Don't call it a video game. Call it a sandbox simulator where you are able to design your own spacecraft and use your designs to reach other bodies, where the mechanics within the game are based on real-life orbital mechanics. Though not perfect, is an accessible way for a person to demonstrate and practice their interest in a complex subject. Explain that the game does not use differential equations (because you're either in the SOI of a body or not) but it does not detract from the lessons you've learned. Be sure that you can also demonstrate your knowledge that you've gained; a bunch of flowery words mean nothing when there's no substance to hold it up.
