Harpoon technology development for the active removal of space debris

Abstract This paper presents the results of preliminary empirical testing and numerical modelling carried out to demonstrate the effectiveness of using a harpoon in an ADR application. Empirical testing involving the impact of blunt and conical shaped steel tips into 3 mm Al plate showed that the ballistic limit varies in proportion to the tip circumference, with conical shapes resulting in a higher relative ballistic limit due to the additional energy required for petaling. The creation of secondary debris was also monitored. 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 with conical and blunt tips showed that the ballistic limit increases with obliquity at a greater rate for blunt tips than conical ones. Impact testing of 3 mm Al plate with conical projectiles at low temperatures showed a more brittle fracture mode when compared with targets impacted at room temperature. As such, the fragmentation and spalling evident in room temperature targets was absent. The energy required to perforate the cooled plates also increased. Impact testing of Al panel 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 upon impact. This testing also used a tensile testing machine to show that both designs could withstand the force expected during deorbiting manoeuvres after impact with Al H/C panels. A parametric simulation comparing the diameter of conical tips with ballistic limits showed a good agreement with the predictions of De Marre’s formula for normal impact. This suggests that the ballistic limit of plates impacted by conical projectiles can be successfully extrapolated with limited experimental data. A SPH solver, which is better suited to modelling impact into brittle materials, was used to model impact into CFRP targets. This showed that the debris formed by conical tips was less coherent and had a higher terminal velocity than that produced by blunt tips. As a result of conducting these simulations, it was shown that numerical modelling can provide an accurate prediction of impact speeds required for a conical projectile to perforate Al plate, excellent prediction of impact failure modes, and good predictions of debris likely to be created during the impact process. Finally, preliminary studies of harpoon impact into low mass targets with up to 3 DOF showed that the harpoon was still able to penetrate such targets under simulated μ-gravity conditions.