Why We Explore

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Voyages of Discovery
Why We Explore

Editor's Note: This is the eigth in a series of essays on exploration by NASA's Chief Historian, Steven J. Dick.

At the core of the Age of Space are the voyages themselves, and not by accident have spacecraft been named Mariner, Voyager, Viking, Ulysses, Challenger, Endeavor and Magellan, hearkening back to a long tradition of exploration and discovery. Journeys during the Age of Space have ranged from the vicinity of Earth itself to the edge of the solar system and beyond.

Voyages to Earth orbit have a special meaning of their own. Aside from the fact that climbing the Earth’s gravitational well put one "half way to anywhere in the solar system" (as science fiction writer Robert Heinlein once put it), humans or robots placed in Earth orbit saw the planet anew, whether for reconnaissance, monitoring weather and climate, imaging Earth resources, or providing a means of navigation and communication. Earth orbit also provided a microgravity environment for experiments, both on the Shuttle and on space stations. Taken together, and perhaps most importantly, all these endeavors provided a new perspective on the home planet. Although still "hugging the coastline" in terms of the analogous maritime history, these endeavors were nonetheless voyages of discovery.

Image of the Barred Spiral Galaxy NGC 1300.
Image left: Image of the Barred Spiral Galaxy NGC 1300 - taken by the Hubble Telescope.

Important as low Earth orbit and geosynchronous orbit are for utilitarian applications, philosophical perspective, and way station status, it is the voyages beyond the Earth that captured the public imagination, particularly those involving humans. Above all are the epic manned voyages of the United States that resulted in 12 humans walking on the Moon, a feat that 500 years from now will be viewed in the same way as we now look back on the Age of Discovery.

Who can forget the feeling when Armstrong and Aldrin touched down on the Moon in July, 1969, with seconds of fuel to spare? Or the harrowing experiences of the ill-fated Apollo 13? Even now, reading one of the classic accounts like Andrew Chaikin’s A Man on the Moon, or viewing its visual HBO counterpart "From the Earth to the Moon," brings a feeling of "did we really do that?," and the question "could we do it again?"

A single voyage, or set of voyages, does not make an Age, and the jury is still out on whether our descendants 20 generations from now will view Apollo as a unique set of bold achievements or the beginnings of an era of human space exploration. As I have said in previous essays, it is a choice that we must make as a society, not an assured destiny.

The achievements of Apollo culminated in 1972, and since then only our robotic surrogates have left the vicinity of the Earth. But they have done a magnificent job in our stead. The Luna, Ranger, Surveyor and Lunar Orbiter spacecraft were the prelude to the manned Moon landings. After a long gap in lunar exploration, Clementine and Lunar Prospector once again picked up the trail. Beginning in the 1960s the Mariner spacecraft took us to Mercury, Venus and Mars, revealing cratered surfaces and, in the case of Mars, ancient riverbeds and much else.

The exploration of those inner planets has been continued to this day by the likes of Pioneer Venus, Magellan, Venera, Viking, Mars Global Surveyor, Mars Odyssey, and Pathfinder. And the Mars Exploration Rovers are still roaming the surface of the red planet.

In what Carl Sagan and others have called the Golden Age of Exploration, in the 1970s and 1980s the Pioneer and Voyager spacecraft took us to Jupiter, Saturn, and, in the case of Voyager 2, all the way to Uranus and Neptune at the edge of the solar system. Galileo revisited Jupiter and its retinue of moons in the 1990s, and Cassini is now exploring Saturn, with its satellite spacecraft Huygens having landed on the huge Saturnian moon Titan.

"Who can forget the feeling when Armstrong and Aldrin touched down on the Moon in July, 1969, with seconds of fuel to spare?"
Moreover, the Voyager spacecraft, with their engraved greetings from Earth, are traveling beyond the solar system on the way to the stars. Other spacecraft have visited comets (Giotto), orbited and even landed on an asteroid (NEAR Shoemaker), and visited the Sun (Ulysses and SOHO).

Meanwhile, space telescopes in earth orbit or its vicinity have in a sense taken us vicariously on voyages beyond the solar system. Those sensors that have pointed upward rather than downward; space telescopes such as Hubble, Spitzer, Compton and Chandra have probed the depths of the universe, produced stunning images, and revealed our place in the history of cosmic evolution.

Two spacecraft, COBE and WMAP, have studied the details of the background radiation remaining from the Big Bang 13.7 billion years ago, and detected the seeds from which galaxies grew. As we once mapped the Earth in the wake of the Age of Discovery, we are now mapping the heavens, both in space and time.


William Burrows, Exploring Space: Voyages in the Solar System and Beyond (Random House: New York, 1990).

Andrew Chaikin, A Man on the Moon: The Voyages of the Apollo Astronauts (Viking Penguin: New York, 1994).

Robert S. Kraemer, Beyond the Moon: A Golden Age of Planetary Exploration, 1971-1978 (Smithsonian Institution Press: Washington, D.C., 2000).

Pamela Mack, Viewing the Earth: The Social Construction of the Landsat System (MIT Press: Cambridge, Mass.: 1990).

Bruce Murray, Journey into Space: The First Three Decades of Space Exploration (W.W. Norton: New York, 1989).

Steven J. Dick
NASA Chief Historian