The Wonderful Flight to the Mushroom Planet is a science fiction/fantasy children's novel written by Eleanor Cameron in 1954. It is set in a beach community in California, as well as on a tiny, habitable moon, "Basidium," in an invisible orbit 50,000 miles from Earth. The "Mushroom Planet," visited by the protagonists David and Chuck, is covered in various types of mushrooms and is populated by little green people who are in a state of distress.
When two boys find a mysterious ad in a newspaper asking for two young boys to build a spaceship, they quickly construct one out of old tin and scrap wood, and bring it to the advertiser. This man is the mysterious Mr. Bass, a scientist living in an observatory who goes unnoticed by most of the townspeople for some reason. He shows the boys a previously undetected satellite of the Earth, the eponymous planet, which can only be seen with a special filter he has invented. He refits their spaceship, giving them some special fuel he invented to power it, and tells them to fly to the mushroom planet (after getting their parents' permission). He warns them that their trip will only be successful if they bring a mascot.
When it is time for launch, they grab a hen at the last moment for a mascot, and rocket into space. They wake up on the mushroom planet, a small, verdant world covered in soft moss and tree-size mushrooms. They quickly meet some residents of the mushroom planet, small men with large heads and slightly green skin, of the same people as the mysterious Mr. Bass. They tell the boys that their planet has had a crisis and that everyone is slowly dying of a mysterious sickness. The boys meet up with the king of the planet, the Great Ta, and end up solving the natives' problem, before returning to Earth.