HARPOON TECHNOLOGY DEVELOPMENT FOR THE ACTIVE REMOVAL OF SPACE DEBRIS

Abstract

This paper presents the results of empirical testing and numerical modeling carried out to demonstrate the effectiveness of a harpoon as an Active Debris Removal (ADR) device. The parameters tested include: the relationship between tip shape and both ballistic limit and the creation of secondary debris; the ability to penetrate targets at oblique impact angles, low temperature and with heat pipe obstructions; the ability to lock onto targets post-penetration and withstand the loads expected during de-orbiting maneuvers; and the effect of tip shape on the penetration of CFRP targets. Testing involving the impact of blunt and conical shaped steel tips into 3mm aluminium (Al) plate showed that the ballistic limit varies in proportion to the tip circumference, with conical shapes having a higher relative ballistic limit due to the additional energy required for petalling. In regards to secondary debris, it was found that blunt shapes created a plug during penetration as a result of shearing around the periphery of the projectile, whilst conical tips resulted in minor spalling and fragmentation. Preliminary oblique impact testing up to 40 showed that the ballistic limit increases with obliquity at a greater rate for blunt tips than conical ones. This was supported by simulations up to a 60 impact angle. Impact testing of 3mm Al plate with conical projectiles at low temperatures showed a more brittle fracture mode when compared with targets impacted at room temperature. This resulted in a cleaner fracture surface and an increased ballistic limit. Impact testing of Al panels obstructed with fixed heat pipes showed that the harpoon could successfully penetrate a target panel with such an obstruction due to shearing of the pipe flange. Testing of two lock-on mechanisms showed that both a spring activated and integrated toggle could reliably open on target penetration. Tensile load testing was also conducted and showed that both designs could withstand the loads expected during de-orbiting maneuvers, with the integrated toggle being more robust. Simulation was used to evaluate the effect of varying the diameter of a conical tip on the ballistic limit. The results showed that the ballistic limit increased with diameter. Finally, a Smooth Particle Hydrodynamics (SPH) solver, which is better suited to modeling impact into brittle materials, was used to model impact into CFRP targets. This showed that, in comparison with blunt tips, conical tips had a higher ballistic limit. In addition, the debris formed was less coherent and had a higher terminal velocity. Further simulation showed that numerical modeling can provide an accurate prediction of the ballistic limit for Al plate impacted by conical projectiles, excellent prediction of impact failure modes, good predictions of debris likely to be created during the impact process, and an efficient means of testing prototype tip shapes.