Review: Solar Sails

by Jeff Foust
Monday, October 6, 2008

Solar Sails: A Novel Approach to Interplanetary Travel
By Giovanni Vulpetti, Les Johnson, and Gregory L. Matloff
Copernicus Books, 2008
Hardcover, 256 pp., illus.
ISBN 978-0-387-34404-1
US$27.50

Solar sails have for decades promised to revolutionize in-space transportation. However, while simple on paper—using large but lightweight sails to reflect solar photons, transferring their momentum to an attached spacecraft—the concept has proven difficult to actually implement, be it because of technological issues or funding problems or just bad luck. Regardless of those setbacks, solar sails still attract interest, primarily because of their potential to maneuver spacecraft through much of the solar system without requiring any fuel. That promise is at the heart of a new book by three scientists who explore how solar sails work and how they can be used.

In Solar Sails, Giovanni Vulpetti, Les Johnson, and Gregory L. Matloff try to serve both nontechnical and technical audiences by dividing the book into four parts. The first part of the book provides an overview of chemical and non-chemical space propulsion, principally for non-technical audiences. The second and third parts of the book review potential missions for solar sail spacecraft and how they would be built, including a review of past solar sail mission efforts like the Planetary Society’s Cosmos 1 mission. The last section is something of a technical appendix, examining the physics and engineering of sails; while the first three sections don’t go beyond F=ma and the rocket equation, the final section is replete with equations and other technical data.

The result is a book that provides does provide a comprehensive yet readable overview of how solar sails work and how they could be used in the near future. Solar sails, for example, could provide stationkeeping for spacecraft at the Earth-Sun L1 point, eliminating the need for chemical propellants and their corresponding mass and limited lifetime. Their continuous thrust also allows for non-Keplerian orbits that can be used for “polesitting” spacecraft that can provide better communications coverage of the Earth’s poles.

So why aren’t solar sails already flying through the solar system? This question doesn’t get that much attention in the book, surprisingly enough, with only a little discussion of recent efforts and near-future plans near the end of the book’s third section. Some proposed missions involving solar sails, like NASA’s Space Technology 9, never got beyond the study stage; Cosmos 1, meanwhile, was built and launched in 2005, but failed to reach orbit because of a failure of its Russian launcher. Japan has tested solar sail deployment technologies on suborbital launches, but doesn’t seem to be in a hurry to deploy a full-fledged solar sail in orbit.

At least a partial answer to that question is tucked away in the back, when the book discusses another non-chemical propulsion system, ion engines, that has found greater acceptance. Ion engines won acceptance once NASA’s Deep Space 1 mission successfully demonstrated its use; that mission paved the way for its use on other missions, like the Dawn mission, where ion propulsion provided clear advantages over chemical propulsion. (Missing from this analysis is the relatively common use of smaller ion thrusters on commercial communications satellites, providing a more efficient alternative to stationkeeping than chemical thrusters.) The authors argue that a successful demonstration of a solar sail can open the door to its use on future operational missions that can either be performed more efficiently with solar sails or can only be flown with them. Until a space agency or private venture steps forward to demonstrate what solar sails are capable of, their promise will likely be contained to the pages of books like this one.

Jeff Foust (jeff@thespacereview.com) is the editor and publisher of The Space Review. He also operates the Spacetoday.net web site and the Space Politics and Personal Spaceflight weblogs. Views and opinions expressed in this article are those of the author alone, and do not represent the official positions of any organization or company, including the Futron Corporation, the author’s employer.

Home