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Souper

Best / most effecient way to reach orbit?

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Do i go at full thrust and turn sharply once in an altitude where the drag won't really matter?

Do i go slow, turn gradually until sideways?

Or do i shoot straight up and circularize once out of atmosphere?

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You start turning almost immediately after launch (as soon as your rocket is stably flying up and accelerating).

You turn very slowly and keep your heading inside prograde marker to maintain stability.
Sharp turns are inefficient.

Edited by Shpaget

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MechJeb (and KER too, I guess) has the feature to show you "dV spent", "drag losses" etc. You can try out a simple rocket and look for the best ascent. You'll find out that you want to do gravity turns starting as low as possible.

if you point your nose too far away from prograde at speed while in mid-thick atmo, your rocket will flip for her "Salto Ascendale" and that will either cost you a good portion of your dV or the whole launch. 

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48 minutes ago, MircoMars said:

MechJeb (and KER too, I guess) has the feature to show you "dV spent", "drag losses" etc. You can try out a simple rocket and look for the best ascent. You'll find out that you want to do gravity turns starting as low as possible.

if you point your nose too far away from prograde at speed while in mid-thick atmo, your rocket will flip for her "Salto Ascendale" and that will either cost you a good portion of your dV or the whole launch. 

Has not seen the drag and gravity loss calculation in modern mechjeb, it was an cool function back before 0.20

As I understand an well balanced rocket will perform gravity turn by itself 

And yes an real life rocket will disintegrate if it comes in sideways at supersonic speed.

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Like how it's done in IRL, or at least close to it.

For bodies with little to no atmosphere you want to turn immediately.

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2 hours ago, Bill Phil said:

For bodies with little to no atmosphere you want to turn immediately.

While keeping an eye for nearby mountains. You may want to avoid those by thrusting at least a bit upwards.

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18 minutes ago, Shpaget said:

While keeping an eye for nearby mountains. You may want to avoid those by thrusting at least a bit upwards.

Yes you need to trust vectored downside so much you don't hit ground, as you go faster you can use more of your trust to gain speed instead of keeping attitude, this is why an very low TWR takeoff is bad also on airless bodies. 

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Combination of option one and option two for most launches. RL is harder than KSP though, owing to things like latitude vs. intended inclination, safe stage disposal, stage performance and other specifically intended things.

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Is there a way to discuss this conceptually without a screenful of greek letters?

Ok, so the throttle back part I think I understand.  At a certain speed, the forces from air resistance are larger than the forces from gravity.  So you throttle back before you exceed that speed, specific to actual drag coefficient and air resistance in the case of an actual rocket.

Or is that not it?  Every unit of time, you're losing upward velocity component due to gravity.  So you want to reach orbit as fast as feasible to eliminate that.  Every unit of time, you're losing velocity as long as you stay in the atmosphere.  So you want to ascend as fast as possible to escape it.  But if you reach a speed where you actually are losing more from air resistance than the derivative of the change of gravity...ok yeah I guess we do need some greek letters here.

The other part I can't quite grasp is why you want to cant over soon after you leave the tower.  Don't you want to escape the atmosphere first and then burn sideways?

 

 

 

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Isn't it depending on your rocket? Different rockets need different flight profile.

1 hour ago, SomeGuy123 said:

The other part I can't quite grasp is why you want to cant over soon after you leave the tower.  Don't you want to escape the atmosphere first and then burn sideways?

Try it in KSP. You would make a highly elliptical orbit that way if you burn straight up for too long before turning side way. Waste more time circularize your orbit. But then, sometimes that is the intention. So maybe we also have to account to the mission objectives and what kind of orbit we want.

Edited by RainDreamer

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If your goal is a circular orbit than your final vertical speed needs to be zero.

Expending any energy to accelerate upwards is a loss. We do it only to get out of the atmosphere as soon as practical/efficient.

There is a sweet spot between getting out of atmosphere as soon as possible and starting the sideways acceleration as soon as possible.

Exact ascend profile greatly depends on TWR, where low TWR requires steeper climb and rockets with higher TWR benefit from earlier gravity turn.

Then there is the ISP that drops with atmospheric pressure. Some engines operate very poorly in thick atmo, while some take only a moderate hit to their performance. Depending on what type you have, you might want to adjust the profile.

Going straight up, then turning is usually not the most efficient way. Not an exact analogue, but you don't go the long way around a park and turn a sharp corner if you can take a diagonal path.

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14 hours ago, Souper said:

Do i go at full thrust and turn sharply once in an altitude where the drag won't really matter?

Do i go slow, turn gradually until sideways?

Or do i shoot straight up and circularize once out of atmosphere?

none of the above go fast, but not to fast, but start your gravity turn at 1km

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1 hour ago, Rolacume said:

none of the above go fast, but not to fast, but start your gravity turn at 1km

That's way too high unless your working with a twr of like.. 1.05. No you should start turning at a couple hundred meters with a decent twr. 1.5+ start soon as you leave the pad.

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