The Apollo program assumed a triaxial ellipsoid model for the Moon's sphericity.
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A NASA Technical Report drawing on Apollo laser altimeter data confirms that the program's geometric evaluations involved deriving the triaxial ellipsoid that best fits the Moon's surface.
Range measurements from the lidar instrument carried aboard the Clementine spacecraft have been used to produce an accurate global topographic model of the Moon. This paper discusses the function of the lidar; the acquisition, processing, and filtering of observations to produce a global topographic model; and the determination of parameters that define the fundamental shape of the Moon. Our topographic model; a 72nd degree and order spherical harmonic expansion of lunar radii, is designated Goddard Lunar Topography Model 2 (GLTM 2). This topographic field has an absolute vertical accuracy of approximately 100 m and a spatial resolution of 2.5°. The field shows that the Moon can be described as a sphere with maximum positive and negative deviations of ∼8 km, both occurring on the farside, in the areas of the Korolev and South Pole‐Aitken (S.P.‐Aitken) basins. The amplitude spectrum of the topography shows more power at longer wavelengths as compared to previous models, owing to more complete sampling of the surface, particularly the farside. A comparison of elevations derived from the Clementine lidar to control point elevations from the Apollo laser altimeters indicates that measured relative topographic heights generally agree to within ∼200 m over the maria. While the major axis of the lunar gravity field is aligned in the Earth‐Moon direction, the major axis of topography is displaced from this line by approximately 10° to the east and intersects the farside 24° north of the equator. The magnitude of impact basin topography is greater than the lunar flattening (∼2 km) and equatorial ellipticity (∼800 m), which imposes a significant challenge to interpreting the lunar figure. The floors of mare basins are shown to lie close to an equipotential surface, while the floors of unflooded large basins, except for S.P.‐Aitken, lie above this equipotential. The radii of basin floors are thus consistent with a hydrostatic mechanism for the absence of significant farside maria except for S.P.‐Aitken, whose depth and lack of mare require significant internal compositional and/or thermal heterogeneity. A macroscale surface roughness map shows that roughness at length scales of 10 1 –10 2 km correlates with elevation and surface age.
Estimates of the moon's geometry using lunar orbiter imagery and Apollo laser altimeter data - NASA Technical Reports Server (NTRS)
NTRS NTRS - NASA Technical Reports Server Search more_vert Collections About News Help Login Press Enter or click the Search button to begin your search. Back to Results Estimates of the moon's geometry using lunar orbiter imagery and Apollo laser altimeter data Selenographic coordinates for about 6000 lunar points identified on the Lunar Orbiter photographs are tabulated and have been combined with those lunar radii derived from the Apollo 15 laser altimeter data. These coordinates were used to derive that triaxial ellipsoid which best fits the moon's irregular surface. Fits were obtaind for different constraints on both the axial orientations and the displacement of the center of the ellipsoid. The semiaxes for the unconstrained ellipsoid were a = 1737.6 km, b = 1735.6 km, and c = 1735.0 km which correspond to a mean radius of about 1736.1 km. These axes were found to be nearly parallel to the moon's principal axes of inertia, and the origin was displaced about 2.0 km from the moon's center of gravity in a direction away from the earth and to the south of the lunar equator. Document ID 19730024010 Acquisition Source Legacy CDMS Document Type Other - NASA Technical Report (TR) Authors Jones, R. L. (NASA Langley Research Center Hampton, VA, United States) Date Acquired September 2, 2013 Publication Date October 1, 1973 Subject Category Space Sciences Report/Patent Number L-8797 NASA-TR-R-407 Report Number: L-8797 Report Number: NASA-TR-R-407 Accession Number 73N32743 Funding Number(s) PROJECT: RTOP 383-09-54-01 Distribution Limits Public Copyright Work of the US Gov. Public Use Permitted. Available Downloads Name Type 19730024010.pdf STI cloud_download content_copy visibility Related Records There are no records associated with this record. visibility_off No Preview Available
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