Locate the point on 3D polyline which is an exact distance from the origin

Hi All,

Here is my challenge: I have a 3d polyline (see the attached dwg, 3d poly in green) that varies in x, y and z.

Then I have a line (green) with the exact length of 10 000 drawing units.

I want to be able to do either of these two things, which really serve the same goal:

1. To rotate the line about the origin in 3D so that the endpoint (10 000 from the origin) touches the 3D polyline.

2. To locate the point on the 3D polyline that is exactly 10 000 units from the start of the polyline/origin (not along the poly, measured as a straight line, therefore similar to point 1.)

Any suggestions are greatly appreciated,

Samu