Library Index » Science Encyclopedia » Introduction to Space Exploration - Ancient Perspectives On Space, Enlightened Observations, Space Travel In Early Science Fiction, The Wright Stuff

Introduction to Space Exploration - Parked In Low Earth Orbit

shuttle leo station nasa

In the minds of most Americans the space race was over the day Apollo 11 set down on the Moon. Although NASA carried out six more Apollo missions, public interest and political support for them faded quickly. Neither the U.S. nor Soviet government was interested in racing to somewhere else in space. Both governments decided to concentrate on putting manned scientific space stations in low Earth orbit (LEO).

LEO is approximately 125-1,200 miles above Earth's surface. Below this altitude air drag from Earth's atmosphere is still dense enough to pull spacecraft downward. Just above LEO space lies a thick region of radiation known as the inner Van Allen radiation belt. This region poses a hazard to human life and to sensitive electronic equipment.

LEO was and is the orbit of choice for most satellites and for all crewed missions. Spacecraft in LEO travel at about 17,000 miles per hour and circle the Earth once every ninety minutes or so.

Soviet Programs

Between 1971 and 1986 the Soviets put eight space stations into LEO or just below it. These included stations called Salyut 1 through Salyut 7 and the more ambitious Mir station. Dozens of cosmonauts visited and inhabited the stations, often for many months. The Soviets repeatedly set and broke human space duration records at their stations. In 1995 cosmonaut Valeri Polyakov (1942–) completed a 438-day mission aboard the Mir station. Even in 2004 this stood as the longest period of time spent in space by any human. Eventually all of the Soviet stations fell out of orbit and were destroyed by reentry to Earth's atmosphere. Although none were meant to be "permanent," the Mir station did stay in orbit for fifteen years.

U.S. Programs

In 1973 NASA launched its own series of space stations called Skylab 1 through Skylab 4. They orbited within LEO at an altitude of 268-270 miles above Earth. NASA wanted to build a very large space station in which to conduct scientific investigations in LEO. Without political support the agency had to put this plan on hold. Instead NASA concentrated on a new type of reusable space plane called a space shuttle. The space shuttle was to be the workhorse of the American space program, ferrying astronauts and supplies back and forth to the space station, once it was built.

NASA got the funding it needed to develop the shuttle by promising to build a vehicle that could carry military, weather/science, and commercial satellites into LEO. Prior to the shuttle program all satellites were launched aboard expendable rockets that could not be reused. The reusability of the shuttle was one of its best selling points. Also, each shuttle could carry a crew of five to seven people that could conduct scientific experiments in LEO and deploy and repair satellites as needed.

Despite a number of design challenges the first space shuttle was ready for flight by 1981. On April 12, 1981, the first test mission was conducted. Before the end of the year a space shuttle carried an orbiting solar observatory into LEO. Two dozen more missions were carried out before disaster struck in 1986. By this time there were four space shuttles in NASA's fleet. Missions were rotated between the vehicles in order to perform needed maintenance and repairs.

On January 28, 1986, the space shuttle Challenger exploded seventy-three seconds after liftoff. All seven crewmembers aboard were killed. The shuttle fleet was grounded for more than two years, while NASA restructured the program and redesigned key elements of the spacecraft. In October 1988 space shuttle flights resumed once again.

By this time the Soviet Union was politically disintegrating. Within three years America's former archenemy had splintered into dozens of individual republics, and the Cold War was over. The republic of Russia took over the space program begun by the Soviet Union. The Soviet space program came under the operation of a new government agency named Rosaviakosmos.

International Plans

NASA and Rosaviakosmos entered a new era of cooperative space ventures. American astronauts visited the space station Mir and Russian cosmonauts traveled aboard U.S. space shuttle missions. In 1993 the United States invited Russia to join in building an International Space Station (ISS) to be put in LEO. The Russians agreed. The ISS program eventually included Canada, Japan, and eleven European nations as full partners and Brazil as a contributing partner.

In 1998 ISS construction began. The station was designed for continuous human inhabitation and detailed scientific investigations. The Russians and Americans took turns adding components to the station and crewing it with astronauts and cosmonauts. All transport of heavy matériel was delegated to the U.S. space shuttle fleet. The Russians did not have a spacecraft capable of carrying heavy weights into LEO. Throughout 1999 and the next three years nearly all shuttle missions were devoted to ISS construction.

During the first mission of 2003 another space shuttle was lost in an accident. On February 1, 2003, the shuttle Columbia disintegrated during reentry over the western United States. Again, seven crewmembers were killed. The shuttle fleet was grounded again, and ISS construction came to an immediate halt. As of February 2006 the partially constructed station is sitting in LEO with only two crewmembers aboard. Since the Columbia disaster Russian spacecraft have ferried supplies to the station and handled crew changes.

In July 2005 the space shuttle program resumed operations with a successful return-to-flight test mission. However, its future and that of the ISS are uncertain due to a shift in American space goals announced in February 2004 by President George W. Bush. After sticking with LEO missions for more than thirty years, the United States has a new goal for its human explorers: to return to the Moon and travel to Mars and beyond. It remains to be seen whether the American public will support this expensive program. However, NASA continues to plan for the future.

Introduction to Space Exploration - Space-age Science Fiction [next] [back] Introduction to Space Exploration - D√Čtente In Space

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

over 11 years ago

FYI, there was only ONE Skylab space station, and multiple crews (3) were launched to it.