The Key: Project Enterprise, Part 1 by Pauline Baird Jones
Summary: Spunky US Top Gun pilot, Sara Donavan’s blasting aliens when she crashes on a deserted planet. Well, almost deserted, another stranded pilot, a seriously hot alien, Kiernan Fyn, rescues Sara and takes her to his cave. When Sara’s crew finds her, she returns Fyn’s favor and takes him back with her to the huge U S spaceship she calls home. Though he fits in well on the ship, and he and Sara have a close encounter–an out-of-this-world kiss–Fyn’s hiding a dark secret. Sara has her own mystery, she discovers a hidden city everyone in the galaxy’s searching for. The lost city is a key to Sara’s baffling abilities and her mother’s past but its discovery also leads dangerous enemies to the Earth Expedition.