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Tried returning to the game


Jasel
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Hey all!  It's been a long while.  Maybe since v 1.0?  Probably since asteroids were introduced.  I used to play the ever living crap out of Kerbal and now it feels like I don't even know which end of the rocket I should point mostly up.  It seems the atmosphere is holy crap unforgiving and I can't even make orbit which is insanely frustrating since I used to do it blind folded...well...not really...  Did they make it so making a rocket is just as hard as making a space plane?  What am I missing?

Hoping some vets will know where I'm coming from and send some tips my way.  I tried watching some vids and they just say to keep pointing prograde, but my rockets don't seem to want to.  This is career mode BTW.  Basic rocket stuff to work with.

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So before, the standard method of getting to orbit was to go straight up til 10000m then turn to 45 degrees.

Now with the atmosphere changes, you actually have to perform a real gravity turn, where you gradually turn towards the east as you ascend. If you can't figure out how to do it, there are videos and forum threads on it, or you can watch mechjeb do it.

If you deviate too much from your prograde marker or your center of drag is in front of your center of mass, your rocket will become unstable and flip end to end. This can be avoided through careful piloting and putting fins at the bottom of the rocket.

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There are more or less working methods for that too. My typical launch is: TWR of 1.22, not less, can be more; at 100m/s start turning a bit so I make ~23° at 5000m, then standard 45° at 10k, 66° at 20k, finally almost horizontal at 40km. Don't make pancakes, they don't fly well anymore. With all that, LKO is doable with less than 3500m/s of dV

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I appreciate the replies @Jas0n and @The Aziz!!!  I'm cool with all of that.  I even tried mechjeb and he couldn't help but flip also.  What about aerodynamics?  Wings, weight /aerodynamics / thrust distribution?

It is unnervingly frustrating that I can't get a simple rocket that I used to fly all the time, and even mechjeb can't put it into orbit, so I'm really hoping to get help.  Here is my simple stupid rocket:

9fuAMgb5G-sv6BilD4pjxc2-T76aVPvsP8ec59sz

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A few comments:

I think that would have needed struts in beta and before.  If you aren't strutting manually, make sure autostrut is on.

I'm pretty sure that is coming back capsule down.  Expect to put a decoupler at the capsule (you won't need the side parachutes).  For low kerbin orbit returns, the heatshield is optional.

I'm not convinced the SAS system is enough to control the rockets and I'd expect needing the main rocket to maintain flight.  SSTOs aren't a good idea (unless jet powered or similar).  Consider putting a terrier in between the two fuel tanks (putting fuel tanks on top of the SSBs is an old trick, and now doesn't even require fuel lines [although kerbal engineer needs them to calculate things]).

But I think your two biggest issues are needing struts on the way up and needing to keep the capsule right way up coming down (perhaps the SAS module can do it, but I'd bring solar panels and make sure I can down on the day side).  Come to think of it, you need to add solar panels anyway (the simple panels would be fine).

And fins.  Definitely fins.

Edited by wumpus
missed the fins
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Like @Rocket In My Pocket said. If you want to see it very simply in picture form, check out the link below. I found it to be the single most informative (though simple) tutorial I've ever seen. It absolutely changed my space career, and rocket flipping has become a thing of the past. I highly recommend giving it a look.

 

I think @klesh is right as well, though I think I'd trade those Kickbacks for Thumpers. When your boosters are taller than your rocket, you can usually downsize a bit. Though I do love me some Kickbacks. :)

Edited by Cpt Kerbalkrunch
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Moving to Gameplay Questions.

@Jasel, other than the excellent advice already offered, a few general design tips to bear in mind about the new aerodynamics:

First, it matters where your CoM is.  You want your CoM to be as far forward as possible.  A rocket with a CoM in the back will be very prone to flipping and there's not much you can do about it.

One good way to put your CoM where you want it is to ensure that bottom tanks drain first, which moves the CoM upwards as you burn.  You can accomplish this by ensuring that "advanced tweakables" is turned on in the game options, then you can use the fuel-flow priority setting on the tanks to control drainage.  Just click on the +1 for the bottom tank and you're good to go.

Similarly:  put fins on the back.  You want them as far as possible behind the CoM, because their effectiveness is directly proportional to their lever arm.

Streamlining matters now.  You want long, skinny rockets, not pancakes.  And make sure that the front ends of things are pointy, not flat-- nosecones and fairings are your friends.

It's better to fly a lot faster now than before.  Efficient rocket launch is a balancing act between "minimize gravity loss" (which wants you to go faster) and "minimize aerodynamic loss" (which wants you to go slower).  With the new aero in KSP 1.0-and-after, the pendulum has swung hard towards "minimize gravity loss".  For any reasonably streamlined rocket, gravity losses are much bigger than aerodynamic losses, so for the most part it's in your interest to burn pretty hard.  Pre-1.0, for example, I generally launched with a TWR of 1.3 to 1.5, but now I go for around 2.0.

Follow a gravity curve.  For example, when I launch at TWR 2.0, I start the gravity turn right off the pad (about 10 degrees or so eastwards) and then just follow :prograde: burning like hell until my Ap gets where it needs to be.  Note:  you'll see a lot of scary-looking flames as you ascend.  Ignore them.  They're harmless and bear no relation to aerodynamic drag.

Orientation to airflow matters now.  I note that your craft is facing the default direction (north), meaning that when you do your gravity turn eastwards, you're going to be yawing right rather than pitching down.  With your big SRBs on the left and right sides of the craft, it means those two big SRBs are going to be experiencing asymmetric aero forces (the one on the left and the one on the right don't get the same airflow), which can make aerodynamic stability trickier.  I'd recommend either rotating your craft so that it faces eastwards on the pad, or (if you really prefer it in this orientation because you're used to yawing rather than pitching), move the SRBs 90 degrees so they're on the north-and-south sides of the craft rather than east-and-west.

 

2 hours ago, Rocket In My Pocket said:

COL should be below COM, you have it way, way up above it.

This one's a red herring, for a couple of reasons:

  • The CoL indicator in the VAB is notoriously unreliable; the displayed position is virtually meaningless.  It can be useful in the SPH, but not the VAB.  Best to just ignore it.
  • In general:  "CoL behind CoM" is a seriously misunderstood mantra, even in the SPH; it does not equate to stability.  Is it good to be behind the CoM?  Sure, for an airplane.  But it's not even vaguely sufficient for aerodynamic stability because it's not the thing that actually matters.  So, I'm not saying ignore it... but it's not as valuable as people often think.

 

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So the problem seems to be solved, but I want to expand the thread a little bit in specific direction, because my curiosity is killing me.

12 hours ago, Jas0n said:

putting fins at the bottom of the rocket.

2 hours ago, Rocket In My Pocket said:

 fins at the back for stability.

2 hours ago, klesh said:

Add fins, will travel.

2 hours ago, wumpus said:

And fins.  Definitely fins.

5 minutes ago, Snark said:

put fins on the back.

 

What's with all that? I can't remember when was the last time I used fins on a rocket, and I'm talking about 2.5 year timespan. My creations fly perfectly well with nothing but an engine at the bottom. Am I that good or..?

 

 

 

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15 minutes ago, The Aziz said:

So the problem seems to be solved, but I want to expand the thread a little bit in specific direction, because my curiosity is killing me.

What's with all that? I can't remember when was the last time I used fins on a rocket, and I'm talking about 2.5 year timespan. My creations fly perfectly well with nothing but an engine at the bottom. Am I that good or..?

It's just the simplest solution to the problem, and the easiest for a new or struggling player to digest; but certainly not the only one.

Gimbal and/or reaction wheels can solve the issue as well.

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1 hour ago, Snark said:

Moving to Gameplay Questions.

@Jasel, other than the excellent advice already offered, a few general design tips to bear in mind about the new aerodynamics:

First, it matters where your CoM is.  You want your CoM to be as far forward as possible.  A rocket with a CoM in the back will be very prone to flipping and there's not much you can do about it.

One good way to put your CoM where you want it is to ensure that bottom tanks drain first, which moves the CoM upwards as you burn.  You can accomplish this by ensuring that "advanced tweakables" is turned on in the game options, then you can use the fuel-flow priority setting on the tanks to control drainage.  Just click on the +1 for the bottom tank and you're good to go.

Similarly:  put fins on the back.  You want them as far as possible behind the CoM, because their effectiveness is directly proportional to their lever arm.

Streamlining matters now.  You want long, skinny rockets, not pancakes.  And make sure that the front ends of things are pointy, not flat-- nosecones and fairings are your friends.

It's better to fly a lot faster now than before.  Efficient rocket launch is a balancing act between "minimize gravity loss" (which wants you to go faster) and "minimize aerodynamic loss" (which wants you to go slower).  With the new aero in KSP 1.0-and-after, the pendulum has swung hard towards "minimize gravity loss".  For any reasonably streamlined rocket, gravity losses are much bigger than aerodynamic losses, so for the most part it's in your interest to burn pretty hard.  Pre-1.0, for example, I generally launched with a TWR of 1.3 to 1.5, but now I go for around 2.0.

Follow a gravity curve.  For example, when I launch at TWR 2.0, I start the gravity turn right off the pad (about 10 degrees or so eastwards) and then just follow :prograde: burning like hell until my Ap gets where it needs to be.  Note:  you'll see a lot of scary-looking flames as you ascend.  Ignore them.  They're harmless and bear no relation to aerodynamic drag.

Orientation to airflow matters now.  I note that your craft is facing the default direction (north), meaning that when you do your gravity turn eastwards, you're going to be yawing right rather than pitching down.  With your big SRBs on the left and right sides of the craft, it means those two big SRBs are going to be experiencing asymmetric aero forces (the one on the left and the one on the right don't get the same airflow), which can make aerodynamic stability trickier.  I'd recommend either rotating your craft so that it faces eastwards on the pad, or (if you really prefer it in this orientation because you're used to yawing rather than pitching), move the SRBs 90 degrees so they're on the north-and-south sides of the craft rather than east-and-west.

 

This one's a red herring, for a couple of reasons:

  • The CoL indicator in the VAB is notoriously unreliable; the displayed position is virtually meaningless.  It can be useful in the SPH, but not the VAB.  Best to just ignore it.
  • In general:  "CoL behind CoM" is a seriously misunderstood mantra, even in the SPH; it does not equate to stability.  Is it good to be behind the CoM?  Sure, for an airplane.  But it's not even vaguely sufficient for aerodynamic stability because it's not the thing that actually matters.  So, I'm not saying ignore it... but it's not as valuable as people often think.

 

Thanks @Snark!  I last played before full release so nose cones just made things look pretty in that atmosphere.  There's a ton of useful advice that makes a  lot of sense here and I appreciate it.  I'm excited to see what I can build now!

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10 hours ago, The Aziz said:

So the problem seems to be solved, but I want to expand the thread a little bit in specific direction, because my curiosity is killing me.

 

What's with all that? I can't remember when was the last time I used fins on a rocket, and I'm talking about 2.5 year timespan. My creations fly perfectly well with nothing but an engine at the bottom. Am I that good or..?

 

 

 

For the most part, I just do it out of habit. 

I haven't built a rocket without fins in years and most of my early game "sounding rockets" are stabilized by having fins that are slightly tilted.

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