Calculating SurfaceMFD Accelerations

[Tachyon]

How did I take all the fun out

You didn't - I'm someone who just jumped into this thread because it looked interesting ..... and then my brain started to hurt. Got worried that somehow knowing a calculation within orbiter might be flawed .... well the whole fabric of space and time might be called into question.

Why do you ask?

Ahhh university .. that was where I learned that I COULD fall asleep anywhere, anytime if the opportunity presented itself. :lol: Students today have it so lucky. In 1981 ... there was one Apple][ on campus ... and that wasn't for "general" use. I can only dream of how much easier life would have been with a laptop and the inter/intra net. Oh well.

Good luck -

 

[Hielor]

I always sort of thought that you weren't even from the US. My brother actually goes to UT @ Austin. (doubt you'd know him though)

You know, I can't decide if saying that I don't seem like I'm from the US is a compliment or not. Considering how most of the rest of the world considers the US these days, i guess it probably is? :lol: And yeah, doubtful I'd know him, unless he's also a CS (or possibly Linguistics) major. It's a big school.

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Back to the original topic:
tblaxland:
I tried the algorithm you gave, but it doesn't entirely avoid rotations. The acceleration vector will be in the ship's local reference frame, and the relative position/velocity that you fetch will be in the global ecliptic frame. One of them must be converted to the other, so you won't be able to completely get rid of rotations.

Moreover, now that we can account for source of the vast majority of the error, we know that the problem isn't coming from the rotation matrices. Thanks though.

I'll post here when I have a way of accounting for this discrepancy. I suspect it would be even more of a problem on say, the Jovian moons, due to the influence of Jupiter.

Haha, I just tried it on Io. The calculation is off by .691 m/s^2 when I'm landed...that's kind of a big error. And another interesting tidbit: due to the gravitational influence of Jupiter, the net gravitational force on the surface of Io is not necessarily straight "down" into the moon, but rather off to an angle with respect to the local horizon. Put yourself on the surface of Io and turn on force vectors! That's just weird.

Anyway. Accounting for the acceleration due to other bodies in the VAccel calculation while landed. I'll get right on it.

EDIT: Apparently i forgot to copy over the new version of my testing code, so the error of .691 was from an older version. The actual error varied between .0038 and .007.

 

[tblaxland]

tblaxland:
I tried the algorithm you gave, but it doesn't entirely avoid rotations. The acceleration vector will be in the ship's local reference frame, and the relative position/velocity that you fetch will be in the global ecliptic frame. One of them must be converted to the other, so you won't be able to completely get rid of rotations.

OK, I missed that the acceleration vector is in the local reference frame.

Anyway. Accounting for the acceleration due to other bodies in the VAccel calculation while landed. I'll get right on it.

Maybe I'm missing something else but the answer seems pretty simple. This error is only due to the contact force when landed, right? Can't you just set VACC=0 when landed (use GetFlightStatus to check)?

 

[Hielor]

Maybe I'm missing something else but the answer seems pretty simple. This error is only due to the contact force when landed, right? Can't you just set VACC=0 when landed (use GetFlightStatus to check)?

That would....um...make too much sense. And be too easy.

I was about to say that that wouldn't work during the takeoff roll since you no longer count as "landed," but the force vector is all over the place during takeoff anyway (turn on force vectors and watch it while you're taking off), so it'll be inaccurate anyway.

Thanks for pointing me to answer on the ground in front of me while I was attempting to find it in the stars above, lol! :rofl:

 

[Hielor]

So since it looks like we've got this pretty well licked, I was going to put it up on the wiki...I haven't posted any articles that didn't already have a stub (KeyComm), where should i put it or under what categories, etc...

 

[tblaxland]

So since it looks like we've got this pretty well licked, I was going to put it up on the wiki...I haven't posted any articles that didn't already have a stub (KeyComm), where should i put it or under what categories, etc...

Type the title into the search box (eg, "Calculating Accelerations along the Airspeed and Local Vertical Vectors") and click "Go". This will give you a link to "create this page". I'd put a link to your article on the References page and also put it in the OrbiterSDK category.

 

[Tex]

I some how managed to miss this valuable thread, thanks for posting it Hielor. Promoted to article and permanent redirect left behind in the SDK forum.