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sebjf

Why does my spaceplane run out of fuel attempting a West-bound/CW Orbit?

Question

Hi,

I am trying to make a spaceplane. I've managed a couple of craft that can get into orbit with 500-1000 m/s dv remaining, but when I try to launch westward (to pick up crews from Asteroid intercepts), I cannot get into orbit at all.

Below is the latest. The ascent profile I aim for is to get to 1300-1400 m/s around 1-2km, then pitch up to 20 deg, and around 9km engage the nukes. (I just tried it just now - 1200 m/s by 3km, engaged the nukes at 12km, burned all engines at 20 deg until the air breathing engines ran out, then burned prograde until AP hit 70km. Orbit established with 830 m/s dv remaining.)

When I aim west though it doesn't work.

I can never get the AP as high before reaching it as I do going east. I know I have to fly against the rotation of Kerbin, but thought that was only 175 m/s or so to cancel the initial rotation?

Can anyone see where my plane is going wrong?

Here is a picture of it, and the craft file: https://www.dropbox.com/s/oo3hpgzdmwh84b1/NX3.craft?dl=0

I haven't unlocked RAPIERS yet.

Sj

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Edited by sebjf

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I'd say its all about lift drag ratio.   You want to get the best exchange rate possible,  that means maintain the nose 5 degrees above wherever the prograde marker is pointing.    When you deviate a couple of degrees off this 5 degree angle of attack your lift to drag ratio goes to hell.

UTSktyw.png

 

Looks like you're able to make this work by getting into a 30 degree zoom climb after reaching 1200m/s at 10km when the Whiplash is still making a lot of power - by the time your upward momentum has run out,  you've gained enough horizontal orbital velocity.

 

My designs are intended for a level flight speedrun at 17km,   then start the nukes, and once the jet power is dying away about 1350 or so,  ease the nose up so it's 5 degrees above prograde and keep it there.   If your lift drag ratio is good enough it should work.    To do that in the above craft i'd want 3 times the wing area and switch to an inline mk1 cockpit.    Pointy cockpits get much hotter,   and with smaller wings relative to your weight,  your craft goes lower in the atmosphere for any given speed when means more friction heating.

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