The Dark Dimensions / The Rim Gods

The Dark Dimensions (1971)
Commodore John Grimes was finally getting his space wings back. On his old ship, Faraway Quest, Grimes was to venture forth to the very Rim of the known worlds, seeking... The Outsider.
"The Outsiders' Ship... is a storehouse of science and technology... we, and the Federation, and the Shaara Empire, and probably quite a few more, have sent expeditions. Everyone of them has ended disastrously."
So, it is out to the Rim and find The Outsider. But the mystery ship is not always easy to find. And other worlds, too, yearn for the treasure of the alien technology. What Commodore Grimes finds at the Rim, and what finds him there, sends him racing through time tracks, surrounded by enemies and temporary friends, trying endlessly to discover the secret and dangers of... The Outsider

The Rim Gods (1969)
John Grimes, Astronautical Superintendent of Rim Runners and commanding officer of the Rim Worlds Naval Reserve, was tired of being a desk-bound space commodore. So when the chance came for him to do a little personal astronautical trouble-shooting, he didn't ask who, why or what - he just went.
Which is how he found himself involved with time-space worlds, predatory starfish, and legendary characters apparently come to life.
That's what can happen when you are out at the galxy's edge and call forth THE RIM GODS.