The International Space Station, orbiting at around 420km is dragged down by atmosphere[1], so I'm going to call that 150km limit an arbitrary one. Also, the Wikipedia article on the subject[2] doesn't appear to consider it worthy of even mentioning.

You are, of course, entitled to define "space" however you want in your own book, but be adviced that a lot of people will disagree with your definition.

[1] https://en.wikipedia.org/wiki/Night_Glider_mode [2] https://en.wikipedia.org/wiki/Atmosphere_of_Earth