Gravicraft (gravitational spacecraft driven by internal motions only)

#VeritasiumContest This video briefly explains the principle of operation of a “gravicraft“ that can escape the attracting celestial body like a star or a planet without any kind of jet engine, due to the internal redistribution of mass only. The gravicraft was invented by Vladimir Beletsky [1,2]. This invention caused controversy, as many had the mistaken impression that the gravicraft violates the laws of conservation of energy and momentum. Nowadays, the gravicraft is mainly of educational value. For efficient operation, its size should not be too small compared to the distance to the center of the attracting celestial body. Therefore, the craft must be huge to operate close to the Sun or Earth. However, near very compact and massive bodies like neutron stars, the craft could be smaller for future construction. The craft does not need to be in the shape of a variable length dumbbell. Any other redistribution of the mass, leading to a change in the net gravitational force, can be used. The motion of t