As the Weeping Somnambulist approaches Ganymede, the star field behind the Jovian moon is accurate - to the moon's right, the belt, sword and shield of Orion; and the star clusters of the Hyades and Pleiades in Taurus, are all clearly visible.
The Purple Heart Gunny Bobbie wears is actually a combination of the ribbon portion from the Marine Corps Good Conduct Medal and Purple Heart pendant.
"Somnambulist" means "sleepwalker".
"Looking a gift horse in the mouth" means showing undue concern over the quality of a gift. A young horse is a good gift, an old horse is a worthless gift. Often the surest way to check the age of a horse is by looking at the teeth. When a horse gets old its gums shrink, making the teeth look longer. Humans experience the same thing - hence "long in the tooth" means rather old.
Dr. Meng (Prax) says that his daughter has a rare genetic condition called Myers-Skeleton Premature Immunosenescence, which is a fictional disease, though it is based off a real condition. The term immunosenescence is used to describe the deterioration of the immune system brought on by aging. As humans get past their middle age (typically over age 55) the immune system begins to lose the capacity to respond to infections and develop long-term immune memory as effectively. So it can be inferred that Dr. Meng's daughter's condition is causing her immune system to weaken in the same manner as it does in the elderly.