Abstract
We model accelerated trips at high-velocity aboard light sails (beam-powered propulsion in general) and radiation rockets (thrust by anisotropic emission of radiation) in terms of Kinnersley's solution of general relativity and its associated geodesics. The analysis of radiation rockets relativistic kinematics shows that the true problem of interstellar travel is not really the amount of propellant, nor the duration of the trip but rather its tremendous energy cost. Indeed, a flyby of Proxima Centauri with an ultralight gram-scale laser sail would require the energy produced by a 1 GW power plant during about one day, while more than 15 times the current world energy production would be required for sending a 100 tons radiation rocket to the nearest star system. The deformation of the local celestial sphere aboard radiation rockets is obtained through the null geodesics of Kinnersley's spacetime in the Hamiltonian formulation. It is shown how relativistic aberration and Doppler effect for the accelerated traveller differ from their description in special relativity for motion at constant velocity. We also show how our results could interestingly be extended to extremely luminous events like the large amount of gravitational waves emitted by binary black hole mergers.
Highlights
We would like to start this article by applying to physics Albert Camus’s words from his essay [1]
The application of our former results is a simple modeling of interstellar travels to Proxima Centauri, located about 4 light years away, with large emission radiation rockets. This example is purely illustrative, and we will not list the numerous engineering challenges that must be overcome in order to even start thinking about such a mission, yet it will clearly show the major impediment of interstellar travel: the energy cost
We investigate spacetime geometry around the radiation rockets through characterizing null geodesics, which are nothing but the trajectories of light
Summary
We would like to start this article by applying to physics Albert Camus’s words from his essay [1]. There has been some renewed interest on relativistic spaceflight using photonic propulsion, along with the Breakthrough Starshot project [4] aiming at sending nanocraft toward Proxima Centauri by shooting high-power laser pulses on a light sail to which the probe will be attached According to us, such a quick analysis as above somehow hides the most important problem—the energy cost— really preventing interstellar travel from becoming a practical reality. We apply Kinnersley’s solution to the modeling of relativistic motion propelled either by anisotropic emission or absorption of radiation This encompasses many photonic propulsion proposals like blackbody rockets [17] (in which a nuclear source is used to heat some material to high temperature and its blackbody radiation is appropriately collimated to produce thrust), antimatter rockets, or light sails [3]. IV by emphasising key implications of our results for the problem of interstellar travel as well as introducing another possible application of the present results to the astrophysical problem of gravitational wave recoil by binary black hole mergers
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