Inconstant Star

Inconstant Star is a science fiction fix-up novel by American writer Poul Anderson. It is formed by the novellas Iron and Inconstant Star, first published in The Man-Kzin Wars (1988) and Man-Kzin Wars III (1990), respectively. The title is from the tumbling alien artifact that sends out radiation. Due to the tumbling effect, the output can only be seen briefly from a given point in space, looking like a star, but then disappearing as the artifact moves.
The title also references another Niven story, "Inconstant Moon", which is not part of the Known Space series. The novel is the story of Robert Saxtorph and his ship Rover, hired for peaceful missions, but which run into Kzinti at every turn.
Plot summary
There are two parts to the novel, Iron, and Inconstant Star.
In “Iron”, Saxtorph and the Rover, hired by the wealthy Crashlander Laurinda Brozik, set out to explore a newly discovered red dwarf star. When they arrive, they are challenged by a Kzinti warship. Separating the crew onto the shuttles, the Rover is captured and landed on one of the moons. The first shuttle sets on Prima, the first planet, and is held fast by a planet-sized organism that begins dissolving the shuttle. They broadcast for rescue, and are refused help by the Kzin.
Meanwhile, helpless to rescue their friends, Robert, Dorcas, and Laurinda make a plan to steal a tug and escape back to friendly space with the news of the Kzin base. Dorcas pilots the tug, and takes out the ship guarding the Rover. Robert and Laurinda land, fight off a Kzinti shuttle, and recover the Rover. They are able to rescue Juan and Carita, and destroy the base with a guided asteroid.