The comics medium takes a good, long time to master. The vast majority of artists don’t hit a peak until they have been drawing and writing and composing pages for decades.

So, when an artist comes along who seems to have a mastery of the form well beyond their years, well, comics fans (and professionals) take notice.

This was the case with comics artist Tillie Walden in 2017, when she was 21 years old and still an Austinite (she recently moved to Los Angeles).

She had already published three shorter works and won two prestigious Ignatz Awards in 2016 — an outstanding artist award for her debut graphic novel, “The End of Summer,” and a most promising new talent award for “I Love This Part.”

But jaws dropped at her 400-page, 2017 comics memoir “Spinning,” a meditation on adolescence, sexuality (Walden is an out lesbian), parent-child relationships and competitive figure skating. The deft line work, the nuanced writing, the savvy layouts, the elegant pacing — all of it spoke of an artist with the skills of someone twice her age.

“Spinning” promptly won an Eisner award (essentially a comics Oscar) in the category for best reality-based work.

And, oh, yeah, this entire time, she was also publishing a web comic, a queer space opera called “On a Sunbeam,” which has now been compiled into a totally excellent, 530-plus page graphic novel, published by First Second Books.

“On a Sunbeam” is the story of Mia, a young woman who joins a crew of mostly queer or nonbinary characters aboard the Aktis, a ship charged with going into deep space and repairing massive buildings, buildings that seem to defy the laws of physics — yet have a tangible feel.

There’s Char, Char’s partner, Alma (both of whom captain the ship), Alma’s niece Jules, and Elliot, who communicates nonverbally.

There is a coziness to the ship that can be tough to translate in space opera stories — Walden nails it with close spaces and lived-in environments. The crew are part art restorers, part contractors, and all well-rounded characters. Her characters have a Studio Ghibli vibe, as does the surrealism baked into the story, its knotty structure and wide-angle climax.

We also see Mia five years earlier at an all-girl boarding school (also in space) as she starts a relationship with Grace, a new student about whom very little is known. The two threads come together in compelling ways, as emotional barriers — the ones we build and the ones we break down — sync up with physical ones as the crew works to literally keep the past intact while moving forward with their own lives.

Also, there are ships that look like flying fish.

Walden’s world-building is deft and detailed, and her use of color to indicate changing (and often complicated) moods is subtle and joyful in equal measure. She is at home with tight spaces as well as vast landscapes.

And since “On a Sunbeam” started as a web comic (and Walden’s first serialized work at all) you can see her growing more confident with the format over time. By the novel’s resonant climax, it’s clear that digital color and composition is yet another tool with which she has likely become expert. Each page has a central color theme that she will accent as needed.

As the story progresses, Mia gets to know her crew and their own complex pasts, and Walden gives them space to grow and change, ultimately leading to a denouement that feels warm, quietly heartbreaking and completely earned.

And to think Walden is just getting started.