Every maneuver to get into low orbit ends with my periapsis in atmosphere

[Nalen_]

I need some help. Every time I try and get a low orbit around Kerbin after doing a maneuver my periapsis ends up in atmosphere causing me to crash.
Every time I set up a maneuver my maneuver node is in the orange on the nav. ball. I'm not sure if that is the main cause or not.
Any help is much appreciated.

Edited December 17, 2022 by Nalen_

[Vanamonde]

I'm not able to visualize what you are asking about. Are you able to get into high orbits? 

[James Kerman]

3 hours ago, Nalen_ said:

I need some help. Every time I try and get a low orbit around Kerbin after doing a maneuver my periapsis ends up in atmosphere causing me to crash.
Every time I set up a maneuver my maneuver node is in the orange on the nav. ball. I'm not sure if that is the main cause or not.
Any help is much appreciated.

Welcome to the forum @Nalen_!

It sounds like you need to circulize your orbit. The way I launch is to get my apoapsis to 75,000m and once I reach it I burn prograde  to raise my periapsis, You can use the orbital information widget on the bottom left of the screen for altitude data:

[Nalen_]

After I'm done setting my maneuver node the orange dotted line reads that my Periapsis and Apoapsis range around 81,000-83,000.
After I finish my burn my Apoapsis is fine but my Periapsis is always under 50,000m causing my to reenter the atmosphere.
I've tried to get into a high orbit I've succeeded in archiving a high orbit though I run into the same problem.
My high orbit's always turn out elliptical rather then circular.

 

[James Kerman]

59 minutes ago, Nalen_ said:

After I'm done setting my maneuver node the orange dotted line reads that my Periapsis and Apoapsis range around 81,000-83,000.
After I finish my burn my Apoapsis is fine but my Periapsis is always under 50,000m causing my to reenter the atmosphere.
I've tried to get into a high orbit I've succeeded in archiving a high orbit though I run into the same problem.
My high orbit's always turn out elliptical rather then circular.

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.

Edited December 17, 2022 by James Kerman
fixed

[Nalen_]

I use a three stage rocket and follow the steps you listed out each time.
My total ∆v is 4,203 so I have no problem on that front.

 

[James Kerman]

30 minutes ago, Nalen_ said:

I use a three stage rocket and follow the steps you listed out each time.
My total ∆v is 4,203 so I have no problem on that front.

The only other thing I can think of is that your rocket may not have enough power during circularisation and you are having to burn well past apoapsis. If this is the case, what is the thrust to weight ratio of the stage you are trying to circularize with?

[Nalen_]

I use the Second and Final stages for circularisation and (decircularisation?).
                            Twr(Max)
2nd Stage = 1.83(2.44)
3rd Stage = 3.62(6.50)

[James Kerman]

3 minutes ago, Nalen_ said:

I use the Second and Final stages for circularisation and (decircularisation?).
                            Twr(Max)
2nd Stage = 1.83(2.44)
3rd Stage = 3.62(6.50)

That should be plenty. Would it be possible to upload an image? The forum itself cannot host files so we post to services like imgur or google drive and link to them here.

[Nalen_]

https://drive.google.com/drive/folders/1-AXJBF-MKp4Zxwl_CvWyFPM8xKDuePHN?usp=share_link
The burn time in the first image was corrected once I got closer to the node.

[James Kerman]

2 minutes ago, Nalen_ said:

https://drive.google.com/drive/folders/1-AXJBF-MKp4Zxwl_CvWyFPM8xKDuePHN?usp=share_link
The burn time in the first image was corrected once I got closer to the node.

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. 

[Nalen_]

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

[Nalen_]

So I ran a few tests and it seems that my maneuver node is to low.
When I took a slightly above (Into the blue on the nav ball) 90° angle on the burn.
Using the maneuver node to keep my self lined up it kept my Periapsis at the desired height.
But my Apoapsis went way far out.

 

[James Kerman]

2 minutes ago, Nalen_ said:

But my Apoapsis went way far out.

You have made orbit!

I usually make my initial apo just above 70,000m and then adjust to the required orbit. Ideally you want to time the circularisation burn to be 50% just before apo and 50% after so if you need a 30 second burn to circularise you should start burning 15 seconds before apo, that should even out.

[Nalen_]

Alright I'll keep that in mind.
Thank you for the help.

 

[king of nowhere]

2 hours ago, Nalen_ said:

https://drive.google.com/drive/folders/1-AXJBF-MKp4Zxwl_CvWyFPM8xKDuePHN?usp=share_link
The burn time in the first image was corrected once I got closer to the node.

your burn is too long and you start it too late. if the burn goes too long, you will reach apoapsis and then start going down. and since you are taking a very steep ascent, you go down fast. you need to ensure to finish your burn at apoapsis, hence you should start the circularization burn earlier. you should also make a much stronger gravity turn, because the way you are doing it, orbiting is a lot more difficult. you should be at least at 1500 m/s when coasting to apoapsis, possibly more.

if you still make a mistake and end up with a low periapsis in front of you - your periapsis is in front of you, like in figure 4 and 5 - you can burn radial (away from the planet) and fix things. if you keep burning prograde, what happens is that you also raise apoapsis, which is why your apoapsis went way up in your last successful attempt.

in general, if you burn prograde at periapsis, you raise apoapsis. if you burn at apoapsis, you raise periapsis. but if you burn in any other place - which is what you are doing, because your trajectory is so steep that you are only near apoapsis for a very short time and your burn is longer - you are going to raise both apoapsis and periapsis. so what happens to you is that you pass apoapsis while still burning, you move forward, and from then on your burn is used to raise both periapsis and apoapsis. and the further you go from apoapsis, the more your burn is used to raise apoapsis instead of periapsis. eventually you get to the point where you have a 500 km apoapsis and still a 40 km periapsis. and by now you're so close to periapsis that burning prograde does little good.

this is why, in contradiction with what suggested by @James Kerman, i recommend finishing the circularization burn slightly before apoapsis (his advice still applies to most maneuvers). it's a lot easier to recover from errors like that. i set up for a 65 km apoapsis, and then burn prograde a minute or two before that. burning before apoapsis will also raise apoapsis, so i will finish out of the atmosphere once the maneuver is done. the advantage of this is that burning before apoapsis is going to retard your apoapsis. you look at the corner of the screen where is your time to apoapsis, and you will see that at some point, the countdown will revert and the time to apoapsis will start going up. at this point i stop the burn. wait a bit, then burn again. apoapsis is getting closer, closer.... the moment it starts getting further, i stop the burn and wait a bit more. until i enter orbit 10 seconds from apoapsis or so. very self-correcting.

another way is to use a radial component. to orbit you burn prograde, which means parallel to the planetary surface. but you can also burn radial, which means perpendicular to the planet surface, in this case pointing upwards. it has the effect of raising orbit in front of you, but lowering it behind you. so, you are at apoapsis, and now you'll fall down towards periapsis; but if you burn a bit above prograde, you can raise orbit in front of you as fast as you are falling, therefore staying at apoapsis indefinitely. and it's not even expensive, it's only a small deviation over prograde; in fact, i think it's one of the most effective ways, though the main difference is for a proper gravity turn (again, i reinstate, you could save at least 500 m/s by making a better gravity turn). anyway, the way to do that is to press alt-f12, go to physics, then aerodinamics, then display aerodinamic window in user interface. it will open a window will a lot of aerodinamic data, which will be of little use to you because you're in near vacuum anyway, but one of those data is ascent speed. before apoapsis, you are moving up, so ascent speed is positive. after apoapsis you go down, ascent speed negative. when you reach apoapsis and ascent speed goes down in the negative, point your nose a bit above prograde, and ascent speed will start increase again. gradually it will become positive again, as apoapsis is again before you. you can go back to burning prograde at this point, or perhaps you can even burn downward if needed to compensate for too much ascent speed. anyway, by pointing your nose just above prograde and making small corrections, you can stay at the same altitude during all the circularization burn. this is also a very self-correcting technique.

in fact, making the circularizaton with a maneuver node is a very uncomfortable way of circularizing. i have no idea why some people prefer it, cosine losses are going to mess you up. i always use one of the two self-correcting techniques i described above.

 

p.s. your rocket has extremely high values of twr, especially for the upper stages. you could be a lot more efficient by using smaller engines, you'd cut down on your dry mass a lot. of course, with lower twr ascent is more difficult, so you should improve on that before lowering twr.