Crowded Orbits asks a fundamental and far-reaching question: will national, international, and commercial efforts to explore and exploit outer space, beginning with Earth orbit and extending to the solar system and beyond, be marked by cooperation or conflict? Space is a commons, owned by no one; yet it is also an increasingly valuable location for a range of military and commercial activities. Moreover, if proponents are to be believed, the seemingly limitless vistas beyond Earth’s atmosphere will become an increasingly scarce and contested resource over the next few decades, as everything from orbital “slots” to metal-rich asteroids become valuable assets in limited supply, and as military forces expand into space for surveillance, communication, and to position defensive and offensive systems.

To address these questions, Clay Moltz offers three useful perspectives. First, he gives a lucid summary of the unique characteristics of the space environment, including a primer on orbital mechanics. Second, Moltz gives a short but complete history of the various national, commercial, and military space programs, from Sputnik to the International Space Station. Third, Moltz describes current and proposed technologies, including launch vehicles, satellite platforms, and crewed spacecraft. In a word, Crowded Orbits gives the reader context – what resources does space offer, how have nations, corporations and other groups tried to tap these possibilities, and how might these efforts evolve in the near term? Throughout the book, Moltz does a superb job of translating complicated concepts, technologies and jargon into explanations that will make sense to the nonspecialist reader.

The underlying argument of Crowded Orbits is that space exploration affords many opportunities for cooperation, but that this outcome is in no way inevitable. Just as on Earth, actors sometimes face strong incentives to free ride. In other cases, the apparent benefits of cooperation may in fact not exist, as interests are opposed rather than complementary. And even when cooperative outcomes have been achieved, these results can be vulnerable to shifts in technology, national interests, or the emergence of new actors. In this sense, while there are clear differences in the nature of interactions on Earth and in outer space, it is also clear that theories developed to explain behavior in one venue retain their explanatory power when moved to the other.

One of the notable strengths of Moltz’ book is its grounding in substance. For example, the benefits of cooperation are illustrated by a discussion of the mechanisms used to allocate the limited number of orbital slots for geosynchronous communications satellites. The response to the increasing threat posed by orbital debris illustrates the difficulty of establishing new rules and norms in the absence of a hegemon. Finally, the development of anti-satellite weapons (and the vulnerability of virtually all orbital systems to these weapons) neatly captures the problem that some nations or non-state actors may face strong incentives to disrupt norms and rules that govern space activities –incentives that grow larger, moreover, as the need for and benefits of these institutions increase, and as the technology for launching attacks against targets in orbit becomes more widely available.

A second strength of the book is its thoughtful use of historical events to illuminate contemporary problems. For example, the various UN treaties that prohibit nations from stationing nuclear weapons in space or that govern the return of astronauts and spacecraft to the nation that launched them demonstrate that there is nothing fundamental to activities in space that limit international agreements. Similarly, Moltz’s account of the development of the International Space Station (as well as the agreements that govern its operation by a 16-nation partnership) highlight both the potential for and limits of efforts at the international level. In both cases, Moltz shows that future outcomes are not set in stone – for example, the fact that NASA and its international partners built and operate the ISS does not make future cooperation inevitable.

In describing the range of activities in space, Moltz admits that he is aiming at a moving target – indeed, the prediction of increasing human presence in space is what drives his argument about the increasing potential for conflict and the opportunities for (and difficulty of) cooperation. The last decade has seen the expansion of exploration, communications, remote sensing, biomedical, and materials science and other activities in space by individual nations, international coalitions, and, increasingly, purely commercial entities. However, while space is large, the opportunities it affords are not infinite. As Moltz shows, past conflicts, such as disagreements over ownership of slots in geosynchronous orbit or inadvertent damage to civilian satellites by tests of military anti-satellite systems, have been short-lived and relatively minor. At some future time, when the potentially vast commercial and military potential of outer space is translated into real plans, programs, and launches, conflicts may become much larger and more intractable than we have seen thus far.

Whether this shift is years or decades away is not clear. In the long-term, it is a safe bet that absent a world-wide catastrophe, individuals, nations, and corporations will explore, exploit, and colonize low-Earth orbit and the solar system. The near-term is much less certain. To paraphrase author Robert Heinlein, space technology is “waiting at your front door – C.O.D. It's yours when you pay for it.” At present, there is no compelling prospect that would justify a major expansion in humanity’s presence in space. Even so, Crowded Orbits provides an important guide to the problems and the opportunities that these moves will inevitably create.