by Igor MITROFANOV, Dr. Sc. (Phys. & Math.), RAS Space Research Institute
Priorities in space studies are determined by the degree they contribute to the solution of basic problems of the mankind's development. Space activity in the new 21st century will set itself the most important task-to master the Moon as a treasure-trove of natural resources, as a unique base for space observatories and as a launching field for man's flights to Mars. So, what do scientists in Russia and abroad have to tell us about the Earth's natural satellite? What will people be looking for on the Moon? What kind of research is planned in this sphere? We can hardly name all questions that may arise. Let's try to answer some of them.
The process of the Moon's mastering was launched on February 3, 1966, when Soviet automatic station Luna-9 first landed on its surface and transmitted a panoramic view of the Sea of Tempests. A month later Russia put Luna-10 space station into the circumlunar orbit. Its research equipment included a spectrometer for registration of gamma-radiation, which is formed in the 1 m surface layer by the effect of galactic rays. Academician Alexander Vinogradov and Prof. Yuri Surkov, among others, discovered spectral elements corresponding to the lines of the nuclear radiation of oxygen, aluminum, magnesium, iron, silicon, potassium and thorium on the basis of the spectrometer data analysis. For the adjustment of the obtained data on the composition of the Earth satellite's surface, it was decided to repeat the experiment on the Luna-12 automatic station in October 1966 by placing
a gamma-ray detector on the consoles outside the station frame. The results of both space flights showed that the level of gamma-radiation produced by natural radioactive elements in all lunar "marine" regions corresponded to the Earth's primitive or oceanic basalts, and the flow of gamma rays from the surface of lunar "continents" proved to be on a lower level and corresponded to our planet's ultra-basic rocks. Those results were subsequently confirmed by a direct laboratory examination of the soil brought from the Moon to the Earth by Luna-16, -20, and -24 stations (1970 - 1976).
The landing on July 20, 1969, on the Moon's surface of the Eagle module of the American spaceship Apollo-11 with the astronauts Neil Armstrong and Edwin Aldrin on board was indisputably a major breakthrough in the mastery of the Moon. The flight of Apollo-11 actually marked an end of the USSR-US lunar race for the priority in space mastery. Twelve American astronauts made six space flights to the Moon, thus displaying to the world their country's technological, i.e. military and political superiority as well. Having survived their bitter defeat, the Soviet space program managers convinced themselves and their foreign colleagues of the advantages of automatic stations and confirmed their stand by bringing successfully lunar soil to the Earth on three occasions. The last sample was obtained at a depth of 2 m by Luna-24 station in August 1976. The work performed by Lunokhod-1 and -2 buggies in 1970 - 1973 was no doubt a success of our lunar program.
The decade of the Soviet-US space race in the 1960s paved the way for pioneering research of the Earth satellite's natural environment. The lunar soil has proved to be exceedingly old. Its composition in the "seas" (basalts about 3.2 - 3.9 bln years old) and in the "continents" (anorthosites about 4.4 - 4.6 bln years old) is different and contains fragments of minerals, melted and baked under the impact of asteroids. Water or any other volatile components are practically absent in the lunar soil. Several kinds of basalt were discovered with a considerable content of potassium and rare-earth elements. And the sample obtained by Luna-24 automatic station at a depth of 2 m contained more aluminum and less titanium than in the soil delivered by Apollo program expeditions. In the course of the experiments it was revealed that a regolite layer up to several meters thick covered the Moon's surface. It looks like a rock, crushed and mixed under the impact of falling cosmic bodies, and enriched by hydrogen and helium under the impact of solar wind. The time of mixing makes up tens or hundreds of millions of years.
The results of the first stage in the Moon's research were undoubtedly of great importance for forming up-to-date notions about it. However, purely scientific interest proved to be insufficient to go on with adequate programs in the past three decades of the 20th century, while political incentives for winning priority in space were absent by that time. Moreover, lunar projects proved to be exceedingly expensive, with an enormous degree of risk. Although both the USSR and the United States in the period of their space race nourished the plans for the construction of lunar inhabited bases, in the 1980s these ideas were relegated to the long-term perspective.
After Luna-24, flights to the Moon ceased for a long time. It was only in 1994 that a relatively "cheap" ($80 mln) Clementine space project was implemented in the United States. It was developed under the Strategic Defense Initiative (SDI) program for the final adjustment of equipment for tracking military targets on the cireumter-restrial orbit. A 150-kg spacecraft was put into the circumlunar orbit, as under international treaties it was prohibited to carry out such tests on the circumterrestrial orbit.
In about two-and-a half months of continuous observations, Clementine obtained 2.5 mln pictures of the Moon's surface in various spectral ranges. Owing to the laser altimeter the Moon acquired a third dimension-height of the relief. It was confirmed that there were numerous craters in the vicinity of the North and South poles. One of them, Ateken, the South Pole, with a diameter of 2500 km and about 12 km deep, is the Solar system's largest impact crater.
The angle of inclination of the Moon's rotation axis to the perpendicular to the ecliptic plane is quite insignificant (1.6°). To compare: the Earth's axis is inclined to it at an angle of 23.5°, and the respective figure for the Moon's orbit plane is 15.5°. If the Moon's surface were of a smooth spherical form, the Sun's rays would have constantly touched its poles. But the Moon's surface has got an intricate relief, and that is why the polar areas should have both eternally illuminated and eternally dark regions. In 1961, Americans Watson, Murray and Brown put forward a hypothesis that in the eternally dark lunar areas, in the period of the Moon's existence, could accumulate ice, which had condensed there as in "cold traps" from the water steam formed as a result of the Moon's collision with comets. Water ice forms the basis of the comets' substance, and lunar water steam atmosphere is formed for a short period of time under each such impact. The H2O molecule captured by the "cold trap" remains there forever. The layered deposits of water ice mixed with regolite reflect, just as the rings of trees, the history of the Moon's collisions with comets and asteroids.
It has been proved according to the data of the Clementine project's altimeter and radar that in the vicin-
Maps of the Moon's surface relief according to the Clementine data (black-and-white) and of the flow of epithermal neutrons according to Lunar Prospector data (colored) in the environs of the Moon's northern (above) and southern (below) poles. The dark areas on the relief maps correspond to the eternally dark regions, and dark areas on neutron radiation maps correspond to the reduced flow of epithermal neutrons.
ity of the lunar North and South poles there are indeed both eternally illuminated areas on hill tops, where the Sun and the Earth are always in view, and the temperature varies from -30 to -50° (an excellent landing field for the lunar base!), and eternally dark valleys on the bottom of the craters, where the Sun's warm rays never penetrate, where temperature is on the level of minus 230° and where water ice deposits may be discovered.
In 1998 - 1999, detailed mapping of the neutron and gamma-radiation of the moon's surface was carried out from the Lunar Prospector research spacecraft, designed under the NASA Discovery program. That comparatively small spacecraft (weighing about 300 kg) carried five research instruments on board. The global maps were drawn up on the basis of nuclear gamma-radiation measurements, showing the presence of potassium, titanium, iron and other elements in the substance of the Moon's surface. They showed substantial variability in the composition of various surface areas. For instance, the area of the Imbrium Sea proved to have great intensity of radioactive potassium radiation. This is quite in line with the data obtained earlier by Luna-10 automatic station and instruments carried by the orbital modules of Apollo-15 and -16. Important results of the possible existence of polar glaciers were obtained in the Lunar Prospector project in the course of measurements of the neutron flow from the Moon's surface in the area of its poles. It should be remembered that cosmic rays form secondary neutrons of about 20 MeW in the one-meter upper substance layer. A considerable part of neutrons leave the surface after multiple collisions with the substance nuclei. As a result, their movement is substantially slowed down. A part of neutrons leave the surface before their energy is transformed into heat-these are epithermal neutrons, while other (heat) neutrons get completely heated before escape. The slowdown process is most effective if neutrons collide with hydrogen nuclei, since proton and neutron have the same weight. As a result, the increased hydrogen concentration in the surface substance leads to the decrease of the share of epithermal particles in the flow of outgoing neutrons and to the increased share of particles with heat energies.
Lunar Prospector data have shown that there is considerable weakening of the flow of epithermal neutrons in the Moon's polar areas, which is attributable to the fact that the lunar soil has an increased content of hydrogen atoms. It was concluded that such content of water ice accounts for about 1.5 percent of regolite. The neutron measurement data had a low degree of space resolution on the surface area of about 100 km. That is why weakening of flow of epithermal neutrons was observed for large surface areas and could not be regarded as an indisputable argument in favor of the presence of water ice deposits in "cold traps" on the bottom of the craters.
If they are finally discovered, the optimal scenario for the Moon's utilization should be drawn up with regard to the fact that water is indispensable for survival on the future lunar base. Oxygen released from water would provide the station with breathable air, and hydrogen would become an effective fuel for spacecraft and motor vehicles. That is why prospecting for water ice deposits in the regions of the lunar poles is a major task for the Earth satellite's utilization. Automatic stations will be used for search of water ice deposits and minerals on the Moon for the first technological experiments. It is planned to choose the strategically most advantageous region for setting up a future inhabited base and launching the construction of the required infrastructure there.
In 2008, the United States is planning to put Lunar Reconnaissance Orbiter (LRO) automatic spacecraft into the circumlunar orbit. It will be the first project of the new NASA program for the Moon's utilization and preparation of a manned space flight to Mars. In the course of its implementation it is planned to check the hypothesis of water ice deposits in "the eternally dark" polar craters. Five American devices and the 24-kg Russian-made Lunar Exploration Neutron Detector (LEND) will take part in the solution of this problem. LEND is currently being designed at the RAS Space Research Institute under the order of the Federal Space Agency. This sophisticated complex will consist of nine individual neutron detectors, with four of them located inside the collimator module that will ensure a high degree of space resolution for mapping the Moon's neutron radiation. LEND has been designed on the basis of the experience accumulated in the process of development of HEND, another Russian device, that is currently operating successfully at NASA's Martian orbital station Mars Odisseus*.
LRO will have a circular polar orbit of Moon around 50 km high. Under these conditions, the space resolution for measurements of the neutron flow from the surface by LEND will correspond to an area with a radius of 5 km. In that case the threshold for hydrogen detection in the Moon's regolite will be on the level of 100 ppm (100 hydrogen atoms per million substance atoms). If LEND discovers local hydrogen patches with a concentration of over 104 ppm in the "cold traps" in the eternally dark craters, that will mean the presence of water ice in the amount of over 10 percent by mass. Such ice content is sufficient for the creation of technological cycles for its production and utilization for the construction and maintenance of the lunar infrastructure. If no ice is revealed, the process of creating infrastructure on the Earth's satellite will be substantially delayed, for water, oxygen and hydrogen will be produced on the basis of more complicated and expensive processes of lunar mineral conversion. This intrigue of the Moon's utilization in our days will reach its climax in 2008, when Russian and American scientists will start Moon studies with the help of the devices on LRO board.
Today other countries are also taking part in the present lunar space program. In 2004 - 2005 the European Space
* See: I. Mitrofanov, "Unlocking Martian Enigmas", Science in Russia, No. 6, 2002; M. Litvak, I. Mitrofanov, "Martian Seasons", Ibid., No. 4, 2000. - Ed.
Agency implemented Smart-1 project. New technologies of interplanetary ion engines were finally adjusted and the Moon's surface in the environs of its poles was surveyed. Japan is planning to launch a Selena research satellite in the next few years. Research equipment on its board will make it possible to conduct geological survey of the mineral composition of the lunar soil. Preparations are also afoot for launching the Indian Chandrayan spacecraft for the solution of similar problems. The space agency of China has also announced grandiose plans for the 2020s and 2030s in this sphere.
As to Russia's national lunar program, regrettably, now it is practically absent. So far the only R&D in the sphere of lunar equipment is associated with the design of LEND for the NASA LRO project. Plans of fundamental space research include the Luna-Globe project but its implementation is being delayed. The successful implementation of the Phobos-Grunt Martian project with the new-generation spacecraft on board* and also the creation of Clipper, a new piloted spaceship, will certainly prove of great importance by offering opportunities for the Moon's utilization. However, these elements are insufficient to form a fundamental national program in this field for Russia. In the process of discussion of the need for such a program, some people object that "our Western well-wishers would like to involve us once again in the Moon race". I do not agree. Firstly, it was our country that had involved the Americans in the "Moon race" by implementing
* See: E. Galimov, "'Phobos-Grunt', the Russian Project", Science in Russia, No. 1, 2006. - Ed.
man's first space flight. Secondly, no second "race" will take place. The concept of space research has been reinterpreted in the United States in the past few years. On the one hand, the concept has become more pragmatic with its clear-cut practical goals, and, on the other hand, it presupposes the implementation of plans at a more rapid or slow rate depending on the attained results and obtained scientific knowledge. Should Russia take part in the Moon's research in our days? I'd like to believe that most of our compatriots would reply in the affirmative. We have not yet lost the lofty pioneering spirit, we should not be satisfied with our past successes, we would like to be citizens of the great space power.
The domestic lunar program should probably be a part of the international labor division system, but it should uphold national interests and be based on national priorities. The vast potential of the Soviet lunar space technology inherited by us is largely outdated and in the absence of new R&D, that potential will be lost. Spacecraft are being designed and developed for many years and even decades. That is why we should set about building lunar fleet today. No one will involve Russia in a new Moon race, but no one will be waiting for us either. There would probably be not so many regions on the Moon with permanent solar light and water resources suitable for lunar bases, while many claimants for their utilization may appear just in a few years.
In conclusion, I'd like to answer the fundamental question: why is the mankind striving to conquer the Moon? There are a few of them. Firstly, it provides excellent conditions for setting up astronomic, helio-physical and meteorological observation stations, i.e., the Lunar Polar Space Observatory. Astrophysics and astronomy are unthinkable today without space telescopes. However, spacecraft operate for a limited period of time, their repairs require enormous outlays and are sometimes even impossible. Once research equipment is placed on the Moon's surface, its maintenance will be carried out on the spot. Moreover, that would rule out the effect of the Earth's radiation, with ideal conditions of space vacuum ensured in the course of various experiments.
Secondly, work on the lunar base will allow scientists to solve the problem of origin of the Earth-Moon planetary system that has not been resolved so far. None of the existing hypotheses, such as the joint formation of this system, the Moon's capture by the Earth's gravitation field, formation of both celestial bodies as a result of the two protoplanets' collision, has won priority. The Moon's "accurate" revolution around the Earth on a practically round orbit (with the eccentricity of only 0.055) and the precision of operation of its rotation axis in relation to the Sun are mysterious and astonishing. That is in line with the model of formation of two space bodies, although the difference in their average density is a puzzle. The nature of lunar mascons-areas of an increased gravitation field under its surface-is not clear either.
Thirdly, once a lunar base is set up, conditions will be created for prospecting and utilization of minerals there. The fact is that production and processing of minerals on the Earth is accompanied by the growing air pollution with chemical and industrial wastes, inevitably leading to heating of the Earth's surface. Even now the degree of this heating is approaching a critical point. If crossed, that may trigger off irreversible climate changes. That is why to remove intensive power-consuming industry to the Moon is the primary task of the 21st century. This is also closely bound up with the problem of expediency of production and delivery to the Earth of helium-3 as a promising power resource. It may be more expedient to remove from the Earth power-intensive and hazardous branches of industry rather than bring additional power resources from the Moon to the Earth.
Fourthly, the need for the Moon's studies consists in the provision of conditions for man's expansion on Mars. It would be probably possible to make initial prospecting expeditions to Mars even without the use of the lunar infrastructure. However, it would be certainly impossible to develop the "red planet" in order to set up a permanent human colony there without using the Moon as a transshipment base. At the close of this century Mars-bound spacecraft would be probably launched from the Moon's surface on a regular basis, having been supplied with fuel and other resources.
And the last but not least: there is a humanitarian reason behind the need to master the Moon and, in the long-range perspective. Mars - guaranteed preservation of human civilization. Regrettably, the Earth will inevitably collide with a large asteroid in the future. These collisions occur regularly at a rate of about several tens of millions of years. It is assumed that episodic climate changes took place as a result of the last collision some 60 mln years ago, and those changes doomed the dinosaurs to extinction*. Modern civilization could be brought to ruin if it remained within the confines of only one planet, the Earth, for even small-scale and brief natural disasters, such as freezing of the oceans or, on the contrary, polar ice thawing, might prove incompatible with power generation and food production for the planet's multi-billion population. One may dispute about chances for preservation of intelligent living beings on the Earth after a new global disaster, but it is only too obvious that the existence of a self-sufficient human colony on the Moon and Mars will make the Earth dwellers' civilization practically immortal (on the time scale of the Solar system's existence). So, once the lunar outpost with its industrial infrastructure is set up in the 21st century, it would be man's first step on the road leading to this goal.
Illustrations supplied by the author
* See: Yu. Avsyuk et al., "Did the Dinosaurs Become Extinct at Once?", Science in Russia, No. 3, 2002. - Ed.
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