So many questions! Top priority, launching dynamics!

[Wolvyreen]

Hello,

Upfront, please go easy on this NOOB! I bow to all of your genius and intelligence and recognise how low my IQ is compared to all of you.  (Not intended to be arrogant but rather humble!)

I know, I know, lots of threads on this but I am not a rocket scientist and nor am I a genius. I have no clue how to calculate launch heading, velocity, thrust etc etc.

Planets obviously have differrent atmo heights but I just cannot figure out how to get in to a stable orbit on my own.  All the threads explain and explain but it goes completely over my head the moment someone brings in trigonometry or formulas etc.

 

Sure the training teaches you how to launch and get in to orbit but that is based on the rocket that they have you build and the power of those rockets etc. and it is based on that specific scenario.

The training also tells you to go turn now and then do this and that but doesn't explain why. So, is it the same heading for all rockets and all engines etc?

 

Is there no simple tool or mod that one can use to say "I want rendezvouz with this orbiting ship... so tell me which direction to head in and what thrust I will need and how much Delta-V"

I'm really struggling and don't want to give up just yet.

 

Thanks in advance.

Edited July 4, 2020 by Wolvyreen

[king of nowhere]

1 hour ago, Wolvyreen said:

Sure the training teaches you how to launch and get in to orbit but that is based on the rocket that they have you build and the power of those rockets etc. and it is based on that specific scenario.

The training also tells you to go turn now and then do this and that but doesn't explain why. So, is it the same heading for all rockets and all engines etc?

 

mostly, yes. i'm sure different rockets would have slightly different optimized launch profiles, but there's no way to optimize so much without complex calculus. but yes, you should turn your rocket. this is the most efficient way to launch. we're talking about a deltaV saving of over 1000 m/s over launching straight up.

consider this: when you raise your orbit (which you have done in the tutorial, burning prograde) you take a curved trajectory. you don't burn up and circularize. launching is a similar movement to raising your orbit, so it would stand to reason that you'd need a similar trajectory
 

Quote

 

Is there no simple tool or mod that one can use to say "I want rendezvouz with this orbiting ship... so tell me which direction to head in and what thrust I will need and how much Delta-V"

I'm really struggling and don't want to give up just yet.

 

as for rendez-vous and docking, i'm not sure about tools, but the game allows you to do it. have you done the docking tutorial? the manuever for rendez-vous is the second shown there: you have fixed your orbital plane, now you need to raise (or lower) your orbit, you need the right time. but the game helps you there, because it shows you the intercept and it lets you find the exact moment where you have to make your transfer burn. and then once you are close to the target you burn retrograde to the target (be sure that your speed is set on "target" and not on "orbit") until your speed is reduced to zero

i could give more detailed instructions, but your questions were rather vague and i don't understand exactly what you want to know.

Edited July 4, 2020 by king of nowhere

[Streetwind]

The thing is, you don't really "calculate" launch heading or the like. KSP is not a hardcore simulation of real-life rocketry, where everything is preprogrammed into the rocket and then you press launch and keep your fingers crossed that you programmed it right while you watch it fly itself. I mean, there's a mod that lets you play like that... but in stock KSP, you're still flying the thing manually to a large extent.

Which means: in order to consistently launch well, you've got to git gud, scrub.

In all seriousness: practice and experience helps. Specifically, experience in judging mid-flight if your current flight profile, heading, etc. is what you actually want/need. And experience in building your rocket. You are correct when you say that the flight profile depends a lot on the rocket, but the lessons from the tutorial are still useful. They represent a fairly average rocket. Typical player-built rockets will cluster around it, assuming they are built halfway decently. And thus, a halfway decently built player rocket will actually not fly all that different from the tutorial rocket.

So, two areas to address: construction, and manual piloting. Let's start with construction.

 

In the editor, did you know that you can click on each stage in the staging list to expand the view a bit? You can even expand the whole staging list at once, and you can customize what info is shown there via the dV tool in the toolbar at the bottom. That tool also allows you to switch between sea level and vacuum views, which are important for judging the capabilities of the rocket you are building. One of the figures shown in the expanded staging list is the thrust-weight ratio, or TWR for short. It's how fast your rocket accellerates. And this is a very important number for launching, because (all other factors being the same) a rocket that accelerates really hard will tend to fly straight as an arrow, while a rocket that can barely fight against gravity will tend to tip over sideways quite quickly. (There's even more nuance here in your engine choice, but that's not really relevant from a newcomer's perspective.) Try and aim for a TWR of between 1.4 and 1.5 in the sea level view. When all your rockets have their acceleration in this range, they will all fly very similarly during the first minute of your launch.

Try for a "two stages to orbit" launch vehicle. Some very simple early-game rockets might be able to fly single-stage, and many later-game rockets may take their second stage well beyond just orbit insertion. But for now, just try to build two stages. You launch stage should contain about 2000 m/s of dV (in vacuum view). Don't sweat if hitting your 1.4-1.5 sea level TWR figure results in a little less or a little more dV than this number, it's just a very rough guideline. Your second stage should start with a vacuum TWR of about 1.0, and it will need another 1500-ish m/s of vacuum dV to insert into orbit. Any extra dV it provides beyond that is your budget for flying around and doing your mission. These numbers remain true in all stages of the game, even if you start carrying third and fourth stages and other such tomfoolery. Once in orbit, TWR becomes largely irrelevant (beyond your own level of patience).

 

Now, manual piloting. To start with, you need to be aware of your sources of information. The altitude in the top middle is obviously quite important, as is the heading display at the bottom of the navball. Next, in the lower left corner, by the pitch/yaw/roll indicators, there's a column of four buttons. The bottom-most one is purple and named "maneuver mode". Not node, but mode. Here you see your current apoapsis and periapsis, and the remaining time towards reaching each of them. Additionally, there are tabs at the top, and the second tab will show you your current inclination. Use this second tab to ensure that your inclination is either as close to 0° as possible (for equatorial launches) or approaches your desired value (for launches into inclined orbits). If you have a contract that gives you very detailed orbital parameters, you can also find them here and later try to hit them while you are aiming to match the contract orbit. Finally, you can even expand the staging list items again, to receive a constantly updating view of how hard you are accelerating and other such info, though that is not nearly as important as altitude and maneuver mode.

Note that in order to make full use of maneuver mode, you may have to upgrade some buildings, if you're playing career mode.

You activate SAS, you throttle up to full, and then you launch. Give it a few seconds, and then ever so slightly tip over towards the east (90° heading on the navball). You have just performed the "pitchover" maneuver to initiate the "gravity turn". A gravity turn is simply the process of your rocket falling over sideways, as pulled by gravity. But if you have the right amount of acceleration to counterbalance this falling over sideways, then you'll end up with a smoothly curved trajectory that is steep at the start to get some altitude, and very flat towards the end to build up the sideways speed required to get into orbit. Or you would, if SAS wasn't actively fighting to keep your rocket straight. Instead, look at the navball, and the green prograde marker  on it. That is where your rocket would be pointing at if it was allowed to follow its natural gravity turn. You should follow this marker with your steering. Ideally, keep your actual heading within the green circle at all times.

Your goal is to learn to pitch over the right amount at the right moment to match your typical 1.4 to 1.5 sea level TWR of your typical rocket. This takes practice, especially since keyboard controls aren't exactly precise. But there are rules of the thumb you can use to judge if your pitchover was successful. For example, by the time your rocket has tipped over halfway (45 degrees), you should be flying between 10km and 12km of altitude. If it's a bit above that, don't sweat it, just throttle down a bit. If it's below that, you might be in trouble. Either way, if you are unsatisfied with your trajectory, revert to launch and try again. Don't be ashamed of reverting frequently. As mentioned, the controls aren't overly precise, and each new rocket will still be a little different. I typically still need 3-4 tries before I can consistently fly a new rocket well.

If you are satisfied with your trajectory, turn your eyes towards the maneuver mode display. Your apoapsis and the time to reach it now becomes important. You want the time to be between 45 and 60 seconds, and you want your final apoapsis to be between 75 and 80 kilometers. If the time to apoapsis is running away from you, throttle down. If your altitude isn't increasing quickly enough for your liking, throttle up. Orbit insertion happens when your periapsis turns positive and exceeds 70 kilometers. But it's very unlikely that this will happen in a single burn. Typically, you instead turn of your engines once your apoapsis is at the right height, then coast to it, and then perform an orbit insertion burn to raise the periapsis.

 

But even if you follow all this advice, you might find that it isn't nearly as easy as I make it sound. Because, for example, your rocket is passively unstable and doesn't want to follow the prograde marker. Or it flexes and wobbles and randomly rolls around. In that case, you should probably redesign your rocket with common best practices in mind. Well-built rockets can follow the prograde marker on their own, with SAS turned off, but this is not always viable depending on your payload. But you can certainly make your rocket very benign and easy to steer with very little effort, once you know how.

Additionally, learn to love SAS Hold Prograde. In career mode, pilots learn this at level 1 - for which sending them to orbit and back once is enough. In the other game modes, Kerbals are max level by default, and pilots always have this. In addition, probe cores starting with the HECS and above will also have this capability. When you use this SAS mode, the rocket will automatically attempt to stick to the prograde marker, and thus fly its gravity turn automatically even with SAS on. This makes launches so much easier. Go level those pilots, you'll not regret it!

Edited July 4, 2020 by Streetwind

[king of nowhere]

17 minutes ago, Streetwind said:

Additionally, learn to love SAS Hold Prograde. In career mode, pilots learn this at level 1 - for which sending them to orbit and back once is enough. In the other game modes, Kerbals are max level by default, and pilots always have this. In addition, probe cores starting with the HECS and above will also have this capability. When you use this SAS mode, the rocket will automatically attempt to stick to the prograde marker, and thus fly its gravity turn automatically even with SAS on. This makes launches so much easier. Go level those pilots, you'll not regret it!

i hae to disagree on that point. a rocket holding prograde won't make a good gravity turn automatically, not unless it is excellently manufactured. most real rockets, in my experience, will fall down too fast, and fail to enter orbit, if they are not given manual correction.

[Wolvyreen]

Thank you for all the answers.  Apologies if my questions were vague.  I'll try be more specific.

So I am in the process of doing the scenarios.  I have worked through all the training scenarios but now I am working through the scenarios itself and then will move on to missions.  My plan is only after this process will I try the career mode because I really want to get to understand all about KSP before I start career so that I don't completely fail when I start my game.

So now, I am in the process of doing the "EVA on Duna" scenario but for the life of me, I have no idea how to know how far I need to go straight up first before I turn and let alone even know in which direction to turn and for how long to get in to a half-decent orbit to catch up to my ship in order to transfer and come home.

So this is what is baffling me.  I habe been trying to figure this out for 2 days now and feel like a bit of a complete idiot!

I'm now learning as I go.

[Spricigo]

1 hour ago, Wolvyreen said:

Sure the training teaches you how to launch and get in to orbit but that is based on the rocket that they have you build and the power of those rockets etc. and it is based on that specific scenario.

That is the procedure. A more powerful rocket will just turn more aggressively (and/or throttle down), while a less powerful rocket will be even more gentle. 

 

1 hour ago, Wolvyreen said:

The training also tells you to go turn now and then do this and that but doesn't explain why.

Because to get in orbit you just need lateral velocity (a lot) but you cannot go sideways immediately because the ground and atmosphere are in the way. You also don't want to go all the way up and make a 90 degree turn because 1)that is the long way, 2)can't do it fast enough. So, we what lets us go sideways as soon as possible, without terrain or atmosphere getting in the way. 

 

26 minutes ago, Streetwind said:

 KSP is not a hardcore simulation of real-life rocketry, where everything is preprogrammed into the rocket and then you press launch and keep your fingers crossed that you programmed it right while you watch it fly itself.

Do you mean I shouldn't be doing thing like https://kerbalx.com/Spricigo/Yuri250-70 ? 

 

[swjr-swis]

21 minutes ago, Spricigo said:

Do you mean I shouldn't be doing thing like https://kerbalx.com/Spricigo/Yuri250-70 ? 

Upvote just for the zero-input gravity turn rocket.

[Streetwind]

1 hour ago, king of nowhere said:

i hae to disagree on that point. a rocket holding prograde won't make a good gravity turn automatically, not unless it is excellently manufactured. most real rockets, in my experience, will fall down too fast, and fail to enter orbit, if they are not given manual correction.

Of course it won't fly a good turn automatically. I never said that it would. It will automatically fly the turn you give it with your pitchover and your rocket's acceleration - as detailed in the rest of my post.

 

49 minutes ago, Wolvyreen said:

So now, I am in the process of doing the "EVA on Duna" scenario but for the life of me, I have no idea how to know how far I need to go straight up first before I turn and let alone even know in which direction to turn and for how long to get in to a half-decent orbit to catch up to my ship in order to transfer and come home.

Ah, I see. In that case, you can probably get away with as flat a trajectory as you have engine thrust for. The only reason to ever fly straight up is to clear the terrain and avoid too much atmospheric drag. But Duna's atmosphere is thin, and the actual dV loss from aerodynamic drag is a minor factor even on Kerbin, with rocket stability being a much larger reason for good aerodynamics. On a gut feeling, I'd probably quicksave, then turn over 45 degrees immediately after taking off, and then see if SAS Hold Prograde will do the job. Keep an eye on apoapsis altitude. The atmosphere ends at 50 km, so you'd aim for 55-60 km. Throttle down and flatten out as you approach that number, until you have only a small orbit insertion burn left. You'll probably need around 2.5 to 3.0 Duna-local TWR from the get-go to make this trajectory work.

As for on-orbit rendezvous? That's an entire chapter in and of itself, but your launch can definitely make it easier later-on.

For starters, you want to launch into the orbit of your target spacecraft. If that spacecraft is in an equatorial orbit, and you have landed on the equator? Well then, the problem just solved itself. Just launch directly eastward as you would on Kerbin. But if either or both of those conditions are not true, then it gets more complicated, unless you have a large amount of spare dV to spend on plane changes in orbit. First, go to the vessel you want to rendezvous with, and look at the maneuver mode readout for the inclination. Then return to your landed vessel. To launch into an inclined orbit, turn your camera in map view so that the target orbit directly crosses over Duna's center. Then, time warp until your landed vessel is almost directly under the target orbit. Now add or subtract the target's inclination to/from your typical eastward launch heading. For example, if your target spacecraft is in a 10° inclined orbit, and it passes from north to south over your landed craft, then your heading should be 100° (90+10, since 0° is north and 180° is south). Launch, and use the maneuver mode readout to monitor your inclination as you make your way to orbit.

Doing this minimizes the on-orbit plane change you need to make later. There are cases though where this doesn't work, for example if you landed away from the equator but your target spacecraft is in an equatorial orbit. Then your lander will never be "under" the target's trajectory. If this happens, just launch directly eastward when you are as close as possible to your target orbit. You will automatically drift into an inclined orbit, which you will have to fix later.

Rendezvous are also made quicker and easier if your two spacecraft are close together from the start. So you want to launch when your target spacecraft is just a few degrees short of passing directly overhead. Try for a 10° angle for starters. But, you might notice that this conflicts with the previous advice. If you must launch when directly under your target's orbit, then you may not be able to wait until the target is close by. In that case, prioritize hitting the orbit. Having a very similar orbit but being far apart is easier (and cheaper) to fix than being close together but on wildly divergent orbits.

As to how to perform the rendezvous itself, there are many well-illustrated guides on the forum, with pictures and sometimes even video.

Edited July 4, 2020 by Streetwind

[Spricigo]

1 hour ago, king of nowhere said:

i hae to disagree on that point. a rocket holding prograde won't make a good gravity turn automatically, not unless it is excellently manufactured. most real rockets, in my experience, will fall down too fast, and fail to enter orbit, if they are not given manual correction.

Sorry to be blunt but if that is your experience It only means you are doing something wrong,

Every single rocket I put in orbit in KSP is by automatic gravity turn: tilt the rocket in the editor, launch with SAS on hold attitude, switch to hold prograde to start the turn.  The only reason to not use hold prograde is because it's unavailable, and then the rocket follows prograde anyway. 

 

[Spricigo]

58 minutes ago, swjr-swis said:

Upvote just for the zero-input gravity turn rocket.

*cough* https://kerbalx.com/Spricigo/hellix08s-Moon-Satellite  

This one was "almost by mistake".  Being way overpowered, it illustrate what Streewind said:

2 hours ago, Streetwind said:

And this is a very important number for launching, because (all other factors being the same) a rocket that accelerates really hard will tend to fly straight as an arrow, while a rocket that can barely fight against gravity will tend to tip over sideways quite quickly.

Which is why I don't follow the "moderate launchpad TWR" rule of thumbs people so often repeat in the forums. One can get away with much more than "about 1.5" if most of it comes from cheap SRBs that will be discarded before smashing into the atmosphere (e.g. 3.6 n the first linked craft).

[Streetwind]

@Spricigo You know what they say - exceptions confirm the rule!

The moderate launchpad TWR way is IMHO the most newbie friendly, which is why I will recommend it to newcomers. I also advise them against side-mounted SRBs because they are a potential source for control issues if attached the wrong way, and often overkill for simple payloads. But there are many correct ways to build rockets in KSP when you know what you're doing.

Edited July 4, 2020 by Streetwind

[Spricigo]

@Streetwind I don't follow the rule but I'm not against teaching the rule to newcomers. One need to learn the rule before learning how to get away with breaking the rule. 

Still, it wasn't of much use for me even when I started. Maybe because I have that unusual preference for fire-and-forget rockets? 

[king of nowhere]

4 hours ago, Spricigo said:

Sorry to be blunt but if that is your experience It only means you are doing something wrong,

Every single rocket I put in orbit in KSP is by automatic gravity turn: tilt the rocket in the editor, launch with SAS on hold attitude, switch to hold prograde to start the turn.  The only reason to not use hold prograde is because it's unavailable, and then the rocket follows prograde anyway. 

 

yes, because you are a better engineer than i am *

but i've totaled enough hours and built enough crafts that i can't really be called a beginner anymore (except for some specialized parts of this game, like building and flying plane, that i didn't spend much time on). hence, if i cannot make a fire and forget rocket, it means it's difficult. hence, i would not suggest it to one who has problems with the basics.

let him learn to make passable rockets before he can make excellent rockets.

 

* actually, i've never tried to make such a rocket. but all the ones i ever made needed corrections.

then again, i like to fulfill as many objectives as possible with as few rockets as possible, making them as cheap as possible. this means i often intentionally make a worse rocket to save some money. and i often have huge, complex, often asymmetric payloads. as long as it saves money. i'd be really surprised if it was possible to make those payloads fly themselves without significant cost increase.

[Wolvyreen]

5 hours ago, Streetwind said:

Of course it won't fly a good turn automatically. I never said that it would. It will automatically fly the turn you give it with your pitchover and your rocket's acceleration - as detailed in the rest of my post.

 

Ah, I see. In that case, you can probably get away with as flat a trajectory as you have engine thrust for. The only reason to ever fly straight up is to clear the terrain and avoid too much atmospheric drag. But Duna's atmosphere is thin, and the actual dV loss from aerodynamic drag is a minor factor even on Kerbin, with rocket stability being a much larger reason for good aerodynamics. On a gut feeling, I'd probably quicksave, then turn over 45 degrees immediately after taking off, and then see if SAS Hold Prograde will do the job. Keep an eye on apoapsis altitude. The atmosphere ends at 50 km, so you'd aim for 55-60 km. Throttle down and flatten out as you approach that number, until you have only a small orbit insertion burn left. You'll probably need around 2.5 to 3.0 Duna-local TWR from the get-go to make this trajectory work.

As for on-orbit rendezvous? That's an entire chapter in and of itself, but your launch can definitely make it easier later-on.

For starters, you want to launch into the orbit of your target spacecraft. If that spacecraft is in an equatorial orbit, and you have landed on the equator? Well then, the problem just solved itself. Just launch directly eastward as you would on Kerbin. But if either or both of those conditions are not true, then it gets more complicated, unless you have a large amount of spare dV to spend on plane changes in orbit. First, go to the vessel you want to rendezvous with, and look at the maneuver mode readout for the inclination. Then return to your landed vessel. To launch into an inclined orbit, turn your camera in map view so that the target orbit directly crosses over Duna's center. Then, time warp until your landed vessel is almost directly under the target orbit. Now add or subtract the target's inclination to/from your typical eastward launch heading. For example, if your target spacecraft is in a 10° inclined orbit, and it passes from north to south over your landed craft, then your heading should be 100° (90+10, since 0° is north and 180° is south). Launch, and use the maneuver mode readout to monitor your inclination as you make your way to orbit.

Doing this minimizes the on-orbit plane change you need to make later. There are cases though where this doesn't work, for example if you landed away from the equator but your target spacecraft is in an equatorial orbit. Then your lander will never be "under" the target's trajectory. If this happens, just launch directly eastward when you are as close as possible to your target orbit. You will automatically drift into an inclined orbit, which you will have to fix later.

Rendezvous are also made quicker and easier if your two spacecraft are close together from the start. So you want to launch when your target spacecraft is just a few degrees short of passing directly overhead. Try for a 10° angle for starters. But, you might notice that this conflicts with the previous advice. If you must launch when directly under your target's orbit, then you may not be able to wait until the target is close by. In that case, prioritize hitting the orbit. Having a very similar orbit but being far apart is easier (and cheaper) to fix than being close together but on wildly divergent orbits.

As to how to perform the rendezvous itself, there are many well-illustrated guides on the forum, with pictures and sometimes even video.

Thank you  for your detailed reply :-)

The problem is that to win the scenario, you are using a ship with very little dV so you have to be efficient. :-(

[Spricigo]

11 hours ago, king of nowhere said:

yes, because you are a better engineer than i am *

but i've totaled enough hours and built enough crafts that i can't really be called a beginner anymore (except for some specialized parts of this game, like building and flying plane, that i didn't spend much time on). hence, if i cannot make a fire and forget rocket, it means it's difficult. hence, i would not suggest it to one who has problems with the basics.

let him learn to make passable rockets before he can make excellent rockets.

What?! You make the rocket stable enough and you get the initial tilt right then you don't need to worry about steering the rocket since it naturally follows the ideal trajectory. 

Only that for me (and Im not saying it should be the same to everyone) is more interesting getting the tilt correct in the editor. But that is not some sort of witchrocketry, just basic things applied. If you don't do in the editor you can do it in the flight scene and even if you don't get it perfectly right the mission can be salvaged 

If a regular player don't get the flight patch correct he will need to adjust the trajectory, if i don't get the flight patch correct I need to go back to the editor and rework my design. That's why it seems to you my rockets are excellent, the passable rocket I do all the time just get a bit of improvement when necessary. (also I don't share the rockets I'm not satisfied with). 

11 hours ago, king of nowhere said:

then again, i like to fulfill as many objectives as possible with as few rockets as possible, making them as cheap as possible. this means i often intentionally make a worse rocket to save some money. and i often have huge, complex, often asymmetric payloads. as long as it saves money. i'd be really surprised if it was possible to make those payloads fly themselves without significant cost increase.

Adjusting the payload to avoid that kind of trouble is part of my process but I don't mind to try, as an experiment, to take one of your payloads and design a rocket for it. 

If you're interested just share the original craft and what is the tech available in a new thread. I'm sure other would like to give their inputs too. 

[Streetwind]

17 hours ago, Wolvyreen said:

Thank you  for your detailed reply :-)

The problem is that to win the scenario, you are using a ship with very little dV so you have to be efficient. :-(

Turns out, I've actually never done that scenario myself. So on a whim, I decided to give it a try today. I made a gallery of annotated screenshots to document how I did it. I mean, you've probably managed it yourself by now, but maybe it gives you some additional insight

[king of nowhere]

7 hours ago, Spricigo said:

If a regular player don't get the flight patch correct he will need to adjust the trajectory, if i don't get the flight patch correct I need to go back to the editor and rework my design. That's why it seems to you my rockets are excellent, the passable rocket I do all the time just get a bit of improvement when necessary. (also I don't share the rockets I'm not satisfied with). 
 

basically, you put in the extra effort, and you have a lot of practice at it. that's how people reach excellence, usually.

Quote

 

Adjusting the payload to avoid that kind of trouble is part of my process but I don't mind to try, as an experiment, to take one of your payloads and design a rocket for it. 

If you're interested just share the original craft and what is the tech available in a new thread. I'm sure other would like to give their inputs too. 

 

how do i share a rocket?

[Spricigo]

2 hours ago, king of nowhere said:

how do i share a rocket?

Find the .craft file in  \Kerbal Space Program\saves\YourSaveName\Ships\VAB and post it in kerbalx.com/ or any file sharing service.