What does your ascent profile look like?

[Pthigrivi]

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?

I've found I've just been carrying over my old ascent profile from KSP1 and its working fine,  but I have no idea how optimal it is. 1st stage has a TWR around 1.5, tilt about 5 degrees after clearing the tower and gun it to about 150m/s. Then throttle back a bit, slowly climbing so I hit 250m/s at 6km. At 6km up I throttle back up and begin a turn to 45% ending around 12km up. I stay at 45 until my Ap hits 40km, then slowly complete the turn to horizontal while keeping time to Ap between about 1m to 1min 30. Once Ap hits 80km I cut throttle and coast up to the circularization burn. I find this to be pretty efficient but its not like a perfectly smooth arc--which Im guessing is better? At the same time I prefer not to stage while turning, so if Ive got a 3 stage rocket its nice to drop side boosters before transitioning to 45 degrees, and drop the 2nd stage at the end of the 45 degree burn.

Edited January 3 by Pthigrivi

[Scarecrow71]

I'm using approximately the same profile I used in KSP1:

• Launch and stay vertical until reaching 95ish m/s speed.  TWR is >= 1.5 but <= 2.0
• At 95 m/s turn over 10ish degrees east
• At an actual altitude of 4000 m, turn over 20ish degrees east.  Maintain TWR set above
• When the Ap hits 20km, begin to turn over east until reaching 45 degrees.
  • This step has to be done slowly as craft might flip over if you go too fast
• When the Ap reaches sub-orbital (>= 70km) turn over east until reaching 20 degrees
• When the Ap reaches 100km (I generally shoot for 101) kill thrust and turn completely horizontal to ready for circularization burn

Keep in mind that I am attempting to maintain a TWR between 1.5 and 2.0 the whole time, but there are times when it dips below or goes over.  It's a bit of guesswork with the throttle as there is no "one size fits all" setting.  And if I get distracted during launch?  Poof!  All my plans go out the capsule's viewing port.

[Periple]

I start it so that I’m at 80 degrees when going 100 m/s, and 45 degrees at 10 km. Adjust for the individual build — high TWR and low drag a bit lower, high drag a bit higher.

[regex]

It varies by launch vehicle, I don't always launch things with a TWR in mind (aside from being > 1). Sometimes I have a low-TWR lower "lofting" a low-TWR upper stage, sometimes I can tilt over at 50m/s with a high thrust rocket, sometimes it's in-between. I usually revert once or twice per launch to get it right since every launch vehicle is different.

[The Aziz]

Unless a rocket is less stable for some reason or has some weird launch TWR values thanks to SRBs, it's pretty much the same as it was in KSP1. Vertical up to 100m/s, 22deg at 5km, 45 at 10km, 70 at 20km, horizontal at 40km.

Of course that's just my plan and sometimes it doesn't quite work, for example, when the second stage is weaker than expected, I have to stay angled longer to keep the Ap rising. The end result also varies, sometimes the parabole is shorter, sometimes longer.

[Superfluous J]

I watch Ap, Time to Ap, and degrees above the horizon.

...and the temperature indicator

Roughly, at Ap 2km I tilt over to about 85°. Then as Ap goes from 2-30km I slowly go from there to 40°, pushing or pulling my prograde vector along with me. Ideally, by 40° my time to Ap is about 1 minute, and I throttle as necessary to keep it there. Around this point I stage my lifter and my 2nd stage tends to have a low TWR. I tend to lock to prograde around here, and use throttle to keep my time to Ap around 1 minute as my Pe rises out of the atmosphere and my orbit flattens out. Once Ap is at my desired orbit altitude (generally 100km) I'm hopefully almost out of my 2nd stage, so I coast up, use up its fuel to nearly circularize (keeping Pe under 70km) and then ditch it to actually circularize with the payload's engine.

That's the ideal ascent. Reality tends to vary somewhat but not all that much.

Edited January 3 by Superfluous J

[Pthigrivi]

One thing new thing that's been happening in KSP2 that I didn't do in the original: for whatever reason I've been oversizing my 3rd stage and using it not just to circularize but also to transit on munar missions, aiming so it plows into the Mun or Minmus and then separating my lander to do the rest. Something about the re-jiggered tech tree has made that more attractive for some reason. 

[hatterson]

I've been doing a steeper ascent trajectory the later I've got into the tech tree because of upper atmosphere heating issues.

Earlier in the tree this wasn't as much as issue since most rockets were topped by either command pods or probes which have decent heat tolerance. However with larger fairings I get weirder designs inside and sometimes the top parts have trash heat tolerance. Combine that with the fairing not properly doing its job and it means me wanting to get fully out of the atmosphere later even if it means a less efficient launch just to avoid stupid things blowing up for no reason.

If upper atmo heating was more reasonable I'd do a more shallow ascent similar to what @Superfluous J described although usually stopping the orbit around 80km for most missions and only going higher if there's a real need. I generally picked that up from the KSP 1 gravity turn mod and just kinda kept it.

I also usually throw a probe core on my launchers so that I can fully deliver the payload to orbit, detach, turn them around, and then deorbit them.

Edited January 3 by hatterson

[regex]

Am I the only one here that slaps the "align to prograde" button after tilting over and just lets the rocket go? Lots of people throttling too, seems all that time playing RO trained me to go full throttle until I hit my second/third stage.

Edited January 3 by regex

[The Aziz]

If my experience told me anything it's this: aligning to prograde often ends up on undesired trajectory, either doing the gravity turn too quickly or too slow. No rocket is the same, and so no launch is the same.

[Meecrob]

For anyone reading this thread for tips, a good way to get a more intuitive understanding of the gravity turn is to launch the same rocket multiple times using different ascent profiles, and check your remaining dV.

These examples up-thread are excellent starting points/reference numbers, but if someone does not know why people are using those numbers, this is more a "give a person a fish," than "teach a person to fish"

 

My personal answer is that since I have hand-flown every ship since I started KSP1 ten years ago, I try to keep it interesting by always changing up the rocket design. Keeps me on my toes. I am more concerned with not leaving debris in orbit, so for example, if I made a rocket that has more dV in a stage than I had planned, I will purposefully make an inefficient maneuver to keep the stage periapsis underground/in the atmosphere.

Everybody plays the game in their own way. I am only making the above comment so that someone does not get stuck in the thinking that they MUST follow a certain ascent profile.

Edited January 3 by Meecrob

[Sammys Stuffs]

heavily depends on the rocket for me, especially because I have reentry heating turned up to 200% on my save file. Some pieces are prone to overheating even before the particle effects start so I need to be pretty careful about how I chart my ascent and at what speeds I hit different heights in atmo. For the most part I do my best to be pure verticle until about 5-10km and from there it's heavily dependent on what the craft is and what I'm doing with it.

[whatsEJstandfor]

23 hours ago, regex said:

Am I the only one here that slaps the "align to prograde" button after tilting over and just lets the rocket go? Lots of people throttling too, seems all that time playing RO trained me to go full throttle until I hit my second/third stage.

This is pretty much what I do, except I do adjust the throttle so that my apoapsis stays around 50 seconds ahead of me at all times. I guess it might not be the most efficient but it seems to work pretty flawlessly for me.

[regex]

1 minute ago, whatsEJstandfor said:

This is pretty much what I do, except I do adjust the throttle so that my apoapsis stays around 50 seconds ahead of me at all times. I guess it might not be the most efficient but it seems to work pretty flawlessly for me.

Yeah, with full throttle I often end up burning radial in on my second stage to manage my AP climb rate. Sometimes I can make a good a launcher that can handle it without throttling by using solid motors and I think that's probably why I prefer to use solids as stage-0 (the Ariane/Atlas/Delta strategy). RO really ruined me though, I refuse to touch the throttle (aside from start/stop) unless I'm doing something like Angara with a throttled central stage.

[The Aziz]

22 hours ago, Meecrob said:

For anyone reading this thread for tips, a good way to get a more intuitive understanding of the gravity turn is to launch the same rocket multiple times using different ascent profiles, and check your remaining dV.

These examples up-thread are excellent starting points/reference numbers, but if someone does not know why people are using those numbers, this is more a "give a person a fish," than "teach a person to fish"

It's worth mentioning that the "45deg at 10km" that a lot of people use didn't come out of nowhere. Back in ye olden days of KSP1 when the aerodynamics were... questionable, at best, the way to go to space was "straight up until 10km and then sharp turn to 45deg until Ap is above 70km". This won't work very well today but the crucial step remained. The difference is, that everything prior and after that is now more gradual.

It's that:

rather than

[Vl3d]

I tilt it ~3 degrees when between 50-100 m/s depending on TWR then lock to prograde and let it do the gravity turn. If it's turning too fast I keep direction vector to the left of velocity vector circle up to 12 km. After 20 km I start to control the angle or the throttle to keep the AP closer than 1m30s. Never go faster than 1600 m/s at 60 km. I shoot for 100-200 km depending on TWR. Ideal orbit at end of burn: ~150 km X 70 km, SLS style with no separate circularizing. It takes a while because you ride the AP but I time warp.

[regex]

And even then, "45° at 10km" isn't always the best ascent profile, especially if you have an anemic upper or a solid kickmotor (for whatever reasons). Although it's usually a good starting point when testing a new launcher.

Edited January 4 by regex

[Wheehaw Kerman]

Here’s something that works for me with my (usually more or less R7-ish quad booster builds - I like Korolev Crosses - sue me  ) craft.  Typically I’ll have four boosters with booster engines and the core of the first stage with a sustainer engine.  I’ll stage the core after the boosters before I get fuel lines, with them after I can feed the core engine out of the booster tanks.  I also tend to imitate the Soviets in having a small second stage with a vacuum engine for the circularization burn.  Yes, I loved the Making History parts…

After launch, I’ll turn five degrees east at 50 m/s, another five degrees at 5km and 8 km, throttling to keep any Mach effects at a minimum, push it over to 65 degrees or so at 10km, then evenly over the next 10km  to 45 degrees by 20km of altitude.  After that I’ll track the periapsis and turn in larger increments every 10km of altitude and try to be pointing at the horizon by the time periapsis hits 70km and burn until the first stage runs dry.  Usually I’ll have sized the boosters so that they run dry when close to horizontal, above most of the atmosphere.  Once the first stage is dropped I’ll coast until apoapsis burn.

[Superfluous J]

On 1/3/2024 at 4:56 PM, regex said:

Am I the only one here that slaps the "align to prograde" button after tilting over and just lets the rocket go? Lots of people throttling too, seems all that time playing RO trained me to go full throttle until I hit my second/third stage.

 In my experience, this leads to the rocket either entering space at an 80° angle, or diving into the ocean at 1000m/s

(I wrote this about 15 hours ago but the forum software wouldn't send it )

[Pthigrivi]

4 hours ago, regex said:

Yeah, with full throttle I often end up burning radial in on my second stage to manage my AP climb rate. Sometimes I can make a good a launcher that can handle it without throttling by using solid motors and I think that's probably why I prefer to use solids as stage-0 (the Ariane/Atlas/Delta strategy). RO really ruined me though, I refuse to touch the throttle (aside from start/stop) unless I'm doing something like Angara with a throttled central stage.

Yeah I would love to do that... maybe I'll experiment a bit. Im generally throttling down (~80% thrust) just a bit for stability reasons so the rocket doesn't flip from getting too far away from prograde when Im going "too fast". The most common moment for this is in the first phase of 6-10km, which can be tough if Im pushing 400m/s that low. If Im careful I can do it but most of the time Im lazy and don't feel like reverting a bunch of times. Throttle down is more reliable.
 

On 1/3/2024 at 6:41 PM, Meecrob said:

For anyone reading this thread for tips, a good way to get a more intuitive understanding of the gravity turn is to launch the same rocket multiple times using different ascent profiles, and check your remaining dV.

These examples up-thread are excellent starting points/reference numbers, but if someone does not know why people are using those numbers, this is more a "give a person a fish," than "teach a person to fish"

Absolutely agree, and maybe we should be describing a bit more why we're turning this way. Im actually surprised folks ascents look so similar--different methods of tracking but the overall effect looks really similar with the rocket hitting the 45 degree mark close to 10k rather than starting the turn at 10k. I think thats because more experienced players have learned its better to slowly make that transition sooner with a goal of getting to that low-TWR 2nd (or 3rd) stage chasing an Ap thats 1m out. High ISP engines do quite well in the upper atmosphere so getting the most out of them 40+ km up is a great way to keep your overall launch mass down.
 

2 hours ago, The Aziz said:

It's worth mentioning that the "45deg at 10km" that a lot of people use didn't come out of nowhere. Back in ye olden days of KSP1 when the aerodynamics were... questionable, at best, the way to go to space was "straight up until 10km and then sharp turn to 45deg until Ap is above 70km". This won't work very well today but the crucial step remained. The difference is, that everything prior and after that is now more gradual.

It's worth bringing up that the KSP2 tutorial on gravity turns still says go straight up to 10k and then turn.  Even for simplified instruction they should probably recommend a lower number. In fact even I should probably be turning earlier. 

[The Aziz]

35 minutes ago, Pthigrivi said:

the KSP2 tutorial on gravity turns still says go straight up to 10k and then turn. 

Yeaouch. That's bad. I mean, for a complete beginner probably works, but that's gonna cost a lot the further they go.

Btw, I never cared for time to Ap, as long as it isn't decreasing, I know I am safe.

[Superfluous J]

Yeah for SURE I came to my personal ascent profile from a semi-ridiculous number of launches with "typical" craft for me, over and over and over, to see what worked, what wasted fuel, and what wasted my personal time playing the game.

That last one is a bit ironic, I guess, spending hours or days trying to shave minutes of time from future launches. But hey irony can be fun sometimes!

The two most surprising parts to me were how TWR becomes unimportant after your nose comes down to the 45° mark or so, and how low in the atmosphere (10km or so) that engines rated for "space" become better than those rated for "atmosphere".

Those 2 things together mean you can use a lightweight Poodle or Terrier on your 2nd stage, if you don't mind the launch taking a bit of time. Which I tend to not. There's something serene about following your prograde vector as your Ap slowly rises past 70km.

Edited January 5 by Superfluous J

[Pthigrivi]

6 minutes ago, The Aziz said:

Btw, I never cared for time to Ap, as long as it isn't decreasing, I know I am safe.

Both to this and to Superfluous J's post: I mostly use this a benchmark to let me know just how low my final stage TWR can be, and high up it can be quite low. I know real launches sometimes 'loft' their 2nd stage as Regex describes but I personally prefer to keep my Ap rising without having to keep my nose up. 

[regex]

1 hour ago, Pthigrivi said:

Yeah I would love to do that... maybe I'll experiment a bit. Im generally throttling down (~80% thrust) just a bit for stability reasons so the rocket doesn't flip from getting too far away from prograde when Im going "too fast". The most common moment for this is in the first phase of 6-10km, which can be tough if Im pushing 400m/s that low. If Im careful I can do it but most of the time Im lazy and don't feel like reverting a bunch of times. Throttle down is more reliable.

I learned that profile playing RO: tilt over 5° at 100m/s and follow prograde to orbit generally works for most things or provides a decent basis for you to adjust from (works pretty good for Redstone, Delta, R-7, and Atlas, sucks for Saturn V). On Kerbin, depending on TWR, you tilt over at 50m/s to 80m/s, sometimes even 90m/s if your upper has terrible TWR (more time to push the PE out). Full throttle all the way. This does not work so well on Kerbin because it's so damn small; depending on your upper, how long your lower burned, and all the TWRs, you'll end up burning radial in or doing start/stops to adjust (I usually do radial in because it lets me do complete burns). I mainly just do that from habit because I genuinely don't really care about efficiency during launch. Efficiency begins in orbit for me.

Edited January 5 by regex

[Meecrob]

4 hours ago, The Aziz said:

 

This is exactly what I am trying to prevent. Thanks for being on the same page.

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.

In any case, there should be a tutorial on how to improve your ascent profile efficiency. I get they have to get newbies into orbit, but like even 2k is a bit much before pitch lol.

 

Edit: 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

Edited January 5 by Meecrob