Confronted with the heat problems associated with its hypersonic speed envelope the original heat-sink structure of the X-15 proved to be up to the task. All changed when the damaged second X-15 (56-6671) was converted into the X-15A-2. Lengthened by 2.4ft and equipped with a pair of droppable tanks (one oxidant-one fuel), the X-15A-2 was designed to achieved even higher speed and during a more prolonged time. It was soon obvious the increased heat and exposure was above the capabilities original heat-sink structure. They went to the cheap and “dirty” solution: a heat-resistant ablative coating similar to the Apollo capsules in concept. The ablator chosen was the Martin MA-25S, which of all the possible colours to be found was a lovely pink. Gladly, the pilots’ usual macho ego was spared: that ablator needed a white-layer of paint as protection against both oxygen spills and moisture.