Because the Soviet rocket program was so secret, scientists and politicians in the United States were surprised by Sputnik. They feared the Soviet Union might be developing other secret projects. A huge effort to catch up began, and it even included building new facilities in schools so young people could learn more science and mathematics to better prepare for the space age.

The former Soviet Union launched many more Sputniks and other Earth-orbiting satellites, with names like Molniya and Cosmos, over the years.

The United States’ first satellite was Explorer 1, which was sent into orbit on February 1, 1958. In that same year, the U.S. government set up the National Aeronautics and Space Administration (NASA) to explore outer space. Other notable satellites launched by the United States included Vanguard, Echo, Syncom, and Landsat.

The European Space Agency, China, India, and other countries have also launched their own satellites. The many uses of satellites include relaying data, transmitting navigation signals, military surveillance, observing the surface of Earth, following the movement of storms and other weather features, and scientific research.

So many satellites are orbiting Earth that you will probably see at least one, about as bright as an average star, moving among the constellations, if you pay attention during the first hour of darkness on any clear night of the year. In fact, companies that build and operate satellite services were a $100-billion-per-year industry around the globe in 2007.

Pioneer 10, which was launched in 1972, flew by Jupiter in December 1973. It was the first space probe to do so, and, in the process, discovered Jupiter’s huge magnetic tail, an extension of the planet’s magnetosphere.

Launched during the early 1960s, the reconnaissance satellites were equipped with infrared sensors capable of detecting the heat of a ballistic missile’s rocket exhaust shortly after firing.

Midas 1 and 2 suffered mechanical failures. The first successful satellite was Midas 3, launched in 1961. The last Midas satellite, Midas 12, was launched in 1966.

Radio contact was lost with the first probe, Venera 1, before it flew by Venus. Venera 2 ceased operation before it flew to within 24,000 km (15,000 miles) of Venus in February 1966. Venera 3 crash-landed on the surface of Venus, 1966, becoming the first spacecraft to strike another planet.

Venera 4 was an atmospheric probe that descended toward the surface by parachute, analyzed the chemical composition of Venus’s upper atmosphere and provided scientists with the first direct measurements for a model of the planet’s atmospheric makeup.

The Venera 9 and 10 landers sent back the first close-up photographs (in black and white) of the surface of another planet. Veneras 11 and 12 conducted detailed chemical measurements of the Venusian atmosphere on their way to soft landings.

Veneras 15 and 16 were orbiters equipped with the first high-resolution imaging radar systems flown to another planet. They mapped about a quarter of Venus’s surface, primarily around the north pole.

Mariner 3 was supposed to fly by Mars, but contact was lost shortly after liftoff. Mariners 4, 6 and 7, and 9 obtained striking photographs of the Martian surface and made significant analyses of the atmosphere of that planet. Mariner was intended to study Mars with Mariner 9, but its upper stage malfunctioned shortly after launch.

Each Vela spacecraft carried radiation detectors sensitive to X-ray and gamma ray emissions. The satellites were always launched in pairs to an orbit of more than 60,000 miles (96,000 km) above Earth.

The first twin craft were orbited on Oct. 17, 1963. By 1967, an advanced version of the satellite had been developed. The new model was equipped with more sophisticated detection instruments and was designed to continually point toward Earth, unlike the earlier version, which viewed the heavens as well.

Zond 4 was placed into an orbit away from the Moon that carried it 330,000 km (205,000 miles) from Earth. When a landing in the Soviet Union became impossible, Zond 4 was ordered to explode in Earth’s atmosphere.

Zond 5 became the first spacecraft to orbit the Moon and return to a splashdown on Earth. Zond 6, 7, and 8 also made circumlunar flights. They carried biological specimens and transmitted photography of the Moon’s surface.

Helios 1 passed within 45,000,000 km (28,000,000 miles) and Helios 2 within 43,400,000 km. Equipped with special heat-dispersal systems, the probes were able to withstand extremely high temperatures, which reached an estimated 700°F (370°C).

Both returned useful data about the sun’s magnetic field, the solar wind, the relative strength of cosmic rays, and measurements of meteoroid loss from the solar system.

After completing nearly year long journeys, the two spacecraft entered orbit around Mars and spent about a month surveying landing sites. They then released their landers, which touched down on fl at lowland sites in the northern hemisphere about 6,500 km (4,000 miles) apart. Viking 1 landed in Chryse Planitia. Viking 2 landed in Utopia Planitia seven weeks later.

The Viking orbiters mapped and analyzed large expanses of the Martian surface, observed weather patterns, photographed the planet’s two tiny moons—Deimos and Phobos—and relayed signals from the two landers to Earth. The landers measured various properties of the atmosphere and soil of Mars and made colour images of its yellow-brown rocky surface and dusty pinkish sky.

After a series of brief studies by infrared instruments carried on sounding rockets had detected about 4,000 celestial sources of infrared radiation, the United States, the United Kingdom, and The Netherlands built IRAS to map the sky at infrared wavelengths It was launched on a Delta rocket from Vandenberg Air Force Base in California into a polar orbit at an altitude of 900 km.

Its telescope was cooled by superfluid helium. This was necessary because if the telescope were not cooled down, its own thermal radiation at infrared wavelengths would swamp the much fainter radiation from astronomical objects. IRAS discovered many previously unknown galaxies that emit most of their energy in the infrared portion of the electromagnetic spectrum (these are known as ultraluminous infrared galaxies), apparently owing to a massive burst of star formation during the merger of two galaxies.

Penzias and Wilson shared a Nobel Prize for Physics in 1978 for their discovery, but, in order to test the theory of the early history of the universe, cosmologists needed to know whether the radiation field was isotropic (the same in every direction) or anisotropic (having spatial variation) The COBE satellite was launched by NASA on a Delta rocket to make these fundamental observations. COBE’s Far Infrared Absolute Spectrophotometer (FIRAS) was able to measure the spectrum of the radiation field 100 times more accurately than had previously been possible using balloon-borne detectors in Earth’s atmosphere. In doing so, it confirmed that the spectrum of the radiation precisely matched what had been predicted by the theory.

The Differential Microwave Radiometer (DMR) produced an all-sky survey that showed “wrinkles” indicating that the field was isotropic to 1 part in 100,000. Although this may seem minor, the fact that the Big Bang gave rise to a universe that was slightly denser in some places than in others would have stimulated gravitational separation and, ultimately, the formation of galaxies. In 2006, John Mather, COBE project scientist and FIRAS team leader, and George Smoot, DMR principal investigator, won the Nobel Prize for Physics for the FIRAS and DMR results.

Dependence is increasing on space-based systems that can be affected by what has come to be called “space weather,” which is largely driven by solar phenomena. Among Ulysses’s discoveries was that the solar wind speed did not increase continuously toward the poles, but rather at high latitudes leveled off at 750 km (450 miles) per second. The elemental composition of the solar wind was found to differ between fast and slow solar wind streams. In the polar regions, the cosmic ray flux was not enhanced as much as was expected because the sun’s magnetic waves, themselves discovered by Ulysses, scattered the cosmic rays.

The U.S. spacecraft Clementine orbited and observed all regions of the Moon over a two-month period in 1994 for purposes of scientific research and in-space testing of equipment developed primarily for national defense. It carried out geologic mapping in greater detail than any previous lunar mission. Some of its data hinted at the possibility that water exists as ice in craters at the Moon’s south pole.

The satellite was able to see through the dust that prevents optical astronomers from viewing the centre of the Milky Way Galaxy and found a large number of red giant stars expelling vast quantities of dust. It made significant observations of protoplanetary disks of dust and gas around young stars, suggesting that individual planets can form over periods as brief as 20 million years.

The satellite also found a large number of brown dwarfs—objects in interstellar space that are too small to become stars but too massive to be considered planets. In its “deep field” survey, ISO found that stars were being formed at a rate several times greater than that inferred from optical observations of the relatively dust-free regions of starburst galaxies in the early universe.

After a 10-month journey, Mars Global Surveyor took up a highly elliptical orbit above Mars on Sept. 12, 1997. It employed a technique known as aerobraking—using the drag of the Martian upper atmosphere on the spacecraft to slow it down gradually— to achieve a final 400-km (250- mile) circular polar orbit in which it circled Mars 12 times a day. This orbital configuration allowed the spacecraft to collect data from the entire Martian surface once about every seven days as Mars rotated beneath it.

In its first three years of operation, Mars Global Surveyor returned more data about Mars than all prior Mars missions combined. Close-up images of erosional features on cliffs and crater walls that resembled fresh-appearing gullies suggested the possibility of recent water seepage from levels near the surface. In addition, the mission yielded new information about the global magnetic field and interior of early Mars, allowed real time observation of the changing weather over the Martian seasonal cycle, and revealed that Mars’s moon Phobos is covered with a dust layer at least 1 metre (about 3 feet) thick—caused by millions of years of meteoroid impacts.

Cassini-Huygens was one of the largest interplanetary spacecraft. The Cassini orbiter weighs 2,125 kg (4,685 pounds) and is 6.7 metres (22 feet) long and 4 metres (13 feet) wide. The instruments onboard Cassini include radar to map the cloud-covered surface of Titan and a magnetometer to study Saturn’s magnetic field. The disk shaped Huygens probe was mounted on the side of Cassini.