A method includes absorbing heat generated at a flight vehicle using a heat sink, where the heat sink includes a matrix. The matrix includes a porous structure having multiple pores at least partially filled with one or more phase change materials. The method also includes converting the matrix into an insulator as the one or more phase change materials change state and exit the porous structure due to the absorbed heat. The matrix with the one or more phase change materials could include an alcogel, and the insulator could include an aerogel. The matrix could reside within a pressurized container that includes at least one seal. The at least one seal can fail due to increased pressure within the pressurized container as the heat is absorbed by the heat sink in order to allow the one or more phase change materials to exit the porous structure.