Help with launches

[uncle natzer]

I'm almost always burning up before entering orbit. No matter what design I make it'll burn up. It's always between 45 and 50k. I use DR but I've rest the values to the default setting and I've tried using the recommended 1.2 to 1.5 starting TWR and I've used a multitude of launch profiles from really steep to really shallow and everything in between. I get through the lower atmosphere with no problems. Any pointers or help would be amazing, um kinda starting to get frustrated...

[astrokerb]

It's hard to know for sure why that keeps keeps happening without a picture of the rocket, although you should Probably just throttle down.

[Friend Bear]

Also, do you mean burning up as in you lose all your fuel or you explode from overheating? If that is the case, you are going too shallow. Your angles may be alright, but you sound like you are at a low degree at too low an altitude.

Let me get you something I typed a while back; copy/pasted. Two different discussions. One is about your apoapsis. The other, attaining orbit.:

---

Your apo is formed entirely from two places: 1) your vertical velocity (if no horizontal velocity exists); 2) your horizontal velocity at the peri. This is oversimplified but drives to my point.

You need high enough vertical velocity, but a fast enough horizontal velocity to prolong your time spent above a certain altitude. In essence, if you gun it straight up..sure you will make it very very high, but you are coming right back down. Similarly, if you gun it straight up, your time spent at the apo is very limited. You extend that time with horizontal velocity.

But of the two lessons above, the most important is your horizontal velocity. And you won't get 2000+ mps when you have only a couple seconds at your apo altitude to complete an orbit (no I won't say circularize. I have no idea why that is trendy to say).

Anyways, this means you need to balance your vertical velocity with your horizontal. But with an atmosphere, you need to do so delicately and not in an aggressive turn.

I shoot for 250-500 mps in vertical within the first 30sec. This is why the first stage is so important and solid booster are amazing. But you need to plan ahead for your horizontal climb while keeping in mind you move faster outside the atmosphere. In essence, make your climb nice and round, but not too round, rather than straight and pointy. This will give you ample time at apo to burn horizontally.

Walkthrough:

At takeoff, depending on the speed (if faster make it slightly more aggressive), IMMEDIATELY turn horizontally about 2+ degrees. You have little atmo resistance and you need to have gravity start helping you with your aim towards the horizon. If you turn too late, it will either be really hard to make the turn and you climb too high/sharp (if you are going fast), or you overturn and the atmo points your ship downward (if you are going too slow).

By setting the degree like this, gravity will slowly point your prograde closer and closer to the horizon as you will slowly accelerate past you 300-500 mps. If it is pointing down too quickly, a lot of the time the cure is acceleration, so just increase your thrust. But too much may kill potential delta v because of wind resistance.

By 30,000 alt, I like to be at about 45 degrees. Compensate accordingly. Slow your throttle as needed. What is important is burn time NOT speed. The longer you burn, the less resistance. Think about it: if you gun it in atmo, you are limited by terminal velocity or the lesser issue of atmo resistance not to the extent of terminal velocity. But by burning long and slow, but in a manner that still gets you out of the atmo, you save all your delta v for lower atmo/no atmo acceleration.

Keep your acceleration consistently and evenly dropping, by gravity, from the 45 deg on through the apo and speed up or slow down as needed (if your apo gets to the altitude you want, you can stop and reignite if atmo slows you down a bit). In that burn, keep the gravity turn going as much as comfortable (20 more deg by 50,000 alt, for example), and use throttle to determine your ultimate apo, pre-final horizontal burn. If you have to, aim below the horizon or higher if you are in the target apo altitude but wish to increase your horizontal acceleration. You don't have to only point prograde once in thinner air.

By the time you hit the apo, you will be at a much much higher horizontal speed, but still need to burn to get into orbit.

Burn before, through, and after the apo as needed. I like to aim so my apo stays on top of me (e.g. pointing up more, 5ish degrees, when I am close to it), but too much of this kills potential horizontal delta v accel.

I'm rushing this at work and didn't proof so I hope it makes sense.

---

As you launch, immediately, and VERY DELICATELY, aim the rocket a degree or two East. From there on, let gravity turn you and use about half throttle. The idea behind the best, most stable climb to orbit is not speed (although you need it to qualify the climb since too slow a climb destroys any chance of horizontal acceleration a minute into your climb to orbit) but insteadburn time. (as for speed; what I mean is that a low speed reduces the usefulness of your overall deltav, while a high speed can do the same. If you are going fast at low altitude, even near horizontally in preparation for orbit, you lost a lot of potential delta v because you fight atmosphere. On the other hand, if you go too slow and lose your asparagus without burning any horizontal, sure you got into space, but now you have to burn 2000+ delta v horizontally to get an orbit in a short window with a single engine because once you are at the peak of your climb, it becomes harder and harder to stay out of the atmosphere with a low horizontal velocity). But careful; this means your gravity turn will be more aggressive. You do not necessarily need to aim into your prograde the entire time. Back off a bit and aim more vertically if it is too aggressive. 45 deg is ideal at 35-45k altitude, for example. This slow, natural turn prevents the bend you are seeing.

[Gaarst]

If by burn up you mean having reentry effects, then it's normal and not dangerous at all. In 1.0.3/.4 reentry effects are common in high atmosphere but are not linked to actual heating of your rocket.

If you really explode, I suggest taking a look at you physics.cfg to see if any value is abnormally high.

[ForScience6686]

Are you actually burning up exploding or just seeing the graphics?

[uncle natzer]

I'm going to post a picture of my rocket and see if you guys can give me pointers and what-not.

It has the dv that it has because it will be doing a Minmus flyby at the very least.

Here is the link also.

http://imgur.com/a/wDhdn

- - - Updated - - -

This is also what my Physics.cfg has set.

dragMultiplier = 8

dragCubeMultiplier = 0.1

angularDragMultiplier = 2

liftMultiplier = 0.036

liftDragMultiplier = 0.015

bodyLiftMultiplier = 18

aeroFXScalar = 1

aeroFXDensityExponent = 0.75

aeroFXStartThermalFX = 2

aeroFXFullThermalFX = 3.5

aeroFXExponent = 3.0

thermalMaxIntegrationWarp = 100

spaceTemperature = 4

solarLuminosityAtHome = 1360

solarInsolationAtHome = 0.15

convectionDensityExponent = 0.5

convectionVelocityExponent = 3.0

convectionFactorSplashed = 5000

fullConvectionAreaMin = -0.2

fullToCrossSectionLerpStart = 0.8

fullToCrossSectionLerpEnd = 1.5

machConvectionStart = 2

machConvectionEnd = 4.0

machConvectionExponent = 3

turbulentConvectionStart = 100

turbulentConvectionEnd = 200

turbulentConvectionMult = 100

machTemperatureScalar = 21

machTemperatureVelocityExponent = 0.75

partEmissivityExponent = 4

radiationFactor = 1

convectionFactor = 6

newtonianConvectionFactorBase = 8.14

newtonianConvectionFactorTotal = 4.0

newtonianDensityExponent = 0.5

newtonianVelocityExponent = 1.0

conductionFactor = 20

internalHeatProductionFactor = 0.025

aerodynamicHeatProductionFactor = 1.0

standardSpecificHeatCapacity = 800

skinSkinConductionFactor = 0.06

skinInteralConductionFactor = 0.4

shieldedConductionFactor = 0.01

Edited October 5, 2015 by uncle natzer

[moogoob]

Those angled fuel tanks might be generating more heat than if they were straightened... I have to reiterate the earlier question - is the ship exploding, or are you just seeing flames? If the former, something's wrong, if the latter, nothing is wrong. In the current aero, I see flame effects on every launch, even nice efficient ones.

[uncle natzer]

It's blowing up at around 45-50k. The angled engines are ditched at around 7k.

[moogoob]

Oooh. Ouch. What does the F3 menu say? What part blows up first?

There are known thermal bugs in the game - I had a recurrent exploding station docking fuselage recently in career mode and had to abandon that design entirely. I think Valentina may have been playing with matches or something.

[uncle natzer]

Haha. It's the fairing that goes every time. It frustrates me that it is that high in the atmo when it does it. At that altitude it really shouldn't because of how this it is, right?

[moogoob]

Haha. It's the fairing that goes every time. It frustrates me that it is that high in the atmo when it does it. At that altitude it really shouldn't because of how this it is, right?

Yeah, it shouldn't happen. Is anything clipping the fairing? Have you tried editing and using a different fairing design? If you have a probe core or reaction wheel or battery attached to the fairing, maybe try switching the part order? On my Nastybird shuttle, it turned out that placing a MK2 drone core attached to a cargo bay was what was making it explode in the upper atmosphere upon re-entry (though only while time-warping... weird). I fixed it by swapping the core and the fuel tank behind it.

[uncle natzer]

Sounds good. I'll start playing around with all of that stuff and see if anything fixes it. Also, I noticed that my imgur pictures didn't show up? How do you post the album correctly?

[Nathair]

I won't say circularize. I have no idea why that is trendy to say

I wouldn't call it "trendy" so much as "accurate". Usually when launching as you first approach apoapsis your orbit is quite elliptical (and often still intersects the surface of Kerbin.) In the vast majority of cases what you want to do is bring about a nice, circular orbit, usually somewhere around 75x75 or so and then go wherever you're going from there. I call it circularizing my orbit because that is exactly what I am doing.

[Friend Bear]

It's blowing up at around 45-50k. The angled engines are ditched at around 7k.

Yeah you are simply just going too fast.

Don't throttle all the way. Not only will you lose potential delta v because you are fighting terminal velocity, but going too fast will make you burn up.

Read my post above. What matters anyways is burn time, not necessarily speed of the climb. Climb more slowly then use all that delta v to attain horizontal velocity necessary for orbit.

Edited October 6, 2015 by Red Iron Crown
Removed off topic content.