What does 'he composed his features' mean?
He wanted to switch it off, but he had to hear it out, he could not stop listening to it, though it hurt him in his heart with the unbearable homesickness of the hopelessly exiled. Even as a cadet this one hymn could fill his eyes with tears; now he kept his face turned away from the others to try to hide from them the drops wetting his cheeks.
When the choir's 'amen' let him do so he switched quickly to some other — any other — program and remained bent over the instrument, pretending to fiddle with it, while he composed his features.
Ordeal in Space By Robert A. Heinlein