To start writing'secret little space fanfiction', begin with an idea for the secret space. Is it a lost civilization's hideout? A portal to another dimension? Once you have that, introduce characters with their own motives and backstories. For example, a young scientist eager to make a discovery. Develop a plot around their exploration of this secret little space.
When starting to write'secret little space fanfiction', consider the elements that make a space story exciting. You could start by imagining a unique secret space, like a floating island in a gas giant's atmosphere. Then, build your characters. They could be a diverse group, like a smuggler, a diplomat, and an engineer. Next, create a conflict. Maybe they all want to use the secret space for different reasons. This conflict will drive the story forward and keep the readers engaged as they explore this mysterious part of the fictional space.