After the last Soviet Moon rover had come to a standstill in 1973 and the third batch of lunar material had been sampled by the Luna 26 robot in 1976, a feat which gave the Soviet Union a unique position in space for a long time, the constant companion of our Earth fell into oblivion. After scientifically significant but brief fly-bys by NASA’s Jupiter probe Galileo during two Earth swing-bys in 1990 and 1992, the Japanese Hiten probe was the first to pay a prolonged visit to the Moon in 1992. It was followed by two American orbiters, Clementine and Lunar Prospector (the latter discovered water ice in deep dark craters at the north and south poles), the first and only European Moon probe SMART-1, the second Japanese probe SELENE, and Chang’e-1, the first Chinese probe.
Finally, in his State of the Nation address on January 14, 2004, President George W. Bush announced that Americans would return to the Moon by 2019 and ultimately travel on to Mars and other more remote destinations. However, President Barack Obama’s administration halted the funding of the Constellation programme for political reasons in 2009, only to announce one year later that the USA intended to send astronauts to Mars by 2035.
In the same year, a renewed Moon euphoria was aroused internationally when the Indian probe Chandrayaan-1 discovered water or, to be more precise, hydroxyl ions in minerals on the surface. When the American Lunar Reconnaissance Orbiter (LRO) which had been launched on June 18, 2009, confirmed this Indian observation a short while later, interest in the Moon was definitely rekindled. Participating in this mission, which is incredibly important for lunar research, are the University of Muenster, represented by Professor Harald Hiesinger, and the Technical University of Berlin, represented by Professor Jürgen Oberst. Both were supported by the DLR Space Administration, from the beginning. Professor Hiesinger is one of the scientists who look after the ‘eyes’ of this Moon probe: two cameras with tele lenses for black and white photographs with a maximum resolution of 30 centimetres and a wide-angle camera with a maximum resolution of 100 metres for colour and UV pictures of the lunar surface. Together, they make up the so-called Lunar Reconnaissance Orbiter Camera (LROC) of the Arizona State University in Tempe. Professor Oberst, head of the Department of Planetary Geodesics at the DLR Institute of Planetary Research, is involved in the Lunar Orbiter Laser Altimeter (LOLA), an instrument belonging to NASA’s Goddard Space Flight Center designed for surveying the global lunar topography with high precision.
LROC and LOLA data provide the basis for an enhanced lunar coordinate system, precise topographical maps of its surface, the search for suitable landing sites for future missions, the search for highly volatile elements, particularly water ice in the craters of the polar areas, and conclusions regarding the frequency of meteorite impacts on the surface and the history of the Moon. The German scientists have been supporting the US teams in choosing observation targets, calibrating the cameras, and correcting raw data. They helped evaluate the stereo image data for the generation of digital elevation models, prepared distortion-free topographical maps of the Moon, computed the age of the lunar surface more reliably than before from the size and frequency of the craters, and surveyed the landing sites of former Moon missions. Moreover, LRO contributed a great deal towards heightening public enthusiasm about the Moon, for in 2017, an American study based on LRO data showed that the concentration of water in the mantle of the Moon is probably similar to that of Earth. So, all at once, the ‘satellite of our Earth’ became interesting again, this time also as a springboard for missions to other planets.
A fresh start to the Moon
When the ‘Jade Rabbit’ covered the first few metres in the Mare Imbrium on December 14, 2013, yet another nation had begun to leave traces on the lunar surface. The rover of the Chang’e-3 mission proved that China was able to play along in the concert of the big space nations, and the next step followed on May 21, 2018, when the Chinese put the ‘Magpie Bridge’ (Quèqiáo) into a halo orbit around the Lagrangian point L2 behind the Moon as the first relay satellite in order to prepare the first soft landing on the far side of the Moon. On January 3, 2019, the Chang’e-4 mission released the second ‘Jade Rabbit’ in the Von Kármán crater in the southern part of the 2,400-kilometre Aitken basin at the south pole. The ‘Magpie Bridge’ will handle the communication because no direct radio contact can be made with Earth from the far side of the Moon.
Among others, the landing probe carries a measuring instrument from Germany, funded by the DLR Space Administration: the Lunar Lander Neutron and Dosimetry Experiment (LND) of the Christian Albrechts University of Kiel permanently measures radiation levels on the surface of the Moon. This is new, as so far radiation was measured only in orbit during two individual Moon missions but not actively on the surface. Consequently, it has so far been unknown what radiation dose astronauts are actually exposed to on the Moon. LND is supposed to change this thus helping prepare further missions to the Moon.
However, the Chinese space programme is not the only one in which the Moon is now firmly established. The Americans, too, have rediscovered our faithful satellite. Trials with the Orion spacecraft are ongoing, which is scheduled to set out for the Moon for the first time from the Kennedy Space Center in Florida in 2020, carried by the new heavy-lift rocket SLS. Uncrewed, the space vehicle will circle around the Moon several times and return to Earth. Only on the second mission, tentatively scheduled between 2021 and 2023, astronauts will travel to the Moon and orbit it in the capsule. While the shape of the crew module resembles that of an Apollo capsule, it is much roomier: not three but as many as four astronauts will find room in it for considerably longer flights. On short-term missions in near-Earth orbits, it will even accommodate up to six crew members.
However, each Orion mission crucially depends not only on the capsule but also on the European Service Module (ESM) which is built in Bremen by order of ESA under the industrial leadership of Airbus. The ESM is based on the experience gathered during the development of the five ATV vehicles for the ISS. It contains the main engine and four solar panels which supply electricity to the entire spacecraft. Its air-conditioning systems ensure that temperatures within it remain optimal for both astronauts and freight. Moreover, the ESM carries fuel as well as oxygen and water for the crew. In the long run, it is intended to carry astronauts even to remote asteroids or to Mars. In brief, Orion is the basis for the new American space programme ‘Moon to Mars’.