Sam Ryan grew up on Orion 3, an Earth colony world with little technology. The original colonists wanted to return to a simpler way of life. They were mostly farmers and miners, working the old way, with their hands. Later on they were too poor to be able to afford modern equipment. Sam saw much unnecessary suffering because of the poor medical facilities. When the colony doctor died, no one could be persuaded to take the post in that backwater, and they managed with a paramedic and a nurse.
Sam’s brother Jacob was injured in a mining accident and lost his leg. He saw traders with prosthetic limbs leading normal lives, but the colony did not have the technology, and his family had no way to pay for it. Jacob died a bitter man, and he wasn’t the only one. Sam became determined to be trained as a doctor and return to help his people, so he left Orion 3 and went to Earth for medical training.
On Earth he had his eyes opened to what was available, not just technology, but the attractions of a modern lifestyle. He completed enough of his training to work as a paramedic and when the opportunity arose to be part of PACT and go into space, he grabbed it. For someone from a backwoods colony everything was new and exciting, and presented him with a dilemma: he doesn’t want to go back. How that dilemma is solved is revealed at the end of the first Kestrel story.