What happened to the Δv needed for LKO?

[reaction_wheel]

It looks like the Δv needed to reach low Kerbin orbit from KSC went down recently from 4,550 m/s to under 3,600.

I've seen references in the forum that suggest that this is due to the new aerodynamics modeling in 1.0.4(?), but can anyone explain why?

[Greenfire32]

The atmosphere is no longer extremely thick and the new aerodynamics no longer affect parts based on how many they are, but rather on their shape. In the past it was more areo-efficient to NOT put nose cones on your rocket because the added weight meant the rocket performed worse in atmo. That is no longer the case. Adding nose cones now makes your rocket slice through the air like a knife, rather than ram through the air like a pancake.

[Temstar]

Back in my days Kerbin's atmosphere was so thick, you could bit off chunks of it and chew it.
*shakes his old man stick*

 

[GoSlash27]

Yup. The difference is due to the change in aero modeling, and it's the only difference. All maneuvers in space or involving the Mun require the same DV they always have.

Best,

-Slashy

[OhioBob]

11 hours ago, Temstar said:

Back in my days Kerbin's atmosphere was so thick ...

This is a common misconception.  Although the atmospheric model did change with the introduction of 1.0, the density of the old atmosphere was only slightly greater than it is now.  The main reason that drag was so much higher in the pre-1.0 days was because KSP used a place-holder formula to compute the cross-sectional area of a rocket that was wildly unrealistic.  Area was a function of mass, so the shape of a rocket was irrelevant.  The place-holder formula turned everything into a flying pancake, with a drag area far greater than it actually had, resulting in a huge drag force.

[Superfluous J]

Also, the thickness of the atmosphere encouraged you to go straight up 10km before cranking over 45 degrees. That meant you burned a LOT of fuel fighting gravity. Now, not only is that unnecessary it can cause your ship to flip out of control (sharp turns in atmo are bad). It's far better to tap over after you get up to 50-100m/s and slowly tilt over throughout the climb, ideally still hitting about 45 degrees at 10km, but doing it gradually instead of all at once. Due to this you fight gravity far less and put your fuel to use giving you sideways velocity.

Don't think this makes the game easier, by the way. It's significantly harder to reach orbit now than it was before, and getting down can be pretty hair-raising as well. And I love every second of it

[rocketbuilder]

As said, the dragyness and gravity turn not being go up to 10k and turn right.

With those massive flat tipped pancake rockets used on 0.90 the DV required for orbit now is about 4500, but a rocket that looks like a falcon 9 or atlas v will take only 3200-3400.

I saw that someone did it with 2800 even. 

Edited December 23, 2015 by rocketbuilder

[Francois424]

It really depends on the shape of whatever you want to send in LKO.  Sometimes I get out with 3.5k, other times it's 4.5k.  A sleek rocket is usually the cheapest, but you gotta send the big station/mothership parts in space sometimes !

[Val]

They also "nerfed" rocket engines by giving them less ISP and thrust at sea-level.

So while the dV needed to get to orbit has dropped, the amount of fuel you need hasn't changed much.

[Snark]

7 minutes ago, OhioBob said:

This is a common misconception.  Although the atmospheric model did change with the introduction of 1.0, the density of the old atmosphere was only slightly greater than it is now.  The main reason that drag was so much higher in the pre-1.0 days was because KSP used a place-holder formula to compute the cross-sectional area of a rocket that was wildly unrealistic.  Area was a function of mass, so the shape of a rocket was irrelevant.  The place-holder formula turned everything into a flying pancake, with a drag area far greater than it actually had, resulting in a huge drag force.

Well, I think that by "thick" in this context, he meant "in the only way that's important to a KSP player", i.e. "how hard is it to shove a rocket through it," rather than the actual density. 

[OhioBob]

9 hours ago, Snark said:

Well, I think that by "thick" in this context, he meant "in the only way that's important to a KSP player", i.e. "how hard is it to shove a rocket through it," rather than the actual density. 

Perhaps, but the original question was "can anyone explain why?"  To that I think a factually correct answer should be given.  Perhaps the initial poster doesn't really care about the details, but if he does, then implying that it's the atmosphere that has changed is not factually correct.

 

Edited December 24, 2015 by OhioBob
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