The Result of Hypervelocity Impact Tests.

A series of hypervelocity impact tests has been conducted to investigate the shield design concept of JEM pressure module, i. e., bumper and isogrid pressure wall, against orbital debris impact. A two-stage light-gas gun has been newly developed for the purpose of improving test capability and the tests were carried out under the impact velocity of up to 6.8km/s with sphere aluminum projectiles of 3-9mm diameters. Main purposes of the tests are to examine (1) penetration hole diameters, (2) unzipping failure (uncontrolled mode of crack propagation) of pressure wall, (3) failure tolerant performance of isogrid pressure wall, and (4) impact damage to pressure wall by inserting MLI. More than 120 impact tests were successfully performed and significant test results were obtained. Summaries of the test results are followings: (1) penetration hole diameters are almost same size as ‘Goodwin;’ prediction, (2) critical crack length, which initiates unzipping failure of pressure wall, is much larger than that predicted by the Newman's static equation, (3) crack propagation is slightly contained by the isogrid rib of pressure wall, and (4) penetration hole becomes smaller, while crack length becomes larger by installing MLI between bumper and pressure wall.