When `Newtypes' first appeared among third generation colonists, the general reaction was shock. The colonists saw them as hope for the future. Newtype children were blessed with powerful mental gifts and bodies extremely well adapted to space and space flight. Their smaller stature and lighter, more agile build made zero-g movement easier, and their mental gifts allowed them to save themselves and others from many space and colony accidents.
The colonists loved them, but many of the people on Earth saw them as freaks and proof that humans were never meant for long term space habitation. In attempt to protect their children from Earth zealots the colonies formed the Ganymede Center, otherwise known as L1 XCC0412. Public schools routinely tested children for Newtype genetics. Those that tested positive were sent to Ganymede Center on full scholarship to study with their peers. As adults all Newtypes were given permanent quarters on Ganymede, regardless of other residences. In this large group situation it soon became apparent that different classes or types of Newtypes existed: there were the telepaths and empaths whose gifts focused on sending and receiving mental projections; the psychokinetics, whose gifts allowed manipulation of objects with the mind; and there were the `Sentinels'.
Sentinels displayed none of the usual mental gifts except for latent telepathy, but their physical senses were enhanced far beyond normal human capabilities. At around the age of ten Sentinels would begin to experience loss of control over these enhanced senses, resulting in sensory spikes and zones where they lost track of everything. Control was only regained by forming a psychic bond with a full telepath or empath who served as a constant baseline for their senses to revert to. In this role, the bonded telepath or empath was known as a `Guide'. Those Sentinels who did not form a bond within several years of this critical point eventually had to be isolated for their own sake; and even then they eventually overloaded on sensation and went insane. Sometimes they even ended up killing themselves. Unbonded Sentinels seldom made it past the age of twenty-five with their faculties intact, and many succumbed even sooner.