How do you Target the Center of an asteroids mass?

[johnnyhandsome]

Clicking "Target Center of Mass" doesn't seem to do anything.

[Superfluous J]

I don't know what that's for, but when you target anything, its center of mass is that purple circle with the dot in it. I've only caught 2 asteroids (an A and a C) but in both cases I was able to push it with no problems when that purple circle was centered.

[johnnyhandsome]

Ooooooooh, got!

[Twreed87]

You need to also activate the Free Pivot. The asteroids CoM will be the purple circle on the navball, and you can pivot your ship around so it's lined up. Then you lock your pivot and you're good to go.

Although I noticed something interesting. I grabbed a Class A asteroid, and I was using a fairly large ship, and instead of the regular circle purple icon, I got the one that indicates you're facing AWAY from a target. I think it's because, since the asteroid is now a part of your ship, the CoM is the CoM for the entire thing, and since my ship was bigger than the asteroid, my CoM was behind my command pod.

[Bearsh]

I usually get close enough so that i can right click on it and it says target center of mass.

I don't know if you can target it in map... But yeah usually you get close enough and right click and press target center of mass and usually it's like a normal targeted object. A glowing greenish line around it/it's orbit.

[HeadHunter67]

OK, I know how to target the center of mass (and how it shows on the navball). I know about the pivot on the claw, but I don't understand how to "pivot your ship around so it's lined up". Lined up with what, exactly? It's already lined up with the purple circle on the navball when I clamp on with the claw - but that doesn't stop the thing from spinning like a rodeo bull when I fire the engines.

Any video tutorials of this? The in-game scenarios are pretty awful.

[diomedea]

OK, I know how to target the center of mass (and how it shows on the navball). I know about the pivot on the claw, but I don't understand how to "pivot your ship around so it's lined up". Lined up with what, exactly? It's already lined up with the purple circle on the navball when I clamp on with the claw - but that doesn't stop the thing from spinning like a rodeo bull when I fire the engines.

Any video tutorials of this? The in-game scenarios are pretty awful.

I'm not good (yet) at making videos, but hope the following can be clear enough.

The spin on the roid is due to torque exerted on it, and the torque is due to how far off from the Center of Mass (CoM) of the roid you direct your thrust. With a normally built ship, your thrust is aligned with the root part, so the direction marker in the center of the NavBall is also showing your thrust direction.

You normally want to push (or pull) the asteroid keeping its CoM exactly aligned with your thrust, therefore with the CoM in the center of the NavBall. Any deviation from true center will impart some spin.

Even a very slight deviation, if kept during a long or powerful enough push, will impart crazy spins. What you want is to change the deviation so to apply thrust that will actually stop that spin.

I normally use to push asteroids (did quite a lot while testing ARM), and when pushing to the left of the CoM, the roid will spin to the right. The same opposite relation goes with any other direction. I use to angle my thrust so to apply spin to the roid towards the direction I want it to rotate, and that way I can not only avoid it spinning wildly, but even rotate where I want more speedily than with other means.

If need be, I use short impulses of thrust, only applied when the CoM is deviated from my thrust direction in the correct direction (I can use whatever means, RCS, wheels to rotate my ship so that the roid CoM comes in the correct position relative to my thrust). And, since the grabbing device is not rigid, but will allow some wobble, I use that wobble to time when to apply thrust in the correct direction, so to keep the roid oriented where I need it to be.

[HeadHunter67]

Academically, that all makes sense... but I'm still not sure how it relates to the whole pivot thing. I'm told that if I'm lined up with the purple circle, it will go straight. That hasn't been the case.

Maybe it's just that the ships designed for the scenarios are crap and don't have enough command authority to handle the thrust. I don't know, all I know is that the means that Squad provided to acquaint us with the new content are leading to my frustration instead of fun.

[cantab]

Although I noticed something interesting. I grabbed a Class A asteroid, and I was using a fairly large ship, and instead of the regular circle purple icon, I got the one that indicates you're facing AWAY from a target. I think it's because, since the asteroid is now a part of your ship, the CoM is the CoM for the entire thing, and since my ship was bigger than the asteroid, my CoM was behind my command pod.

That probably just means your command module was facing the opposite way from the claw.

[diomedea]

Academically, that all makes sense... but I'm still not sure how it relates to the whole pivot thing. I'm told that if I'm lined up with the purple circle, it will go straight. That hasn't been the case.

Maybe it's just that the ships designed for the scenarios are crap and don't have enough command authority to handle the thrust. I don't know, all I know is that the means that Squad provided to acquaint us with the new content are leading to my frustration instead of fun.

I may say I am sympathetic with what you're saying. I didn't use scenario ships, but my own (so can't and won't judge about those ships from Squad). The dimension (mass) of the roid is really of much importance, the same kind of ship I used without any trouble with Class C roids (about 100 tons) had a very hard time with a Class E (3500 tons). Those are sluggish, take a lot of time and attention to be oriented correctly, and I could only apply a fraction of thrust or the ship would go to pieces. But, even in that case, it was possible for me to bring that roid where I wanted by applying that "trick" with oriented thrust.

Yes, if you can keep the roid lined up with your ship (so CoM and thrust aligned), it will go straight. For small roids, it is easy. It should also be easy with pulling roids, rather than pushing them (so you have to use a ship with the grabbing device in the same direction of the thrust of your engines, similar to the one shown in the video from MaxMaps), but I never went with that. But for pushing bigger roids, you can't keep the "purple circle" aligned, even the slightest deviation will make for increasing torque and spin. So the only way is to reorient the ship and counter that spin.

[HeadHunter67]

OK, I think I've got it now. If I'm thrusting at a maneuver node, the CoM is still lined up with my previous vector (likely my prograde). So what I need to do is to free the pivot and align it with the blue maneuver marker? So if that's the case, the only question that remains is, how do I do that? Do I need to unclamp it completely, or is there a way to move the angle of the ship? RCS, perhaps, or even just capsule torque? Or does that not change the orientation?

[diomedea]

OK, I think I've got it now. If I'm thrusting at a maneuver node, the CoM is still lined up with my previous vector (likely my prograde). So what I need to do is to free the pivot and align it with the blue maneuver marker? So if that's the case, the only question that remains is, how do I do that? Do I need to unclamp it completely, or is there a way to move the angle of the ship? RCS, perhaps, or even just capsule torque? Or does that not change the orientation?

Very possibly yes, you got it.

But let me make it in a way that could be good for others, too.

So, you planned a maneuver with the roid grabbed, and have the blue marker for that. What you want is to align the CoM of the roid with that marker, and that most probably means orienting the roid. If a small roid, you can orient it with RCS or wheels on the ship, keeping the grabbing device pivot fixed after having oriented the ship to be alinged with the roid CoM. But with a large roid, you'll end your monoprop and even all electricity in the effort of orienting with RCS and wheels. My suggestion is then to free the pivot and let the ship orient so to have the thrust in the opposite direction (in respect of the roid CoM) than the blue marker. Thrusting will then make the roid rotate towards the blue marker. Actually, you need to plan for stopping that spin when CoM and blue marker are aligned, and that requires to reorient the ship in advance, while the roid is rotating, with a reversed deviation than the one used to make it spin. To orient only the ship (not the roid), RCS or wheels are good, so it shouldn't require much effort (unless the spin of the roid is so fast to be out of control, but then it is best left go or it will crash the ship). If the timing is just right, the spin will be cancelled when CoM and blue marker are aligned, so what's needed is just to realign the ship's thrust with the roid's CoM. If the ship was really perfectly aligned, then thrust would be all used to achieve the maneuver as planned. But, while pushing the roid, any slight deviation will again generate spin. It is then when I use the "wobble" effect, so if the roid begins a spin to the right (so the blue marker goes to the left), i wait when my thrust (NavBall center marker) has wobbled even more to the right than the CoM, and apply thrust then, with the effect to reduce or even reverse the spin and bring the roid orientation back where I want it to stay.

Edited April 4, 2014 by diomedea
spelling mistakes

[Riftmann]

Oh I'm so confused.

The first time I did it, I looked at the tracking station and one of the first asteroids I see is a Class E asteroid coming within 50 km of Kermin. I cobbled together a ship, using a modified old ship.I 'docked' with it with no problem and pushed it easily into a 100 km periapsis, highly elliptical orbit... I've tried several asteroids since and I spin around like a carousel. Beginner's Luck? And I'm kind of new, what's all this 'pivot' stuff?