197 1 year, Apollo 14 and Apollo 15 also installed this special reflector on the surface of the moon. Another mirror made in France was installed on Lunokhod 2, the former Soviet lunar rover that landed on the moon in 1973. Before 1970, the moon 17 mission of the former Soviet Union also installed reflectors. In other words, on the moon, humans left five mirrors.
This is a key device that enables scientists to measure the distance between our planet and its satellites with unprecedented accuracy. This experiment is not only very important to test the general theory of relativity and understand the subtle swing of the moon when it rotates around its own axis, but also its operation and operation principle are very simple and practical compared with the great complexity of the whole task.
1963, James Ferrer joined the Astrophysics Laboratory jointly established by the National Bureau of Standards and the University of Colorado at Boulder. As a graduate student of Princeton University, he wrote a paper entitled "Planned Lunar Module: Corner Reflector on the Moon" in the late 1950s. He envisioned deploying a durable reflector weighing only 2 to 3 pounds on the moon and emitting a beam of light from the earth at the reflector. The instrument will detect the laser and reflect it back to the earth. It is written in the paper that the distance between the earth and the moon can be accurately measured by calculating the time it takes for light to travel from the earth to the moon and back to the earth.
In less than ten years, the whole world will know how insightful and predictable FALLER's original idea was. He and his colleagues set up a lunar ranging team to explore the feasibility of installing reflectors on the moon. No one can guarantee that this experiment will really work, and other teams are competing to be selected for Apollo's historic space voyage.
An angular cube reflector can work in theory, but it always needs to point to the origin of the incident light accurately, so that the light beam can be directly reflected back to the light source for accurate timing. However, because the moon rotates around its own axis and the earth, this perfect alignment will only happen in rare cases. Even in this case, a slight pointing error will cause the light to return to a different position. The mirror designed by FALLER will be composed of three mirrors, which are exactly set at right angles to each other, just like the inner corner of the carton. This design forces the incident light to bounce off three surfaces, and the laws of optics ensure that it always bounces directly back to the light source. In the end, Farrell's design was selected into the final plan of NASA.
Its working principle is an observatory. Usually the MacDonald Observatory in Texas sends a laser beam to the moon. Although there is some dispersion, the laser beam remains closely focused for a long distance. When the light beam is reflected from the mirror back to the earth, its diameter has expanded to 20 kilometers, and the dispersion of this light beam makes it more difficult to observe the reflection. At present, the Apollo Lunar Laser Ranging Operation at Cape Apache Observatory, located in the southeast of Alamodo, New Mexico 10 mile, measures five retroreflector arrays every hour, with an average of six times a month.
The reflector itself does not need any power support, which is why it still works after other instruments on the moon stopped working for decades. According to the Jet Propulsion Laboratory (JPL) of NASA, the instrument includes 65,438+000 cubic prisms (also known as fused Shi Ying semi-cubes), which are placed on a 46-square-centimeter square aluminum plate. Because of the shape of these cube corners, any laser beam directed at them will directly reflect the light back. Over the years, due to the application of better lasers and computing equipment, the measurement of the distance between the earth and the moon has become more accurate.
Once the laser beam hits the reflector, scientists at the Observatory will use sensitive filtering and amplification equipment to detect any return signal. The reflected light is too weak for human eyes to see, but under good conditions, a photon is received every few seconds, which is the basic particle of light.
In order to receive this weak signal, it needs to be observed for more than a few hours. By averaging these signals, researchers can calculate the distance of the moon with an accuracy of less than 2 cm. Considering that the average distance from the earth to the moon is 384,400 kilometers, which is about 30 times the diameter of the earth. The distance between the earth and the moon is so far that it took Apollo astronauts three days to get there, so the margin of error is quite small.
Researchers have collected data for 50 years by sending lasers to the lunar reflector, and physicists now determine that the moon is spiraling away from the earth at a speed of 3.8 centimeters per year. When Armstrong and Aldrin placed the first set of reflectors on the moon, they also became the first surveyors to work on the surface of the moon.
Although the experiment is famous for its distance measurement to the moon, researchers can also use these data to prove that the moon has a fluid core. The round-trip time of laser provides evidence to support Einstein's general theory of relativity. The theory holds that, to some extent, the speed of light in vacuum has nothing to do with the movement of any observer. According to NASA, the experiment also shows that the gravitational constant of isaac newton is extremely constant, and its change is less than a part from 1969 to 2004.