Towards the end of his career, RAH's novels got very long, very meandering, explicitly sexual, and very weird. Turned out, he had a tumor that was blocking the flow of blood to his brain (really!) and after it was removed, his fiction (and, reportedly, his personality) really changed again.
And it was those giant, pervy books that Charlie was setting out to pay tribute to.
Saturn's Children is that novel. It's the story of Freya, a sex-bot who was engineered (along with her untold legion of near-identical, near-immortal sisters) to be the perfect pleasure-toy for human masters. Unfortunately, the human race went extinct before Freya was ever booted up, leaving her (and the rest of the robots that comprise galactic civilization) with no purpose in life.
Robot society is sick -- because it was created in the image of our own. Robots are hardwired to obey humans and to serve them and their governments. When humans let themselves go extinct, the robots divided into two castes: those who wired to be empathic and those who were not. The non-empaths seized the moment: they formed shell corporations that bought their robot bodies from their dead and absent owners, and effectively owned themselves. Once this aristocracy of "free" robots was established, they ruthlessly enslaved the rest of robot society, seizing their deeds and slave-chipping them into obedience.
The robots yearn for -- and dread -- the reappearance of humans. The hardwired robotic obedience to humans means that the robots clique that successfully engineers a new human (preferably without releasing the dread "pink goo" -- the robotic bogeyman of self-replicating organic material) may be able to liberate robotkind, or enslave it forever.
Against this backdrop, Freya lives and (nearly) dies as she finds herself embroiled in a series of interplanetary intrigues, shuttling from world to world in realistic (and therefore slow and miserable) spaceships that can take a decade or more to reach Eris and the rest of the outer system. In a book laden with science-fiction in-jokes, philosophy and sly critiques, this may be the very best fillip. Stross puts the terrible lie to the idea of sub-lightspeed space-travel and explores the only way a species could effectively colonize our own system: by turning into robots, willing to amputate limbs to reduce payloads (or, in extreme cases, to simply ship "soulchips" bearing copies of their personalities around), willing to perch atop highly radioactive fission reactors, willing to take a one-way ticket to the outer reaches of our system.
What's more, Stross manages to find the narrative juice hidden in this constrained version of space-travel: to tell a tightly plotted, Maltese-Falcon-esque thriller with reversals and surprises galore, spread out across decades of objective and subjective time.
It's quite a remarkable trick. It's one that neither Heinlein, nor Asimov (the other author to whom the book is dedicated -- as is only proper, given Asimov's prominence in society's conception of what a robot is) managed. This is a fabulous book, a witty and deep critique of the field's shibboleths, and well worth the price of admission.