Other-Worldly Dreams

A selective and copiously documented tour through the science, engineering and history of unmanned space flight.

Dreams of Other Worlds: The Amazing Story of Unmanned Space Exploration. Chris Impey and Holly Henry. 472 pages. Princeton University Press.

Image of Saturn composed last month, from NASA's Cassini spacecraft. Credit: NASA/JPL-Caltech/SSI/Cornell.
Image of Saturn composed last month, from NASA’s Cassini spacecraft. Credit: NASA/JPL-Caltech/SSI/Cornell.

Dreams of Other Worlds is actually Chris Impey and Holly Henry’s dreams of the universe (and, briefly, other possible universes). It uses the backbone of robotic space missions, primarily conducted by the United States and Europe from the 1970s to the present and builds from it a skeleton of science results to describe how knowledge about space and our place in it has grown.

Dreams is interesting, but it’s not light reading. It’s heavy on science details—both historical and from projects. Each chapter describes a mission and the science it produced, and each chapter builds on the ones before it. The book also covers the general progression of scientific thought, of which space missions are only a part.

But Dreams is selective about the missions it covers. Some of my personal favorites (Mariner Venus Mercury in 1973 and Mars Pathfinder, for instance), either aren’t mentioned or get more attention in the notes than in the main text. The notes, in fact, are worth browsing. They’re informative and easy to read and include considerable historical information on, for instance, the Greek philosophers and Galileo and other early observers. The authors even mention prehistoric structures like Stonehenge and other Neolithic monuments to give the beginning of Dreams some historical context. The bibliography lists a number of books for those curious about the missions and the science.

In terms of missions, Dreams largely ignores the Earth and moon and begins with the Viking Mars orbiters and landers in 1976, focusing on the search for life. When I joined NASA’s Jet Propulsion Laboratory in 1966 as an aerodynamicist designing trajectories for atmospheric entry bodies, there were vast uncertainties in our understanding of the Venus and Mars atmospheres. Even the successful early flybys of these two planets gave only a rough idea of the atmospheric densities. The 1971 Mariner 9 orbiter (another Mars mission the book doesn’t mention) supplied crucial data to design the Viking landers, greatly improving the odds they would succeed. The two Viking orbiters also avoided dangerous landing sites by carrying the landers, giving scientists time to study the terrain from orbit before committing the landers to entry. In this way Dreams demonstrates how one mission gathers data to inform design of the next.

As an engineer, I was especially interested in the technical aspects of the spacecraft and instruments, and Dreams describes some challenging engineering achievements, including the sky crane that landed the Curiosity rover on Mars in 2012. I also participated in some missions covered (Mars Exploration Rovers or MERs, the Voyagers’ Grand Tour and the Cassini Saturn orbiter), so I was pleased to see the authors get the mission stories right. It also was gratifying to read their descriptions of NASA’s struggles in the always-difficult federal funding environment—something I lived through as a manager at JPL. These details give readers a context in fiscal reality to go with esoteric science explanations.

The rover missions are winkling out information on likely sample collection places.

The book flows outward—from Mars (Viking and the MERs) to the outer planets (Voyager and the Cassini orbiter), to Stardust collecting comet dust and SOHO staring at the sun. Hipparchos mapped our home galaxy, the Milky Way, and put the equivalent of stakes in the ground so astronomers could establish the locations and define the movements of other galaxies. Spitzer, Chandra, Hubble and other orbiting and ground-based telescopes brought the beauty of the universe (and its science) to earth in images spanning the electronic spectrum from the infrared through the visible to the ultraviolet and even to X-rays. And WMAP, building on the success of COBE, reaches back in time to nearly the Big Bang itself to study the universe’s formation.

Dreams frequently refers to the search for life, from Viking’s controversial soil analysis to the current efforts to identify extrasolar planets with orbital and ground-based telescopes. Some missions are bringing bits of solar wind (Genesis) and comet tails (Stardust) to Earth.

The Mars Sample Return mission is the Holy Grail in the search for life on that planet. But there are two main obstacles: the enormous cost for a sample-collecting rover plus a sample-return system; and the lack of exact knowledge of where the most likely life-containing sample can be found. The rover missions (Pathfinder’s little Sojourner in 1997, the MERs in 2003, Curiosity in 2012 and a planned rover in 2020) are winkling out information on likely sample collection places.

Increasingly competent orbiters abet these rover missions: Odyssey, launched in 2001, the European Mars Express in 2003 and the Mars Reconnaissance Orbiter in 2006.

The book also focuses on the increasing capability of telescopes to find planets outside the solar system, from spotting motions planets induce on their stars to detecting spectral signatures related to life.

The last chapter, “Conclusions,” details projects carrying on the search for knowledge. It describes Curiosity’s first year on Mars, following its slow progress toward a mountain in the center of Gale crater (stopping frequently to do science on the way). Kepler, launched in 2009, and the forthcoming Gaia mission seek Earth-sized planets. Planck, launched in 2009 and just turned off after completing its mission, was the European successor to WMAP in the search for the universe’s edge.

New science continues, using reams of data Hubble collected to direct ground-based searches. For instance, in October 2013 the Keck observatory in Hawaii discovered the most distant galaxy yet found. Finally, Hubble’s heir—the long-delayed and incredibly expensive ($8 billion and counting) James Webb Telescope—soldiers on toward a 2018 launch.

These missions and others extend the search for life, especially life like us, to the end—maybe—of the universe.

Donna Shirley is president of Managing Creativity. She managed the Jet Propulsion Laboratory’s Mars Exploration Program and recounted that experience in Managing Martians (Broadway Books, 1999.)