Investigation of hypervelocity impact damage to Space Station truss tubes

摘要

On the average, every square meter of the Space Station truss will be subjected to 335 impacts per year from 0.01 mm and larger meteoroid and orbital debris particles. The objectives of this study were to (1) determine how susceptible the truss tubes were to failure from hypervelocity impact, (2) assess how tube properties (such as ply orientation, fiber elastic modulus, wall thickness, and surface coatings) affect the extent of impact damage, and (3) assess how projectile parameters (size, density, velocity, and impact obliquity angle) affect target damage. The study involved hypervelocity impact testing using light gas guns at the NASA Johnson Space Center (JSC) and at NDE Technology, Inc. in Torrance, California. Aluminum, glass, and nylon projectiles from 0.55 mm to 4.4 mm diameter were launched at velocities ranging from 4 to 7.5 km/sec. Data from 58 shots was used in the correlation analyses. Most of the shots were made at an impact angle normal to the target surface (0 degrees obliquity). Unavoidable aiming dispersions resulted in impact obliquity angles of up to 40 degrees for some of the tube shots. Intentional oblique impact shots were performed on selected tube specimens at a 45 degree angle to the longitudinal axis and 45 degrees to the axis defined by a radius connecting the tube center and impact point. The materials and construction of the graphite-epoxy tube and flat plate targets were chosen to be representative of potential Space Station truss structures. They were manufactured from unidirectional plies and were constructed with three different layups, two fiber elastic moduli (34M and 75M psi), and three thicknesses (nominally 0.07, 0.11, and 0.14 in.). Candidate coatings for atomic oxygen protection, 2 mil and 6 mil aluminum foil, were bonded to selected tubes for impact testing. Additional tubes, including some made by filament winding, were donated by other companies for comparison purposes. The results of the impact testing revealed that fiber modulus influenced the magnitude of hypervelocity impact damage to a greater extent than ply orientation.