Satellite mechanics: linear and rotational momentum

[vasya]

If you choose an axis on the line of motion of the mass centre then it does not contribute any angular momentum

it does. A rotary one. Moment of inertia*angular velocity

 

[haruspex]

it does. A rotary one. Moment of inertia*angular velocity

No, I wrote that the linear motion would not contribute to the angular momentum about that axis.
Please post the details of your calculation that arrives at 1/3 and 2/3.

 

[jbriggs444]

*shudder*. I think I see it. 100 kg m/s of linear momentum and 50 kg m²/s of angular momentum from rotation. He is taking the ratio of two quantities which have different units and pretending that the result is a dimensionless two to one ratio.

Naturally, the linear momentum is also 10,000 kg cm/s of linear momentum and 500,000 kg cm²/s of angular momentum from rotation for an equally defensible one to fifty ratio. "Equally defensible" because neither is at all defensible as a dimensionless ratio.

Two per meter and one per fifty centimeters are both the same ratio. Both have units.

 

[haruspex]

*shudder*. I think I see it. 100 kg m/s of linear momentum and 50 kg m²/s of angular momentum from rotation. He is taking the ratio of two quantities which have different units and pretending that the result is a dimensionless two to one ratio.

Naturally, the linear momentum is also 10,000 kg cm/s of linear momentum and 500,000 kg cm²/s of angular momentum from rotation for an equally defensible one to fifty ratio. "Equally defensible" because neither is at all defensible as a dimensionless ratio.

One half per meter and one per fifty centimeters are both the same ratio. Both have units.

Yes, that's probably the blunder. I was thrown by

angular momentum in linear … motion

taking that mean the linear momentum's contribution to angular momentum.

 

[vasya]

An expanding plume of rocket exhaust of unknown mass and velocity that has 100 kg m/s of linear momentum at an offset of 0.5 meters from the craft's center of mass for a total of -50 kg m2/s.

look more closely on first picture in this thread. thruster has offset of 0.25m of y-piersing-through-the-center-of-mass axis

 

[jbriggs444]

look more closely on first picture in this thread. thruster has offset of 0.25m of y-piersing-through-the-center-of-mass axis

Thank you. That explains the factor of two discrepancy in our two evaluations for rotation rate.