Recently, NASA announced that it has delivered the first spacecraft flight hardware of the Lunar Pathfinder mission to the European Space Agency (ESA). In this delivery task, the laser retroreflector array (LRA) in the flight hardware has become a highlight.
Previously, NASA's Goddard Space Flight Center in Greenbelt, Maryland, developed a laser retroreflector array, which scientists will use to test new navigation technologies for lunar missions. This kind of navigation capability is very important for the future lunar exploration mission. It is reported that the laser retroreflector array will enable the "Lunar Pathfinder" probe to be accurately positioned by the Earth's laser ranging station when flying around the moon. This centimeter laser measurement will use Galileo and GPS signals to determine its position at a distance of 400000 kilometers from the Earth, which is expected to prove the concept of "lunar satellite navigation".
NASA and the European Space Agency plan to launch the "Lunar Pathfinder" through the future commercial lunar payload service. In addition to testing navigation capabilities, the "Lunar Pathfinder" will also operate as a commercial communications relay satellite to provide communications services for lunar surface exploration missions.
Specifically, the laser retroreflector array (LRA) is a group of special mirrors that can reflect the laser back to the light source, unlike ordinary mirrors, which reflect light at a certain angle. In satellite laser ranging, the laser emitted from the telescope on the earth reaches the retroreflector on the spacecraft or celestial body, and the retroreflector reflects the light back to the telescope.
Laser retroreflector is a mature space technology, which is usually used to accurately determine the orbit of satellites around the earth. By measuring the time when the laser pulse leaves the telescope and the time when the return pulse arrives at the telescope, engineers and scientists can calculate the precise distance between the object and the ground station. Laser ranging is more accurate than similar methods using radio waves because the wavelength of the laser is much shorter.
In terms of method, they are similar to the mirror "cat's eye" embedded in the highway, which accurately reflects the light back to the light source through the complex internal reflection device. The laser retroreflector array (LRA) this time has a total of 48 "corner cubes", whose (optical) performance has been strictly checked and measured one by one in the laboratory.
The laser retroreflector array (LRA) is about the size of a laptop, and this delivery version has further expanded the volume. Stephen Merkowitz, manager of NASA's space geodesy project, said: "It will emit 12 times more laser than LRA on LRO, because it has 48 angular cubes with a diameter of 4 cm, while LRO has only 12 reflectors with a diameter of 3 cm."
At present, the International Laser Ranging Service has four stations capable of laser ranging the distance to the moon, three in Europe (Grasse, Wetzel, Matera) and one in the United States (Apache Point). In addition, ESA is considering using its own laser ranging station in Tenerife, which is currently being upgraded.
The "Lunar Pathfinder" mission is led by Surrey Satellite Technology in Guildford, UK. The European Space Agency has arranged this mission to provide communication services for NASA. The team from NASA, ESA and Surrey Satellite Technology Co., Ltd. (SSTL) in Guildford, UK completed the inspection after the arrival of the laser retroreflector array and handed it over to SSTL, where it will be successfully installed on the satellite, which will ensure the maximum improvement of positioning accuracy.
In the next ten years, the dedicated "Moonlight" satellite and other hardware on the moon surface will establish a common communication and navigation infrastructure for all lunar missions, making the moon closer to the earth and become the "eighth continent" of the earth.
Source: OFweek
