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Circular orbit speed is given for a tangential velocity  

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Diederick
(@diederick)
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Joined: 2 years ago
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September 5, 2018 4:37 am  

Can someone explain to me what this exactly means, specifically in the game? I can more or less understand what a circular orbit is, but how is its speed "given for a tangential velocity"?

Thanks!


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nozmajner
(@nozmajner)
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Joined: 3 years ago
Posts: 260
September 5, 2018 7:37 am  

You wound that commented out orbital nav aid? Note that it will go away with the UI rewrite, but we also want to introduce a proper orbit display into the HUD to aid navigation.

Tangential speed means your speed parallel to the ground, let's say. For any given height, a certain speed in a certain direction means a certain shape of orbit (another simplification).

But I'd suggest don't worry much about it, use the orbital display instead for orbital stuff. First you should fly to a good height (100km for Earth is about the minimum), then rotate your ship parallel to the ground. Side and down views are helpful for that, or the HUD indicators. After that start accelerating in manual flight (W) and without releasing the button, press F2 or the Orbital map button on the top. This will open up the map, but the engines won't turn off, even if you release the accel button. (Which is actually a bug, but a useful one) Now you can watch how your orbit changes in real time. And when you are at the correct shape, you can go back to the Worldview (F1) and your engines will be turned off, since you no longer pressing the button.
There's also an orbit planner function you can play with, setting up changes in speed on three axes. It will display a marker and needed deltav, burn time on the HUD, if you set up something there. Kinda like in KSP.


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ubervison
(@ubervison)
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Joined: 4 years ago
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December 16, 2018 3:16 pm  

Hello, I just got into Pioneer and I am having lots of fun flying around the solar system. There is one thing that I don't understand: the prograde and target prograde marker.

I more or less understand that the prograde marker shows us the direction the ship is moving (like we were looking through the butt of a velocity vector), but I don't understand how to interpret the target prograde marker. The wiki says that the target prograde marker shows the direction we are traveling relative to the target. What does it mean? If both markers show us the direction we are traveling, how are they not always in the same position? After all, we can only go in one direction, so I feel like I'm missing something here.


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nozmajner
(@nozmajner)
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December 16, 2018 8:24 pm  

Hi!
The prograde vector treats your frame of reference as a stationary point of reference, but in most (if not all) cases, your target moves relative to it. So usually your and the targets vector will not line up.
This is why you only have one marker, if your target is the frame of reference.
Or to paraphrase it: you aren't going in one direction, because direction (and speed) only makes sense if you measure it relative to something.

Also, you will notice that the target prograde can change a lot, especially if it is going around on a tight, fast orbit. So if you want to fly manually from a city to an orbital, even with that marker, you need to lead your target some. (Hopefully we will have a closest approach marker eventually, and orbit displays during flight, to help with that.)
And the faster you go, the closer the two markers will be together, because the target speed is very low compared to your 1000s of km/s. Or the furthest you are from them, the smaller the difference.

Hope this helps!(I thing I might add a clarification to this on the wiki as well)


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ubervison
(@ubervison)
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December 17, 2018 3:44 am  

Hey thanks nozmajner, I think I get it now. It's very counter intuitive to reason about velocity when all the the target and the frame of reference are all in motion relative to each other, and I think the sheer scale of the game universe make it seem that it is all static whenit is really not. One thing that helped get it is rendezvous with Torvalds platform from Earth and see how the Earth target vector behave once I'm in orbit


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nozmajner
(@nozmajner)
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Joined: 3 years ago
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December 17, 2018 8:58 am  

No probs.
This whole orbital stuff is quite unintuitive to us landrats. You could look up some KSP tutorials about orbital mechanics can clarify a lot of things.
Obligatory XKCD quote:
KSP Orbital mechanics


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