The Chang’e-4 lunar lander landed on the side of the moon invisible from Earth on January 3, 2019. It had a German instrument designed to measure cosmic rays – Lunar Lander Neutron and Dosimeter (LND) on board. Since then, this instrument has accurately measured cosmic rays at various times.
This is the first such measurement in history, because earlier devices of this type could only record the entire “mission dose” of radiation at once. In the magazine Science Advances An article has already been published on the work of an international group of scientists involved in LND measurements, including scientists from the German Space Center DLR (Deutsches Zentrum fuer Luft- und Raumfahrt). These studies included the most accurate measurements of cosmic rays recorded on the moon to date.
Various countries plan to send manned missions to further explore the moon in the coming years and decades. However, cosmic rays pose a serious threat to human health – both in space and on the Silver Globe itself. Already, the astronauts of the Apollo program wore devices for measuring radiation levels called dosimeters on their bodies.
– But this only allowed to determine a certain exposure to radiation during the mission – says Oliver Angerer, LND project manager at DLR Space Administration. – With the LND instrument, you can measure different radiation field characteristics at different time intervals, every 1, 10 or 60 minutes. This will allow scientists to calculate an “equivalent dose” which is much more important for the correct estimation of biological effects in the human body.
The cosmic radiation exposure now measured by scientists is a much better indicator of the radiation inside a space suit. These measurements yield an equivalent dose rate – biologically weighted radiation dose per unit time – of the order of 60 microsieverts per hour. For comparison – during a long-haul flight from Frankfurt to New York, the dose rate is 5 to 10 times lower. On the surface of the Earth itself, it is already nearly 200 times lower. In other words, a long stay on the moon presents a medical and logistical challenge, as it exposes the astronauts’ bodies to quite high doses of radiation.
– Human bodies are simply not exposed to such cosmic radiation in natural conditions adds Robert Wimmer-Schweingruber from the Christian Albrecht University (CAU) in Kiel, whose team designed and built the LND instrument. “On longer missions to the moon, astronauts will have to protect themselves from it somehow – for example by covering their lunar habitat with a thick layer of moon rock. This can reduce the risk of subsequent cancers and other diseases caused by the long time spent on the moon.
The instrument developed in Kiel continues to measure throughout the lunar day, but like all other scientific devices installed on this lander, it remains switched off also throughout the extremely cold, around two-week lunar night – to conserve energy needed for start-up, for example. The instrument and lander were designed to take measurements to last at least a year, and this goal has in fact been achieved. Data from the LND and the lander are sent to Earth via a satellite relay Queqiao (“Magpie Bridge”), which is located above the “side” (hemisphere) of the Moon, invisible from Earth.
Cosmic ray data is also important for future interplanetary missions. Since the Moon has neither a protective magnetic field nor an atmosphere, the radiation field on its surface is similar to what could be measured in interplanetary space.
‘LND measurements are also used to develop computer models useful for calculating the expected radiation exposure and refining our models, thus contributing to the work of protecting astronauts from radiation in future space missions. It is important that the detector also allows conclusions to be drawn about the composition of the radiation field, for example the number of neutrons and high-energy charged particles present in it. – adds Berger.
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Source: DLR
Prepared by: Elżbieta Kuligowska
Pictured: Chang’e-4 Lunar Lander pictured by the Yutu-2 rover.
Source: CNSA / CLEP / NAOC
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