DECONTAMINATION AND COOLDOWN

To preserve Euclid's immaculate telescope and payload, the spacecraft and instruments have been built and launched in extremely clean conditions. Nonetheless, some residual contaminants remain in the spacecraft, embedded in the spacecraft material. The spacecraft will also take water vapour from the Earth's atmosphere with it into space. The freezing vacuum of space naturally causes the contaminants to emerge into the interior spaces ('out-gassing'). This combination of contaminants and water vapour will naturally condense onto the coldest surface.

The spacecraft is kept warm for several days and left to cool under carefully managed conditions to ensure the optical surfaces remain at their highest possible performance. The NISP instrument is partially activated during the LEOP phase to control the temperature with its enclosure.