How Cold Space Really Is, and Why Spacecraft Struggle to Keep Cool

Space is called cold, and in one sense it is: the glow left over from the early universe measures about 2.7 degrees above absolute zero. But cold, for any object, means losing heat, and heat leaves a body in three ways, by touch, by moving air or water, and by glowing. Empty space removes the first two, so a spacecraft can shed heat only by glowing it away, slowly. The episode walks one idea up four rooms, a cooling mug on a kitchen table, the airless lunar surface in day and night, the ammonia radiators of the space station, and the five-layer sunshield of the JWST, and ends on the honest bounded verdict: space is cold, but it is a poor thief of warmth. Subscribe to The Measured Sky for more calm listening.