CRATERING AND PENETRATION EXPERIMENTS IN TEFLON TARGETS AT VELOCITIESFROM 1 TO 7 KM S/

We conducted impact experiments into Teflon(FEP) targets of widely var iable thickness to assist in the interpretation of craters and penetra tion holes in the similar to 20 m(2) of thermal blankets that were exp osed for 5.7 years in low-Earth orbit by the Long Duration Exposure Fa cility(LDEF). Soda-lime glass spheres of similar to 3.2 mm diameter (D -p) were used as projectiles ranging in impact velocities (V) from sim ilar to 1 to 7 km/s. Teflon fails in a largely brittle fashion; substa ntial spall zones were developed at the target's front side, and espec ially at the rear side, if penetrated. Crater diameter (D-c) varies wi th V-0.74. Penetration-hole diameter (D-h) depends on specific target thickness (T) and can be larger than D-c over a limited range of T(0.5 > D-p/T < 1.0), because rear-spallation processes intersect the targe t's front at radial ranges larger than D-c. D-h becomes smaller than D -c at relative target thicknesses of D-p/T. 1, and systematically decr eases as T decreases to eventually approach the condition were D-h = D -p at D-p/T > 100. D-h also increases with increasing V, yet the rate of increase depends on T, yielding a wide variety of velocity exponent s that depend on D-p/T. The velocity exponent is highest for massive t argets and decreases with decreasing T to approach the condition of D- h = D-p at D-p/T > 100, regardless of the velocity. The relationships of D-h, T and V are sufficiently systematic that unique solutions for projectile dimensions are possible from the diameter measurement of an y penetration hole in teflon targets of any thickness. This renders th e ''calibration'' of individual penetration holes equivalent to that o f individual impact craters. Thus, improved analysis of literally thou sands of penetration holes and craters in the LDEF thermal blankets se ems possible.