35 years after placing the small mirror on the moon, NASA is investigating how to improve its function, and is working to establish a facility in New Mexico that will make better use of it
18.3.2005
By: Yoram Ored, Galileo
The Apollo operation took place in the sixties and seventies of the last century, during which manned spacecraft were sent to the moon, placed on its surface and returned safely to earth. The landing of the first spacecraft on the white face, Apollo 11, took place in July 1969.
This event left behind, apart from the footprints of the astronauts Armstrong and Aldrin, also a small souvenir from the Earth - a board in which are embedded a hundred small mirrors that together form one mirror aimed at the Earth. Flashes of light from Earth were sent to this mirror - and are still being sent, more than 35 years after it was placed on the moon - to check its distance from us, the change in its orbit, and more.
Both in the past and today, laser flashes are sent from the Earth towards the mirror: the laser light crosses the space between the Earth and the Moon and hits the mirror. The mirror is built in such a way that the laser light beam that hits it is returned exactly to the direction from which it came and thus returns to the Earth and after a while hits it. This is how you can measure the time that has passed from the moment the beam is sent until it returns to Earth and knowing the speed of light (about three hundred thousand kilometers per second in a vacuum) you can calculate with great precision the distance of the Moon from the Earth at any given moment.
The researchers who have used this mirror over the past decades have made important findings. One of them pointed out that the moon moves away from us every year at a rate of 3.8 centimeters. Another finding hints that the moon probably has a liquid core. Researchers also used this lunar mirror to test the truth of Einstein's theory of general relativity, which received further confirmation from the findings.
Not only has this old lunar mirror not yet been restored, but NASA and the National Science Institute of the United States are now funding the construction of a new facility in New Mexico that will make improved use of the mirror. The intention is to build a facility that will be equipped with a telescope with a diameter of 3.5 meters. The facility will be able to measure, using the technique of sending laser pulses, the distance of the moon from us with greater precision.
The old mirror on the surface of the moon will continue to function indefinitely. This is because it does not get covered in dust, has not (so far) been damaged by small meteorites (something the Apollo planners feared) and does not need any source of energy for its operation.
