Flight Question "Prograde" confusion

[Dennyc39]

My prograde orientation is not what I would expect.

I am on a return trajectory from the moon, roughly halfway, and I hit the "Prograde" button (in my DGIV), expecting to get a view of the earth, but instead it turned me around and pointed me somewhat toward the moon, definitely backwards with respect to my current velocity.

I am 246M from the earth, moving 1.200 k/s, and my Orbit MFD shows me definitely progressing toward the earth wit a current PER of 11.2M. The Orbit:Earth MFD shows a G of 0.51, and the Orbit Earth Hud has the bullseye vector symbol (circle-dot) about in the middle of the HUD. So why does the "Prograde" autopilot have me facing back looking at where I've been?

 

[insanity]

Hello and welcome to a fellow Oregonian (Ashland raised/OSU alum here)! Did you double check that the Orbit HUD is showing your reference to Earth? If so, does this seemingly false prograde persist well into the SOI?

 

[Izack]

Hello, and to the forum!

Roughly halfway from the Moon to Earth, your primary gravitational influence is the Sun. You are indeed pointing prograde, but in reference to your solar orbit. So like Insanity said, try setting your Orbit HUD to reference Earth (ctrl+o.) The autopilot will still not point you in the direction you want, but it is just as easy to follow the pitch and yaw ladders to 0 degrees and have a good look at your destination.

 

[Dennyc39]

That would explain it, except the HUD does say "Orbit Earth". The Orbit MFD has reference set to Earth.

I am roughly 50% of the way home from the moon.

 

[blixel]

That would explain it, except the HUD does say "Orbit Earth". The Orbit MFD has reference set to Earth.

I am roughly 50% of the way home from the moon.

Note the bottom of Orbit MFD. When Earth is not the dominant contributor to the gravity field, the G (gravity) reading is red. When Earth becomes the dominant contributor to the gravity field, it turns green. Once it turns green, the Prograde/Retrograde AP will orient relative to the earth as opposed to the sun.

 

[Cras]

in the mean time, you can always use Attitude MFD to keep yourself point at Earth (or the Moon, or the Sun, or anywhere you want)

 

[agentgonzo]

Roughly halfway from the Moon to Earth, your primary gravitational influence is the Sun.

No no no no no no no! Bad Izack. Half way between the Earth and the moon, your primary gravitational influence is the Earth. If the primary influence was the Sun then you'd leave Earth orbit and orbit the sun.

 

[Urwumpe]

No no no no no no no! Bad Izack. Half way between the Earth and the moon, your primary gravitational influence is the Earth. If the primary influence was the Sun then you'd leave Earth orbit and orbit the sun.

Wrong. Remember Lagrange points? While you are technically still in the gravity well of Earth, you are getting more influence by the sun, than by Earth and Moon together, because they neutralize each others.

 

[agentgonzo]

Wrong. Remember Lagrange points? While you are technically still in the gravity well of Earth, you are getting more influence by the sun, than by Earth and Moon together, because they neutralize each others.

Not half way between them you don't. The Earth-Moon L1 point is much closer to the moon due to it's lower mass.

 

[Urwumpe]

Not half way between them you don't. The Earth-Moon L1 point is much closer to the moon due to it's lower mass.

Yes, but in terms of flight time, it works out approximately. I don't want to get into details there, if I don't need to.

 

[Dennyc39]

It is green now (G = 0.51), and it does now work the way I expect.

Thanks for the clarification.

Greetings from Mill City, Oregon.