Initial motion of a rocket moving on a stretched cable

Abstract

The practicability of using a stretched cable for a rocket launching device is dependent primarily upon the transverse movement of the rocket and the stresses involved in the system. This requires analysis of the effects of the moving rocket mass on the cable from the instant of contact, and the problem reduces to one of wave propagation. The analysis here is restricted essentially to developing a procedure by which the initial motion of the mass can be calculated, and an expression is obtained which permits determination of the deflections. The problem is approached by first assuming that the mass exerts a constant transverse force on the cable. Admittedly, this is a simplifying assumption, and the result is not valid for the instant the mass hits the cable or for a short time thereafter because the inertia of the mass is not considered. Next, the problem is solved by taking into account the dynamics of the mass, and the solution reveals that the path of the actual mass deviates from the force path by as much as twenty percent during the initial motion but soon returns to the force path. The mass does not exert its full force on the cable at the instant of contact, but comes down on the cable with full force a short time later. Since maximum stresses on the system occur at this time, this factor is an important result of the analysis. Further, it is shown that increased velocity of the mass increases the deviation from the force path, and increased mass lengthens the time of return to the force path.