Note: I received this book from Good Reads for a review.

An entrepreneur has financed a mining ship to the asteroid Ryugu some time in the near future. The purpose is extract resources and send them to cislunar orbit, where they can be harvested and used to set up an independent economy. As the book begins, this mission has been underway for some time, and three of the original astronauts have died. Three more have been sent back to earth to get help, on a ship that may or may not actually make it, leaving the two remaining crew members on the ship to continue mining and, hopefully, await rescue. An unknown spacecraft appears, docks and lands a crew, which turns out to be a Korean mission to take over the operation. That's the introduction. The three crew members sent back to earth do survive, and despite American, Russian and Chinese attempts to get the valuable material from them, they manage to get to the moon where a space station has been under construction with the materials. They manage to build an entire economy on this station, despite problems with the three super powers on Earth, and begin construction on a rescue ship to hopefully, return the the asteroid and rescue the remaining crew when the launch window opens again. This is just the mere outline of part of what this book is about. It's a great story, and a great read. Like "The Martian", it should be considered "hard" science fiction, because everything described is actually possible, based on physics as we currently know them. In other words, there's no "hyper-" or "warp-" drive, since such things don't, and, to our knowledge will probably never exist. For fans of really good, serious and logical science fiction, this book is highly recommended. If you want dragons, look elsewhere. ( )

This is the sequel to Delta V. James Tighe and his compatriots have safely returned to Earth, and now are focused on returning to space to rescue their crewmates who are still stuck at the asteroid Ryugu. It starts on the Konstantin, where Isabel Abarca and Adedayo Adisa detect an incoming space craft, soon after the departure of their crewmates. It turns out to be a North Korean crew come to board the ship and take command. And then we leave them and don't return to the Konstantin until the tail end of the book. (I actually like this choice- keeping the reader wondering along with Tighe and the others what has become of them).

Then the reader is taken through the creation of a space station in upper lunar orbit by the vestiges of Catalyst Corporation. They have to deal with the politics on Earth, getting to orbit with some subterfuge, and then establish an entire economy in cislunar space through the use of blockchain tokens (which doesn't age so well post-Samuel Bankman Fried. Suarez seems to be a cryptocurrency believer). All of it culminates in getting a ship built and launched to rescue Abarca and Adedayo.

My main complaint with the first book was that it spent too much time on the training portions. This book too has a bloated middle, and frankly I checked out and skimmed 200 pages to get through it. Credit to the author for a really realistic-seeming course of events- things go wrong, people die randomly, a solar flare causes great danger, etc. And he's really thought through the science and does a great job imparting the difficulty likely to accompany the "pioneering" phase of space exploration- there are no Star Trek gleaming corridors and bullshit "artificial gravity" here.

So a worthwhile read, and I see my rating is well below the average so obviously lots of people liked it more. I just want the author to be more economical with his story. ( )

Great as a stand alone and as a sequel. The hard science is impressive, and the plot engaging. Working to return to the spaceship by the asteroid and rescue friends. Also working to abate climate change. A nuclear powered space ship. ( )

as much as i loved the lead-up to the the denouement, it came and went so quickly i almost missed it. with less than 30 pages to go, i was seriously expecting a cliff-hanger, with a third book handling the rescue attempt. instead, not only were most of four years of storyline tied up with bows, it was as if the author simply ran out of ideas and took the easy way out... ( )

Critical Mass is a close sequel to Daniel Suarez’s Delta-V (2019) in which cave diver James Tighe is hired to join a private expedition to begin an asteroid mining industry. In Critical Mass, Tighe has returned home, but now he must organize a team to build a space station and a nuclear spacecraft at a lunar Lagrange point. He intends to lead a mission to rescue the teammates he left behind. The story is heavy on engineering detail, which I consider a feature rather than a bug. Critical Mass is the first novel I have read that seriously discusses plumbing issues on a space station using spin gravity. Tighe is a well-rounded character, and there is enough action to make the exposition go down easy. Recommended. 4 stars. ( )