Castle in the Stars: The Space Race of 1869 by Alex Alice

His mother is an adventurer and she takes off in her air balloon in search of aether.  She finds it but she loses her life...

First Second Books and Net Galley allowed me to read this graphic novel for review (thank you).  It will be published September 15th.

He and his father are deeply saddened and move on with their lives but it's not the same.  They are still working with hot air balloons.  When someone asks them to meet them in another location to get the wife's logbook, they go.  Then they find out the Prussians are after them!

Escaping takes a lot of work but escape they do.  Then they go to the Prince's castle.  He's also interested in hot air balloons and gives them an assignment.  They recognize one of the Prussians who tried to detain them as a member of the household but they can't accuse him. There's no proof.  They do create false architectural designs to throw him off. Soon there's mutiny in the castle and the only way to get away is on the air balloon...

This is first book in the series and it's entertaining.  I'll be watching for the next novel.