By now most readers have heard of Robert Zubrin's proposal for Mars Direct: an innovative way to stage manned missions to Mars and create the framework for permanent habitation and colonization of the red planet. So why buy and read a book about it? While you may be familiar with the concept, you may not be aware of more the details, history, and rationale of the proposal. The Case for Mars provides all that and more, and leaves you hard-pressed to find a reason why not to support it.
     Zubrin lays out the plan in detail, but at the level of the layman. One spacecraft is launched to Mars, where it creates fuel for the return trip. If that spacecraft succeeds, two more are launched at the next opportunity: one with crew and another return vehicle. The crew lands near the first return vehicle, explores the planet for up to several hundred days, then returns in that vehicle. The second return vehicle lands elsewhere on the planet and makes fuel for the second crew, and the process continues.
     This book works on many levels. For someone not acquainted with Mars Direct, The Case for Mars provides a thorough introduction to how the mission would work. Those already acquainted with Mars Direct will enjoy reading how Zubrin, David Baker, and others at Martin Marietta developed the proposal in the wake of the infamous "90-Day Study" which estimates a half-trillion cost for a Mars mission. There's also enough detail to satisfy the more technically and scientifically inclined.
     Everyone, though, will appreciate the epilogue, where Zubrin lays out the rationale for human exploration of Mars as part of the frontier analogy. Here we find a reason to go to Mars that is much more powerful than any scientific explanation or political program. The frontier has been a vital driver of technological and social progress, and without such a frontier we risk stagnation. It's a theme you've probably heard if you've seen him speak, but he makes it just as forcefully here. The Case for Mars lives up to its billing: it provides one of the most realistic, feasible plans for human exploration of Mars, and gives perhaps the best rationale to date for going there.

Within the last few years,. we have seen a number of new proposals for new launch vehicles aims solely at commercial markets. As new communications networks are established and the need for satellites to relay this traffic increases, more companies need to launch satellites and are looking for the best possible deal. Even more would do so if only the cost were lower, hence the interest in developing new, reusable launch vehicles that promise cheap access to space. G. Harry Stine looks at the history and future opportunities for reusable vehicles, specifically single-stage to orbit technology, in Halfway to Anywhere.
     Stine gives an insider's history to the development of cheap, reusable commercial launch vehicles. Starting with Phil Bono and his ROMBUS and other proposals for single-stage vehicles, he proceeds through a history of case studies and proposals by industry and entrepreneurs, none of which succeed. Much of the book is devoted to the most famous SSTO project, the DC-X/DC-XA. Here Stine gives a blow-by-blow account of the ups and downs of this project.
     Stine makes no attempt to present a detached, unbiased account of events. The book is couched in the struggle of the good guys (the people developing SSTOs, like McDonnell Douglas, Bono, and Gary Hudson) and the bad guys (NASA and other government agencies), who will stop at nothing to preserve their launch monopoly. While it's certain that there are people in government who are not at all fond of private developments, the constant portrayal of NASA as an evil bureaucratic entity does get tiresome after a while. (Dan Goldin does get some praise from Stine, though, for his efforts to promote reusable launch vehicles.)
     Although on a few occasions facts get lost in the struggle (Stine states that the X Prize is a project of the Space Frontier Foundation, when in fact it's a separate entity) the book is still an enlightening, enjoyable read. Stine's inside knowledge of events gives him the unique ability to provide a detailed, knowledgeable history of SSTO efforts and the prospects, both technical and economic, for the future. Halfway to Anywhere is more than halfway to being a good book.

Books about the threat posed by asteroid and comet impacts are raining down on bookshelves like, well, a meteor shower. It's not good enough now to simply write a book about the possibility of an impact and what would happen during an impact, as there have been too many books on that subject alone. Instead, the book must go further afield in some way and set itself apart from other works. While Impact tried to do this to some degree, it doesn't quite succeed in carving a niche for itself in the asteroid and comet impact bookshelf.
     Verschuur, a radio astronomer by training, covers much of the same ground as other books here. He provides a detailed history of the discovery of the Chicxulub impact crater in Mexico, now widely regarded as the impact event which killed off the dinosaurs and other species 65 million years ago. Other chapters explore the impact threat of asteroids and comets, and how they have been viewed throughout history. A later chapter describes the impact of comet Shoemaker-Levy 9 with Jupiter in 1994, and another explores methods of preventing future collisions.
     Verschuur tried to cover new ground by exploring a hypothesis that a giant impact almost 10,000 years ago took place on Earth and perhaps helped spur the development of civilization. Most of the evidence for this, though, is based on possible interpretations of myths from a number of cultures, with only a small amount of scientific evidence. This hypothesis hasn't attained wide support among scientists, especially in the United States, though, so we're left with little more than an interesting idea.
     A couple of years ago, before the rain of impact books began hitting the bookshelves, Impact would have been an outstanding, interesting, piece of work. Today, though, much of what's told here has already been described in equal or better detail by other authors, leaving little unique material or new explanations for this book to stand on. This is not to say Impact is a bad book, but there are other books, possibly better ones. (A couple good examples are Rain of Iron and Ice by John Lewis and Rogue Asteroids and Doomsday Comets by Duncan Steel). If you've read those books, there's little reason to read Impact.