In the near-ish future, a gifted engineer dreams of repairing the flaw in the fuel cells designed by her uncle that doomed a long-distance space mission. Her uncle has recently died when narrator June is sent to the school named for him on the National Space Program campus. She's only 12, but she has learned from her famous uncle to always ask of a piece of machinery, "What does it do?" This phrase echoes throughout the text as June trains for work in space; Day does a terrific job of making an engineer's thought process as exciting as a thriller's chase scenes. June and her classmates are obsessed with Inquiry, the first-ever craft using the fuel cells invented by her uncle with a team of his students, which has lost propulsion control while orbiting Saturn. Some of them helped design the fuel cells, others have friends or lovers on the crew, so all are devastated when NSP cancels a planned rescue mission in Endurance, a craft powered by the same suspect cells. The novel blends fraught personal relationships with intricate engineering as the narrative moves forward six years, when June is sent to the Pink Planet to work with James, one of her uncle's students, whose debates with his lover, Theresa, about the fuel cell design forecast similar conflict between him and June while they work on repairing the cells' flaw. Nonetheless, they become intimate--until she uncovers a grim secret that ruptures their partnership. June flees the station into the Pink Planet's unforgiving atmosphere, nearly dying in a harrowing scene that again displays Day's gift for gripping suspense that unfolds largely in the narrator's head. Regrettably, the author is not as skilled at gathering together her plot strands, and an abrupt ending leaves many unanswered questions about the characters she has somewhat elliptically developed. An interesting idea that doesn't quite gel. Copyright (c) Kirkus Reviews, used with permission.

In Day's uneven latest (after If, Then), a precocious girl grows up to be an astronaut in a near future of expanded space exploration. June Reed, 12, lives with her aunt Regina, who raised her along with June's late uncle Peter, a brilliant engineer for the National Space Program. Shortly before Peter died, he developed a fuel cell for Inquiry, a spacecraft that lost power as it was beginning its orbit around Saturn. After June hears that the blame is being put on a fuel cell malfunction, she becomes obsessed with fixing the design flaw and rescuing the four astronauts aboard the craft, and Regina sends the mischievous June away to boarding school to prep for astronaut training. Despite being younger than her peers, June's tenacity earns her a spot on a space station, where she and her uncle's protégé fix the faulty cell to power a rescue shuttle. While Day does a decent job developing June as a curious girl who claims to be "better with machines than with people," the haphazard plot feels rushed and the prose can be clunky ("My eyelids were like lead. They lowered. They lowered. They lowered again"). This is primed for launch, but it doesn't really take off. Agent: Brettne Bloom, the Book Group. (Mar.)

Day's latest (after If, Then, 2019) features a protagonist who is a real space case. June's uncle invented the batteries that will power the next generation of space travel, but there's a fatal flaw that no one catches until it's too late. Haunted by this failure, June becomes one of the youngest astronauts in history due to her unique problem-solving perspective. Will she be able to fulfill her uncle's legacy before it's too late and figure out her own love life, all while living on the surface of a hostile planet? June's path to the stars, as well as the science behind the trip, feels both realistic and accessible. Day's descriptions of the cold lethality of space make the final frontier feel like a character itself, and, indeed, each location described feels tangible. The action sequences are brutal and breathtaking, but the novel focuses most on June's emotions and relationships with her fellow trainees and astronauts. Perfect for fans of realistic depictions of space travel like Andy Weir's The Martian (2014) and Jeremy K. Brown's Zero Limit (2018).

This unconventional futuristic tale of space exploration is introspective. At its start, June Reed is a misunderstood child prodigy who designs spaceship components and has trouble relating to others and fitting in with classmates. June becomes an adult who's obsessed by the mystery of her uncle's spacecraft, which went missing, with its crew, years earlier; she and her colleagues are compelled to unravel its fate. Rather than a space rescue mission, this story becomes a work of scientific investigation and puzzle solving (with a romance shoved in for good measure). Rebecca Lowman narrates the book clearly, with distinct voices for each character. VERDICT Fans of Andy Weir's The Martian and similar sci-fi will enjoy this slow-moving but gritty space tale with a dash of mystery.--Denise Garofalo, Mount Saint Mary Coll., Newburgh, NY