My time off last week really was refreshing, although it coincided with the same heat wave that has kept the Eastern US under duress for many days now, especially dangerous for those who lost power because of severe storms. Fortunately, I used part of my time to fly to San Jose to participate in Steve Durst’s Galaxy Forum (sponsored by the International Lunar Observatory Association), where I spoke on destinations in the outer Solar System and beyond as we make our first tentative steps into the galaxy. It was a good gathering, with lively talk from Seth Shostak, Jon Lomberg, Tony Cardoza (who signs people up to travel on future flights with Virgin Galactic), and Durst himself. It was also a pleasure to meet Centauri Dreams regular Alex Tolley. Blissfully, the temperatures never got out of the low 70s, with a refreshing breeze that made walking around downtown a pleasure.

Miles, my older son, lives near San Francisco and the trip was also a wonderful chance to reconnect. I can recall walking around the Air and Space Museum in Washington with him when he was just a boy, talking about the various planetary missions and speculating about what might come next. In our San Jose conversations, we talked about the attention now being paid to interstellar flight and what has changed over the years, ideas I reflected on while flying back to the East Coast. It’s really only been in the past 50 or 60 years that scientists and engineers have focused on the problems of interstellar flight, and even then mostly as extra projects in their spare time.

How exactly did the idea grow in the scientific community, and who were the early players? In an essay on fusion propulsion in the Johnson/McDevitt book Going Interstellar, Greg Matloff fixes on Freeman Dyson as a pioneer in what we could call the ‘interstellar movement.’ Dyson had been working with Ted Taylor on Project Orion, which saw its high-water mark in the early 1960s as a propulsion system that could take astronauts on interplanetary journeys, and do so not in the cramped quarters of an Apollo-style capsule but aboard a massive vehicle that could hold a crew of a hundred or more. Orion used the explosion of nuclear devices behind a massive pusher plate to drive the vehicle, ruling out launch from Earth, but there were serious studies of using Orion principles in a Saturn rocket upper-stage, a design that could not only reach Mars in about a month but could carry greenhouses, livestock and building materials.

Image: Freeman Dyson in earlier times, when Orion ideas were in the air and all things seemed possible. Credit: New York Times.

When the Atmospheric Test Ban Treaty (1963) made Orion obsolete, Dyson wanted to save the idea, fearing it would be buried in some government vault and never resurrected. Matloff sees a cunning strategy in what happened next:

Being a physicist, Dyson planned to publish a paper describing the potential of Orion in a journal. But most physics, astronomy, and astronautics journals have circulations of only a few thousand. He chose to publish in Physics Today, a semi-popular monthly organ of the American Institute of Physics. Many public and university libraries subscribe to this magazine — its monthly readership would therefore be much larger than that of more technical physics journals. Dyson planned a paper that would outline the concept of Orion in visionary terms, and do so in a manner that would not violate his oath of secrecy.

And there’s the key, to get the Orion idea out to the public, which Dyson could do by using openly available information, such as the publicly available yield in equivalent megatons of a deuterium-fueled thermonuclear explosive. Going on to develop the Orion idea, Dyson could show that a fusion-pulse ‘worldship’ could reach the nearest stars in approximately 1800 years, carrying a colony of 20,000 to settle on whatever new worlds would be found at destination. The Dyson colony ship had an acceleration time of 500 years, to be repeated in the deceleration phase, but a much leaner Orion-based design could reach velocities of 10,000 kilometers per second, arriving at the Alpha Centauri stars in a scant 130 years.

Image: An interplanetary Orion departs for Mars. Credit: Adrian Mann.

It was the decision to make the Orion concept visible that distinguished Dyson’s approach. He had labored in Bomber Command for the RAF during World War II, an experience that made him all too aware of how a sluggish bureaucracy can stifle creativity and prevent needed change. I believe that Dyson’s starship ideas were deliberately provocative as he attempted to spark interest in the general public in a propulsion scheme he saw primarily as an interplanetary technology — he would later come to see Orion’s demand for nuclear explosives as both dangerous and impractical. But the key was to get across the fact that working within the laws of physics, a craft could be designed that could, in theory, cross the interstellar divide.

Dyson’s paper “Interstellar Transport” ran in Physics Today in October of 1968 (pp. 41-45), and it’s still a classic of interstellar studies. Tomorrow I want to dig into it in a little more detail, as we’ve never really gone through it in these pages. But I don’t want to stop with Dyson. There are a number of scientists whose early contributions helped to launch this field. Some honed their skills on the intractable problems of power and distance in scientific journals, seeing where the equations led under a variety of novel propulsion schemes, while others saw their work transformed as it entered popular culture, an outcome that few could have anticipated. All of them transformed our thinking as interstellar flight began to be seen as a remote but real possibility.