14 CFR § 101.25

At any altitude where clouds or obscuring phenomena of more than five-tenths coverage prevails;

At any altitude where the horizontal visibility is less than five miles;

Into any cloud;

Between sunset and sunrise without prior authorization from the FAA;

Within 9.26 kilometers (5 nautical miles) of any airport boundary without prior authorization from the FAA;

In controlled airspace without prior authorization from the FAA;

Unless you observe the greater of the following separation distances from any person or property that is not associated with the operations:

Not less than one-quarter the maximum expected altitude;

457 meters (1,500 ft.);

Unless a person at least eighteen years old is present, is charged with ensuring the safety of the operation, and has final approval authority for initiating high-power rocket flight; and

Unless reasonable precautions are provided to report and control a fire caused by rocket activities.