While the circumnavigation of the solar system seems farfetched, it may not be once the problem of effective anti-gravitational control is solved. In this book I have assumed that the many researchers now actually at work on this problem will achieve such a result in the next decade. It is not at all impossible that they may - for we all know that the more minds that work at a problem, the sooner it will be solved. The discovery of a means of negating, reversing or otherwise utilizing the immense force of gravitation for space flight purposes is now thought to be within the bounds of probability. It should occur some time within the next hundred years, possibly in even the short period I assume here...