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That's a tricky question you shoot at us. And the only answer we can give without any risk of being wrong or, at least, imprecise is: Depends on a lot of variables. Let's elaborate a bit on that. The Gravity Turn is regarded as the most efficient way to get into a orbit just outside the atmosphere. In a nutshell: give a small nudge towards west shortly after taking off and let the rocket steer itself into orbit and control the throttle to go neither too fast (because aerodynamic drag will be an issue), neither too slow (because some of the power/deltaV will be used to counter gravity until the craft get up to orbital speed). There is also the most efficient way to go from a low orbit to a higher orbit, the Hohmann Transfer. In a nutshell: a single burn prograde to raise your orbit so it touches the higher orbit in a single point, then another burn prograde at that point to match the orbit. In a ideal world, we could just combine both the Gravity Turn and the first leg of the Hohmann Transfer in a single maneuver to have the most efficient way to go to a higher orbit. But Kerbin is not ideal, it have an atmosphere. And the atmosphere will take a toll if you combine the maneuver, both in increased losses due aerodynamic drag and reduced Isp of engines. We also don't have ideal engines (weighting nothing and capable of instantly execute the maneuvers) thus resulting in further losses either way. And all that assuming heating will not be an issue. And it will be different for each different craft you launch. So, the most efficient way is probably something along a Hohmann Transfer right after a quite aggresive Gravity Turn. But I guess most players will not consider trying to find that precise trajectory as the most efficient way to expend his/her game time. Considering the chance of being too aggresive, maybe doing a regular gravity turn and a Hohmann Transfer once in space is a better idea.

@Ariggeldiggel I downloaded the craft file, and I was able to use it. I ran a few tests on the craft, launching it and trying both manually and using MechJeb to get this thing into orbit. And even MechJeb couldn't do it. The simplest explanation here is that your lifting stage just doesn't have enough power to get this thing to orbit. The craft starts with a TWR of 1.05 at liftoff, which is barely enough to get off the ground. In fact, it took several seconds to get off the ground, which just burned fuel. Both manual flying and using MJ, I started the gravity turn at 100 m/s, and this is where things really went wonky. For myself, flying manually, I couldn't get this thing above 20km without it flipping. I checked all the parts, and I checked the fuel drain, and all that. It simply would not stop flipping. So I added a fairing to the top of your craft, just above the reaction wheel you've got in the middle of this thing. And then it couldn't fly because it was too heavy. The fairing gave it aerodynamics, which it desperately needs, but it was just too heavy. I let it run for a few seconds, and it eventually got off the ground...but wasted half the fuel in the first stage to do so. After that happened, I removed the fairing and launched this thing with MechJeb's Ascent Guidance. Again, TWR at launch is 1.05, and the gravity turn was started at 100 m/s. Which, coincidentally, was at about 3500m. You should reach 45 degrees somewhere in the neighborhood of 10km, but even MJ didn't hit that until about 19km. And at 20 km, she started to turn over 45 degrees. Which isn't all that bad, but with TWR was still under 2 at this point. At 22.5km the first stage burned out and the boosters on the side ejected. TWR dropped to 0.6, and for the rest of the flight it never got above 0.65. She reached an Ap of 38501m, at which point she started to come back down to Kerbin. Even with MJ flying, it would not get into orbit. My first suggestion is to redesign the lifter stage and add some thrust/power there. The craft simply does not have enough juice to get off the ground and get to orbit. My second suggestion is to ask why you have a large reaction wheel in the middle of the craft? Normally, reaction wheels (from what I've seen) go near the engines to use their thrust to help with turning. I'm not saying where you have it is wrong, I'm just questioning why.

You would need an autopilot mod, such as Mechjeb, or Gravity Turn

Hello! So, this may sound nooby or such. However, I have been having problems with rockets that are PERFECTLY stable on ascent. When I start the gravity turn though, even my most perfectly stable ships start tumbling uncontrollably. Not only are these rockets stable, they have worked on previous launches, and now, even if I just nudge the rocket into a slight angle, it falls over and tumbles uncontrollably. Even rockets I have used dozens of times. Anyone else having this issue???

Was there any change to the aerodynamics or pod torque that I'm not aware of?

The optimum trajectory is: as flat as possible. There are only two reasons for it not to be perfectly horizontal on lift-off: you cannot accelerate hard enough to go fast enough to reach orbit before you start falling down to the ground again you cannot get streamlined enough to avoid huge drag losses in the lower atmosphere. The answer to issue 1 is essentially the same as on any airless body: you start going upwards to clear the terrain, then burn as horizontally as possible while maintaining a minimal positive vertical component to your velocity. In other words, head for the horizon on the navball while making sure that the prograde marker stays very slightly above it. The added complication of having an atmosphere is that your ship has drag, and that drag is probably (assuming normal ship design) going to be lowest when you're pointing nose directly forward and engines directly rearward. Therefore your only efficient solution is to be pointing prograde at all times. Drag also affects control over the ship, and you probably also have best control (assuming normal ship design...) when pointing exactly in the direction of travel. And this brings us to neatly to issue 2: you want to get out of the lower atmosphere quickly, while always pointing in the direction of travel (especially while in the lower atmosphere...). Therefore you have to start vertically and make a gradual turn to horizontal as soon as possible but slowly enough to get out of the thick atmosphere. That compromise: "as soon as possible but slowly enough to get out of the thick atmosphere", is your gravity turn. So, the gravity turn has to be: perfectly smooth (therefore minimising drag and control problems), i.e. facing prograde exactly at all times, at full power at all times (otherwise you could use less engines, saving weight), ideally, at lower altitudes, executed at a speed not exceeding the terminal velocity of your ship at that point (since on reaching terminal velocity, drag = 1g, rising exponentially: you'd lose less by climbing for a bit longer rather than trying to climb a bit faster). This is really only an issue for the first few mostly-vertical kilometres. Exactly what the gravity turn looks like will depend on your thrust-to-weight ratio. A high TWR means you reach orbital velocity faster. Therefore the gravity turn has to be finished quicker - which means starting it more agressively off-prograde or launching at less than 90°. Therefore you end up going a lot faster in the lower atmosphere and losing more energy to drag (converted into a lot more heat on your ship's skin). A low TWR means that the gravity turn has to be much more gentle. At the lowest feasible TWR, your gravity turn only comes to an end when you reach orbital altitude: you burn constantly from lift-off to orbit circularisation. You lose less to atmospheric drag and much more to gravity losses. What you lose on fuel, however, you more than make up for on cheaper and lighter engines. And finally, to find that best trajectory, one of the easiest tools to use is available in vanilla via the map: time-to-Ap. On lift-off, time-to-Ap is necessarily zero and rising. It therefore doesnt help much as you try to start your gravity turn right. However, it becomes a very good indicator of efficiency when you're at around 8-12km altitude, 45° inclined to the horizon. At that stage, time-to-Ap should be around 30s or 40s or so, climbing slowly before stabilising, then remaining that way until you're nearly in orbit. The lower your TWR, the higher this number has to be. For a low TWR ship, you need to stabilise at around 50s. For a higher TWR ship, at 40s or less. Maintaining prograde lock and this time-to-Ap should get you very efficiently to orbit. And conversely, if you have a low TWR and time-to-Ap starts falling below about 40s or 35s, you know that you've messed up and are losing vertical speed too fast. It's only recoverable (if at all) by aiming a lot more radially out, meaning a big loss of efficiency.

I'd prefer at least 200 or 300 m/s for docking then. As for low TWR, what it means is that: 1. if I try to launch vertically with a standard gravity turn, it takes a lot of time to build up vertical speed - during all that time gravity is pulling down and costing delta-v. 2. If I use my plane ascent profile, I lose slightly more delta-V to drag. However, I cans till get going quickly as the wings help provide lift to keep the SSTO in the air, while the engines provide half vertical and half horizontal thrust. 3. TWR is really only an issue during the earliest parts of the ascent, as when the craft burns off its fuel it becomes much lighter. As for wing placement, the center of lift is where it should be on a good plane. It's slightly below the center of mass so the wings can sort of shield the fuselage, but the plane flies well. The plane is balanced so that the center of mass does not shift when fuel drains, like a jet SSTO, and there is enough wing area to not be too much of a brick. A fighter jet it is not, however.

Your gravity turn is SUPER late. You don't start the turn until you're already going over 100m/s and barely even try to turn until you're well past 10km. If I had to guess, you learned that either from playing before 1.0 or from watching videos from before 1.0 on how to do a gravity turn. Try this instead: At 50 m/s turn 5 degrees East so you're at 85 degrees East on the navball. When your Ap (Not altitude) is 5km, bring that down to 70 degrees East. When your Ap is 10km, turn 60 degrees East. When your Ap is 15 km, turn 50 degrees. When your Ap is 20 go to 40. When your Ap is 30 go to 30. When your Ap is 40 go to 20. When your Ap is 50 go to 10. When your Ap is 60 go to 0, and leave it there until your Ap goes to your target altitude. I like 80 or 100 usually. The whole time you're doing this, throttle down if you either see heat (flame is fine, only slow down when things start getting heat gauges) or your time to Ap goes over 60 seconds. A good gravity turn does not shove the Ap way ahead of the craft. Note: Throttling down is generally bad and if you're throttling down a ton, redesign your craft to just not have so much power at those stages of flight. This is not the "best" but it's pretty darn good and gives you an idea of what you should be shooting for instead of what you're doing. Also, I assume by "up" you mean "South" and that's semi normal. Any small deviations early on tend to get worse and worse as you fly. It's far less noticeable when you turn more strongly as I did above, and to correct it, you just need to "break the arm the other way" and aim a bit North until the prograde marker is back where you want it.

Taking a gravity turn angle of sixty I still ran into the same problem.

Looks like you are on a very steep ascent, this means you are moving quite slowly when you get to apo. I think you need to be more aggressive with your gravity turn to stretch out your arc. This will give you a higher velocity at apo and make it easier to circularise.

Are you attempting to get into orbit with a single burn from launch? If so that is quite hard and I think what is happening is that your node is going to need an element of anti-radial to swing your orbit circular and doing this means you are spending lots of time and DV in the atmosphere which drags down your periapsis. Because Kerbin is a fairly small celestial body I normally break launch into orbit into 3 parts; 1) Launch and begin your gravity turn to get a ballistic arc until you are a bit over your target apoapsis (the reason for this is also to account for atmospheric drag) and stop burning. 2) Make a node a few seconds before apoapsis and then just add prograde until you get your required periapsis. 3) That burn (we call it circularisation) should then put you into your desired orbit.

So is there a table somewhere that shows altitude verses speed and gives an indication of when it is best to start your gravity turn after launch? I hear some say 30k is the best altitude and some say 40k. Some say it depends on your craft. Unless I\'m mistaken, the true factor is your speed. If you have a lot of speed then you can afford an early gravity turn but if you\'re going slow then you\'ll have to reach a higher altitude so the atmosphere doesn\'t pull you back down. Is there a \'optimum curve\' to work this stuff out, assuming a constant target altitude? Cheers.

Hi all, Been playing for a while. I tend to design my rockets using the same general approach since I've found something that works. My designs seem to work fine with the 1.25m rockets but when I get into the bigger rockets I really have trouble. The way I like to launch is to accelerate directly upward to about 100m/s with SAS on and then do a 5-10 degree eastward pitchover. I then turn the SAS off and allow gravity to pull me through my gravity turn, adjusting throttle to keep my TWR ~1.5. Once I hit about 35,000m I turn the SAS back on and pitch over to full horizontal acceleration. On some of my 1.25m rockets this works beautifully allows me to fly a smooth gravity turn all the way to 80-100,000 meters altitude and puts me in a nice 0 degree inclination orbit. On my bigger rockets I have problems with persistent yaw and sometimes roll during the portion of the gravity turn when SAS is off. Attached is an example design I've been having trouble with. Basically it starts to yaw at about 10,000m and puts me into a highly inclined orbit unless I leave SAS on and fight it all the way to orbit. I've confirmed COT is midline and CoM is ahead of COL. I've tried more fins, less fins, fins with and without control surfaces with no apparent affect (though I did notice that when I had control surfaces they seemed to be fighting the engine's thrust vectoring and it steered better without control surfaces). I've tried every conceivable symmetry of fins. At first I was having trouble with the rocket pointing straight up in flight (basically partway up around 10k meters it swings like a pendulum and starts flying straight up). I've never figured out the cause exactly of this problem conceptually but I encounter it commonly with my rocket designs. It seems some how to be like the reverse of flipping. Adding fairings to complex payloads seems to solve it. Then I was having trouble with the rocket flipping so I changed the fuel prioritization to burn the posterior tanks first followed by the anterior tanks and this was solved. Nonetheless the northward yaw persists and I can't think of anything else to try to fix it other than scrapping my design. I don't mind starting over but this seems to come up again and again and I'd really love to understand what is happening here. Thanks in advance. Screenshot **Update** Thanks all for the many responses. I have done some more extensive testing with very little success so I figured I'd report the results of some experiments. 1.) Tried resetting trim. Trim was already zero'd (flying with keyboard not joystick so no dice). Tried trimming out the yaw. Too finicky. 2.) Tried removing the side booster fins. Tried more fins, bigger fins, w/ and w/o control surfaces. Nothing consistently made a difference. Enough fins would make it fly straight but then it couldn't be steered. 3.) Adjusted the fairing to cover the knuckle in the fuselage. This got rid of the vertical stability issues (flipping, penduluming) but didn't fix the yaw/roll problems. 4.) Got rid of the asymmetrical fuel lines. This did reduce the torque on the stages. 5.) Carefully removed one part at a time to try to figure out where the S0 and S4 torque in KER is coming from. Guess what, it is coming from the engines themselves. 6.) Tried gimble locking the bobcat and steering with control surfaces. Steers better in SAS but no change to the problems when SAS is off. 7.) Switched to a skipper (in spite of the size mismatch) thinking maybe it was the bobcat. Slight improvement? Not enough to matter. 8.) Tried stabilizing the side boosters with different configurations of struts. Current thought: could there be inherent torque from the engines and my rocket is just too short thus doesn't have enough of a lever for my fins to counteract the torque? Tried switching to a skipper and adding two additional of the tall 1.875m fuel tanks. And it's...better. Still yaws to the north and rolls a bit but it can fly all the way to 35km when I reengage my SAS while only accumulating a few degrees of inclination. Of course it is way more DV than I need for this payload. Current Added query - the reason the original was so short is that the bobcat doesn't have enough thrust to lift more central fuel tanks since it still has a full fuel loadout after the side boosters drop because of the asparagus staging. Is it just not viable as a core stage engine with asparagus staging? **Final Update** See my reply to OHara below. Here is the final design. TL;DR: - Fuel lines in radial symmetry introduced asymmetry. They were functionally unnecessary - Rocket was too short - Payload was too draggy - Side booster fins were exaggerating any asymmetric forces that developed during flight - Bobcat has slightly asymmetric thrust, consider reserving for very stable rockets and/or using SAS - 4 symmetric fins as far to the rear as possible on the center stage, with control surfaces worked best

Well, sure, if you're doing the launch-straight-up thing. (Note that when I say "launch straight up", I'm also including your description of doing a little-bit-of-a-gravity-turn, since you're not accomplishing much difference by doing it just a little. Unless you're already going nearly horizontal by the time you leave Kerbin's atmosphere, you're missing most of the benefit of the gravity turn. For maximum effectiveness in getting to Jool, you want to be traveling Kerbin-prograde at the time you leave Kerbin's SoI. So if you're launching straight up (or nearly so), naturally time-of-day makes a big difference because that will affect the direction you eject from Kerbin. On the other hand, if you do a gravity turn and then circularize in orbit, you can set a maneuver node at your leisure, so that lets you get everything lined up just so and it doesn't matter what time of day you launched the rocket. On the third hand, if you do a gravity turn, and you're relying heavily on SRBs so you can't circularize and just burn until you eject, then yes, it would once again matter what time of day ...though in general the "right" time of day would be different from a straight-up launch. For a straight-up launch to go to Jool, the right time of day would be just before sunrise. The more you curve, the earlier you'd launch. For a gravity-turn-with-horizontal-departure-from-atmosphere, you'd want to launch a bit before midnight if you're not circularizing. Actually, if you're launching straight up (or doing just a slight turn, so you're still going mostly vertical when you leave atmosphere), then fighting gravity is exactly what you're doing. You're avoiding cosine losses by following prograde, but you're not avoiding gravity loss. The way to stop fighting gravity (and avoid the gravity loss) is to do a harder gravity turn so that you're spending most of your dV going mostly horizontal. If I'm reading your screenshot correctly, you're basically launching on 56 Kickbacks all at once (seven of them in a row, with 8-fold symmetry), with fairly neglible mass besides those (since the Kickbacks alone will be 1344 tons). I assume you've got their thrust cranked up all the way to 100%, which is the default. That would give you a TWR on the pad of about 2.5. If you're launching with a decent gravity turn, you can get by with a considerably lower TWR, and use additional staging to save. For example: Suppose you set up the staging (and add some radial decouplers) so that instead of firing all 7 Kickbacks in each row straight from the pad, you fire 5 of them. In other words, your rocket would be built with 8 decouplers around the central core (the way it is now), then each row would have 2 Kickbacks, then a radial decoupler, then the remaining 5 Kickbacks. With a scheme like that, you still have 56 Kickbacks, but you're not using all of them at launch; you'd only be using 40 of them off the pad. This would give you a TWR of 1.8, which is plenty good enough if you're doing a gravity turn. You'd nudge it to start the turn practically right off the pad. By the time the first set of 40 Kickbacks burn out, you'd already be going fast, high in the atmosphere, going mostly horizontal. When those first 40 Kickbacks burn out, you'd stage them away and then fire your 16 remaining Kickbacks, sending you on your way. You don't have to do the above, of course.... but you'll find that if you do, you'll get a lot more bang for your buck. Not only will you be saving scads of dV due to not fighting gravity, but you also won't be lugging the dead weight and drag of those first 40 Kickbacks all the way to space (that's significant-- that's 180 tons of dead weight you'd be shedding), and as an added bonus, your final 16 Kickbacks will be doing all their thrusting in a near-vacuum where their Isp is significantly higher than it is on the pad.

I did some testing with the turn shape. Turn start was 8 km and turn end at 50 km for all launches, with target orbit either at 100 km or 400 km. Testing was done with a pretty simple 5000 Dv (atmo) rocket and with Corrective Steering on for all launches. TWR in the lower atmosphere was mostly between 2.0-2.5, dropping to 1.5-2.0 in the middle (for 60 seconds) and rising back to 2.0-3.0 in the upper atmosphere. Bolded lines mark the most effective launch trajectories: Target orbit at 400 km: With 33% trajectory the remaining Dv at the end of the gravity turn was 1030 m/s. With 40% trajectory the remaining Dv at the end of the gravity turn was 1092 m/s. With 50% trajectory the remaining Dv at the end of the gravity turn was 1124 m/s. With 66% trajectory the remaining Dv at the end of the gravity turn was 1100 m/s. Target orbit at 100 km: With 33% trajectory the remaining Dv at the end of the gravity turn was 1281 m/s. With 50% trajectory the remaining Dv at the end of the gravity turn was 1335 m/s. With 66% trajectory the remaining Dv at the end of the gravity turn was 1264 m/s. (When the apoapsis was raised further to 400 km from the 100 km periapsis, the craft had 1071 m/s Dv remaining at the end of the maneuver, meaning that launching directly to a target altitude of 400 km was more effective than first reaching a 100 km orbit.) Tweaking the turn end altitude: Considering that 50% turn shape gave the best result in both scenarios, I tested the effect of changing the turn end altitude to 70 km for both launch scenarios: With 50% trajectory the remaining Dv at the end of the gravity turn was 1107 m/s - compare to 1124 m/s Dv remaining when the gravity turn ended at 50 km. With 50% trajectory the remaining Dv at the end of the gravity turn was 1431 m/s - compare to 1335m/s Dv remaining when the gravity turn ended at 50 km. Conclusion: The difference in fuel consumption with different turn shapes is ultimately quite small, with changes in the turn shape saving less than 2% of the craft's total Dv or between 5-8% of the craft's remaining Dv at the end of the gravity turn. The effect of changing the gravity turn end height from 50 km to 70 km was inconsistent, but seems to favor ending the gravity turn lower in the atmosphere if your target orbit is not much above the limit of the atmosphere. With a higher target orbit a longer gravity turn is marginally more efficient. It would be interesting to test the effect of the turn start altitude together with different turn shapes, but with no time warp available during burns it's way too time consuming for me to bother testing it further, given that the differences found in these tests proved to be so small (although not insignificant, depending on your mission and its margins of error your craft has for pulling it off successfully).

As folks have observed, a lot depends on your preferred play style and design types. There are many different "right" (i.e. efficient, effective) ways to get to orbit. Unfortunately, there are many times that number of wrong ones. So here's what I do in my own gameplay-- not saying that this is any more "right" than any other means, just that it works well for me and is totally consistent with minimal guesswork. I never do this, myself. If engines are ever running at under 100%, that means wasted efficiency. If I don't need the full power of my engines, it means I'm carrying too much engine and am wasting dV due to hauling too much engine mass as dead weight. And as long as your launchpad TWR is no higher than 2 and you're reasonably streamlined, it's always most efficient to go at max throttle, because gravity losses far outweigh aero losses. The only time I ever launch at under 100% is if I have the rare occasional "freak" vessel that's ludicrously un-streamlined due to needing to lift a really awkward payload, or something. However, since you were mainly asking about repeatability rather than efficiency per se, I'll say this: I've found that it really, really helps to have a rigidly consistent launchpad TWR. Rationale: As long as all of my spacecraft have the exact same TWR on the launchpad, that means that my initial pitch-angle for the gravity turn will be the same. So holding the TWR constant means that I take the guesswork out of the pitch angle. Myself, I like a launchpad TWR of 2. No particular reason, that's just how I like to fly. That's about the highest that's practical; anywhere from 1.3 to 2.0 can work (though that would entail a different design strategy, and the lower your TWR the less initial pitch angle you'd want). Yes, the TWR will change as the rocket ascends (i.e. it climbs during each stage, then drops when I move to the next stage), but I've found that in practice that matters very little. I just design my rockets so that they have a consistent launchpad TWR, launch at 100% throttle, and stay at 100% during the entire boost phase until Ap gets where I want it. I don't do any of this. There's no wait, there's no unlocking of steering, and there's no "gravity turn speed" as a variable. And "angle" isn't a variable either, because I always pitch by the same angle because I always launch at the same TWR. What I do is this: Launch Immediately pitch east. I mean, the instant it lifts off the pad. The angle is fairly small, and depends on the TWR. It takes a little bit of trial and error to find the right angle initially... but if you always launch with the same TWR, then once you find the right angle, you just use it all the time. Also immediately, set SAS to hold . That's it. That's all there is. No steering, that's why it's called a "gravity turn", because gravity is doing the steering for me. I just hands-off the controls except for staging. Yup. Exactly what I do too, no differences there. Well, I don't do that, mainly because I don't use kOS or any autopilot mods. What I do is just wait until the craft leaves atmosphere, then go to map mode and drop a maneuver node right at my Ap point, with enough dV to circularize. Then the burn timer on the navball takes the guesswork out of when to burn. If you're using an automated tool that needs to run on a script, I understand that that might not work well for you. However, I think you can take the guesswork out of step 7. If the script knows the apoapsis, and knows the current and desired periapsis, then it's a fairly simple bit of math to calculate the amount of dV you'll need. A bit more simple math (based on your TWR) will tell you how many burn seconds you need. Start the burn half of that time before Ap, and there you go. So, to summarize: You mention the following variables in your OP: Target Ap and Pe Target TWR Pitch angle Gravity turn speed Seconds before apoapsis #1 will obviously be different on every launch, since that's your target orbit and will depend on the mission. But the above technique eliminates basically all the other variables. TWR goes away, because it's always the same, and throttle is always at 100%. Ditto pitch angle. "Gravity turn speed" simply isn't a thing, and "seconds before apoapsis" is a trivial bit of math based on Ap, initial and desired Pe, and TWR. Does that help?

Gravity loss is a far bigger concern than drag for "reasonably" aerodynamic rockets. It sounds like you could be more aggressive with your gravity turn, especially with a starting TWR of 2.0. While you can get into orbit more efficiently in terms of ∆v, you probably will be better served by not having so much dry mass in engine weight. I have found that a starting TWR around 1.3 to work best for me. Have you experimented with different launch profiles? I have done some experimenting and found a fairly aggressive gravity turn to work best.

Which TWR is "right" depends on a lot of factors, including how you like to fly and what sort of payload you have. In general, you never want to go higher than 2.0, and usually no lower than about 1.2. The optimal rocket design changes quite a lot based on the TWR. If you have a very "draggy" payload (which most of your rockets look to be-- you've got a lot of flat surfaces, these are not very aerodynamic), then usually a lower TWR tends to work better, at least for the first several kilometers of ascent. This is because a high TWR causes you to go too fast when you're still too low, so you're wasting all your fuel trying to shove a draggy thing through thick soupy atmosphere. Taking off a bit more slowly, to keep drag down, may help. (Normally, the solution people go for is to make their craft more aerodynamic and then raise the TWR, which is more fuel efficient. But if you have an awkward payload that has to be draggy, you may have better luck starting off a bit slower.) In general, the most efficient (and stable) ascent path is called a gravity turn (that's a good term to search the forums for, if you'd like to read about it). The basic idea of a gravity turn is that you nudge the craft just a little bit eastward, practically right off the pad... and then you just set SAS to hold all the way up. No steering needed, you're just going all the way, as your ship gradually and naturally pitches farther and farther eastward as it climbs. Just how much of an initial "nudge" you should give it is the tricky part, of course. There's no one right answer, because it depends on your TWR and how aerodynamic you are. But there's a fairly straightforward way to find out: Launch to the pad. Take off! Immediately upon lift-off, pitch a small amount eastwards. (Just take a guess, as to how much.) As soon as you do that, set SAS to hold Don't do any further steering. The only time your hands should touch the controls is to jettison empty stages when the time comes. Take a note of what your trajectory is like when you reach an altitude of 10 kilometers. Specifically, how fast are you going? what angle are you pitched at? Ideally, you should probably be pitched roughly 45 degrees at that point, and traveling something like 300-400 m/s. If (at 10 km) you are going too fast, or pointing too vertically: This means you didn't pitch quite enough in step 3. Revert to launch, and repeat, and pitch it a bit more this time. If (at 10 km) you are going too slow, or pointing too horizontally: This means you pitched too much in step 3. Revert to launch, and repeat, and pitch it a bit less this time. Keep repeating steps 2 through 7 until you're going about the right speed and angle when you're at 10 km. At this point, you're in the pipe and probably going to space, as long as your fuel holds out. The above is only a very rough rule of thumb, but I've found that it works pretty well for most people most of the time, and at least is a pretty good starting point for flying your ship. Really don't do that. Very very fuel inefficient, and will waste scads of dV. That's also very inefficient, and likely to cause control problems, as you have no doubt discovered. The moral of the story is: You want your rocket to be traveling at all times. Never point more than just a couple of degrees off while thrusting, if you can help it.

ok...i made a video of me flying a straight-to-circular orbit and reaching a previously targeted altitude with a gravity turn... this also shows a new type of solid booster i made which burns weaker for longer (more realistic).... but the main thing is that it demonstrates how it's possible to perform the direct-to-orbit launch and become circularized at the target altitude before 12 minutes in flight i hope it's possible to learn a thing or two from it.... not sure if i explained it well enough (i was kinda busy with the flying and all) : :cheers:

Thanks! . o O (hmmm.... interesting...) It pitches over more aggressively than I do. (Which is not surprising, I like getting out of the atmosphere early!) What I didn't understand at first is that it doesn't throttle up after staging: apparently it doesn't know about the TWR of the stages and just keeps the throttle setting the same until the AP time decreases to the lower limit, then it increases the throttle to what is needed to keep the AP time constant. Again we see that the difference between a "perfect" gravity turn and a "meh, good enough" gravity turn is very small. So there is IMHO little use in trying to get ones strategy perfect. (In contrast a way "too flat" or way "too steep" ascent will cost you significant dV!) And as already discussed: getting of the launchpad with a too high TWR will cost you dV, either in gravity losses (too steep ascent) or in atmospheric drag (matched gravity turn that then stays too long in the lower atmosphere) or by lugging around an oversized engine that you aren't using (if you throttle down from the very beginning). Well IMHO I won(TM) if you got a better understanding how the launching a rocket works and what to look out for to improve your rockets and ascent profiles.

With the science update I learned to build my rockets small. With the contracts update I am learning to build cheap. Which leads to boosters. Lots of boosters. (Jebediah style, so to speak) Sometimes rockets and/or payload aren't small. Currently I am building a fuel shuttle to be used on Mün and Minimus. Two of the biggest tanks, a 12-ring of nuclear engines, landing abilities. Of course, it lifts off empty besides the 12 tanks for the radial engines. It is a tanker to be refueled on Mün. No sense lifting up full tanks. But still, this beast has more than 100 tons on the launch pad. The first stage consists of a big bunch of the large boosters. Gets that thingie basically to space. But I can only get it up straight. That thing won't TURN. I can't for the life of me get it to do the gravity turn. I tried putting a bunch of SAS modules on it. No use. I tried RCS in different configurations and in different places. Tried the "new" RCS-outlets that run on liquid fuel. Last try I had 16 of them. Still, that beast does not turn. It gets to about 10 degrees off the straight line and no amount of RCS or SAS usage gets it to turn further. I do have Wings on that vessel. But still, no use. So I get it to 75 km. More or less straight up. Boosters burn out, get discarded, vessel turns just fine (a bit sluggish, of course). But the circulation burn is about 2000, which takes forever with the nuclears and doesn't work at all, because I get into the atmosphere again. TWR of the payload is not so bad considering that the vessel is almost empty. 0.6. So, anyone any idea how I can get this beast to actually turn east? Hm... maybe put some liquid engine in the middle of my booster pack? The boosters accelerate the rocket well beyond terminal velocity. (Not too much. Just barely fireworks... What else can I do? Put lateral engines on it and disable them once the turn is complete and the solid fuels are discarded? Deliberately put the vessel off balance? Hm... that might be an idea....

nope, no RO or other tweaks. after reading all the stuff RO does, i decided some of that was too annoying to keep track of. as for other tweaks, I decided to go rss to increase difficulty, balance tweaks would defeat the purpose. The rocket is the one here As it is, it keeps crashing the pc because it's too big and complex. I know that with one less stack of boosters the pc can handle it, but i missed orbit by some 200 m/s. I'm trying to see if I can optimize the ascent profile to recover those 200 m/s. It's a big asparagus stack, it starts with twr 1.8 and it gradually goes down as more boosters are discarded. Last stage is twr around 1, with 2000 m/s. Everything before that is no less than 1.4 I don't want to use mechjeb or anything. plus, seeing as how mods increase lag and my pc is already crashing, i don't want to add mods just on principle. Normally, I would have gone for a more horizontal profile. Especially with a rocket so big, aerodinamic losses are less than gravity losses - despite the draggy payload. However, a flatter ascent profile means that I will level up early. This can easily be countered by pointing upward of prograde just enough. But that beast is already very draggy - even on a purely vertical ascent, maxQ is around 30% of weight; pointing above prograde while in the lower atmosphere would increase drag immensely. Which is why I was reluctant to do it. Also, I've seen real rockets and they go straight up for several km before starting the gravity turn, so I figured it could be the best way. I will have to try that, though. If nothing else, because I already spent 2 whole afternoons trying to launch that monster and getting the pc crash every single time. Once I even reached the second-to-last stage, wasn't even lagging so hard anymore, and then it still crashed.

I've said it before (in other threads) but its worth mentioning again: In an ideal gravity turn, there are no* sideways forces at all! *Except for the initialisation of the turning (if it were designed to point directly upwards, as rockets are by default when built in the VAB), the gravity turn is like dropping a broom balancing on your fingertips, very gradually, from vertical to horizontal. The sideways imbalance results in the actual, very slow, rate of turn which occurs as it goes over. In theory you could turn off SAS and let it do its own thing. Indeed, people have demonstrated on YouTube this is possible. In reality, the closer you can get to this ideal, the less the sideways forces from whatever source, which need to be countered by SAS reaction wheels and/or gimballing engines. KSP doesn't help with its keyboard controls which bang in control inputs at either 0% or 100%, and some engines are very jerky with their gimbal (Thud) so its something you need to work around. But its possible that a beautifully designed rocket can be misflown and go bonkers; or a complete dog is launched in an apparently perfect ascent by an expert (or a good autopilot).

Hi all, I feel I've started to get the hang of my rocket designs from reading some good posts on the forums as well as from lots and lots of trial and error (feels like the scene from October Sky). I still have some challenges with the in-atmosphere performance of some of my rockets that have been pernicious and I was hoping some of you experienced designers could enlighten me on some more theory. For reference, I am playing vanilla KSP current release career mode and have all the 90 science parts unlocked except the aircraft tree with a few 180 science parts. With some help from the forums I've basically solved my "flippy rocket" problem. What has helped me as far as design principles are: Rockets fly in atmo like a badminton shuttlecock. You want mass in the front, drag in the back and for stability you want some distance between them. So for solving flippy rockets you can: 1.) Move your center of mass forward. This seems to be difficult as generally your payload is your payload and the basic layout of the booster rocket is often driven by the TWR of the engines you have access to. The main helpful tip here for some rockets has been turning off fuel consumption in my most anterior second stage fuel tank and releasing the fuel only after the after tanks have been nearly exhausted. 2.) Don't fly too fast. Throttling my LF engines to keep TWR around 1.5 has worked well for me. Knowing that I can throttle down SRBs in the vehicle assembly has also been helpful when working with lighter payloads. 3.) Add drag to the back. For me this has been the most helpful (though still feels like the least elegant solution). Sometimes you just need MOAR fins at the back of the rocket. I would love any other tips to help with this problem that are more elegant than MOAR fins, but in general, my problem with rockets taking a nosedive mid gravity turn have disappeared. Unfortunately another trickier problem has cropped up. I've managed to solve it eventually for my various rockets, but I haven't been able to figure out the principles behind why it is happening and how to prevent/fix it. The basic probably is that mid gravity turn, the rocket suddenly swings like a pendulum and points straight up. I feel like this may be related to the "flippy rocket" problem, the two solutions I've found on specific rockets have been adding MOAR fins on one rocket and using a fairing to cover a very draggy payload on another rocket (to much drag on the anterior part of the craft??). Like I said, I would love some help understanding the "why" this happens so I can avoid it in my designs and fix it without so much trial and error (I admit, I play hardcore once I get my flights into space, but I do use the revert flight option if I have problems in atmo and consider it the roleplay equivalent of the simulations and wind tunnel testing one would be able to do in real life). Here is an example of the rocket where I solved the problem by adding the fairing. (Can't figure out how to upload images, hopefully can access through the links). Original design without fairing Original Design penduluming during gravity turn Successful design with fairing For reference if needed, my typical flight profile is launching 90 degrees eastward with SAS enabled. I make a 5-10 degree gravity turn once velocity exceeds 50m/s and turn off SAS once it stabilizes (usually by 100 m/s if I fly well). I then adjust my throttle to maintain TWR ~1.5 until I reach 35km and reengage SAS, adjust course as needed to circularize as quickly as possible w/ apoapsis between 80-100 km

So, when I'm doing a gravity turn. I always have SAS on, I know how to get into orbit and do a gravity turn. Though, recently when I've been doing a gravity turn. My pro grade pitches slightly up, note that i'm not giving any input for it to be doing that. Not sure why, and like I said. I've done this so many times before, and i've done it really good. Though now that I do a gravity turn, I have this problem. I usually use stock KSP rockets as I'm not very creative. And if its built by the KSP team, its impossible to be a design flaw. The only thing I add onto the stock ksp rockets is the mechjeb case which I usually place at the command pod. I'm not quite sure as to why this might be happening. I'll be sure to answer any questions you guys have!