Deep Space Propulsion: A Roadmap to Interstellar Flight Author: K F Long Publisher: Springer ISBN: 978-1-461-40606-8 Price: $40.99 (Pb) 367pp
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Back in 1978, members of the British Interplanetary Society presented the results of Project Daedalus, an epic five-year design study for a starship, to make the point that - cost excepted - it wasn't beyond the bounds of realism to one day voyage between the stars with current or near-future technology (e.g. nuclear fusion). One year later, Astronomy Now's Contributing Consultant and AstroFest Chairman Iain Nicholson released the epic The Road to the Stars, an overview of potential modes of traversing the light years between the stars. Now, Kelvin Long's Deep Space Propulsion is a worthy effort to sit on the bookcase beside both.

Long is in prime position to write about this subject; after all, he's the founder an Vice-President of Project Icarus - the follow up to Daedalus (www.icarusinterstellar.org; also see The stars my destination, AN, January 2012). The first couple of chapters move rapid-fire through many different propulsion systems (21 variations in all) and reasons why we should dream of interstellar travel. Cynics may initially sneer, but in the subsequent chapters Long rigorously describes the workings of electric and nuclear-based propulsion, fusion drives, solar sails and the possibilities of antimatter and Bussard Ramjets, charting their development all the way back to basic flight principles including the propellor. It is serious science. These rigorous workings include many mathematical proofs, but the non-mathematical enthusiast shouldn't be put off - it's good to try and follow the maths, although for the general reader it isn't essential and can be skipped over.

Long goes beyond propulsion technologies to look at general mission design and architecture, which is where the book really earns its stars to become the very roadmap that Long asks for within its pages. His (self-confessed) optimistic timeline on page 321 has technology demonstrator missions blasting off in the next few decades, sending a pathfinder probe to 1,000 astronomical units (the outer edge of the Focal Point zone where the Sun can be used as a gravitational lens); the first interstellar probe launches in 2100 to arrive at a nearby star (possibly the alpha Centauri system) by 2160 and the launch of the first human interstellar colonising mission by 2250. To put this into context, popular science fiction such as the original Star Trek and Babylon 5 are set around the 2250s and Long notes that without a breakthrough discovery that could revolutionise space travel, such as warp drive or wormholes, meeting the expectations of those SF tales is going to be difficult. Yet 'hard' science fiction, such as the works of Long's idol, Arthur C Clarke, can give us ideas to follow up on, and inspiration to stay the course. As Clarke would have said, we can only accomplish this by overcoming our collective "failure of nerve" that has thus far seen us stuck in low Earth orbit since the early promise of Apollo.

Some readers may find it surprising that Deep Space Propulsion is mostly rather grounded in the sober realms of current mathematics, physics and engineering; what dreamy romanticism for space travel there is in the book is reserved for the initial and concluding few chapters. Indeed, some of the chapters can be quite rigid in their style of prose. However, Long hits his stride best when discussing the overall structure of mounting an interstellar mission; on the other hand, some early chapters about exploring the Solar System and beyond seem rather incongruous amidst the discussion of propulsion and mission technologies and, as a result, the text here feels uneasy, listing facts about the planets that needn't be in a book about propulsion. One feels that editorial should have trimmed these sections, but then one unfortunately gets the feeling that when Long's manuscript landed on the sub-editor's desk at the publisher, they were asleep at the time - spelling mistakes and missing or double words litter the pages far beyond the point of annoyance. It's a shame as Long and the book deserve better than this and I hope that Springer one day see fit to print a second edition with the typos corrected.

Nevertheless, typos aside, Deep Space Propulsion is an otherwise excellent guide to starship design and the chapters almost seem to have been arranged to suitably fit a lecture course on the topic, replete with practice exercises at the end of each chapter (and not all of them are mathematical, giving readers of all abilities a chance at having a go). If you have the time, this 'homework' is well worth the effort and is a really nifty idea on behalf of Long.

As a casual read, Deep Space Propulsion may be a little too dense, but for anyone with a serious interest in the subject, Kelvin Long's essential book may be the best around.

Keith Cooper