A grieving father and his teenage daughter teams up with four other cadets to stop androids from invading Earth from an evil emperor.

1) They have a great bond together.
2) They are space cadets. He is their leader.
3) The emperor wants the robots to invade the planet.

Sounds cool, consider the following to strengthen your logline:
1. Why a father and daughter team to save the world? What’s makes them qualified?
2. You mentioned cadets, what kind of cadets are you referring to, and can your protag father being linked as their leader or teacher – hope you see where I’m going with this.
3. Who is your baddie (emperor) and what is his goal? Think about all the Sci-Fi shows we’ve seen, what makes this emperor and his minions unique?

Keep going!