I am not even sure if it could be calculated. To overcome the inertia of that much mass is going to be stagering. Then there is no way to apply the power required other than another body of some mass acting against it in reverse rotation.

Come to think of it I have never looked for the information of what enables the continued basically same speed rotation to continue. There has to be a major extenal force or there is so much original inertia to overcome with time as to be unbelievable. Yet if that is the case the earth will eventually stop turning some day.

The actual drag against a space enviroment might be almost neglishable. So the question then becomes what got the spinning rotation going initially.

When the gyroscopic effect on the mass is reduced beyond a certain point the earth may become unstable. These events may be so far in the future as to be measured in millions of years.

I have always thought that mankind abuses his privilage of being here and takes it far too much for granted. We should at least be aware that cognizantly we have no other options. It is also very reasonable to believe that the earth will not support the human race at some point. Specis have been extinguished over time already.