Temperature in space is complex, particularly for spacewalking astronauts. Unlike on Earth, where air provides a medium for heat transfer, the vacuum of space presents a unique thermal environment. Understanding heat behavior in this void is important for grasping the challenges astronauts face.
Understanding Temperature in a Vacuum
On Earth, heat transfers through conduction, convection, and radiation. Conduction involves direct contact, while convection relies on fluid movement. In the near-vacuum of space, however, few particles exist for conduction or convection.
Heat transfer in space is dominated by radiation. Objects absorb radiant energy from the Sun and radiate their own heat. Without an atmosphere, there is no single “ambient temperature.” An object’s temperature depends on its exposure to direct sunlight or shadow, and its material properties.
The Extreme Temperature Range Spacewalkers Face
Astronauts conducting spacewalks experience significant temperature swings. In direct sunlight, surfaces can heat up considerably. For instance, objects in low Earth orbit can reach 121°C (250°F).
Conversely, in Earth’s shadow, temperatures can plunge to approximately -157°C (-250°F). This vast difference arises because objects absorb solar radiation in sunlight and then radiate their accumulated heat into the cold, dark void. These are temperatures objects exposed to space would reach, not the internal temperature experienced by the astronaut.
How Spacesuits Provide Thermal Protection
Spacesuits use multiple layers and active systems to protect astronauts from thermal extremes. The Extravehicular Mobility Unit (EMU) includes a multi-layered insulation (MLI) system, also called the Thermal Micrometeoroid Garment (TMG), which serves as a passive thermal barrier. This outer layer, often white to reflect sunlight, insulates against heat and cold, and provides protection from micrometeoroids.
Underneath these insulating layers, astronauts wear an active thermal control system. The Liquid Cooling and Ventilation Garment (LCVG) is a close-fitting undergarment with flexible tubes circulating cool water against the astronaut’s skin. This water absorbs excess body heat generated during physical activity, helping to maintain a comfortable core body temperature.
The Portable Life Support System (PLSS), worn as a backpack, is integral to this system. The PLSS circulates the chilled water to the LCVG and cools it in a heat exchanger before recirculation. This backpack also manages other aspects of the suit’s internal environment, such as providing breathable oxygen and removing carbon dioxide.