When you think of exploring someplace, you probably think of going there and looking around. However, with the exception of our own Solar System, astronomical exploration is done remotely, by looking with specialized instruments. Most of these are right here on our planet. While none of you in this class can remember a time when we didn't have the Hubble Space Telescope or the Space Shuttle, it was really not so long ago that none of these existed. For most of the past 400 years, since the invention of the telescope, earth-bound telescope were the only way to explore space. But since then, spacecraft have advanced quickly.
Solar System Spacecraft
The first spacecraft didn't go far, venturing barely outside Earth's atmosphere. The first of these was the Soviet sputnik (which just means satellite) launched in 1957. It was in some ways more a "proof of concept" than anything else and, at that time, due to the competition between the USA and the USSR, it was a chance fot the USSR to claim the lead on the "space race." Sputnik 1 was followed by Sputnik 2 which carried a dog named Laika. The dog travelled into space and returned home safely. While it may seem obvious today, before Sputnik 2 it was not known if living creatures could survive in space.
The USA followed with the Explorer 1, 2, and 3 satellites. Explorer 2 failed to reach orbit. Explorer 3 carried a Geiger counter, a special instrument for detecting radiation. This experiment was designed by James van Allen and it discovered the existence of zones high above the Earth's atmosphere where the Earth's magnetic field trapped radiation from the Sun. Today, those regions are still called the van Allen radiation belts.
In the 1960s, most of the attention about spacecraft was focused on manned spacecraft like the USA's Mercury, Gemini, and Apollo missions. The Mercury spacecraft carried only one person, the Gemini two, and the Apollo three. At that time, the focus was a space race to the Moon. However, manned spacecraft were not the only ones.
Starting in 1962, NASA launched a series of spacecraft called Mariner to explore Venus and Mars. The first one failed during launch and was destroyed. However, of the 10 attempts to launch over the next 11 years, 8 were successful and provided the close looks at those planets. During the same time period, the USSR launced a series of spacecraft to explore Venus called Venera. Venera 1 was actually the first successful interplanetary probe. Later, in December 1970, Venera 7 became the first spacecraft to land on another planet (Venus) and transmit data back from the surface.
The Pioneer series of spacecraft were first launched in 1958. However, the most "famous" were Pioneer 10 and 11, launched in 1972 and 1973, respectively. Pioneer 10 was the first spacecraft to travel to Jupiter, and Pioneer 11 the first to travel to Saturn. The power source for both have failed and while they are still travelling away from the Sun, it is no longer possible to communicate with them.
The two oldest spacecraft still transmitting are Voyager 1 and 2, both launched in the late 70s. They are far past the orbit of Pluto now. Voyage 1 is about 106 time s farther from the Sun than the Earth while Voyager 2 is "merely" 85 times farther. Both are still working and sending back useful information about the far reaches of our Solar System. Both visted Jupiter and Saturn, the first spacecraft to do so. Voyager 2 was also able to visit Uranus and Neptune. You can learn more about them at http://voyager.jpl.nasa.gov/.
For the past 4 years, the two robotic landers Spirit and Opportunity have been cruising around the surface of Mars. The images they have sent back have made it hard to remember that less than 100 years ago, people still believed Mars might harbor large creatures and canals full of water!
The two most recent additions to NASAs interplanetary explorers are MESSENGER, which has recently begun to send back images and other information from Mecury, and New Horizons, which is on its way to Pluto.
Everyone knows about the Hubble Space Telescope which was carried into orbit by the Space Shuttle in 1990. But it was not the first space telescope.
In 1970, NASA launched Uhuru, also called the Small Astronomy Satellite 1 (SAS-1) which was the first to study the sky using X-rays. It was followed by SAS-2 and SAS-3 which also studied X-rays.
NASA launched three X-ray telescopes, one each in 1977, 1978, and 1979. Like infrared electromagnetic radiation, X-rays are also blocked by Earth's atmosphere.
The Infrared Astronomy Satellite (IRAS) was launced in 1983 and was the first spacecraft to study most of the sky using infrared electromagnetic radiation. Most of this type of electromagnetic radiation is blocked by the Earth's atmosphere. IRAS only lasted about 10 months.
The Solar and Heliospheric Observatory (SOHO) studies only the Sun. It can take pictures of the Sun using specific wavelengths of light emitted only by helium, calcium, or iron. It also has a special instrument called a coronograph which blocks out the body of the Sun and allows only the Sun's corona to show around the edges. These images are very useful for studying the solar wind which is made of the gases blown off by the Sun. You can see the latest images from SOHO at http://sohowww.nascom.nasa.gov/.
Robots in Space
When someone says robot you probably don't think of spacecraft. But that's exactly what they are. Because of the great distances involved, may of these spacecraft have computers on board which not only gather information and transmit it back to Earth, but also make decisions on what to take pictures of an what to send back. Many of the "decisions" these robots make are simple to us, like keept the antenna pointed at Earth, but they have to be made without anyone there to fix things.