The Measure of the Moon

FRONTISPIECE.The tripod-like object just outside the shaded area is the gnomon and photogrammetric chart assembly which is used as a ~hotographicreference to establish local vertical Sun angle, scale, and lunar color. The gnomon is one of the Apollo Lunar Geology Hand Tools. The author took this photo (December 13, 1972) of Astronaut Eugene A. Cernan standing near an over- hanging rock during the third Apollo lunar surface ex- travehicular activity (EVA) at the Taurus-Littrow landing site. DR.HARRISON H. SCHMITT* NASA Manned Spacecraft Center Houston, Texas 77058 The Measure of the Moon The detailed geometry and orientations at sample localities were obtained largely through roughly horizontal stereophoto pairs using a special gnomon for Sun-line and vertical control. HE COMBINED efforts of geologists and pho- the detailed geometry of large- and small- Ttogrammetrists have been the major con- scale features, and the positions and orientn- tributions to establishing the geometric con- tions of samples relative to this geometry, text of the data from the Apollo program. and relative to the Sun and space. For the most part we applied the techniques We required the topography, slopes, and of classical photogrammetry to the problems inertial positions of the landing sites for the of modern exploration. The problems were safe and precise attainment of our science also classical. We needed to establish the objectives. Finally, and perhaps most im- cartographic positions of data points (at portantly, we needed the fundamental con- widely varying scales) relative to each other straints on our evolution models for the and relative to the whole moon. We needed hloon, which photogrammetry provides, such Presented as the Keynote Address at the An- as the relations between the center of mass nual ASP/ACSM Convention in Washington, and the center of figure of that planet. D.C., March 14, 1973. To tackle such problems our techniques ranged from the simple to the sophisticated. through which we can now solve manv of L, We used simple panoramas and our local and lunar-wide control problems. three-point resection for much of our lunar The details of all of these efforts are best surface position control. Perspective (Cana- left to the experts; I am merely one of hun- dian) grids were used in situations lacking dreds of consumers of their contributions. planimetric control, but with eventual base Through these and the contributions of all control provided by metric photographs from scientists and engineers involved in Apollo, orbit. we have in our hands, if not yet in our minds, The detailed geometry and orientations a first-order understanding of another planet, at sample localities were obtained largely our Moon. In the remainder of this presenta- through roughly horizontal stereoscopic pairs tion I wish to review that understanding by of photographs using a special gnomon means of an orbital tour of the Moon. (Frontispiece) for Sun-line and vertical con- I shall try to outline the pattern of our trol, for scale and for photometric calibration. present understanding of the evolutionary Reseau marks provide geometric control of sequence through which this sister planet of the film. In most instances analytical plotters ours has passed over the last four and one- were mandatory in the analysis of what are half billion years. Understanding, however, is almost random sets of photographs. For some a transient thing and even today alternative unusual photographic combinations measure- explanations exist for the phenomena we have ments were accomplished by special point- observed. On the other hand, the sequence by-point analytical programs. to which I shall refer is consistent with most, Our most modern approach to lunar pho- if not all, of our present knowledge. This togrammetry came from orbit. The introduc- interpretive sequence gives a framework for tion into lunar orbit operations of precision future investigation, including a new look at metric and panorama cameras and laser al- our Earth through the corrective vision of the timeters provided the photographs and data Moon. Astronaut Cernan makes a short ch~ckor~tof the Lunar Roving Vehicle during the early part of the first Apollo 17 EVA. This view of the stripped down Rover is prior to loadup. Eq~~ipnlentlater loaded on the Rover in- cluded the ground controlled. televkion assembly, the lunar antenna, aft tool pallet, and lunar tools and scien- tific gear. Cernan is the Apollo 17 commander, and the picture was taken by the author while Astronaut Ronald E. Evans remained with the Command and Service Motl111esin lunar orbit. The mountain in the right back- gro~lnclis the east end of South Massif. THE MEASURE OF THE MOON 817 1 APoLLo REQUIRED a Newtonian match be- through the accumulation of the heat of radio- tween the explorers' sunrise and the Moon's active decay, gradually reached temperatures sunset. Sunset on the far side of the Moon by which it could begin to influence the char- was not always so starkly tranquil as it is acter of the surface regions. First, a hot core now. About 4.6 billion years ago, when the of a liquid solution of sulphur and iron appears Moon was approximately its present size, the to have accumulated, and in this core a re- Sun probably set on a glowing, seething sea markable and still little understood phenom- of molten rock. Storms of debris still swept enon occurred: an electric dynamo probably its surface, mixing, quenching, outgasing, and came into existence, began to perpetuate it- remelting a primitive meIted shell while in- self, and produced a magnetic dipole field side the shell the crust of the Moon was about 1/25th of that presently associated gradually taking form. with the Earth. Although the dipole field has By about 4.4 billion years ago the Moon's disappeared, the magnetic anomalies persist crust must have looked not unlike the high- to the present. land areas we see today, although still hot The second event generated by the Moon's and violently changing in appearance as the interior processes was the apparent eruption debris storms continued their declining, on the surface of light-colored materials com- though still dominant, ways. This cratered posed largely of the pulverized remnents of and pulverized outer crust is composed the ancient crust. These light-colored felds- largely of plagioclase feldspar, a mineral rich par rich materials appeared to have partial- in calcium and aluminum, although other ly filled all the great basins that then existed, minerals and elements are also present. such as Gagarin. Their irruption may As the residue of creation was consumed have been driven by the melting and up- by Earth and Moon alike, the debris storms ward migration of the materials, rich in radio- decreased in frequency, although not with- active and gaseous components, that were out occasional unusually massive reminders left over after the crystallization of the of the past. Sometime prior to about 4.1 or Moon's melted shell. 4.2 billion years ago, large basins, such as As the last of the large basins were created the lngenii, began to form by major about 3.9 billion years ago, the final major I impact events at a time when they could not internally generated episode of evolution took' be obliterated by more numerous smaller place. This chapter tells of the flooding of all, collisions. the great basins on the front side of the Moon by vast, now frozen, oceans of dart basalt. Only the very deepest of basins on DURING THIS same time the Moon's interior, the far side, such as Tsiolkovsky, werd The author, Scientist-Astronaut and lunar module pilot, is photo- graphed seated in the Lunar Roving Vehicle at Slation 9 (Van Serg Crater) during the third EVA. The photograph was taken by Astronaut Cernan, commander; he and the author had descended in the Lunar Module Challenger to explore the lunar surface. PHOTOGRAMMETRIC affected by the formation of the maria, al- isfied with only the beauties and comforts of though to some degree all portions of the Earth. Paradoxically, we also found enhanced outer crust must have been permeated up to awareness and appreciation of those beauties a general mare sea-level. and comforts we were now so willing to leave behind. THIS TmMENmus upwelling and extrusion As we progressed toward our historical of molten rock was probably triggered by goal of a lunar landing (the Smythii Mare), heat from radioactive elements and, in this Apollo 10 provided the final technological instance, portions of the Moon's deep inner verification that we were ready. While show- crust or even deeper outer mantle melted. ing the world an orderly progression of en- Variations in the internal composition of gineering and orbital procedures, the mission the Moon caused the period of mare flooding emphasized how ordinary, but then how ex- not only to span the time from 3.8 to about traordinary, the new breed of explorers were 3.2 billion years ago, but also to cause pro- to be. found chemical differences in the character The far horizon of Mare Tranquillitatis of the basalts that were produced as this holds a unique place in the annals of Man. time passed. Even though we speak personally in so spe- Then a relative quiet settled forever on cial a way about Apollo 8, the event that the surface of the Moon. When the waves history will remember as having changed the and currents on the maria had finallv been course of that same history was the landing arrested, the Moon's appearance differed only of Apollo 11. The returns of that mission will slightly from that of today.

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