ball would fall back down. If you, on the other hand, threw the ball a little harder, it would travel away from the Earth for a while, slowing down as it moves further away, and eventually falling back down and speeding up to the height and speed that you originally threw it at. The path of the ball now forms an oval (an ellipse). The highest point your ball reaches on this oval is typically called the apoapsis, and the lowest point is called the periapsis. There are other terms that describe this oval, but for your purposes those are the two you'll want to know. You're probably wondering, what do rockets have to do with this? Well, just trying to throw a ball (or a spacecraft, or a car, or whatever) isn't entirely practical. The speed you'd have to get to in order to orbit the Earth at 200 km up, for example, is approximately 7,790 m/s, which is 28044 km/h or 17425 mph. Way faster than you could throw, or even a bullet from a high-powered rifle. Plus, you'd need to have a starting point that's 200 km up. The highest point on Earth is Mount Everest, which is 8.8 km up. Not nearly high enough. This is where the rocket comes in. A rocket is just a means of getting your ball up to the correct height and correct speed, which it typically does by flying a curved path known as a gravity turn. This path heads straight up at the beginning, then slowly curves over to one side to build up the speed needed to get into an orbit. We have to use rockets because they're the only sorts of things that have enough thrust to take off from Earth and that work in space. Aircraft, for example, rely on the presence of the atmosphere, and so aren't useful sending things to orbit. The numbers are different for KSP (the game's solar system is built to 1/10th the scale of ours), but the concepts and physics are the same. If you have any questions, feel free to ask. I will do my best to answer.

Yes, very. It's not the coasting to apoapsis that's the problem, it's the "going straight up" part. As @AHHans points out, it's a lot more efficient to do a gravity turn. Basically, what you do is to start your eastward turn practically right off the launch pad. Just a smidgeon-- how much is "right" will depend on what your TWR is. If you have a low TWR (e.g.1.5 or below), you only want a degree or two. If it's high TWR, like 2.0 or close to it, you'll want a bigger angle, like 5-10 degrees. Having done the initial eastward nudge right off the pad, you then just follow all the way up. No steering needed. Keep burning full throttle, staging when needed, until your Ap gets up to where you want it. Then coast up to Ap and circularize. Judging the "correct" angle to nudge it off the pad takes a bit of practice, but you'll find that you quickly develop a feel for it (especially if you tend to build your rockets with a consistent TWR). A good way to judge whether you've nailed it is, look at what angle from the vertical you are when you reach 300 m/s. At that point, you should be tipped probably about 45 degrees from the vertical. If you're much more vertical than that, your initial nudge wasn't big enough; if you're much more horizontal than that, it was too much. So, if you get to 300 m/s and see that you're way off 45 degrees, just revert to launch at that point and try again. (Also, note that there's nothing "wrong" with how you're doing it now, if you like it that way. It's just somewhat wasteful of dV, is all. A good gravity turn can save you several hundred m/s of dV compared with an inefficient ascent profile, so it's up to you how much you want to fine-tune your ascent.) If you're only 1 km apart, then for all practical purposes you might as well be in "flat space", i.e. you don't need to think about orbital mechanics, just treat it as if you were both floating out in deep space with no gravity involved. So you can just point your nose directly at the target and thrust to a reasonable closing speed that will get you there in a minute or less (say, 10-20 m/s), then take it from there. The reason that works is that with such a short separation, 1. there's not much difference in the gravity vector that the two craft experience, since the separation is tiny compared with the radius of the body you're orbiting, and 2. if the closing time is only a minute or less, you won't have orbited much of a fraction of an orbit in that time, so motion is pretty close to the classic inertial case. If you were significantly farther apart-- for example, if the target were 50 km away instead of just 1 km-- then you wouldn't want to do this; it would be better to take the orbital-mechanics approach, unless you're in a big hurry and have lots of dV to spare.

The way you described it, it probably is. Not so much because you need to coast to apoapsis, but because by first going straight up and then tilting over by 45 deg you are not thrusting in the direction that you are already going, so you are fighting against the velocity that you already gained. The most efficient ascent is a gravity turn, where you tilt over a bit shortly after leaving the launchpad and then lock prograde, thus letting the gravity pull your velocity vector more and more horizontal. The exact parameters for an optimal gravity turn depend on your launch vehicle: its TWR and drag during the ascent. A typical gravity turn for me looks like this: when the I get to 20 - 30 m/s it tilt over by 10 - 20 deg, when I get to 120 - 150 m/s I lock to prograde, I'll stay there until the apoapsis is where I want it, and then I'll coast to apoapsis and circularize. If I have high TWR I tilt over soon(er) and more and lock to prograde earlier, with low TWR I tilt over less and later, and with high drag (but high-ish TWR) I first go up quite a bit before I tilt over. I kind of try to keep the coast phase, i.e. the time to apoapsis when my apoapsis gets out of the atmosphere, at about 1 - 2 min: if the time to apoapsis increases too fast then I need to tilt over more (or reduce thrust), if the time to apoapsis decreases during ascent, then I tilted over too much. At 1 km distance I usually go for the direct approach (even if it isn't the most efficient). I.e. I thrust towards the target, and then use the method for "Fine tuning the rendezvous" from @Snark's Illustrated guide to docking, to keep my prograde vector pointed to the target.

That's probably going to be fine. It looks like you have a terrier like my example above. If you switch the dV reading to vacuum, you'll see the dV of your upper stage with the capsule shoot up. You also might want to fire your core engine at launch and just leave the throttle down so you have some real pitch and yaw authority. Would make doing your gravity turn easier.

Just rewind a bit....... When you say "1st stage" - what do we mean? Are you launching from KSC, and if so how much deltaV is in the first stage? The "traditional" amount you might use is ~1000m/s if its SRBs, maybe a bit more say up to 1500-2000m/s if its a liquid fuelled 1st stage. If you're doing a gravity turn to build up horizontal velocity too, that won't get you out of the atmosphere. From memory, my most recent launch with a ~1600m/s 1st stage decoupled it at around 25km. With the other stages on top and a sensible engine in the 1st stage, it might start out at TWR 1.3 and end up with TWR ~3 - certainly not enough to "go crazy" but a nice kick to get uphill. And I've always made my rockets more/less balanced, in terms of side-to-side mass variation. If not cylindrical, then obviously an amount of thought put into the design to balance the weight on each side to match. In a gravity turn, or any launch really, you shouldn't need to be gimballing except when changing direction - and that should be minimal (it doesn't make sense to burn in one direction, change drastically, then burn in another).

By uncontrollable, do you mean that it just tips forward/backward on launch, or it just spins out of control when you are in the atmosphere? If it's the first one, you could try rotating the engines on the actual shuttle piece towards the center of mass, as said by Cantab, but if that doesn't work for some reason or is just too hard to get working, you could simply just mount two shuttles on either side of the big fuel tank like this: This works quite well, but is pretty cursed and might not satisfy you if you're trying to build one similar to or a replica of the American space shuttle. If it is the second thing, it might be caused by there being too much weight at the top of the craft, which you can fix by simply doing a steeper gravity turn, adding more fins to the sides of the orbiter, or maybe both if one doesn't fix it. Again, adding fins might ruin the American-space-shuttle feel your going for, but do remember that the space shuttles were some of the hardest to fly spacecraft ever made, and you might not get the hang of the art of space shuttling on your first few goes. Hope that helped, Jaq

Some general suggestions based on the info you've given so far: If you are trying to turn east after liftoff, that means you are trying a gravity turn. Which is a perfectly good thing to do, but it's a little tricky so it makes your life harder. It takes more fuel to go straight up, and then turn east after you are above, say, 55km -- but at least your success rate will jump from 1% to 100%. Gravity turns are nicely efficient on the one hand, but I repeat occasionally that failed launches are 100% inefficient, too -- it's something to keep in mind. To do a gravity turn successfully is a rather gentle process, and generally requires that you can do "prograde hold" -- which needs a HECS probe core, or a 1 star pilot. If you've got that, try this: at launch, turn on SAS and hit Z. You won't be able to select prograde until you hit space. So hit space, immediately click prograde (have your mouse hovering over it), and then start tapping D to turn east. As soon as it gets just a little off vertical, stop tapping D and just let the rocket go up. It will do the rest of the turn east by itself -- which is the whole point of a gravity turn. The more you get it off vertical to begin with, the more severe the gravity turn will be. Beyond that, there are several reasons for a rocket to go out of control during launch: 1. Using the controls to push it too far off vertical. Rockets are gravitationally and usually aerodynamically unstable -- if you push them too far, they will flip. 2. Too much drag at the front end. Your upper stage is where all the good stuff is, but it all usually makes the front end draggy which is aerodynamically unstable. 3. CoM problems. 4. Not enough drag at the back end. 5. Not enough control surfaces and reaction wheels. It sounds like you have several of these covered already, but I just wanted to list them to make sure.

Here you've lost me. I totally get that it's not very steerable... but what does that have to do with anything? It's a gravity turn. The whole point is that the rocket steers itself; if you're trying to steer it, you're doing it wrong. Gravity just naturally takes care of curving the rocket's trajectory for you, and aerodynamics takes care of keeping it pointed prograde. The rocket doesn't need the ability to turn itself. Of course, you do need that little tiny eastward nudge right off the launchpad to get the turn started, but if your rocket has so little control authority that it can't even do that, you can cope with that easily enough by just mounting the rocket on launch clamps (so that the rocket itself isn't resting on the pad, and then in the VAB tipping the rocket ever so slightly eastwards, just the right amount to start the turn. Like this: (for context, that's a rocket put together for a challenge I posted, to build a completely unguided rocket that goes to orbit without any autopilot and without any control input whatsoever from the player, other than initial launch) Not so. I've launched plenty of big, hard-to-steer rockets to orbit atop Kickbacks, using appropriate gravity turns, with no trouble at all. The main thing is to make sure that your rocket is aerodynamically stable, like an arrow-- i.e. it needs to want to point straight into the wind, to stay prograde. Otherwise it won't work. Fortunately, that's easy to do by sticking some fins on the back. It is. Not just in theory, but it's been proven experimentally in KSP, per that thread I linked to you earlier. Had a little trouble parsing that sentence, but I'm guessing what you mean is that currently, with your straight-up launch, you can get to Jool, but don't have quite enough dV (i.e. you're 1000 m/s short) to be able to slow down enough to capture to Jool orbit, yes? If so, then yes. This should help you, a lot. You should be able to save several hundred m/s of dV, just from the trajectory change alone. Furthermore, depending on how your rocket is designed, you could seriously boost your dV even further by breaking up the staging on those Kickbacks. One of the benefits of doing a gravity turn rather than accelerating straight up is that since you're doing most of your acceleration mostly horizontal, you don't need so much TWR for most of the ascent, which allows you to design more efficient rockets. For example, I don't know what kind of TWR you have off the pad, but if you've got 36 Kickbacks with a light payload, that's really inefficient, and I suspect that your TWR is far higher than it needs to be for a gravity-turn ascent. So suppose, for example, you only fire, say, 30 of them off the pad; then, when those burn out, you stage them away and fire the remaining 6. You'll get enormously more dV out of it that way, since you're not lugging the dead weight of all thirty of those extra Kickbacks all the way up to the velocity where you release your LFO stage. One last thing to consider: If your goal is to achieve orbit around Jool... are you using a reverse gravity assist from Tylo or Laythe upon arrival? If you're not... you really should. A well-executed reverse assist from Tylo or Laythe can shave a lot of dV off the needed capture burn. In fact, if you've got a good transfer orbit from Kerbin, you actually can capture to Jool orbit (admittedly, a highly elliptical one) with no burn at all, using only the gravity assist.

As others have said, yes, it can be done. One way is to throttle down and use a low simmer to keep your apoapsis in front of you until you circularise, but in fairness, shutting off the engines and restarting is just a special case of this where low burn becomes no burn. The way that real rockets do it, at least occasionally, is to burn full blast but to turn radial inward to adjust both apoapsis and periapsis so as to achieve a circular orbit with one burn. This necessitates a bit of planning and a willingness to use more fuel. I don't think that anyone has answered this part yet. You can adjust the ascent profile in MechJeb in a couple of ways. One is to adjust the gravity turn profile, but you probably don't want to do that. The other thing that you can do is to adjust the orbit altitude setting, along with the thrust and turn limiters (and the other settings) in the appropriate panel. I believe that MechJeb more or less assumes that you'll need to coast to a circularisation burn (it's a consequence of Kerbin being a toy-sized planet; real rocket ascents take twenty minutes or more), but with a bit of tweaking, I think that you can get it to put you in orbit with a continuous burn. Note that as @bewing said, the exercise is academic in terms of practical use; it saves neither time nor fuel. That's not a recommendation against trying it--by all means, do so; it's your game--but a caution that most people here chase efficiency and so there probably isn't much material to guide you: you'll need to figure out the appropriate settings for yourself. That being said, if you do manage it, then please do post the settings here; you can help to establish the guidance material for anyone else who wants to do what you're attempting.

With all due respect: it doesn't require 4000 hours, nor does it need to be perfectly attuned. I did mention 'reasonably designed', yes? There's tutorials up the wazoo explaining what a good rocket looks like. KSP's simulation offers very wide margins of error (so wide, that people routinely put contraptions into orbit that by all rights shouldn't be able to even lift off). Besides, OP is past the point of basic rocket design already. A gravity turn is the easiest possible way of launching a rocket into orbit, because it allows the rocket to follow a natural course, requiring only minimal input at the start. Think of it this way: most kids learn pretty quickly to throw a ball into a basket. The entire path of the ball is determined right at the start of it - how hard you throw, and at what angle. If you missed, adjust those two parameters and try again. Cutting down to basics, a real gravity turn only requires you to observe when you nudged and how hard, and from the path followed after that, you can easily tell which one you need to correct and how. This helps a new player to learn to put things in orbit much faster for two reasons: without the stressy need to continuously steer (and then correct, and then correct some more, and then -wait stage first!- then correct again, oh dear why is it not steering where I tell it to OH I FORGOT TO STAGE AGAIN!!!) the player actually has time and opportunity to observe what the rocket is doing all by itself, and what made a difference in which way. Additionally, manual steering is highly inaccurate in KSP, and tends to introduce random path deviations, which just complicate things further. Teaching newbies (or leaving them in the belief) that flying a rocket into orbit is some kind of arduous manual technique that requires thousands of hours to follow a specific path is a disservice, when they could instead be watching and learning while sipping a cup of their preferred beverage, calmly observing just the one or two actually important variables that will help them make a successful launch.

And I disagree to that When I built a new rocket (doesn't happen that often nowadays, I have a good variety of crafts), I usually come close to a good "auto-gravity-turn" design, just by experience. Might need a few iterations (tweaks, in particular thrust percentage for the different stages), but even the initial build is not that far of. But I've been playing KSP for some 4000+ hours. A beginner just doesn't have the experience, naturally (check out any KSP beginner stream at Twitch). Hence my words "Almost no craft is that perfectly attuned that it can do a perfect gravity turn after the initial pitch by just following prograde"

I disagree. Any reasonably designed rocket will have a completely natural tendency to follow a standard gravity turn, requiring minimal input. You really only need to pay attention to two variables. With any reasonably designed rocket, the standard launch-into-easily-repeatable-gravity-turns procedure is: set SAS to hold stage to launch wait until X nudge the nose Y degrees East switch SAS to prograde take your hands off the stick/keys and just stage if and when required, until Ap reaches a few km over your desired orbit altitude coast circularize (manually or with a node) X = Either a specific speed or altitude, whichever seems more convenient for you. I usually go by speed, and find the right moment to be often somewhere between 80-120 m/s, depending on the flight characteristics of the rocket. Finding the sweet spot takes a bit of trial and error, but usually within that range you still make orbit, just not as efficient. Correcting for a less than perfect launch is simple: if it's too shallow, wait longer; if too steep, wait less. Y = I usually nudge no more than 5 degrees. Much more than this tends to cause unwanted deviations in the flight path that will require additional corrections later. If you want to turn the above almost perfectly repeatable, use launch clamps and pre-incline your rocket 5 degrees east. That way you literally only need to figure out X (the exact moment when you need to switch SAS to prograde), and never even need to perform any steering inputs at all. I would posit that getting used to performing launches as described here will not only allow you to repeatably achieve near-circular orbits, but also make it a routine thing that will allow you to get most launches with new rockets right in just one or two (test) launches. Ahem.

Assuming you're launching a rocket, vertically, you need to do a gravity turn. This amounts to tipping toward the east (D key, if you built the rocket with the default pod position in the VAB) by a few degrees when your rocket gets between 50 and 100 m/s, then following the prograde marker until apoapsis is around 80 km. Throttle down to zero and make a circularizing maneuver at your AP marker, and when that's done, shazam! you're in orbit. The amount of tilt needed at the start of the gravity turn is dependent mainly on your TWR -- if it's 2 you'll need a lot more tilt than if it's 1.2, because you'll gain speed along your heading faster, and therefore have less time to build up horizontal velocity that tips the prograde marker toward the horizon. This method hasn't changed significantly since at least 1.2 (I first played in 1.2.2). Earlier (before 1.0?) there was an alternate method required by the "soup" of the atmosphere, to fly to 10 km before turning over, then immediately yaw to around 45 degrees and follow prograde (from there on, it's pretty much the same) -- but the atmosphere was changed in 1.0 or 1.1 to have less drag at sea level and to gradually taper off, more like a real atmosphere, so the gravity turn works better now. The one exception is if you're trying to launch something like a complete space station all at once -- something big, fragile, and draggy may still get to orbit best by launching vertically to clear most of the atmosphere, then turning over to the east to build horizontal velocity after you have enough vertical speed to coast completely above the air. For spaceplanes, the technique is completely different from what I've given here, but since I've never flown a horizontal launch spaceplane to orbit, I'll let those who have advise on how to do that.

yes, i could have used a swivel, or i could have added reaction wheels. i didn't because i wanted to figure out what was wrong. a well-crafted rocket should not need either. i generally accept that i'm flying an inferior rocket as long as it does the job, or that i'm flying a cumbersome payload and stability problems can't be avoided. but in this case i wanted to know. so, let me get this straight: i always considered the gravity turn a manuever to be performed, but perhaps i was wrong here. you are telling me that all rockets will capsize, no matter how well balanced they are. and that a succesful gravity turn does not entail steering along the trajectory, but accelerating at the right speed so that your rocket will capsize at the right speed to make you turn successfully? seen in that light, it makes everything clearer. i don't marvel anymore that most rockets will capsize. the fins were not there in the first design. i went through several iterations. in fact, the first attempt i made at this rocket was very much along the lines you suggest: higher TWR in the first stage, compensated by another intermediate stage higher on, and no fins. it also didn't work. in fact, the first stage almost got there, but as soon as i detached the first stage, the rocket went wild. anyway, i said i eventually did launch it with a bobcat engine.

Not really the correct line of reasoning. It's the other way around. The prograde marker is an effect, not a cause. If the prograde marker is moving, it's because the ship's direction of motion is changing. IOW, to move the prograde marker, you have to move the rocket's nose OFF the prograde marker and hold it there until vector addition eventually causes the prograde marker to catch up with the nose marker. So, with a true gravity turn, you're not giving any control inputs and, as you say, the aerodynamics are trying to keep the rocket weathervaned in the direction it's already going. So why is the prograde marker moving towards the eastern horizon despite its natural tendency to drift slightly west (due to Kerbin's rotation) as the rocket gains altitude? Because gravity is pulling the rocket over like a falling tree. As the rocket falls more and more towards the horizontal, its thrust vector also points more and more horizontally. This causes vector addition to drag the prograde marker in that direction. If the prograde marker wasn't already moving "under its own power" (as in, being moved by something external to the rocket, like gravity), then SAS prograde lock would NOT make the rocket turn. The prograde marker would stay in the same place (apart from westward drift due to Kerbin's rotation under the rocket while in Surface mode) and the rocket would keep going in that same direction relative to the ground under it as before. In a gravity turn, the torque comes from gravity. The aerodynamic forces resist this, trying to keep the rocket going the same direction as before by weathervaning it, but they're not strong enough to stop it. Thus, they only slow the rotation being caused by gravity, so that the rocket doesn't fall parallel with the ground below until it's at the desired orbital altitude and velocity. It goes like this.... When the rocket spawns, it's (usually) pointing straight up on the pad. When you fire the 1st stage, it will thus go straight up, and then the prograde marker appears right where the nose is pointing, straight up. At the appropriate time, you give your 1 and only control input to kick the nose very slightly east off the prograde marker. Because the rocket isn't going very fast yet, the prograde marker almost instantly latches back onto the nose marker. At this point, you set SAS prograde lock. So why does the prograde marker fall all the way to the eastern horizon? It's because the rocket is now at an angle to the ground below. Thus, it's CoM is off to the side as well, so the direction of the pull of gravity no longer coincides with the rocket's axis. And neither do the aerodynamic forces, which are acting through the CoP some distance behind the the CoM. So, you have an upwards force acting at the CoP and and dowmwards force acting on the CoM some distance away, resulting in a turning moment (aka torque). This is what makes the rocket turn without further control input. But you have to design and tune the rocket so that this resultant moment is small, to keep the rocket's rotational velocity at just the right magnitude. Too much and the rocket flips. Too little and it doesn't level off at the right place at Ap.

Using throttle to limit yourself to get a "neater looking path" is really bad idea. A "gravity turn" is better since there are no "steering losses". However steering losses are very very small compared to the gravity losses. So limiting thrust (and thus "burning longer" increases gravity losses. The improvement in steering loss can never offset this. The other loss is of course drag, but even for drag it's better to "steer later and more aggressive" than "lower thrust". Actually a "90 degree initial turn" would be ideal if there would be no gravity. initially one does have a sideway velocity but no vertical velocity, in other words if kerbin would suddenly become a point mass we'd be at the apoapsis of an elliptical orbit, the best way to raise periapsis is not to "travel outwards" but to travel forwards (sideways). The only reason we go "up" first (apart from the very few km for ground clearance is to get out of atmosphere.

Where did I do that? I am not talking about the trajectory at all, I'm just outlining a baseline for calculations. You are the one making a statement, so the burden of proof falls upon you. Again I'm not talking about a straight line. Though I'm considering a simple trajectory where you always fire prograde, but instead of lowering thrust to make a "gravity turn" you turn just like doing a hohman transfer. Indeed I am. However as the vacuum specific impulse is not that much higher than the sea level impulse. Combined with the fact that the more simple proposal, of just firing much more straight/with full thrust, and "firing again during apoapsis", means a larger proportion is fired in vacuum. Not at all, I'm not talking about thrust to weight ratio. The gravity loss I do consider to be equal, since the distance traveled (70km) is small compared to the total radii (600 and 670 km). Again not at all, where do you get his impression? What we need is something that can easily be repeated by anyone. Something that can be verified, a craft with instructions how to fly. Either a video talk about the control input and design or something else. So long as anyone can repeat your results. I'll test out the design later once I got time away from the family. This I get a chuckle with "fuzzy math". If there's one field you simply cannot be fuzzy in it's math. I come back to my earlier statement which is that the burden of proof lies with the claimer, the "simple" formulas show otherwise. As for why you see such low thrust to weight ratios in real life applications: this is due to (a) payload restrictions, and (b) it's hard to make rockets with more thrust, and more thrust means often much less thermal efficiency. No what I propose is just firing enough power to get a short burn to get the apoapsis up, the direction I am not even talking about, I'm just talking about doing a very short burn. Doing a short burn will mean you will fly "straight" as you call it for the latter part/coasting to the end of the atmosphere. After which you complete the circulation near the apoapsis. I am advocating always burning at full thrust, or at least after reaching a minimum altitude, and not lowering thrust to "keep doing a gravity turn". The direction I have not made any statements about.

ADDIT: Oh wait! Gravity TURNS you're asking about. I thought this thread was about gravity-ASSISTS (as in using Mun close flyby to get to Minmus cheaper). There are players who question the efficiency of gravity turns? Really, I just assumed that everyone used those. You literally just go STRAIGHT up to orbit!? Excuse my simplistic biologists conceptions of gravity, but why one Kerbin would you imagine that is in anyway "competitive" with doing a gravity turn? You're fighting Kerbin's gravity 100% when you are thrusting normal and I'd guess that at 45% pitch relative to the horizon you are fighting it about half as much, somewhere closer to 0% when at a pitch close to horizontal, no? Once I learned how to basically play the game, I try to generally fly by intuition, and forego all the maths and efficiency analyses, though I can certainly understand how that is appealing. My general procedure on a craft without special considerations or on a mission without special considerations: 1. Launch at about 1.3 to 1.5 TWR 2. Lower TWR to the 1.2 to 1.35 range during the first few seconds (I frequently have a single throttle controlled engine that has enough oomph to handle the whole thing which is in the same stage as a few SRBs which are also powerful enough to lift the whole thing, although perhaps marginally at the initial launch, so launch may be: start with throttle at 1/3, taper back to nearly zero [to retain the gimbal from the liquid fueled booster] then as the SRBs deplete, throttle back up to hit the 1.2 to 1.3 ballpark. 3. Try to keep acceleration under control until about 35,000 m (thick air = resistance so more power = heat and not > velocity). 300 m/s at 35,000 seems about right, and from there, acceleration can proceed at will without much impact from air resistance (all gut intuition here, no background research done to confirm/deny this) 4. I try to be about a 60-degree pitch by the 25 to 35,000 ball park, 50/45 ballpark pitch by the 45,000 ball park, and generally just leave it there until apo gets past 70,000m maybe pitching down a bit more toward the horizon, but I've been burned a few times where my orbital insertion burn was too shallow and I wound up losing my upward momentum and had to whip the ship back around to normal to regain upward velocity a few times so I avoid flattening out the trajectory too soon. 5. Once I'm past 70,000m, and my apo is perhaps 85,000 or 90,000 (at least) and velocity sufficient that apo is increasing "rapidly" going flat to push out peri. Now contrast this with setting up the first couple "short-range only" RemoteTech satellites, where the initial ascent was much more steep (retained nearly vertical pitch until about 50,000 or 55,000m, and only a minimal turn from there till 70,000 when fragile gear is deployed and the "horizontal" burn to push out the peri is undertaken . . . these launches certainly seemed to use up more fuel overall. Based on these general principles "working" I doubt I'm patently wrong on any of this, though might well be confused or "less than optimal" on most or all of it. However, one thing that remains outside my "intuition grasp" is the issue of TWR once one is past the pesky atmosphere. Obviously some times you want your burn to happen FAST, because you want to take advantage of the effects of doing a burn at a very specific point in your orbit, and in those instances large dV changes are better suited by a short, sharp high TWR burn. But what about: I'm in space, I really don't need to move my apo out any farther, I just want to get my peri to ~71km as "cheaply" (meaning as much fuel as possible left over): what is optimum then? TWR in the 1.05 ballpark? or as much as one can muster? heading pointed slightly above horizon? right at horizon, or perhaps even slightly below? I have some payloads that are really pushing the limits of what is doable for a given launchers size and TWR (think top heavy . . . I'll have to post files of my space station core and modules 2, 3, and 4, which are all in orbit now, but which were quite "delicate" to get up there). The gravity turn (and its benefits in terms of fuel use) have to be moderated by the need to: a. get past the thicker parts of the atmosphere, but not too fast that resistance and turblence are created too much; b. wait to turn until velocity is high enough that forward momentum "overrides" the radial momentum created by the turn. On these, I generally "quadruple" the initial thresholds of my "standard" launch = start gravity turn at 250 m/s instead of 50 m/s; only shoot for ~80degree pitch at 25,000 to 35,0000 (instead of 60 degree). Even in the upper atmosphere and in LKO, a really top heavy ship has to be handled differently or it can get itself into trouble. Wow, I was just wondering this exact same question, and came on here to post a thread that addressed these very same questions!

Maneuver nodes assume instantaneous change in velocity. With that in mind at each burns of a hohmann transfer the maneuver node is exactly in the same direction of prograde/retrograde. However in real maneuvers change in velocity its not instantaneous and you will lose efficiency anyway, if you are pointing in direction of maneuver node there is a difference in direction between velocity and burn, if you are holding pro/retrograde there is change in direction of your burn. For what I know both cases are equivalent in regard of efficiency, if something holding pro/retrograde its more prone to inaccuracies due to piloting/SAS. Its the same situation for a constant descent trajectory, for the part of our thrust we are not using to counteract gravity. Not enough data to know (from my part at least). But seems plausible a combination of both that end with a better overall efficiency (eg we start following a constant descent trajectory and finish a gravity turn) More to the point if there is a atmosphere you want to reduce drag what you archive reducing the cross-sectional area perpendicular to the airflow. In a gravity turn you are already keeping the thurst pointed in the (opposite) direction of the airflow so you get two benefits(the other being minimal cosines loses) with the same trajectory. Without delving in maths or experimenting we don't know which one is better for a airless body . To me it seems that if the gravity losses are a major concern constant altitude is better, if steering losses are a major concern gravity turn is better. But there is several catches: 1.It may be the case that we are just trading one kind of loss for another in similar amounts. It helps nothing if to reduce gravity loss in 200m/s we lose the same200m/s due steering. 2.We may be doing a efficient maneuver in a inefficient way, (eg not burning at full throttle, letting the craft wobble) 3.Other variables may be a greater concern than either gravity or cosine loss (eg low control authority). 4.Its possible that the ideal trajectory is part constant descent, part gravity turn.

Depends on TWR. Well no, actually it doesn't -- the ideal landing works like a gravity turn, but in reverse. That is difficult to plan and execute, though. With lots of thrust, a suicide burn is virtually indistinguishable from a reverse gravity turn -- if you can pull it off. Braking too early may lead to you effectively hovering for tens of seconds, and braking too late is, well, suicidal. With a local TWR > 3, your timing and steering errors will have more of an effect than the theoretical difference between suicide burn and an ideal landing. With TWR <2 you want to get into a low orbit first, and try something like a constant-altitude landing, as demonstrated by @Kosmo-not in this classic: That video is very old, the Mun was much flatter then. He also has a very low TWR, so as to better be able and demonstrate the technique. You can usually do better, dV-wise, by doing more of a "controlled descent rate" landing rather than "constant-altitude". The beauty of that method is that it can be flown seat-of-your-pants style, with little regards to planning or split-second timing, and with some experience and educated guesses, the controlled descent approach can come very close to the reverse gravity burn.

TBH doing a gravity turn in a true Fire'n'Forget manner is quite rare, and not really worth anyone's time except for the challenge/cool factor. But IMHO that is reason enough to try to do it al least once. The effect may be small, but gimbals, active fins, reaction wheels, RCS still help to "cut the corners" and make the path a bit closer to the ideal. And those are things that you often already included in the design because of "reason" , so we use it if we can. (e.g. You took the skipper engine for his thrust, and it comes with gimbals; you have a probecore that can provide a small torque and prograde hold) Another issue is error propagation, starting the gravity turn with just a little difference (e.g. +0.5° or -100kg) and no correction may easily prevent a capable rocket to reach orbit or even leaving the atmosphere, so you need extreme precision (we know that stock controls, in flight and at the editor, don't help much with this). Is particularly problematic (both challenging and inefficient, still possible) to make the rocket perform a correct circularization without any control input after launching. So, for the sake of precision and clarity: My approach take all those factor in consideration and, because of that, my rocket are designed to do the gravity turn with little pilot input. This input is limited to: 1)staging, 2)change of SAS mode, 3) Orientation for circularization(only if the craft cannot hold prograde) 4) throttle control for the circulation. My launch vehicles tend to have little to no gimbals, reaction wheels and control surfaces. again: Stable == not likely to change. In fact is exactly what you mean when you use that word. Our divergence resides in a different point. And that is where our divergence is. Interestingly enough, you show there that you comprehend exactly what I'm saying: The qualifier aerodynamic defines that my frame of reference is relative to the airflow. To say anything in physics is necessary to define a frame of reference. I'm defining a frame of reference where all the position are measured relative to the CoM of the Rocket. That is the context where my statement need to be considered. A person in the ground is not in this context, thus his observation are meaningless for what I'm saying. And there an excellent reason for me to not take gravity in account: the frame of reference. Any position is considered relative to the CoM of the rocket, thus we immediately see that there is no translation of the rocket. We don't need to consider any force for that conclusion this is already given by how is defined the frame of reference. In fact, if you sum all the forces acting upon the rocket and the result is different of zero that is because we are not considering a force (or several forces) that actually exist in that frame of reference (we may even give a name for that force(s) e.g centrifugal, coriolis, sugar, spice, everythingNice,...) For rotation we need to consider not only the force, but the sum of Torques relative to the CoM. But then we notice that the force of gravity (a.k.a. weight) is acting exactly at the CoM, thus producing no torque. So yes, I'm not taking in account what's going on with gravity. Because in the frame of reference I took, gravity does nothing. All my considerations were about aerodynamic stability (with respect to the airflow). Whatever happens relative to the surface have nothing to do whit what I was saying. In fact, I used a frame of reference that is moving relative to the surface (with changing velocity!!). With make evident that what is stable in my frame of reference cannot be stable relative to the surface. As explained above, for usual gameplay I take some shortcuts. But I did it for real: no autopilot, no SAS and not even a control point.

The trick to launching really heavy stuff is to build a suitably large and powerful rocket. You'll need two key values- TWR, Thrust to Weight Ratio, and delta-V, effectively how much acceleration your rocket has and thus how far it can go. Delta-V varies depending on your rocket's weight, engine efficiency (ISP) and ambient pressure- more atmospheric pressure = less efficiency and so less thrust from your fuel. To get more delta-V, add more fuel or strap on some extra boosters. TWR is important mostly in the lower stages when you're launching from the surface- it needs to be above 1 or your rocket simply won't produce enough thrust to overcome gravity, and 1.4 is a good number to aim for. You can see both of these numbers in the stage list at the right side of the screen in the VAB (and SPH) and there's a toggle to switch between surface and vacuum values. In atmosphere, the air gets in the way and reduces your rockets' power, but powerful lifter engines like the Mammoth and Mainsail are designed to produce lots of power even at sea level to haul your rocket off the launch pad. Vacuum-optimised engines like the Terrier and Poodle are nowhere near as good at sea level, but are more efficient when in space; use those on your upper stages. You'll get less delta-V in atmosphere but you should make sure that your TWR on each stage is above 1 and preferably above 1.2 in surface mode to ensure your rocket will make it into space without wasting fuel. Around 3400m/s of delta-V should be enough to make it into a low (80x80km) orbit of Kerbin, but it never hurt to have a bit more than that in case your launch profile isn't particularly efficient. The best way to launch a rocket is with a gravity turn- launch straight up until you get some speed up (100m/s should do, but it can be less if you have a lot of thrust to spare) and then start gradually turning to the east to gain orbital velocity. Drag in the atmosphere bleeds delta-V so launching up will reduce that loss, but to stay up you'll need to go sideways to pick up orbital velocity and in the upper atmosphere drag is minimal. Check out the Gravity Turn mod which automates this whole progress, you can learn a lot from watching it try (and occasionally fail) and use that information to improve your own technique and your rocket designs. To build your rocket, start at the top: what size of fuel tank are you trying to put in orbit? Bigger is better for refueling purposes but if you're just using plain stock parts (no mods or DLCs) then 3.75m is as big as it gets, so try using the second-largest Rockomax 2.5m tank and see how you get on with that. One possible design for a dockable fuel tank would be: Bottom- Clamp-O-Tron Senior port (2.5m version) > large monopropellant tank with 4x RCS thrusters > 2.5m battery > Rockomax 32 fuel tank with some solar panels in the middle (small deployable or just static would do) > large reaction wheel > large RGU (if you have unlocked it) with 4x RCS thrusters > C7 fuel tank adapter (2.5m to 1.25m) > Clamp-O-Tron port (1.25m version) > nose cone on the top. It should be flyable enough to dock to a space station with either docking port and will also have plenty of fuel in it. Docking ports can be used as decouplers if you right-click them and select 'enable staging' - you might require advanced tweakables to be switched on in the game settings to see this option - so you can stick the top of your final rocket stage straight onto the larger docking port. For a 2.5m fuel tank of that size, you're probably going to need a Skipper engine to make it into orbit and move it around with any kind of acceleration. Don't forget your reaction wheels, but you can skip the RCS and probe core on the rocket stage. Your first stage will probably have to be a 3.75m one using a Mammoth engine, with some form of additional boosters on the sides. Useful tip: if using solid boosters, set the radial decouplers to enable crossfeed and stick some fuel tanks on top of the SRBs which will provide extra fuel to the core engine and then dumped when they are empty along with the spent SRBs. Struts are required for heavy rockets with big boosters to stop the boosters wobbling themselves loose and causing destruction and when using additional fuel tanks on top of SRBs, use the move tool to slide the boosters down so that they get jettisoned properly; sepratrons with ~1-2 fuel should be enough to throw them clear if they don't drop away on their own. The biggest rocket I've ever built is below- it launched 610 tons of fuel tanks into a 150x150km orbit around JNSQ's 2.7x larger Kerbin, requiring over 5000m/s of delta-V. Most of the parts were from Near Future Launch Vehicles which adds 5m and 7.5m fuel tanks, and the whole rocket used 7.5m fuel tanks, with eight(!) strap-on liquid fueled boosters that were each 5m wide and had a combined first stage thrust of 87 meganewtons- that's 87,000kN! Monstrously large, hideously expensive and I can still smell the overheated electronics as my (pretty good) PC struggled to cope, but over 600 tons in one launch!