Iron troll

An American Ohio class nuclear submarine can carry 20 Trident II D5 missiles. Each weighs nearly 59 tonnes, contains three enormous solid rocket motors and can carry multiple independently targetable nuclear warheads. The remarkable part is that these weapons may never be fired in combat, yet must remain ready through decades of service. Their solid propellant contains both fuel and oxidizer, sealed inside the rocket motors. Over time, those energetic materials can age, develop defects or lose their original mechanical properties. The Navy must continuously inspect, qualify and replace ageing components. In 2019, the admiral overseeing the program revealed that all three rocket motors in one successfully tested Trident were almost 27 years old. Launching one presents an entirely different engineering problem. The first rocket motor cannot simply ignite inside the submarine. Instead, expanding gas ejects the nearly 59 tonne missile from its launch tube, pushing it through seawater until it breaks the surface. Only after clearing the water can the first rocket motor ignite, at precisely the right moment. Too early would endanger the launch, too late, and the nearly 60 tonne missile will lose momentum and fall back into the sea. Its three solid-fuel stages accelerate the missile beyond 20,000 km/h, shedding their empty structures as each successive motor takes over. Published maximum-range estimates reach approximately 12,000 kilometres. And throughout powered flight, the missile must maintain an extraordinarily accurate understanding of its own movement. Precision gyroscopes measure changes in orientation, accelerometers track acceleration, and an onboard computer calculates its motion. A stellar camera can observe stars to correct accumulated navigation errors, allowing Trident to navigate without continuous GPS signals. After powered flight, its nuclear re-entry vehicles continue along their ballistic trajectories before descending through the atmosphere. One W88 warhead alone has an estimated explosive yield of 475 kilotons, more than 30 times that of Hiroshima. A single Trident can carry several such re-entry vehicles. Now consider the engineering responsibility. The missile must remain dependable through repeated deployments, maintenance and ageing, while its nuclear payload must remain protected against unintended detonation even when surrounding electronic systems malfunction. The safety requirements are extraordinary, under normal conditions, the permitted probability of premature nuclear detonation is no greater than one in a billion over a weapon's lifetime. Trident entered service in 1990. More than three decades later, America continues modernising its electronics, guidance and nuclear components around an established missile architecture. A weapon designed to deter a nuclear war that may never happen, yet engineered and maintained for decades so that, if the unthinkable ever occurs, it must work flawlessly on its very first use, even after 25 years of service.