SDR 510018298 Gulfstream 500S Landing gear extension system roll pin failed. Nose landing gear unsafe light during down selection. Aircraft landed and NLG collapsed, causing minor damage to doors, linkages and belly skin. A previous possible ground handling mishap had put strain on the NLG steering actuator, causing the roll pin in the spacer assembly to fracture and allowing the hinge pin to eventually fail which caused the actuator shaft to foul on the fuselage and prevent the NLG from fully extending. P/No: ES10119