# High School Earth Science/Recent Space Exploration
## Lesson Objectives

* Outline the history of space stations and space shuttles.
* Describe recent developments in space exploration.

## Space Shuttles and Space Stations

While the United States continued missions to the Moon in the early 1970s, the Soviets had another goal: to build a space station. A space station is a large spacecraft on which humans can live for an extended period of time.

### Early Space Stations

The Soviet Union put the first space station, Salyut 1, into orbit on April 19, 1971. At first, the station had no crew. Three cosmonauts boarded the station on June 7, 1971, and stayed for 22 days. Unfortunately, the cosmonauts died during their return to Earth, when the return capsule lost pressure while still in the airless vacuum of space. Salyut 1 left orbit on October 11, 1971, and burned up as a result of friction with the Earth's atmosphere.
Between 1971 and 1982, the Soviets put a total of seven Salyut space stations into orbit. Figure 23.25 shows the last of these, Salyut 7. These were all temporary stations that were launched and later inhabited by a human crew. Three of the Salyut stations were used for secret military purposes. The others were used to study the problems of living in space and for a variety of experiments in astronomy, biology, and Earth science. Salyut 6 and Salyut 7 each had two docking ports, so one crew could dock a spacecraft to one end, and later a replacement crew could dock to the other end.
The U.S. only launched one space station during this time—Skylab, shown in Figure 23.26. Skylab's design was based on a segment of the Saturn V rockets that were used in the Apollo missions to the Moon. Skylab was launched into low Earth orbit in May 1973. It was damaged as it passed out of Earth's atmosphere, but repairs were made when the first crew arrived.
Three crews visited Skylab, all within its first year in orbit. Skylab was used to study the effects of staying in space for long periods. It was also used for studying the Sun. Skylab reentered Earth's atmosphere in 1979, sooner than expected. It was so large that Skylab did not completely burn as it reentered the Earth's atmosphere. As a result, pieces of it fell across a large area, including some of western Australia. News headlines read, "The Skylab is Falling!"

### Modular Space Stations

The first space station designed for very long-term use was the Mir space station (Figure 23.27). Mir was a modular space station, which means it was launched in several separate pieces and put together in space. The core of Mir was launched by the Soviet Union in 1986. Mir was put together in several phases between 1986 and 1996. Mir holds the current record for the longest continued presence in space. There were people living on Mir continuously for almost 10 years, falling short of the 10-year mark by just eight days. Mir was taken out of orbit in 2001; it fell into the Pacific Ocean, as the Russians had planned.
Mir was the first major space project in which the United States and Russia (after the fall of the USSR) worked together. In 1993, U.S. Vice President, Al Gore and Russian prime minister, Viktor Chernomyrdin announced plans for a new space station, which would later be called the International Space Station, or ISS. They also agreed that the U.S. would be involved in the Mir project in the years ahead. Space shuttles would take part in the transport of supplies and people to and from Mir. In addition, American astronauts would live on Mir for many months. This cooperation with Russia allowed the United States to learn from Russia's experience with long duration space flights. Figure 23.28 shows Mir with an American space shuttle attached.

### The International Space Station

Early space exploration was driven by competition between the United States and the Soviet Union. However, since the end of the Cold War, space technology and space exploration have benefited from a spirit of cooperation. The International Space Station, shown in Figure 23.29, is a joint project between the space agencies of the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and several European countries (ESA). The Brazilian Space Agency also contributes.
The International Space Station is a very large station with many different sections. It is still being assembled. The first piece was launched in 1997. The first crew arrived in 2000, and the station has had people on board ever since. American space shuttles carry most of the supplies and equipment to the station, while Russian Soyuz spacecraft carry people. The primary purpose of the station is scientific research, especially in biology, medicine, and physics.

### Space Shuttles

The spacecraft that NASA used for the Apollo missions were very successful, but they were very expensive, could not carry much cargo, and could be used only once. After the Apollo missions to the Moon, NASA wanted a new kind of space vehicle. They wanted this vehicle to be reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in Figure 23.30. Although this vehicle is sometimes referred to as "the space shuttle", the U.S. has actually had five working space shuttles—Columbia, Challenger, Discovery, Atlantis, and Endeavor. The Soviet Union built a similar shuttle called Buran, but it never flew a mission with humans aboard.
A space shuttle has three main parts, although you are probably most familiar with the orbiter, the part that has wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large booster rockets.
Figure 23.31 shows the stages of a normal space shuttle mission. The launch takes place at Cape Canaveral, in Florida. The booster rockets provide extra power to get the orbiter out of Earth's atmosphere. When they are done, they parachute down into the ocean so they can be recovered and used again. When the fuel tank is empty, it also falls away, but it burns up in the atmosphere. Once in space, the orbiter can be used to release equipment such as a satellite or supplies to the International Space Station, to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter.
When the orbiter is done with its mission, it re-enters Earth's atmosphere. As it passes through the atmosphere, the outside of the orbiter heats up to over 1,500°C. The rockets do not fire during re-entry, so the shuttle is more like a glider than a regular airplane. Pilots have to steer the shuttle to the runway very precisely. Space shuttles usually land at Kennedy Space Center in Cape Canaveral, Florida, or at Edwards Air Force Base in California. However, if weather is bad at both these landing sites, a shuttle can land at one of many backup sites around the world. It can later be hauled back to Florida on the back of a jet airplane.

### Space Shuttle Disasters

The space shuttle program has been very successful. Space shuttles have made possible many scientific discoveries and other great achievements in space. However, the program has also had some tragic disasters.
From the first flight in 1981 to the end of 1985, space shuttles flew over 20 successful missions, including many satellite launches and missions for scientific research. On January 28, 1986, the space shuttle Challenger launched carrying seven crew members, including Christa McAuliffe, who was to be the first teacher in space. Just 73 seconds after launch, the Challenger started to break apart, and most of it disintegrated in mid-air, as shown in Figure 23.32. All seven crew members on board died. Later study showed that the problem was due to an O-ring, a small part in one of the rocket boosters. Because of this disaster, space shuttle missions were put on hold while NASA studied the problem and improved the safety of the shuttles.
Shuttle missions started again in 1988, and there were over 87 consecutive missions without a major accident. However, during the takeoff of space shuttle Columbia on January 16, 2003, a small piece of insulating foam broke off the fuel tank. The foam smashed into one wing of the orbiter and damaged a tile on the front edge of the shuttle's wing. These tiles are heat shield tiles that protect the shuttle from extremely high temperatures. When Columbia returned to Earth on February 3, 2003, it could not withstand the high temperature, and broke apart. Pieces of the shuttle were found throughout the southern United States, especially in Texas. As in the Challenger disaster, all seven crew members died.
After the Columbia disaster, shuttle missions were stopped for over two years while NASA worked on the problem. One year after the disaster, President Bush announced that the space shuttle program was to end by the year 2010, and a new Crew Exploration Vehicle would take its place. The Crew Exploration Vehicle, now known as Orion is currently expected to be ready by 2014. All the remaining shuttle missions will be to the International Space Station, except for one repair mission to the Hubble Space Telescope.

## Recent Space Missions

Since the 1986 Challenger disaster NASA has focused on missions without a crew, except for the International Space Station missions. These recent missions are less expensive and less dangerous than missions with a crew, yet still provide a great deal of valuable information.

### Earth Science Satellites

In recent years, NASA and space agencies from other countries have launched dozens of satellites that collect data on the current state of Earth's systems. For example, NASA's Landsat satellites take detailed images of Earth's continents and coastal areas, such as those in Figure 23.33. Other satellites study the oceans, the atmosphere, the polar ice sheets, and other Earth systems. This data helps us to monitor climate change and understand how Earth's systems affect one another.

### Space Telescopes

Some of the greatest astronomical discoveries—and greatest pictures, like the one in Figure 23.34, have come from the Hubble Space Telescope. The Hubble was the first telescope in space. It was put into orbit by the space shuttle Discovery in 1990. Since then, four shuttle missions have gone to the Hubble to make repairs and upgrades. A final repair mission to the Hubble is scheduled for 2008.
NASA has also put several other telescopes in space, including the Spitzer Space Telescope, the Chandra X-Ray Observatory, and the Compton Gamma Ray Observatory. The biggest and most advanced space telescope yet, the James Webb Telescope, is scheduled to be launched into orbit around 2013. The James Webb will replace the Hubble Space Telescope and will have an even greater ability to view distant objects. Other countries, including Russia, Japan, and several European countries have also put space telescopes in orbit.

### Solar System Exploration

We have continued to explore the solar system in recent years. In 1997, the Mars Pathfinder rover landed on Mars. A rover is like a spacecraft on wheels (Figure 23.35). It can move around on the surface of a moon or planet and collect data from different locations. Two more rovers—Spirit and Opportunity—landed on Mars in 2004, and as of 2008 are still sending data back to Earth. Amazingly, both rovers were only designed to explore Mars for 90 days—they have now worked for more than 15 times their intended lifespan. Several spacecraft are currently in orbit around Mars, studying its surface and thin atmosphere.
The Cassini mission has been studying Saturn, including its rings and moons, since 2004. The Huygens probe, built by the European Space Agency, is studying Saturn's moon Titan. Titan has some of the conditions that are needed to support life.
Some missions are studying the smaller objects in our solar system. The Deep Impact probe was sent to collide with a comet, collecting data all the way. When it hit the comet, the impact made a cloud of dust. Space telescopes and telescopes on Earth all collected data after the impact. The Stardust mission collected tiny dust particles from another comet. Missions are currently underway to study some of the larger asteroids and Pluto. Studies of smaller objects in the solar system may help us to understand how the solar system formed.

## Future Missions

In 2004, President Bush proposed a "new vision for space exploration". He set the goal of putting humans on the Moon again by 2020. Unlike the Apollo missions, however, Bush proposed that reaching the Moon would only be the beginning. He also proposed building a permanent station on the Moon, which could serve as a base for missions taking humans to Mars and beyond. He announced that the space shuttle program would be retired after the International Space Station was complete (around 2010). A new kind of space vehicle, now called Orion, will be developed to take humans to space.
President Bush also explained we would meet these goals cooperatively, more like the International Space Station than the missions during the Space Race. He said, "We'll invite other nations to share the challenges and opportunities of this new era of discovery. The vision I outline today is a journey, not a race, and I call on other nations to join us on this journey, in a spirit of cooperation and friendship." Meanwhile, China, Russia, and Japan have all said they are planning to send humans to the Moon and establish Moon bases of their own.

## Lesson Summary

* The Soviet Union put seven Salyut space stations into orbit between 1971 and 1982.
* The United States' first space station was Skylab. Skylab was in orbit from 1973 to 1979.
* The Soviet (later Russian) space station Mir was the first modular space station. Both Russian and American crews lived on Mir.
* The International Space Station is a huge project that involves many countries. It is still being assembled.
* Space shuttles are reusable vehicles for American astronauts to get into space. A space shuttle takes off like a rocket and lands like a glider plane.
* The space shuttle program has had two major disasters—the Challenger disaster in 1986 and the Columbia disaster in 2003. In each case, the spacecraft was destroyed and a crew of 7 people died.
* Recent space missions have mostly used small spacecraft, such as satellites and space probes, without crews.
* The United States plans to send humans to the Moon again by 2020, build a base on the Moon, then send humans to Mars.

## Review Questions

* Which space station was built and launched by the United States alone?
* How many years was the Mir space station in orbit?
* Which space station was the first to involve several countries working together?
* Describe two ways in which space shuttles were an improvement over the spacecraft used for the Apollo missions?
* Name the five fully functional space shuttles that the United States built. Which of these were destroyed?
* Describe the space shuttle Columbia disaster, including its cause.
* Describe two recent or ongoing space missions.
* Is the Space Shuttle more like a rocket or a plane? Explain your answer.

## Vocabulary
### orbiter

    The main part of the space shuttle that has wings like an airplane.

### space shuttle

    A reusable spacecraft capable of carrying large pieces of equipment or pieces of a space station.

### space station

    A large spacecraft in space on which humans can live for an extended period of time.

## Points to Consider

* To date, a total of 22 people have died on space missions. In the two space shuttle disasters alone, 14 people died. However, space exploration and research have led to many great discoveries and new technologies. Do you think sending people into space is worth the risk? Why or why not?
* In the past several years, private companies have been developing vehicles and launch systems that can take people into space.
* What applications can you think of for such vehicles? What advantages and disadvantages are there to private companies building and launching spacecraft?
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