Getting orbit with heavy payload

[Spaceman83]

When i built rocket for heavy load and get it on the orbit i usually burn my boosters first and then fire second engine to get sub orbit and last one to get orbit of course but i usually tilt rocket 5 degrees before it is about 20 to 30km when dump my boosters and launch second one! Then start to tilt 90 degrees! This because rockets have heavy payload and if i try to follow youtube tutorials like ignite boosters and second stage rocket at the launch i dont have enough fuel get to the orbit or if i tilt 45 degrees 10km like they advise my rocket will lose control so is there better way i know this works for me but if there is i like to know?

[steuben]

Now, pics of your rocket will help.

How much payload are you lifting? What is it's shape?

One general solution would be  to add more reaction wheels to it.

Another one is to forgo the classic launch profile, especially with oddly shaped or payloads at the limit of your launcher's rating. Launch straight up to about 45-50 km, turn right 90 degrees and burn till orbit.

Edited September 1, 2016 by steuben

[Palaceviking]

Pics please. 

 

I'd recommend only two stages for obscene loads, go big and dumb, go fast and use aerodynamics to your advantage (tail fins/rudders)

[mk1980]

research the concept of a "gravity turn". i think there is at least 1 (probably more) discussions/guides about it in the tutorial section of the forum.

that's the most efficient way to get stuff to orbit with rockets, basically.

you may have to use fairings or some special design tricks if the payload is particularly bulky / un-aerodynamic, but "heavy" isn't really a bad thing. quite the opposite, really. a heavy payload on top of a rocket makes it inherently more stable.

[Aegolius13]

How fast are you turning when you do the 45 degree option?  You want to do it very gently, starting soon after launch.  I usually tip over about 10 degrees when I hit 50 m/s, and then let SAS Hold Prograde do most of the rest.

What's your TWR when you drop the boosters? If it's too low, gravity may pull you down.

Fins on the back are often a quick fix for instability, but are generally not necessary on a clean rocket.

For heavy payloads, I love radially attached TwinBoars.  It's practically indecent how much four of those things can lift.

Edited September 1, 2016 by Aegolius13

[Snark]

So, a few things to be aware of.

First:  If you're watching tutorial videos, be very careful about WHEN the video was made.  When KSP 1.0 arrived, in April 2015, there was a huge change to the way aerodynamics works in KSP.  This required completely changing the way rockets are launched.  It was like a whole new game.

Before 1.0, the way to get to orbit was generally "fly straight up to 10 km, then crank it sharply over to 45 degrees."

After 1.0, that is not the way to fly it.  So if you're looking at videos that were made before April 2015, they're completely wrong and irrelevant and won't work for you.  Don't even look at them, they'll just steer you wrong, literally.

3 hours ago, Spaceman83 said:

i usually tilt rocket 5 degrees before it is about 20 to 30km when dump my boosters and launch second one! Then start to tilt 90 degrees!

That's your problem there-- flying in that way is extremely inefficient.  By the time you're at 30 km altitude, you should already be mostly horizontal.  If you're still going nearly straight up, that's a problem.

1 hour ago, mk1980 said:

research the concept of a "gravity turn".

^ This.  This is how you do it.

Basically, what you do is start your turn really really early, practically right off the launchpad.  Almost immediately after liftoff (say, when you get up to 20 m/s so your prograde marker is reasonably stable), give your ship just a slight eastward nudge, so it's pointing just slightly eastward of straight up.  Then just set it to "hold prograde" and fly it to orbit with your hands off the controls-- the only thing you should need to do is operate the staging controls when a stage burns out, or maybe to adjust throttle (but not much of that, you should generally be at full throttle the whole way up).

There are no sharp turns involved.  Your rocket will just naturally, gradually tip over farther and farther.  The higher it gets, the more horizontal it is.  You stop burning when your Ap has reached the desired altitude for your target orbit.  Then you coast up to Ap, and do a horizontal burn to circularize.

The only tricky part in the whole operation is judging just how much of a tiny nudge to give your rocket at the start.  It really is tiny, just a degree or two, which means it's very sensitive:  if you're even a little bit too big or too small of a nudge, you'll end up with an unsuccessful launch.  It's touchy.  However, the good news is that it gets a lot easier with practice.  Try it, see how it goes, and if it fails, just "revert to launch" and try it again with a slightly bigger or smaller nudge.  Pretty soon you'll get a feel for the right amount.

Here's how to tell if you've judged it right:  when you reach an altitude of 10 km, you should already be tipped to an angle of about 45 degrees, and traveling significantly over 300 m/s.  If you're a lot steeper (more vertical) than 45 degrees at 10 km, you didn't nudge enough; revert and try again with a smaller nudge.  If you're a lot shallower (more horizontal) than 45 degrees at 10 km, you nudged too much; revert and try again with a bigger nudge.  The nice part is that it doesn't take very long to reach 10 km, so you find out pretty quickly after launch whether you nudged too much or not enough.

One more thing that can help you learn this faster:  try to design your rockets to always have the same TWR on the pad.  Pick a number you like (I prefer about 1.5 or so, myself) and stick with it.  If you always launch with the same launchpad TWR, then all your rockets will fly with a curve of approximately the same shape, which means they'll all need about the same amount of "nudge" to start the turn, which makes it easier to learn with practice since it's consistent.  If you don't do this, then the amount of nudge you need will be different for every rocket, which makes it trickier (though not impossible) to learn.

[Plusck]

3 hours ago, Spaceman83 said:

... if i tilt 45 degrees 10km like they advise my rocket will lose control ...

That 45° at 10km is very very old advice, that hasn't worked for the last two years. The people with the videos showing wrong info should tell youtubers that it doesn't work anymore. They have a whole info box under their videos to do so.

If you try to do that, you will lose control. As others have said, you need to do a proper gravity turn.

Also, there is no hard and fast rule about starting on boosters then igniting the main engine. After all, the space shuttle visibly did not do that. The main thing is you don't want to waste fuel in an engine which has poor thrust at ground level, but then again you don't want any engines not firing all the time... so it's a compromise. I personally prefer firing all engines at once, but throttling down the LF engines so as not to waste fuel in the low low atmosphere, maintain control for a nice smooth gravity turn, and hit the perfect speed at 10km with the rocket gently falling all on its own to 45° by that time.

[Spaceman83]

Wow thanks guys!!! Real difference i just tilt 5 degrees after launch and put prograde my rocket rise smoothly sub orbit save fuel much much more than my old style my rocket even have too much fuel nowI quess i watched those old tutorials didn't know they don't work!

[foamyesque]

The old videos were wrong even when they were made, unless they're really old ones with the atmosphere ending at 34.5km. The correct course was still a gradual tilt to orbit, people just didn't do it.

[Spaceman83]

12 minutes ago, foamyesque said:

The old videos were wrong even when they were made, unless they're really old ones with the atmosphere ending at 34.5km. The correct course was still a gradual tilt to orbit, people just didn't do it.

Yes i didn't actually dare to tilt rocket anymore because rocket just loose control when i tilt too much looks like many videos still say turn 45 degree 10km! So i keep it 5-10 degrees too long 20km-30km because i scared i loose it if i tilt more! Well now i know to just put it prograde and let it just turn smoothly.

[OhioBob]

On ‎9‎/‎1‎/‎2016 at 2:03 PM, foamyesque said:

The old videos were wrong even when they were made, unless they're really old ones with the atmosphere ending at 34.5km. The correct course was still a gradual tilt to orbit, people just didn't do it.

Well, there was certainly an incentive to maintain vertical ascent longer back then to get up and out of the lower atmosphere as quickly as possible.  This was, of course, because of the absurd drag model that was in place back in the pre-1.0 days.  Though you are correct that large sudden turns are never good, even back then.  Back in those days I still performed a gradual turn similar to what I do now, I just started it much latter in the ascent.  If I remember correctly, I think I started turning around 5 km.

Edited September 2, 2016 by OhioBob

[Plusck]

4 hours ago, Spaceman83 said:

Yes i didn't actually dare to tilt rocket anymore because rocket just loose control when i tilt too much looks like many videos still say turn 45 degree 10km! So i keep it 5-10 degrees too long 20km-30km because i scared i loose it if i tilt more! Well now i know to just put it prograde and let it just turn smoothly.

There's a good recent thread about that, called "a degree makes a difference":

 

[foamyesque]

2 hours ago, OhioBob said:

Well, there was certainly an incentive to maintain vertical ascent longer back then to get up and out of the lower atmosphere as quickly as possible.  This was, of course, because of the absurd drag model that was in place back in the pre-1.0 days.  Through you are correct that large sudden turns are never good, even back then.  Back in those days I still performed a gradual turn similar to what I do now, I just started it much latter in the ascent.  If I remember correctly, I think I started turning around 5 km.

 

Mm. I turned off the pad, but the atmo was so thick you needed to do it slowly, so the net result was more or less the same.

 

 

 

 

[Snark]

20 hours ago, Spaceman83 said:

looks like many videos still say turn 45 degree 10km!

Actually, "be at 45 degrees at 10 km" is good advice now.  But that doesn't mean "go straight up to 10 km and then suddenly turn 45 degrees," the way it used to.

What it means is, start a gradual turn right off the pad, and don't do any sharp turns at all, just stick pointing perfectly prograde all the way.  Your rocket will just naturally gradually turn due to gravity (thus the term "gravity turn"), so that by the time you get to 10 km altitude, you should not only be pointing the rocket at 45 degrees, but also you're traveling at a 45 degree angle.

I suspect that the unfortunate coincidence between the terms "10 km" and "45 degrees" for old aero versus new aero is what causes a lot of the confusion.  People just see a long complex explanation as "...blah blah blah 10 km blah blah 45 degrees blah blah blah..." and it's easy to miss that pre-1.0 and post-1.0 are very different beasts.

[RL-10]

If anyone's still here, I just wanted to ask, I have a duna spaceship that's designed for an aerobrake, and therefore has very un-aerodynamic heat shields on the front, and I want to send it into orbit. Any advice?