Eve phase angle

[DunaManiac]

I've launched missions to eve but never got the phase angle right. I've googled phase angle charts but none are up to date. Does anyone know the eve 1.1 phase angle. Thank you.

[Spricigo]

maybe ask alexmoon or olex

[HebaruSan]

3 hours ago, DunaManiac said:

I've googled phase angle charts but none are up to date.

How are they out of date? Was there a release that changed Eve or Kerbin's orbital characteristics? I'm not finding mention of such in the wiki's version history.

[Weywot8]

It's entirely possible that you have the 'correct' phase angle but have not taken into account

• Eve's phase angle requires it to be behind Kerbin
• Eve's inclination
• your ejection angle retrograde is important, a few degrees off here can have a noticable effect on intercept.

"Sweep" Eve's orbit by / after you have adjusted inclination / to get the two orbits to intercept. You will need to make some adjustment's anyway because the phase angle calculations assume circular orbits.

Or if you feeling really keen, calculate the phase angles yourself to confirm.  Kepler's Third law to get you started : (Orbital Period, OP)² α (Semi-major Axis, SMA)³. It's all a bunch of ratio's after that.

Spoiler

Kerbin SMA: 13599840256m  - from center of Kerbin and the Sun

EVE SMA: 9832684544m 

Simplifying for later math: SMA_eve = 0.723 SMA_kerbin, OP_eve = (0.723)^3/2=0.61476261028 OP_kerbin

SMA_{transfer orbit} = (SMA_kerbin+SMA_eve)/2 = 0.8615 SMA_kerbin

OP_{transfer orbit} =0.8615^3/2= 0.79961866 OP_kerbin

So we leave Kerbin, and arrive at Eve's orbit takes 1/2 OP_{transfer orbit} = 0.39980933 OP_kerbin

We want to encounter Eve at that point so working backwards, Eve's travels a ratio of its full orbit  = 360 degrees *  OP_{transfer orbit}/OP_eve 

= 360/2*(0.8615/0.723)^3/2= 180*1.30069502 = 234.13 degrees to intersection point. 

But we leave Kerbin 180 degrees, directly opposite, the arrive point so Eve will be located 180-234.13 = 54.13 degrees behind Kerbin

This is exactly the same result from this excellent tool

Eccentricity  is 0.01 = 1% change of SMA giving ~ +3.45/-3.55 degrees error at most but that's well within ejection angle error for a lower TWR ship.

Nothing has changed. 

Edited July 5, 2017 by Weywot8

[DunaManiac]

On 7/4/2017 at 5:52 PM, HebaruSan said:

How are they out of date? Was there a release that changed Eve or Kerbin's orbital characteristics? I'm not finding mention of such in the wiki's version history.

Sorry, just wanted to be sure.

On 7/4/2017 at 9:08 PM, Weywot8 said:

It's entirely possible that you have the 'correct' phase angle but have not taken into account

• Eve's phase angle requires it to be behind Kerbin
• Eve's inclination
• your ejection angle retrograde is important, a few degrees off here can have a noticable effect on intercept.

"Sweep" Eve's orbit by / after you have adjusted inclination / to get the two orbits to intercept. You will need to make some adjustment's anyway because the phase angle calculations assume circular orbits.

Or if you feeling really keen, calculate the phase angles yourself to confirm.  Kepler's Third law to get you started : (Orbital Period, OP)² α (Semi-major Axis, SMA)³. It's all a bunch of ratio's after that.

  Reveal hidden contents

Kerbin SMA: 13599840256m  - from center of Kerbin and the Sun

EVE SMA: 9832684544m 

Simplifying for later math: SMA_eve = 0.723 SMA_kerbin, OP_eve = (0.723)^3/2=0.61476261028 OP_kerbin

SMA_{transfer orbit} = (SMA_kerbin+SMA_eve)/2 = 0.8615 SMA_kerbin

OP_{transfer orbit} =0.8615^3/2= 0.79961866 OP_kerbin

So we leave Kerbin, and arrive at Eve's orbit takes 1/2 OP_{transfer orbit} = 0.39980933 OP_kerbin

We want to encounter Eve at that point so working backwards, Eve's travels a ratio of its full orbit  = 360 degrees *  OP_{transfer orbit}/OP_eve 

= 360/2*(0.8615/0.723)^3/2= 180*1.30069502 = 234.13 degrees to intersection point. 

But we leave Kerbin 180 degrees, directly opposite, the arrive point so Eve will be located 180-234.13 = 54.13 degrees behind Kerbin

This is exactly the same result from this excellent tool

Eccentricity  is 0.01 = 1% change of SMA giving ~ +3.45/-3.55 degrees error at most but that's well within ejection angle error for a lower TWR ship.

Nothing has changed. 

Woah.

[Cpt Kerbalkrunch]

On 7/4/2017 at 1:33 PM, DunaManiac said:

I've launched missions to eve but never got the phase angle right. I've googled phase angle charts but none are up to date. Does anyone know the eve 1.1 phase angle. Thank you.

What's a @DunaManiac goin' to Eve for anyway? 

[Spricigo]

1 hour ago, Cpt Kerbalkrunch said:

What's a @DunaManiac goin' to Eve for anyway? 

Wrong turn at Albuquerque? 

Or maybe it's a Different Duna the object of his mania.