What does your ascent profile look like?

[Pthigrivi]

2 hours ago, Meecrob said:

Wait? The tutorial is literally setting up players to be inefficient? Straight up to 10k? I could be wrong, I didn't do the tutorial, someone mentioned it upthread.

I double checked and yes, the gravity turn tutorial says to fly straight up and begin the gravity turn at 10k (including wildly overpowered twr booster stage.) Now, granted, its designed to be simplified for newbies and some consideration needs to be given to controlability at high speeds at low altitudes and starting at TWR 1.5 creates legit issues in dense atmosphere (hence many of us doing a faux max-q throttle-down.) To their credit the narrator also explicitly tells players this is not optimal and as they get better they can launch more efficiently. Still, I think the demo vehicles should be reasonably optimized as a means of guidance and they should tell players to start their turn at 6-7km and do so more slowly. This same tutorial also introduces the navball to players for the first time, which should probably be its own tutorial and come a bit earlier. 

[regex]

4 hours ago, Meecrob said:

just want to re-iterate that everything I am saying is for people looking for tips, I didn't mean to hijack this thread. If all you fellow board members want to do is compare numbers, I totally get that. Sorry, lol

I'm pretty sure this thread already has some good tips for newbies on several ways to get to space, without doing something dumb like the old souposphere launch. There's no reason it can't serve multiple purposes.

[The Aziz]

2 hours ago, Pthigrivi said:

(hence many of us doing a faux max-q throttle-down.

Aah! But here's the thing. It's not about the TWR or time, or physical stress, but about drag. At least it used to be in KSP1, feels like aero was slightly less forgiving, but here's why: KSP1 had this pretty aero overlay with colorful arrows, showing lift, drag and whatnot. And the drag was important because, while doing manual gravity turn, you'd have to steer slightly off prograde, and that generates drag from the side of the rocket. But with higher Mach numbers, that drag arrow was longer, hence it was much much easier to flip. So I'd do throttle down to shorten that drag arrow and make the rocket less likely to flip while flying manually.

[Dakitess]

I had a whole article about that, with some diagrams and abacus to be able to get some proper real Gravity Turn based on the TWR at liftoff, considering that it's design is OK-ish.

We spent something like a hundred hours coding an empirical method to plot the very best PitchOver Speed and PitchOver Amplitude, with some automation and some variable, and then coding a whole Perfect Gravity Turn kOS code, quite better and more versatile than the Gravity Turn mod for instance.

Unfortunately, this article is lost at the moment, we are transiting from a website to another one.

I can anyway provide this abacus : 

It shows the PitchOver Speed trigger and the PitchOver Angle amplitude, relative to the LiftOff TWR.

How it reads : for a given TWR, say 1.5 which is quite a "normal" TWR, you can Pitch Over at 14m/s and 65° (from the horizon, so 25° from the vertical), or 62m/s and 85° (so 5° from the vertical). Both would perform quite similarly, BUT the lower the amplitude, the better : you don't want to pivot 25° abruptly at high speed when you can do otherwise and smoother : it would be unaesthetic, dramatic for the structure even if KSP would allow it, and can lead to loss of control because of the AoA, even if at those speed and with gimbal, it should be fine.

You'll say : it depends on the rocket, yeah, of course it does ! It depends of its Solid to Liquid fuel ration, the TWR of the upper stage, but also the Sea Level to Vacuum ISP ratio, the Stages mass proportion, etc etc etc. Of course. But you'll find by experience that the very main parameter is the LiftOff TWR, assuming that your rocket has a "normal" configuration : not a crazy large fairing, not an anemic or overpowered 2nd stage, not an unrealistic asparagus mess, etc. Even though it would be a good start and it's easy to spot when a GT is going too low or too high within the first 30s (or even sooner) of a launch

Also : most of these parameters are addressed in the final code, the OptiGT kOS script, which handle many things. It's based on a dichotomies approach but include some shortcuts and clever adjustments, as well as a very very nice GUI ! I would love to get your feedback about it, it's for KSP1 but I'm pretty sure a lot of us are still using it. Don't see it as a cheaty autopilot, more of a Perfect GT finder, to learn how it's doing and develop the "sense", the feeling of a good GT. And it's very very handy when you're optimizing every drop of fuel as well :p

https://github.com/PhilouDS/opti_gt

Anyway, as a way shorter answer to the question : I always, alwaaaaays to the Follow Prograde method, the only good looking GT method :p And with quite some experience, I can perform a perfect GT in a couple tries as well as ensuring that the first one with be "good" at least  It's very satisfying, and it's soooo much more efficient than any other kind of ascent trajectory. Ho, also, never ever throttle down your engines. NEVER. I've never encountered a single rocket launch when it would be preferable. Change your engine if it's too powerful, you'll gain Mass and ISP most of the time. Be aware that Atmospheric drag is WAAAAY over estimated by players, Gravity Losses are the most important one. At least with a proper GT, of course, in follow prograde :p It does not prevent you to do an active GT though : you feel you're leaning too fast ? Hold that SAS button a couple seconds, it will help a lot, especially if noticed during the first 15s of flight !

There is some "key points" that 90% rockets will follow : 25° from vertical at 3500m, 45° from vertical at 8000-10000m, 70° from vertical at 25000-35000m. The very first 2 key points are essential, they can vary, a TWR = 2 will lead to something very aggressive with 45° as soon as you hit 3000m, especially for light sounding rocket, but for 1.4-1.6 TWR, you'll have a good feeling of a GT being too low or two high with theses key points.

[Vl3d]

18 minutes ago, Dakitess said:

25° from vertical at 3500m, 45° from vertical at 8000-10000m, 70° from vertical at 25000-35000m. The very first 2 key points are essential, they can vary, a TWR = 2 will lead to something very aggressive with 45° as soon as you hit 3000m, especially for light sounding rocket, but for 1.4-1.6 TWR

This is not KSP 1 anymore. The heating and atmosphere has changed. If you go "25° from vertical at 3500m, 45° from vertical at 8000-10000m, 70° from vertical at 25000-35000m" you will burn up.

[Meecrob]

1 hour ago, regex said:

I'm pretty sure this thread already has some good tips for newbies on several ways to get to space, without doing something dumb like the old souposphere launch. There's no reason it can't serve multiple purposes.

Yeah, so you are on the same page. I get you like being grumpy, lol

[Vl3d]

3 hours ago, Pthigrivi said:

fly straight up and begin the gravity turn at 10k

This is correct. No turning more than 10 degrees before 10k. I would actually be conservative and say that you should not go more than 30 degrees before 20 km. Never aim for close to 70 km AP. You will burn at 60-70 km and 1800-1900 m/s.

Edited January 5 by Vl3d

[Meecrob]

21 minutes ago, Vl3d said:

This is correct. No turning more than 10 degrees before 10k. I would actually be conservative and say that you should not go more than 30 degrees before 20 km. Never aim for close to 70 km AP. You will burn at 60-70 km and 1800-1900 m/s.

What?  For maybe new players?

Edit: Sorry, I don't men to gatekeep, but I'm sure most of you will agree that "10 degrees at 10k" is not good advice

There are literally the ideal numbers to hit upthread. For a regular rocket...1.4-ish T/W ratio...go by those numbers, do not listen to this person.

Edited January 5 by Meecrob

[Hotel26]

On 1/5/2024 at 4:58 PM, Dakitess said:

you can Pitch Over at 14m/s and 65° (from the horizon, so 25° from the vertical), or 62m/s and 85° (so 5° from the vertical)

First of all, I heartily endorse your methods and reasoning.  This jives with everything I (think I) know.

Would you please check your sentence quoted above, and then also check the color-coding, because I think your pale blue line is the 5-down pitch, which can potentially occur at a lower speed.  Your sentence currently seems to read in reverse that a bigger pitch-down can occur at a lower speed., which is precisely counter-intuitive and counter to what I think you are really intending to say.

Tres bien!!  I have to say.  (I may add more down-thread at a later time...)

Edited January 7 by Hotel26

[Mikki]

I have allways this ballistic shape in mind, its a quarter of an ellipse and not perfectly ballistic but pretty well enough.

And 1.4 TWR is sufficient for me to launch my rockets, too much thrust at start can get you in trouble. And i keep mostly full throttle all the way up therefore.

This is an example of an unpropelled projectile`s ballistic curve:

Edited January 5 by Mikki
stuff and a typo

[Jeq]

I made some tests at KSP 1 and for me best way to launch rocket is to think it being throwable object.

 

1) i try to throw rocket to point at 45km altitude, best way to throw object is certain angle above desired point, i have figured that best for me is to aim prograde direction (not your nose) 68degrees east, until speed is about 250m/s. When speed is 250m/s i aim nose to prograde. I stop burning when apoapsis is at 45km and time to apoapsis allows second twr to make safe ascent. if twr is 1, you want time to apoapsis be at least 60seconds, if twr is 2 then 30seconds is enought. And so on...

2) i let rocket to coast(wait without doing anything) last possible time until i start burning to prograde. Timing is determined about what your TWR for next stage is so you make it in time. This burn i make so apoapsis is over 70km.

3) Circulazing burn happens at last possible time too, again to prograde.

 

For me most important rules are:

You must be at wanted altitude with enought time to apoapsis for second stage.

Keep time to apoapsis as small as possible and this is most efficient way your rocket can make it to orbit.

Any burn away from prograde is waste of fuel.

Any burn away from horizontal is waste of fuel.

 

Edited January 5 by Jeq

[Dakitess]

3 hours ago, Hotel26 said:

First of all, I heartily endorse your methods and reasoning.  This jives with everything I (think I) know.

Would you please check your sentence quoted above, and then also check the color-coding, because I think your pale blue line is the 5-down pitch, which can potentially occur at a lower speed.  Your sentence currently seems to read in reverse that a bigger pitch-down can occur at a lower speed., which is precisely counter-intuitive and counter to what I think you are really intending to say.

Tres bien!!  I have to say.  (I may add more downthread at a later time...)

Totally right, typo haha ! Can't edit, there is new rule (I guess) with a limit edit time... Arf !

3 hours ago, Vl3d said:

This is correct. No turning more than 10 degrees before 10k. I would actually be conservative and say that you should not go more than 30 degrees before 20 km. Never aim for close to 70 km AP. You will burn at 60-70 km and 1800-1900 m/s.

I hope it's not really the case OR it will be fixe ASAP as I won't ever launch this way after such a good experience in KSP1. It would not make any sense, like, at all. No launch will suddenly pitch by 10° at high speed, this is absurd, even for a game.

Edit : misread the Vl3d quote, my bad, you're not saying we should angle 10° at 10km, but rather that the angle should not exceed 10° by 10km. Which I still strongly disagree, of course, it would be a VERY vertical non-Gravity-Assist ascent, very unoptimized, something like 10-15% less efficient than a correct GT. But it might necessary with the actual KSP2 release, did not try it : if it's the case, yeah, I confirm, it's very very bad, but we would have seen way more complaints about it I guess, I did not see anything about it, past your experience.

Edited January 5 by Dakitess

[regex]

6 hours ago, Dakitess said:

 for a given TWR, say 1.5 which is quite a "normal" TWR,

lolwut? I really am built differently, most of my launchers are in the 1.3 range, give or take. 1.5 is excessive.

6 hours ago, Meecrob said:

Yeah, so you are on the same page. I get you like being grumpy, lol

My apologies, that was meant to be encouragement. Offer tips, I think everyone's learning.

[Jeq]

13 minutes ago, regex said:

lolwut? I really am built differently, most of my launchers are in the 1.3 range, give or take. 1.5 is excessive.

My apologies, that was meant to be encouragement. Offer tips, I think everyone's learning.

TWR is what you are willing  to lose. If 1.3 is okay for you then you lose 75% of deltaV each second you burn up.  1.5TWR you lose 66%. and 2TWR you lose 50%. This only affects start of flight tho.

Ofcourse your TWR increases when you burn more fuel but because we don't have money in game then it is probably slighty more better to have more TWR than less.

Edited January 5 by Jeq

[Dakitess]

Yeah 1.3 is really the lowest TWR you wanna have. To suit some RolePlay crewed mission for instance, this is what I do. Otherwise, best performance is around 1.8 to 2.2 depending on the rocket (sounding very aerodynamic tiny rocket can get way higher as an optimum). It really changes everything. Can be hard to find the sweet GT spot though, 1.4 to 1.6 is the easier.

[Pthigrivi]

8 hours ago, The Aziz said:

Aah! But here's the thing. It's not about the TWR or time, or physical stress, but about drag. At least it used to be in KSP1, feels like aero was slightly less forgiving, but here's why: KSP1 had this pretty aero overlay with colorful arrows, showing lift, drag and whatnot. And the drag was important because, while doing manual gravity turn, you'd have to steer slightly off prograde, and that generates drag from the side of the rocket. But with higher Mach numbers, that drag arrow was longer, hence it was much much easier to flip. So I'd do throttle down to shorten that drag arrow and make the rocket less likely to flip while flying manually.

Exactly. Thats why I say “faux” max-q throttle-down rather than actual max q because its about stability rather than pressure. @Dakitess is absolutely right (thanks for your excellent breakdown, btw!) ideally I wouldn’t be throttling down and I think with some practice I can get the ‘lock on prograde’ method to approximate a good arc. Or maybe it’ll be enough to just start the turn even earlier? Its really just about avoiding large deviations from prograde that risk flipping. 
 

As to upper atmosphere heating: there is at least some bugginess here (parts overheating inside fairings) and that makes it tough to know what the intended behavior is for very high altitude (60+km) So far Ive found keeping the fairing on until Ive fully cleared the atmosphere solves most of the issue and maintaining a more ideal GT to 80km Ap works fine. This is more true to life as fairing separation usually happens at 130km up, above the point where reentry effects become noticeable. That would make 70km on Kerbin roughly equivalent to 120km on earth. Or maybe 70km is meant to be the Karman line? (Kerman line?)

Edited January 5 by Pthigrivi

[The Aziz]

7 hours ago, Vl3d said:

If you go "25° from vertical at 3500m, 45° from vertical at 8000-10000m, 70° from vertical at 25000-35000m" you will burn up.

Uh yeah no. Angle doesn't matter, the speed does. Check your 1st/2nd stage TWR values as I have a feeling that your attempts at 70⁰@30km were around 1500m/s at that altitude. ⅔ of orbital speed at less than halfway to orbit is risky.

Unless your rockets have completely flat fronts or you don't use fairings, then yes, things will burn up.

[Jeq]

And yes we kerbalists like to throw rockets more horisontal than real life counter parts. Main reason for this is that real life has safety management, it is lot safer to bring more fuel and go straight up more than necessary before going horisontal. This is exact reason why tutorials teaches to rocket go straight up long before gravity turn, because it is safer and more predictable, you don't want new player to follow rules which risks whole operation to blow up. And Kerbin is small marble ball compared to Earth, curvature of atmopshere comes lot sooner in KSP.

Edited January 5 by Jeq

[regex]

42 minutes ago, Jeq said:

And yes we kerbalists like to throw rockets more horisontal than real life counter parts. Main reason for this is that real life has safety management

Well, wait a second, that really depends on launch efficiency and stage TWRs as well. It's even more important to get the most out of your rocket when you need to reach an orbital velocity of around 7500m/s (compared to Kerbin's 2300m/s, both ballparks, don't @ me). Launchers like Ares and Minotaur with high TWRs tilt over quite early while other rockets tilt over later (or slower) because their upper stages usually have <1 TWR. The idea there is to loft the stage above the target orbit so you have time to burn into orbit. Remember also that IRL rockets don't often enter a coast phase until they reach orbit but because Kerbin is so small and easy to launch from you will often coast your second stage because it makes sense. That means you can launch more horizontal, especially if the upper has a higher TWR.

[The Aziz]

The best I could do was start coasting with Ap about 90deg from the launch site. Anything further out and the circularization costs started taking more % of the remaining fuel in the stage. But then, it rarely happens, usually the trajectory after hitting desired Ap is much more steep.

[Rocktagon619]

The TWR of the Saturn V was 1.59, if numbers from Wikipedia are correct.

[Bej Kerman]

Just now, Rocktagon619 said:

The TWR of the Saturn V was 1.59, if numbers from Wikipedia are correct.

At launch or near separation?

[regex]

20 minutes ago, Bej Kerman said:

At launch or near separation?

Near sep it was almost or greater than 5 gees 4 gees. The central engine was shut down to manage that.

E: Here's a thread with some great information, including pitch-over angle. In the first image you can see a point labeled "S1C-CECO" (Central Engine Cut Off). Also, I was wrong, it reached nearly 4 gees, not 5.

Edited January 5 by regex

[JoeSchmuckatelli]

On 1/3/2024 at 1:59 PM, Pthigrivi said:

Just a fun one: how are you all doing your gravity turns? Do you have a formula in your head or do you kinda wing it? Does it vary from rocket to rocket much?

My favorite ones are those where I Neanderthal (eyeball) a ship that looks like it has just enough thrust to get to orbit and then I burn for a long time until I've got the ship almost completely heeled over to parallel just as I reach 70-80km.  No coasting, just a steady burn through to orbital altitude.

I've got a craft set up with medium tanks and two-ish stages to orbit (don't know how people call dumping external SRBs when the central LFR burns from launch through SRB sep).  Bottom stage is Mainsail set to 78%, with a pair of Kickbacks - gives me abt 1.3 TWR.  I push the whole thing up to 100m/s then tilt to the first circle on the NavBall.  That starts a slow fall to 45, where along the way the Kickbacks expend - and I dump them, while bringing up the Mainsail to full.  Somewhere along the way the Mainsail stage loses fuel & I dump it and let the Skipper take over - driving a still falling NavBall through when AP gets to ~ 75km and the NavBall is just about parallel to the surface.  Skipper has enough juice left in the tanks to circularize and normalize with my target... and maybe enough to start the exit burn.  (Just finished a launch as I'm writing this - and the sustainer has 300 deltav remaining - which is plenty to circularize (67), normalize (100) and then start the exit.

I have no idea whether this is an efficient or inefficient burn - but its one I like from a gameplay perspective.  Doesn't feel overbuilt... and if I don't get it right (adjusting thrust when needed) I can get too low of an AP and need to revert to launch.

Edited January 6 by JoeSchmuckatelli

[regex]

1 hour ago, JoeSchmuckatelli said:

(don't know how people call dumping external SRBs when the central LFR burns from launch through SRB sep)

Typically I've seen the SRMs called "stage 0" if the central stage starts at the same time. Same with the R-7 and the liquid-fueled outers.