This chapter examines Darwin’s analysis of emotional expression. It is widely accepted that Darwin wrote Expression to refute Sir Charles Bell’s theory that God created humans with special muscles to express their emotions. However, scholars have overlooked the fact that Bell developed his theory to refute Erasmus Darwin’s associationist analysis of emotional expression, inspired by David Hartley, and that Charles Darwin defends his grandfather’s analysis against Bell’s objections. I demonstrate that Charles’s defense of Erasmus’s associationist theory, which denies that expressions occur for the sake of communicating emotions, explains Charles’s puzzling reluctance to claim that expressions evolved to serve as signals in communication.

The obligation to support space exploration can be defended in at least three ways: (1) the ‘argument from resources,’ that space exploration is useful for amplifying our available resources; (2) the ‘argument from asteroids,’ that space exploration is necessary for protecting the environment and its inhabitants from extraterrestrial threats such as meteorite impacts; and (3) the ‘argument from solar burnout,’ that we are obligated to pursue interstellar colonization in order to ensure long-term human survival. However, even if we accept all three propositions, that space exploration will give us access to asteroidal and other resources; will allow us to defend ourselves against meteorites (by intercepting or destroying them); and finally that interstellar colonization might be useful in saving us from solar burnout, it does not follow that we have an obligation to do any of those things. What follows is that we have reasons to take those actions as practical measures that will bring about the ends in question. But no obligation per se arises from the fact that those measures will be helpful in attaining those ends.

The Project Orion spacecraft is by common consent the craziest interstellar flight concept ever devised. Ironically, it was also the spacecraft design that received the widest support by scientists, the military and other branches of the US government, as well as by private industry. It was as if all of these people had collectively lost their minds. The basic idea was utterly simple and so intuitively obvious that it could be understood by a child. This was a craft whose propulsion system was built upon the Newtonian principle of action and reaction. The central notion was that of placing a bomb under a rocket and then detonating it to loft the rocket up and away – exactly the same process as putting a firecracker under a tin can and watching it blow sky high. To keep it going up, of course, a series of bombs detonated in sequence would be required. And so the Orion rocket would be propelled through space by a stream of bombs, in fact nuclear bombs, exploding one after another behind it, thereby continuously accelerating the craft. That was the project’s key concept, and as such it was simultaneously perfect and insane.

The chapter describes three iconic interstellar travel vehicles: the Bernal sphere, the Bussard Interstellar Ramjet, and Project Daedalus. Nobody took the Bernal sphere seriously. The Bussard vehicle would not work as intended, and the Daedalus vehicle lacked a credible propulsion system. The principal difficulty with star travel is that the stars are very far away, at distances measured in light years.

Let us optimistically assume that sooner or later a workable interstellar propulsion system will be found, and also be built and successfully tested in space. While this would be a great advance toward making interstellar travel possible, it nevertheless does not automatically follow that a voyage to the stars will in fact be attempted. There are a few other issues that must also be settled first: for example, a habitable exoplanet must be identified. It must be suitable for human colonization and ought to be a reachable distance away from Earth within a reasonable period of travel time. Second, engineers must provide a plausible space vehicle design architecture, and a spacecraft of that design must then be constructed, and tested successfully. Such a craft does not exist as yet, one among many reasons being that the specifications for it depend in turn upon the size and makeup of the likely boarding population. But both of those factors are still unknown. In addition, and perhaps most important of all, an unprecedented level of funding and resources must be allocated to the project.

This, then, was the final culmination of a succession of dreams that had emerged progressively in 11 steps or stages that had begun in antiquity. In logical order, the several steps were from: (1) the birth of ancient Greek and other myths of flight, to (2) proposals for machines that would make flight possible by mimicking the flapping wings of birds, to (3) actual attempts at human flight, to (4) successful human flight through the air by means of balloons, to (5) powered, controlled, sustained human flight through the atmosphere by winged vehicles, to (6) fictional accounts of flying to the Moon, to (7) the invention of rockets leading to an understanding of the principles of space flight, to (8) the Apollo Project Moon landings, to (9) fictional accounts of traveling to Mars, to (10) actual landings on Mars by rockets and robotic rovers, to (11) the idea of leaving Earth and colonizing the universe.

DARPA and NASA had jointly realized that nobody in their right mind formulated plans and undertook projects on anything like the 100-year time horizon that they thought was needed to design, build, outfit, and launch a crewed interstellar vehicle. So they wanted to seed-fund some private organization to do so, and for an essentially backdoor reason: namely to reap whatever possible spinoff technologies might accrue from such an endeavor. “DARPA also anticipates that the advancements achieved by such technologies will have substantial relevance to Department of Defense (DoD) mission areas including propulsion, energy storage, biology/life support, computing, structures, navigation, and others.”

While the fate of a multigenerational interstellar population cannot be predicted with anything approaching certainty, the many dangers presented by the instantaneously lethal environment of space, plus the interpersonal pressures and conflicts that might result in social breakdown, make it doubtful that a successful transit to another star system with all the successive onboard generations remaining safe, healthy, and happy across time, is a realistic possibility. It is far more likely that the crew would suffer one or another kind of irremediable catastrophe en route than that everyone aboard would survive, and that the final, arriving generation would get there intact. But if that is true, then the question arises whether it would be morally justifiable to launch such an expedition to begin with, given its immense costs, high probability of failure, and lack of any benefit accruing to the sponsors back on Earth who had paid for it all.