Does anyone have an idea what sort of design could achieve the proposal near the end: > Clearly the immense loss of energy by gravitational radiation is an obs

Does anyone have an idea what sort of design could achieve the proposal near the end: > Clearly the immense loss of energy by gravitational radiation is an obstacle to the efficient use of neutron stars as gravitational machines. It may be that this sets a natural limit of about 108 cm/sec to the velocities that can be handled conveniently in a gravitational technology. However, it would be surprising if a technologically advanced species could not find a way to design a nonradiating gravitational machine, and so to exploit the much higher velocities which neutron stars in principle make possible. From my dim memory of Kip Thorne's popular book, a spinning black hole could be used in this way, which would mean there's at least one solution.