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Q&A What is the most economical barrier that can physically prevent any spaceships from trespassing into Earth?

In the 22nd century C.E. human already colonised the entire Solar system, and Earth becomes a dangerous place to live because of the spread of deadly synthetic virus that kills every animals and sc...

5 answers  ·  posted 7y ago by user6760‭  ·  last activity 7y ago by user6760‭

Question space planets technology space-constructs earth