Evaporation and sublimation into a vacuum is called outgassing. All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. In man-made systems, outgassing has the same effect as a leak and can limit the achievable vacuum. Outgassing products may condense on nearby colder surfaces, which can be troublesome if they obscure optical instruments or react with other materials. This is of great concern to space missions, where an obscured telescope or solar cell can ruin an expensive mission. COUNT 3
QSN1 what is evaporation and sublimation in a vacuum? ANS1 outgassing QSN2 Why can outgassing products ruin a space mission? ANS2 obscure optical instruments QSN3 When does outgassing become important in all solid or liquid materials? ANS3 vacuum pressure falls below this vapour pressure