Answers(?) For the first two unasked questions via vimanas nextday.
What does `reduce constant energy of rest` mean? This means not a decrease in the number of particles constituting the vimanas nextday (molecules, atoms …). Their number remains unchanged. Changes energy of rest each particle of each atom (the speed of one tenth speed of light can be achieved by decrease by half a percent energy of rest each particle).
Is the speed of one tenth speed of light can be achieved? Yes, in theory so it is. In practice, such a quick result means the equivalent of acceleration of 500,000 m/s or 50K g. If using the gravitational technology will be created modified gravity at least with the heterogeneity of more than one thousandth percentage, then this means the impossibility of such a quick result for passenger vimana (bio-body would be stretched). There are minimum two options. Or increase the time to achieve the required speed, Or research how to create (and regulate) the most homogeneous gravity in the desired volume.
Appendix. Some time ago strongly thought that the dreams of founder of the Gravity Research Foundation Roger Babson forever will remain only dreams and approval in the book (that is does not exist) that ancient vimana was a device that used for movement gravitation is highly false. I never watched either vimanas or flying saucers or any other flying objects similar to them. Maybe they are not really, maybe yes. However, creating similar devices, as it turned out, is quite possible for several decades … if you want