The center of pressure of a projectile is caused to move upon the occurrence of an event that changes the static margin, such as the jettisoning of a body previously attached to the projectile, as noted above. The optical fibers of the two layers intersect a vector extending radially from the optical fiber at the center to an outer surface of the tow cable. For instance, a search region for detecting position gaps is set at 4 pixels, while on one substrate are mounted a plurality of video processing circuits, each being constructed with an LSI which can perform processing of k channels, thereby realizing a high-speed video processing portion having a small size. The fastening mechanism includes a bolt having a bolt head and a bolt post extending from the head for extending through transverse holes in the hitch receiver. The leading portion is withdrawn from the mold cavity against an undercut portion of the resilient projection, folding the resilient projection into the space left by retracting the following portion.