Explore the Moon
Lunar Exploration
The Idea of Space Exploration
The dream of space travel is an ancient one. The first known description of a flight to the Moon is from an ancient Greek writer. Lucian of Samoset (190 A.D.) had one of the characters in his story don eagle wings and fly to the Moon, in order to learn how the stars came to be “scattered carelessly up and down the universe.” Since then, many have dreamed of traveling to the Moon, other planets, and even stars.
Most people don’t realize that our ability to fly spaceships to the Moon or Mars is a direct result of Newton’s work in the 1600s! The idea of space exploration is an extension of the Copernican revolution, and the actual scientific basis of space travel came from Newton. How fast do you have to go to escape Earth’s gravity and fly into space? How long would it take to fly to the Moon? What orbit would require the least energy (and the least fuel) to reach Mars? These questions can be answered using Newton’s simple laws of gravity and motion. Students in introductory physics classes learn how to answer them, too.
Newton realized that a satellite could be launched into space. In his 1687 masterwork, Principia, he described a “thought experiment” to see how it could be done. A thought experiment is a hypothetical experiment – a physically reasonable idea that is difficult to carry out in practice. For example, one of Newton’s laws of motion states that an object in uniform motion (constant velocity) will continue in uniform motion (the same velocity). But projectiles are subject to air resistance, and rolling objects are subject to friction. So Newton’s ideal of a uniformly moving object couldn’t be realized in actuality. However, he could use a thought experiment to imagine that if friction or air resistance was eliminated, uniform motion would be the result.
This was Newton’s thought experiment for launching something into orbit: imagine a mountain so high that it projects above the Earth’s atmosphere (you see why this would be a difficult experiment to actually perform!). Now imagine a cannon pointing out from the mountain top, parallel to the Earth’s surface. If you fired a cannon ball at modest speed, the ball would fall near the foot of the mountain. At a higher speed, the ball would fall farther away. At a high enough speed, the ball would be falling towards the Earth (due to the force of gravity) at exactly the same rate that the curved surface of the Earth is “falling away” from it. In this case, it would continue to travel all the way around the Earth. This is exactly how we define an orbit. Note that each path obeys Kepler’s laws: even the paths that hit the Earth’s surface are segments of ellipses around the center of the Earth. The final orbit is the special case of an ellipse that is a circle. Thus, launching a satellite into orbit around Earth is in fact a 17th-century idea of Isaac Newton!
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Humans have been dreaming of space for thousands of years. Newton provided the physical laws that form the basis of travel beyond the Earth, but for several hundred years the technology to implement those ideas didn’t exist. Now, with the space age less than fifty years old, we have traveled beyond our own solar system.
During the Cold War period, both the United States and the Soviet Union developed plans to launch the first artificial satellites into space for military purposes. Space was a new arena for conquest. The Soviet Union won this race when they launched the first successful artificial satellite in 1957, a small science probe called Sputnik I. This unexpected success shocked the world and prompted the speedy development of an American space program. Meanwhile, the Soviet Union launched the first person into space in 1961, when popular Soviet pilot Yuri Gagarin made the first trip around the world in space. The Soviets also crash-landed the first human-made object on the Moon and launched probes toward Mars and Venus.
In response to these achievements, the United States made ambitious plans to improve science education and research funding. President John F. Kennedy made space exploration a centerpiece of the U.S. program to win the Cold War. NASA – the National Aeronautics and Space Administration – was founded to be a leading force in space technology and science. Kennedy committed the U.S. to land humans on the Moon by the end of the 1960s, galvanizing the American space effort. The result was the Apollo program. We now know the Soviets secretly started their own Moon landing program at the same time as Apollo, building an enormous rocket booster and a lunar landing module. They abandoned this program after unmanned tests of their large rocket failed in dramatic explosions. In 1968, the astronauts of Apollo 8 were the first humans to leave Earth’s gravity, in a scouting expedition for a lunar landing site. A year later, Neil Armstrong and Buzz Aldrin were the first humans to set foot on another world.
Public interest in the space program peaked at this time. Moon landings over the next three years placed 12 Apollo astronauts at six different lunar sites. However, public appetite for the expensive Apollo program diminished, and it was abandoned in 1972.
Meanwhile, several nations sent robotic probes to other planets, returning the first close-up views of their surfaces. A Soviet robotic probe returned the first soil samples from the Moon. Another Soviet probe survived a descent through the hot, turbulent atmosphere of Venus, and took the first photos of its surface. The Soviets also crash-landed probes on Mars, and later a U.S. spacecraft landed on Mars and returned the first photos of its surface. A pair of American probes explored all four giant planets and their satellites, and the European Space Agency, a consortium of European nations, launched the first probe to make close-up images of the nucleus of a comet. The result of all this activity is that we have made fly-bys and taken close-up pictures of every large solar system object except Pluto.
Meanwhile, human space flight also moved forward. The U.S. developed the Space Shuttle system for delivering satellites and scientific experiments to orbit. The Space Shuttle was originally designed to be a “space truck,” with weekly launches and eventually even paying passengers. But technical problems and the catastrophic losses of Challenger and Columbia have slowed the program. Nevertheless, the shuttle remains the best way for the U.S. to get a large payload into orbit.
Meanwhile, the Soviets concentrated on building a space station. Russian cosmonauts on the Mir space station set world records for living more than a year at time in orbit. Understanding the effects of extended weightlessness on humans is essential if we are ever to send people to Mars or other planetary destinations.
The space age was born out of the competition and paranoia of the Cold War. The superpowers raced to lead the world in science and technology. Since the end of the Cold War, budgets for space exploration, as well as broader scientific research, have been cut. Space exploration is expensive. In an era of tight funding, international collaboration is required to make progress. The International Space Station has been an example of successful cooperation between the U.S. and Russia since its launch in 1998. Similarly, current plans for robotic probes to Mars involve the coordinated efforts of the U.S., Russia, Europe, and Japan. A race that was initiated by competition between nations is now only possible with their cooperation.
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