Career mode, stuck on orbiting

[Ben the ever Curious]

Hello,

     Can anyone give me tips for how to make turns to due east after liftoff?  I've designed rockets that one time in a hundred will make it to orbit and back.  The other 99 they either shake out of control or refuse to turn whatsoever.  I've tried vectored thrust with boosters, straight solid fuel for the first stage, all vectored for the first (just spins out of control at altitude).

     I've got Winglets to stabilize, but I either get insufficient control to counter natural instability and make any controlled changes, or it shakes apart, usually after spinning out of control. 

     I've tried single, triple, five, and seven structure designs.  I've added braces to dampen shaking apart, but then my designs either don't turn enough or start to wildly turn out of control until breaking apart.

   I'm in career mode so I don't have stabilization available yet.  I'm just trying to complete the orbit contracts to research these, but am stuck.  The only missions available are orbit missions and a 1% success ratio is just no fun.

     I'd like to post the design, is there a way to copy and paste images into the forums?

Thanks!

 

 

Edited January 5, 2017 by Ben the ever Curious

[Vanamonde]

To display pictures here, upload your screenshots to a picture hosting service such as Imgur.com, then use the link they provide in your post. We should be able to give you some advice then.

[bewing]

Some general suggestions based on the info you've given so far:

If you are trying to turn east after liftoff, that means you are trying a gravity turn. Which is a perfectly good thing to do, but it's a little tricky so it makes your life harder. It takes more fuel to go straight up, and then turn east after you are above, say, 55km -- but at least your success rate will jump from 1% to 100%. Gravity turns are nicely efficient on the one hand, but I repeat occasionally that failed launches are 100% inefficient, too -- it's something to keep in mind.

To do a gravity turn successfully is a rather gentle process, and generally requires that you can do "prograde hold" -- which needs a HECS probe core, or a 1 star pilot. If you've got that, try this: at launch, turn on SAS and hit Z. You won't be able to select prograde until you hit space. So hit space, immediately click prograde (have your mouse hovering over it), and then start tapping D to turn east. As soon as it gets just a little off vertical, stop tapping D and just let the rocket go up. It will do the rest of the turn east by itself -- which is the whole point of a gravity turn. The more you get it off vertical to begin with, the more severe the gravity turn will be.

Beyond that, there are several reasons for a rocket to go out of control during launch:

1. Using the controls to push it too far off vertical. Rockets are gravitationally and usually aerodynamically unstable -- if you push them too far, they will flip.

2. Too much drag at the front end. Your upper stage is where all the good stuff is, but it all usually makes the front end draggy which is aerodynamically unstable.

3. CoM problems.

4. Not enough drag at the back end.

5. Not enough control surfaces and reaction wheels.

 

It sounds like you have several of these covered already, but I just wanted to list them to make sure.

[DD_bwest]

by shaking, do you mean a wobble where your ship is partly like a wet noodle?    this is often caused by sas over correcting itself, and limiting engine vectoring can help reduce it.

getting a gravity turn right can be a real challenge, and takes some experience to be able to tell how much your initial tip should be given your TWR, and to tell how good your trajectory is early enough that you can take some decent corrective action.  

if your really having trouble getting into orbit, sometimes its just easier to over build and fly up well over the thick atmosphere before you start to turn.

and as for COM problems, should it be the case,  If you turn on advanced tweakables, you are able to pick the order the tanks drain in,  so you can make them drain bottom up.  this will  move your COM forward during flight, thus increase your stability

[Tyko]

Hey @Ben the ever Curious, welcome to the forums. It's really easy to overbuild your rockets and once your start overbuilding each lower stage ends up having to compensate for the extra weight. This may be the cause of your issues because it makes rockets heavier and harder to control. Something that helps me avoid overbuilding is to start building from the top of my rocket and working my way down to the launch stage.

Some basics:

• Start with your payload, this is what you're trying to get into orbit - usually your command pod or probe core plus parachutes, heat shield, etc
• After your payload is designed, add your 2nd stage behind it. This is the stage that will push you from high atmosphere into your final orbit. you can use a vacuum engine for this stage because by the time if fires the air will be really thin.
  • Read up on the engines, right click on each one and look for ISP numbers. ISP (Specific Impulse) tells you how fuel efficient they are and it's broken down by Atmosphere (ATM) performance and Vacuum (VAC). Look for an engine with really high VAC ISP for this stage (300 or higher)
• Below the 2nd stage build your 1st stage. This should have an atmosphere engine - pick an engine with a high ATM ISP for this stage (250-270 is about normal).

If you're running on a PC/Mac/Linux machine you may want to install Kerbal Engineer Redux. It's provides in-game calculations that are really helpful when designing rockets. Kerbal Engineer (KER) will let you see the results of each item you add so you can plan your ship better. if you're using KER, you can get down into the actual numbers a bit more by fine tuning your Thrust to Weight Ratio (TWR) and your DeltaV

• 2nd stage - TWR of 1.0, DeltaV of ~1700-1800
• 1st stage - TWR of 1.5, DeltaV of ~1700-1800

Edited January 5, 2017 by Tyko

[Ohm is Futile]

5 hours ago, Ben the ever Curious said:

I'm in career mode so I don't have stabilization available yet.

You do, unless you're talking specifically about the tech tree node called stabilization. Basic SAS attitude hold is available to any ship controlled by a pilot in a command module such as a mark 1 command pod.

 

4 hours ago, bewing said:

If you are trying to turn east after liftoff, that means you are trying a gravity turn. Which is a perfectly good thing to do, but it's a little tricky so it makes your life harder. It takes more fuel to go straight up, and then turn east after you are above, say, 55km -- but at least your success rate will jump from 1% to 100%. Gravity turns are nicely efficient on the one hand, but I repeat occasionally that failed launches are 100% inefficient, too -- it's something to keep in mind.

This is pretty good advice. Though, if I may, I'd like to add that there are some fairly safe maneuvers you can pull off to save a lot of fuel and still have a very high success ratio. First thing you should do is wait to be between 1 and 5km up, depending on how unstable your rocket feels, before tapping the controls to go east. Just get your prograde marker a little off center and then all you should do is try to keep your rocket pointing inside the prograde marker's circle. It will keep going further east on its own and if it feels too fast then pull to the west edge of the marker and if it's too slow then pull to the east edge of the marker but always keep your rocket pointing inside the marker.

A good target to reach is to be pointing roughly 45 degrees at around 20km up, but don't panic if your rocket is less inclined than that. bewing mentioned 55km, but honestly it's pretty safe to maneuver at 30km altitude. Don't be afraid to wait until you reach that altitude before making any significant changes to your heading. All you need to achieve to reach orbit is to get above 70km and have an horizontal velocity around 2,200 m/s. Once you reach 30km altitude and a projected apoapsis above 70km, you can pretty much turn your rocket completely horizontal and hold it there until you reach orbit.

You may even want to turn off your engines if your apoapsis gets too far away and wait to get closer to it to start burning again for more efficiency.

 

3 hours ago, Tyko said:

If you're running on a PC/Mac/Linux machine you may want to install Kerbal Engineer Redux. It's provides in-game calculations that are really helpful when designing rockets. Kerbal Engineer (KER) will let you see the results of each item you add so you can plan your ship better. if you're using KER, you can get down into the actual numbers a bit more by fine tuning your Thrust to Weight Ratio (TWR) and your DeltaV

• 2nd stage - TWR of 1.0, DeltaV of ~1700-1800
• 1st stage - TWR of 1.5, DeltaV of ~1700-1800

I second this.