But that signal had a singular strength. It heralded a new era. Sputnik 2 soon followed, carrying Laika, a stray dog plucked from the streets of Moscow to be the first living traveler in space. Sputnik 3 packed a whopping 1 1/2-ton payload, proving that it was possible to move substantial objects through space, including atomic bombs - a real fear at the time.
It would be four more months before the United States - after some spectacular
failures - would successfully launch its first space satellite. Explorer 1 weighed just 18 pounds and was the size of a grapefruit, but the race was on. The Space Age had begun.
The race basically ended with Neil Armstrong's lunar stroll in 1969. There hasn't been a comparable effort in almost 35 years. But if manned missions have languished, human activity in near-space has not. Sputnik opened a floodgate. More than 25,000 satellites have been launched since 1957. Most have since come down, burned up on re-entering the atmosphere.
At last count, though, there were at least 863 active satellites, according to the Union of Concerned Scientists, each circling or hovering somewhere between 49 and 22,356 miles above the Earth's surface.
EYES IN THE SKY
Unlike Sputnik, these modern working satellites are marvels of technology and purpose. Two-thirds are involved in communications, some military, others civilian, handling everything from phone calls to television to the Internet.
The remaining third perform a wide array of functions and jobs.
Surveillance is a primary occupation. Almost from the beginning, the military has employed satellites to monitor real or suspected enemies. The unfettered success of Sputnik - it was allowed to pass without challenge over the United States seven times a day during its two-month life in orbit - made possible and defensible later flights by U.S. spy satellites over the Soviet Union and other foreign countries.
The first spy satellites snapped relatively low-resolution pictures that were ejected inside canisters and retrieved midair by planes as the canisters parachuted earthward. The latest imaging satellites beam pictures digitally to Earth, some using cameras able to see softball-sized objects from several hundred miles away.
Satellite imagery, for better or worse, has changed the nature of war. It was key to arguments for invading Iraq in 2003. Matthew Brzezinski, author of "Red Moon Rising" (Times, $26), a new history of Sputnik and the space race, notes that the "2003 invasion of Iraq was the first military campaign in the history of warfare run almost entirely remotely, via satellite."
Many Earth-observing satellites, however, pursue more benevolent or humanitarian goals. They monitor and measure environmental systems on Earth, from melting ice caps to ozone holes to expanding deforestation. They map places humans cannot reasonably explore, such as the floor of the deepest oceans. They have pinpointed the buried walls of ancient Troy, found the location of a 5,000-year-old lost city called Ubar in the Middle East and discovered the remains of an ancient Saharan river as big as the Nile.
High-resolution satellite images have been used to chronicle human rights violations in Myanmar, documenting government destruction of villages and forced relocations.
They trace the paths of incipient hurricanes and the migrations of animals. Recently, scientists reported that a bar-tailed godwit, a kind of shorebird, had been tracked by satellite flying from New Zealand to Alaska and back to New Zealand - a journey of 18,000 miles in just seven months.
Previously, no one had imagined any bird species could fly so far so fast with almost no rest. The godwit flew 7,203 miles across the Pacific Ocean nonstop in just eight days.
Satellites keep us from getting lost ourselves. The global positioning system consists of a planet-cloaking grid of 31 satellites in medium Earth orbit (between 1,243 and 22,236 miles up). These GPS satellites transmit precise microwaves that allow receivers on the ground (in planes, cars, boats and hand-held devices) to triangulate location, speed, direction and time.
The system is now so ubiquitous that some carmakers use it to automatically adjust climate controls in moving vehicles.
"In my opinion, the most profound influential effect has been what we now take for granted in everyday life," said Supriya Chakrabarti, a professor of astronomy at Boston University. "We get live images from places across the globe where no telephone poles exist. We see global weather maps in the palms of our hands that are only minutes old. We find our way using GPS to places we have never been before.
"Satellites have made the world smaller."
MIXED RESULTS
Science has always laid large claim to satellite technology. Explorer 1 carried a Geiger counter, which provided the first evidence of the existence of bands of charged particles trapped in space by the Earth's magnetic field. The discovery of the Van Allen Field, named after American physicist James Van Allen, has had major ramifications in spacecraft design and in efforts to protect astronauts from deadly cosmic radiation.
Not all satellites necessarily look inward toward the Earth. The International Space Station (ISS), which orbits 199 to 215 miles up and can be seen with the naked eye, is a multinational effort intended to develop and test new space technologies, examine the effects of prolonged space exposure upon humans and explore questions of basic physics and science.
The history of the space station, first conceived in the 1980s, is decidedly mixed. Supporters say the ISS provides a critical test platform for future space exploration. Critics say it's a colossal waste of money: NASA alone spends roughly $2 billion a year on it. Either way, the station's days are numbered: It is scheduled to be fully built out by 2010, and remain in operation until 2016. That's just nine years from now.
If the space station is perceived as a boondoggle, the Hubble Space Telescope is widely admired. Since its launch in 1990, the $1.5 billion telescope has become one of the most important tools in the history of astronomy, recording unprecedented images of the universe and leading scientists to a number of breakthroughs in astrophysics.
The first telescope designed to be serviced in space by astronauts (which has happened four times), the Hubble is slated to be succeeded in 2013 by the bigger and better James Webb Space Telescope, though the Hubble will remain in limited operation.
Most space programs are finite. The costly and fragile Space Shuttle, for example, will be grounded in three years, as soon as the space station is finished. The future of satellites, though, seems as expansive as space itself.
"Future satellites will be a lot more complex and capable at smaller sizes and less cost," said Bob Twiggs, director of the Space and Systems Development Laboratory at Stanford University. "There will be significantly more uses of satellites for science and exploring outside of NASA than by NASA."
Indeed, the race into space has expanded greatly. At least eight countries have independently launched satellites into orbit. Many more countries, from Bangladesh to Ukraine, own or operate satellites launched by other entities, including private companies.
In 1998, the satellite industry boasted revenues of about $38 billion, according to a Merrill Lynch study. Projected revenue for 2008 was $171 billion. Advocates say the sky's the limit.
Which raises the question: Will there be enough space?
SIDEBAR
Junkyard in space
By Scott LaFee
Sputnik 1 fell back toward Earth, burning up, almost three months to the day after it was launched Oct. 4, 1957. A similar fate has met most of the 25,000-plus payloads sent aloft since Sputnik.
Nonetheless, space has become a crowded place. The Union of Concerned Scientists estimates there are at least 863 active satellites orbiting the Earth. The Satellite Encyclopedia puts the satellite total at 3,211, but includes abandoned and nonfunctioning satellites.
More troubling is the problem of space debris, which includes everything from nuts and bolts to old rocket boosters. The U.S. Space Surveillance Network tracks more than 10,000 man-made objects in space, all larger than a baseball. Tens of thousands more are not tracked. The total number of man-made objects in orbit has been estimated in the hundreds of millions.
These objects - some racing at speeds exceeding 17,000 miles per hour - pose a real threat to working satellites, spacecraft and astronauts. The orbits of the space shuttle, International Space Station and other satellites are regularly altered to avoid collisions.
The first confirmed collision occurred in 1996 when a piece of space junk knocked a boom off of the French satellite Cerise. Returning space shuttles have had windows chipped by flecks of paint traveling at 6 miles per second.
So far, space debris collisions have not caused major disasters or fatalities. But the problem is likely to worsen. More and more satellites are being launched by more and more countries. And early this year, the Chinese tested an anti-satellite weapon, shooting a missile into one of their old weather satellites. The impact added an estimated 35,000 more bits of orbiting junk.
