Their evidence suffers from sampling bias.

The core questions this book attempts to answer are simple:  Is space expansion, as its advocates insist, a positive development for humanity and the Earth? Is space expansion desirable because it has produced and will produce the positive consequences anticipated by visionary space advocates? Or are actual and prospective space expansion more mixed in their consequences, perhaps even largely negative? These very broad questions unfold into a cluster of interrelated, more specific questions: Have space activities altered global closure and helped reduce planetary vulnerability? Or have they intensified global closure and increased planetary vulnerability? Can the large-scale development of Earth orbital space make important, even decisive contributions to solving Earth problems? Or are such schemes unlikely to contribute to solving these problems, while entailing substantial unanticipated risks? And is the expansion of humanity into a multiworld species likely to beneficially transform the overall human situation? Or is such an expansion more plausibly viewed as the source of great, perhaps ultimately fatal perils for humanity? How this flock of questions about space are answered clearly has profound implications for both the space prospect and the contemporary debates about the human situation on Earth.

Unfortunately, answering these questions with any degree of certainty is very difficult in some cases, and probably impossible in others. Space is filled with a great many “known unknowns,” things we know we do not know, as well as “unknown unknowns,” things we do not even know we do not know anything about. Despite these many hurdles, an assessment still has great potential value, if only because space expansionists continue to provide strong answers to these questions, often with a great deal of certainty. If the topic of space is so full of unknowns, how can space expansionists be so confidently certain that space expansion is desirable? Thus even if a full assessment of the space expansionist claims faces great uncertainties, it can still be very valuable simply by showing that the strong claims offered by space expansionists rest on erroneous, contradictory, implausible, or speculative grounds.

Surprisingly, no general assessment of the overall net impact of all actual space activities exists.4 Also surprisingly, there exists nothing approaching a full critical assessment of whether the larger space projects envisioned by advocates are really as desirable in their consequences as is widely thought. Indeed for many space ventures, past and prospective, simply asking questions about negative impacts alongside positive ones is itself a novelty. The existing literature on space, while enormous and filled with many outstanding works, is largely written by advocates and sympathizers of the overall enterprise. And while existing treatments of space are numerous, they are also very fragmented. They typically examine some space activities, while largely ignoring others. Some examine what has actually happened in space, while others focus on prospective space activities. The treatment of military space activities has tended to be isolated and fragmented. Some focus solely or primarily on military activities, while many others downplay, segregate, or even ignore the military dimensions of space, both actual and prospective. Furthermore, while it is universally acknowledged that military activities have played a very large role in actual space expansion, prospective military activities and scenarios for large-scale violence largely disappear in nearly all visionary schemes for the industrial development and colonization of space near the Earth, as well as for space expansion across the solar system. If, however, the prospect of military activities occurring in the course of ambitious prospective space activities is not assumed away, the potential consequences, and thus the desirability, of these grand schemes may look very different.

Many arguments of space expansionists are space-political arguments, about the broad political consequences of space. They employ claims related to some of the most basic and contested questions in political science, political geography, and international relations but have never been systematically assessed as propositions in these social sciences. Instead of analyzing the political impacts of space expansion, the few political scientists who examine space topics have concentrated their efforts in offering explanations of how political factors, such as interstate rivalry, helped bring about space activities. In short, existing political science analyses of space largely explore the causes of what has happened in space, not the consequences. 5