Spacecraft Collision Probability, F Kenneth Chan, AIAA, 2008, 323pp, $79.95, ISBN 978-1-8844989-18-6 [hardback]
Orbital debris is a subject that has seen an increasing amount of interest in recent years, not only among researchers, but also among the space community at large. The reasons include the apparent increase in the frequency of debris impacts on operational spacecraft, not least the Space Shuttle, and the well-publicised collision between a retired Russian weather satellite and an operational Iridium communications satellite. Since in-orbit collisions are now real as opposed to ‘theoretical’ or ‘predicted’, the release of a book on the probability of spacecraft collision is timely.
Prospective buyers should be aware from the outset that this is a highly technical text book, dominated by graphs and mathematical equations (probability is of course a mathematical subject). It is aimed, therefore, at university students and researchers. On the other hand, it is intended to be a practical book, since the subject has an entirely practical application. Indeed, determining the probability of collision between two orbiting objects would be pretty high on your agenda if you happened to be on board one of those objects at the time!
According to the author, the book’s primary objective is “to derive analytical solutions that are fairly simple in nature but still capture the essence of the problem”. He says that the approach ensures that “the logic is mathematically correct and the assumptions are physically meaningful”. The book also discusses the accuracies of the models and the limitations of the analytical solutions. Of course, the accuracy of a prediction is of paramount importance in the real world, because it represents the difference between manoeuvring a satellite or space station in the face of an imminent collision, or not. If the prediction comes with excessively large error bars, it is essentially useless, because manoeuvring the object may actually move it into danger. For example, as far as collision cross-sections are concerned, standard NASA models treat the International Space Station as “a sphere with a radius of approximately 60m”, but a new model described by Chan allows much greater detail, even taking into account the relative angle of the solar panels.
The book covers subjects such as different types of encounters, the extent of encounter regions and transit times, probabilities of collisions for a variety of orbits and circumstances (including encounters with multiple objects), and the all-important evasive manoeuvres. It is well produced and clearly laid out, and the volume includes a number of technical appendices and an index.
Written by one of the foremost researchers in the field, this book will be essential to those studying collision probability…and may one day even save lives in orbit!