Outer space, including the Moon and other celestial bodies, shall be free for exploration and use by all Nations.

—United Nations Treaty of 1967

Although the National Aeronautics and Space Agency (NASA) is the best-known space organization in the world, it is not the only one. The U.S. military and many foreign governments also have active space programs. In fact, the U.S. military program existed even before NASA was formed. Most modern military space ventures center around ballistic missiles and data-gathering satellites. These are unmanned projects. The United States officially holds the policy that it will not develop space weapons, only defensive systems. Some critics complain that the line between the two is growing vague. Increasingly the U.S. military is being criticized for developing spacecraft that could be considered weapons. For example, the Near Field Infrared Experiment is a satellite originally designed with a system capable of destroying other satellites in space. This capability was eventually dropped from the design.

Chief among the foreign governments with space programs is the Russian space program operated by an agency called Rosaviakosmos. The Russian agency continues the program begun by the Union of Soviet Socialist Republics decades ago. For about half of the twentieth century the Soviet Union engaged in a bitter Cold War rivalry for space supremacy with the United States. The Soviets achieved many milestones in space ahead of the United States, including the first manned spaceflight in 1961.

In 1991 the Soviet Union splintered into individual nations (including Russia) that were friendlier with the United States. Civilian space agencies in the United States and Russia struggled to carry on ambitious space programs as their funding was cut. They began working together on many space ventures. Eventually space pro-grams sprang up in Europe, China, Japan, and other countries. This presented opportunities for new alliances in space.

In the past private organizations contributed to space exploration indirectly by promoting space programs and gathering together individuals interested in rocket science, physics, astronomy, space travel, or space commerce. In 2004 the private sector opened a new era in space exploration when the first privately funded manned vehicle traveled into space and back. Private space ventures are expected to grow quickly during the twenty-first century.