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Review: Fly Me to the Moon

Fly Me to the Moon: An Insider’s Guide to the New Science of Space Travel
by Edward Belbruno
Princeton Univ. Press, 2007
hardcover, 176 pp., illus
ISBN 0-691-12822-7

For decades—indeed, since long before the first satellite was launched 50 years ago—spaceflight has been governed by a relatively simple set of means of getting from point A to point B. These trajectories, primarily Hohmann transfer orbits and the like, can be easily calculated and carried out by spacecraft. However, they are not the only, nor necessarily the best, means of traveling around the solar system and beyond. A small group of scientists has worked on new orbits that take into account the inherently chaotic motion of objects in a multibody system (see “From chaos, a new order”, The Space Review, March 6, 2006). One of the innovators in what is known as “capture dynamics”, Ed Belbruno, provides a basic and eminently readable introduction to the topic in Fly Me to the Moon.

Belbruno offers a human touch as he explains the idea as he developed it, rather than take on a more sterile, technical approach.

Belbruno notes that while Hohmann transfer orbits are easy to compute and have been used for all sorts of spacecraft over the years, they are not terribly efficient in the use of spacecraft propellant—“gas hogs”, as Belbruno calls them. Given the expense of putting mass into space to begin with, whether it’s spacecraft dry mass or propellant, alternative approaches that don’t require as much propellant to get spacecraft to a particular destination can be cost effective. This alternative uses what are known as weak stability boundaries, which Belbruno describes as “no-mans-lands” where the gravity of two bodies—say, the Earth and the Moon—balance out, allowing a spacecraft to be captured in orbit with very little propellant.

It’s very easy when examining an abstract, complicated subject like this to get bogged down in physics and mathematics that bewilder the average reader. Belbruno avoids this: there is not a single equation in the book. Instead, he mixes illustrations (drawn by the author, who is also an artist) with an explanation of the topic in layman’s language. Belbruno takes the reader through his own history of the subject, starting with some work he did at JPL in the late 1980s on a proposed small lunar spacecraft to later assistance with a stranded Japanese lunar spacecraft, Hiten, and later, and more famously, the rescue of AsiaSat 3/HGS-1. Belbruno offers a human touch as he explains the idea as he developed it, rather than take on a more sterile, technical approach. (For those who want more details, though, Belbruno did write a more technical book in 2004, Capture Dynamics and Chaotic Motions in Celestial Mechanics)

The latter part of the book explains some future applications of capture dynamics, such as lunar missions that are part of the Vision for Space Exploration, and their role in nature, manipulating the orbits of comets and even playing a role in the formation of the Moon. Capture dynamics was initially treated with skepticism, as Belbruno recounts in the book, and today is still used very rarely. However, books like Fly Me to the Moon can help raise awareness of the concept to a wider audience, and may hasten the day when such trajectories are more commonplace.