Confusion about Delta-V to orbit Kerbin

[Mr.T]

Hello KSP forum. First off, I would like to say that you guys are awesome; I love the community and I've been spectating the forums since I got this game in March of 2014. Much of what I've learned about the game has come from reading here and on the wiki, which I'm just gonna assume some of you guys also have a hand in maintaining. So thank you for all that.

Now that my introduction is out of the way...

I'm perplexed by something that happened today. I created a standard heavy ascent stage (3.75m parts, asparagus staging, etc.), put a fairly heavy payload on top to test it, and as I've become accustomed to doing, I calculated the Delta-V by hand. I came up with something like ~3800 m/s sum total for the first 3 stages. The thing that confuses me is that I'm able to easily get this thing into a 75 Km orbit around Kerbin with some fuel still left in the 3d stage, but everywhere I look the Delta-V that is needed to get into orbit around Kerbin is about 4500 m/s. I downloaded MechJeb (I hadn't used it before and I must say I've been missing out on something amazing) and it confirmed my calculations, listing my Delta-V in the first 3 stages again around 3800 m/s.

So my question is: What am I forgetting to factor into this? I know I'm thinking about this wrong somehow, I just want to understand exactly what I'm doing/thinking wrong. Does it have something to do with the free orbital velocity one gets from launching in the direction of the rotation of Kerbin?

Anything you guys can tell me to help me figure this out would be greatly appreciated!

Here's a link to a photo of the rocket in case it helps to see it; all engines firing are Mammoth engines.

http://steamcommunity.com/profiles/76561198036634230/screenshot/544154344546083166

Edited June 7, 2015 by Mr.T

[Harry Rhodan]

What am I forgetting to factor into this?

That all those charts still show the value you needed to go through the pre-1.0 souposphere.

[maltesh]

All the sources you're looking at were from before 1.0. In 1.0, the new aerodynamics lowered the delta-V to reach LKO to about 3500 m/s.

[Master Tao]

Welcome to the forums!

There are some updated delta-v charts in this thread. KSP 1.0 overhauled the aerodynamics and thrust simulations, so the delta-v requirement to Low-Kerbin Orbit has dropped quite a bit from the old 4500 m/s.

[cybersol]

It was never a single number, even before version 1.0. How long you stayed in the gravity well affected your gravity losses, but staying below terminal velocity was enough to minimize your drag losses. However, in 1.0+ it really depends much more on how much drag you experience, which is a combination of design and piloting. With high TWR (1.7-2.3), an aerodynamic single stack design, and a quick gravity turn with a low ascent profile you might manage around 3200. With low TWR (1.3), a fairing the size of Gilly, and a late gravity turn with a high profile to prevent wobble you might take 4200. A good conservative number to use for planning is probably in the 3600-3800 range, with the lower end for those who favor high TWR and full throttle and the higher end for the low TWR and reduced throttle crowd.

[Coga19000]

The variables are always a major factor in how much Delta -v you need. However, is more or less what the others said -now that the atmoshpere is actually half decent, there is certainly 1 km of difference from the thin ocean of fluid that we called atmospheric air.

[Mr.T]

That makes complete sense. Ok thank you all very much!

[SanderB]

On kerbin you can get as low as ~3,000m/s dV to LKO with a very shallow ascent, very high TWR and very high mass rockets.