Frontiers of Propulsion Science Editors: Marc G Millis and Eric W Davis Publisher: American Institute of Aeronautics and Astronautics ISBN: 978-1-56347-956-4 Price: £94.50 (Hb) 739pp
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The stars our destination: will we ever be able to venture into deep space and voyage to nearby stars? This hefty tome examines our current knowledge of advanced spacecraft propulsion as well as probing the possibilities of breakthrough physics. Readers should be forewarned that the treatises inside this book are highly technical and often at graduate level, but for those with a technical background and an interest in advanced propulsion this is an essential book.

Marc Millis led the Breakthrough Propulsion Physics Project at NASA's Glenn Research Center between 1996 and 2002, and many of the essays within this book are based on work conducted during that time. The project was designed to explore new physics that could one day lead to new technology capable of propelling a spacecraft - manned or otherwise - on an interstellar voyage of discovery. This new physics included experiments with the Casimir effect, anti-gravity effects from superconductors, the Alcubierre warp drive, quantum entanglement and theoretical tachyons and wormholes. There were no major breakthroughs during those six years at Glenn, but plenty of lines of research to be explored not only within this book, but as part of future studies. To fill the gap left when NASA's funding of the Breakthrough Propulsion Physics Project ended, Millis - a staunch believer in interstellar flight - created the Tau Zero Foundation to help facilitate these studies, a Foundation whose motto is 'ad astra incrementalis', meaning 'to the stars in steps, where each is greater than before'. Meanwhile, co-editor and author Eric Davis is a physicist at the Institute for Advanced Studies at Austin and a former contributor and consultant to the Breakthrough Physics Project. Together he and Millis, along with the other contributors to this book, have the expertise to diligently examine future prospects.

Following a foreword by Burt Rutan - winner of the X-Prize in 2004 and a true space pioneer - Robert Frisbee's excellent examination of how far it is possible to take standard future propulsion systems such as nuclear fusion, solar sails and ramscoops provides an overview of the field. Then we're headlong into discussions of propulsion without rockets, focusing strongly on the manipulation of gravity by spinning theories out of relativity, superconductor physics and zero point energy. Most fascinating is James Woodward's contribution regarding an interpretation of Mach's Principle, in which the motion of a local frame of reference, for instance water in a bucket being spun around, is affected by the distribution of matter in the rest of the Universe, and how Woodward's experiments suggest there may be a way to manipulate Mach's Principle in inertial frames of rest to produce thrust. In lesser hands such discussions, however technical, could easily collapse into a morass of pseudo-science and crack-pottery, but these are real, working scientists and the emphasis of each chapter is squarely on a rigorous adherence to the scientific method, and the editors and authors should be congratulated for not being afraid to show where their research simply hasn't worked, describing experiments that produced null results and what lessons can be taken from their failure. For instance, in Chapter 6 Millis himself looks at the claims of anti-gravity devices throughout the years and shows why these are not breakthroughs but often merely previously established physical principles in unfamiliar settings, leading to them being misunderstood.

As the book progresses it delves into an even riskier topic, namely faster-than-light travel. We've witnessed how errant neutrinos have thrust faster-than-light travel into the spotlight recently, and all of a sudden the concept doesn't sound quite as crazy as it did to some critics before. The neutrino finding has come too late for inclusion within this book, but those who like 'spooky' particle physics may appreciate John Cramer of the University of Washington's chapter on quantum entanglement, which is the eerie way in which particles, once interacting but now separated by perhaps as much as the diameter of the visible Universe, seem to be able to posses a link by which they are able to share information instantaneously, apparently breaking the light speed barrier in the process. And although faster-than-light travel through our space-time is forbidden by Einstein's Special Theory of Relativity, travel outside of our space-time through wormholes may not be held to account by relativity in the same way, writes Davis in Chapter 15, but the energy requirements to open and hold a wormhole stable may be off the scale. Energy considerations are further examined in the fourth section of the book, looking again at zero point energy and null results of experiments attempting to replicate claims of being able to harness this energy.

Beyond Robert Frisbee's early piece, there's not a great deal here on 'conventional' advanced propulsion - fusion drives, solar sails, that sort of thing - but those are known technologies based on known and fairly solid physics. Where Frontiers of Propulsion Science dares to tread are the areas where the physics isn't so well known, but which could provide the vital breakthrough one of these days, a breakthrough that would not just benefit space travel but perhaps our everyday lives too. As a primer on this speculative but pioneering field, Frontiers of Propulsion Science is really the only book so far that does the topic justice. Book-ended by highly readable pieces on the history of advanced propulsion research by Centauri Dreams' Paul Gilster and how we should approach the subject in the future by Millis, the concepts discussed within make you realise that perhaps interstellar travel will be possible one day.

Keith Cooper