Troika by Alastair Reynolds

Set in a future where humanity has colonized the solar system, the story follows a retired cosmonaut who is drawn back into the world of space exploration when a mysterious alien artifact, known as the Matryoshka, is discovered orbiting the sun. As he joins a mission to uncover the secrets of this enigmatic structure, he confronts not only the challenges of deep space but also the political tensions and personal demons that threaten to unravel the mission. The narrative weaves together themes of discovery, sacrifice, and the enduring quest for knowledge, culminating in a gripping exploration of humanity's place in the cosmos.