The separation dynamics of the COMET FreeFlyer and an upper stage STAR-48V rocket motor

An investigation into the separation dynamics between the COMET FreeFlyer and a STAR-48V solid rocket motor is performed in this thesis. This is accomplished by first determining the time histories of the forces and moments that are applied to the STAR-48V and the FreeFlyer. Since there is difficulty in determining these forces and moments in an inertial coordinate system, a body-fixed coordinate system is chosen so that the time histories of the forces and moments can be determined and so that the principal moments of inertia will be constant in this coordinate system. These results, as determined in the body-fixed coordinate system, are then placed into the equations of motion as described in a rotating reference frame.

The differential equations of motion for each body are then numerically integrated using a fourth order Runge-Kutta numerical integration scheme. This integration provides the translational velocity vector and the angular velocity vector of both the STAR-48V and the FreeFlyer as described in the body-fixed coordinate system. In order to determine the separation distances between the center of mass of the STAR-48V and the center of mass of the FreeFlyer, both the translational and the angular velocity vectors of both bodies are transformed into an inertial coordinate system. This is accomplished by determining the Euler angles used in a 3-1-3 Euler angle transformation and then applying this transformation to these vectors. Once this is determined, the velocity vectors, as described in an inertial reference frame, are integrated, thus providing the separation distances between the STAR-48V and the COMET FreeFlyer. From these separation distances, it can be determined if the two bodies will collide with each other after the separation process has been initiated.

From this analysis, and some basic assumptions about the initial conditions of the STAR-48V/FreeFlyer vehicle, it is concluded that the STAR-48V will not collide with the FreeFlyer if the separation occurs at the presently designed separation delay time of 180 seconds. In fact, this separation delay time could be shorter. However, it is recommended that this separation delay time be as large as possible in order to reduce the possibility of collision.

In addition, a parametric study of the effects that different configuration variables have upon the success of the separation is conducted. From this investigation, it is concluded that the probability of any one of these variables causing a significant effect upon the success of the separation between the STAR-48V and the COMET FreeFlyer will be minimal.

With this in mind, it is concluded that the STAR-48V, as presently designed for the COMET mission, will not collide with the COMET FreeFlyer as long as a separation delay time of 180 seconds is used and as long as the STAR-48V nozzle can be gimbaled by at least 4° from its primary axis.