Bird is a bright, empathetic seventh grader who is deeply fascinated by mechanics and space exploration. She keeps a detailed notebook filled with hand-drawn schematics of household appliances she takes apart to understand. Dreaming of becoming an astronaut for NASA, she eagerly anticipates her science class's unit on the upcoming Challenger launch. Within her household, she often acts as a quiet peacemaker, trying to ease the constant tension between her arguing parents.

Fitch is Bird’s twin brother, a seventh-grader who frequently battles a quick temper and impulsive frustration. He finds his greatest sense of control and peace at the local arcade, where he dedicates his quarters to mastering the challenging space game Major Havoc. His difficulty managing his emotions often causes friction with his family members and leads to volatile interactions with his peers at school.

Cash is the eldest Nelson Thomas sibling. Currently repeating the seventh grade, he feels left behind by his peers and friends who are advancing toward high school. After breaking his wrist and losing his position on the school basketball team due to low grades, he searches for a new activity or skill to boost his falling self-esteem and find his own unique talent.

Tammy is the mother of Cash, Fitch, and Bird. She works full-time and maintains a highly volatile relationship with her husband, Mike. Her frequent, verbally explosive arguments with him create a stressful environment that deeply affects all three of her children.

Mike is the father of the Nelson Thomas siblings. He regularly clashes with his wife over household duties and holds traditional, often sexist views about gender roles. He freely expresses his criticisms of his wife’s career ambitions, ignoring how these disputes impact his children.

Ms. Salonga is a science teacher at Park Middle School. She designs a special curriculum centered around the January 1986 Challenger launch, deeply engaging her students in the process. She serves as an inspiring figure for Bird, who admires both her teaching abilities and her rule-oriented, peaceful family life.

Amanda is a seventh-grade student who sits next to Fitch in science class. She develops a crush on him, frequently giving him stickers and calling him by his given name, Henry, which deeply aggravates him. She becomes the target of cruel gossip among their classmates.

Vern is Fitch’s closest friend at school. He frequently aggravates Fitch by teasing him about Amanda Piper’s crush, intentionally pushing his friend’s buttons for his own amusement and inciting conflict.

Dani is a classmate of Bird who takes on the role of shuttle commander in their science class mock crew. She invites Bird over after school, introducing her to a calm, organized household environment that contrasts sharply with the Nelson Thomas home.

Penny is a student at Park Middle School and the object of Cash’s crush. She is an organized student who is currently dating an eighth grader, complicating Cash’s awkward attempts to win her attention.

Jessica is a student in Bird’s science group. She frequently offers unsolicited opinions on social matters, unintentionally damaging Bird’s self-confidence by pointing out that being pretty is not Bird's strong suit.

Devonte is a fellow member of Bird’s mock space crew. Rumors circulate in class that he harbors a crush on Bird, prompting awkward interactions when Bird tries to set boundaries with him.

Marshall, often called Marsh, is a young boy who frequents the local arcade. He watches Fitch play Major Havoc with deep admiration, constantly asking for tips and trying to learn from the older boy.

Coach Farnsworth is the athletic coach at Park Middle School. He previously had to cut Cash from the basketball roster because of poor grades, but remains an encouraging figure who suggests alternative sports.

Judith Resnik is a real-world engineer and astronaut scheduled to fly as a mission specialist on the Challenger. She serves as an imaginary confidante for Bird, who silently asks her for advice on beauty, space, and the future.

Rachel is a popular girl at Park Middle School. Vern harbors a crush on her, though she reportedly shows interest in boys with a rebellious reputation.

Jessica Brantley is a student at Park Middle School who gossips with her friends about the social dynamics and dramatic moments occurring in their classes.

Brant is one of Cash’s friends. He frequently hangs out with Cash outside of school but occasionally teases him about being held back in the seventh grade.

Kenny is another of Cash’s friends who participates in their wall-jumping games and discussions about moving on to high school.

Charlie is an honors student in the eighth grade. He is currently dating Penny Barnard, making him a source of insecurity for Cash.

Mr. Wills is a social studies teacher at Park Middle School. He leads a particularly dry class that Fitch attends on the day of the Challenger launch.

Chekov is the Logan family’s elusive pet cat. He represents the peaceful consensus and harmony present in Dani Logan’s household, as his name was chosen without argument.