I finished this book only so that I could feel justified in writing this review.
If I could rate this book Zero, or even less, I would.
If you have any self respect, and/or enjoy reading, particularly good Science Fiction, don't read this book. I paid $2 for the book on Kindle, and feel completely ripped off.
Okay, so what is wrong with it? Everything. Read the other one star ratings to see more detail. They are all pretty accurate. The two start ratings are far far too generous.
The science and engineering is atrociously bad. Completely wrong in places. The book has been compared to the film "Gravity". Well, Gravity also had terribly bad science, although the sets were good. Bruce Willis' "Armageddon" had better science than either story.
Most of the engineering in this advance culture seems to come from the 1950s and 1960s NASA activities. I suspect that the author read an old "History of NASA" book and got all his ideas from there. He has mostly written historic books previously. The author kept quoting from NASA and space development history. A Moose, rejected earlier, now on a tiny escape vessel? Then it failed very very early in the fall, but Caitlin's suit survived without harm to her, at supersonic speeds! Have you read the history of high altitude parachute jumps Jeremy?
News flash: Science Fiction is supposed to be about advances in science, and at best an extrapolation of current science to what might be possible.
As others have said, the book reads like a movie script, describing stuff that isn't needed, and then forgetting important stuff. The situations are completely contrived and feel like it. At every point there was a dramatic moment, suddenly solved and then forgotten. Just like an action movie, or an episode of a TV series. It just reads badly as well. The flashbacks to the "Campaign" were completely unnecessary, and annoying. I speed read all of them.
The constant talking about the past, the daughter, the few miners on the asteroid. The world was about to lose billions of people! Who cares about the individuals?! The girly discussions between Sara and Caitlin were just laughable.
The way the characters reacted to situations was not believable. They were all shallow. The characterisation of the president was a joke. It was definitely a poke at Trump.
Solving the problems:
There is a whole department, the Planetary Defense Coordination Office (PDCO) that is responsible "for the early detection of PHOs - Potentially Hazardous Objects - that might pass by Earth at a distance deemed too close for comfort", and that department doesn't have any real ideas how to deal with an asteroid? Really? The team has to come up with ideas from scratch? Then several old ideas surface days and weeks later, as having been developed but never used? Really?
When the problem first arose, why weren't ten space tugs sent from the Moon to gently push the asteroid back onto course? One ship exploding caused the problem. Ten tugs could have fixed it. One could get to the rock and match speed and direction, so others could do it.
The was a large cruise ship at the Moon earlier in the story. That could also easily be used to gently push the asteroid back on course. Sure, it might get a bit damaged, but what the hell. Save the world vs a little damage?
The ramming ship that missed. Couldn't it be recovered and used again, properly?
Why would you send lots of little ships with lasers close to the asteroid, when you could fire them all from any distance and have the same effect. In fact, the whole "fill craters with ice to get better propulsion" was silly. If there was surface water, there would be sub-surface water. Bath the asteroid in lasers and it would act like a comment, with steam and ablated rock etc. blasted off in a known direction. Job done.
Why was every option discussed never prepared and ready to go when needed, instead taking yet another two days or so to be able to launch?
The RCS failed in Diaz's suit. Catlin saved him by jumping and grabbing him and using her RCS to bring him back to the asteroid. Then he was blasted off the asteroid again. Why couldn't Caitlin go after him again, and repeat the rescue process? She was able to bring herself back down.
When Diaz and Vee are "lost" to Caitlin, why can't they talk on their suit radios? Line of sight radios of even low power would work for a very long distance. Surely they would have talked.
The EMP took out the re-entry programs on the escape pod, but the AI still worked fine? Everything Caitlin needed failed, but lots of other systems on the pod came back online? Not believable. Just a way to create a situation in the story, like so many other issues.
Anyway, I could write a book on what was wrong with this book, but I would have to read it again and make notes to do so. That isn't going to happen.
So Jeremy, I don't want to discourage you, but this story should never have been published. It should have been put aside as a learning experience. You should have gotten some honest reviews before publishing. (How on earth could anyone give this five stars, as some have, I will never know. But I assume there was some reason.) You had science advice? Really? You have written for young adults previously. Was this written for young adults? Because it is a copy of many previous stories, and not even a good one.
Anyway, that is enough. Don't buy or read this book.