Lunar Orbiter Spacecraft Research Articles

ОЦЕНКА РАДИАЦИОННОЙ ОБСТАНОВКИ ПРИ КРАТКОВРЕМЕННЫХ ПОЛЕТАХ НА ЛУНУ

Background: The issue of assessing the features of factors affecting the formation of radiation doses of astronauts while in orbit of the Moon and on its surface remains insufficiently studied, which is important for ensuring the anti-radiation safety of astronauts on lunar missions. Purpose: To analyze the factors influencing the formation of the radiation dose of astronauts at the stage of finding the spacecraft in orbit of the Moon and the lander on its surface. Material and methods: The features of the dose load levels on astronauts at the stages of the Moon’s orbit and on the Moon’s surface are analyzed and generalized, calculation methods are used taking into account the orbit of the spacecraft around the Moon, the anti-radiation properties of the materials of the lander and spacesuit and the time spent in them during a short-term lunar mission. Results: The total radiation doses of astronauts for 14 days, calculated according to dosimetric measurements during the years of low solar activity (2009 and 2018‒2019), are 19.5‒23.2 mSv for astronauts staying in a spacecraft in lunar orbit, and from 22,7 to 24,0 mSv for astronauts on the Lunar surface, depending on the mass thickness of the protection at the maximum permissible 250 mSv for 1 month. An increase in the mass thickness of the anti-radiation protection of the lander in the equivalent of aluminum from 1.5 to 3-5 g/cm2 and the lunar spacesuit in the equivalent of aluminum from 0.2 to 0.5‒1 g/cm2 will reduce the total radiation dose of astronauts no more than 1.3 times during a 14-day stay on the surface of the moon. The results indicate that in order to minimize the radiation doses that astronauts receive during a lunar mission, it is important to take into account the forecast of solar activity in order to optimize the launch time of the spacecraft in the «windows» with minimal levels of radiation exposure. Conclusion: When predicting radiation hazard levels for astronauts during a short-term lunar mission, it is necessary to assess the levels of exposure to cosmic ionizing radiation both in the orbit of the Moon, depending on the lunar trajectory of the spacecraft, and on the surface of the Moon, taking into account the time spent in the lunar module and in a spacesuit, as well as levels of solar activity. It is important to take into account the analyzed features of the formation of cosmonauts’ radiation doses while orbiting the Moon and on its surface when predicting the time limits of the lunar mission, anti-radiation protection of astronauts and their compliance with the regulatory limits of exposure.

Transformative science from the lunar farside: observations of the dark ages and exoplanetary systems at low radio frequencies.

The farside of the Moon is a pristine, quiet platform to conduct low radio frequency observations of the early Universe's Dark Ages, as well as space weather and magnetospheres associated with habitable exoplanets. In this paper, the astrophysics associated with NASA-funded concept studies will be described including a lunar-orbiting spacecraft, DAPPER, that will measure the 21 cm global spectrum at redshifts ≈40-80, and an array of low frequency dipoles on the lunar farside surface, FARSIDE, that would detect exoplanet magnetic fields. DAPPER observations (17-38 MHz), using a single cross-dipole antenna, will determine the amplitude of the 21 cm spectrum to the level required to distinguish the standard ΛCDM cosmological model from those produced by exotic physics such as nongravitational dark matter interactions. FARSIDE has a notional architecture consisting of 128 dipole antennas deployed across a 10 km area by a rover. FARSIDE would image the entire sky each minute in 1400 channels over 0.1-40 MHz. This would enable monitoring of the nearest stellar systems for the radio signatures of coronal mass ejections and energetic particle events, and would also detect the magnetospheres of the nearest candidate habitable exoplanets. In addition, FARSIDE would provide a pathfinder for power spectrum measurements of the Dark Ages. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades'.

Optical characterization of laser retroreflector arrays for lunar landers.

The Laser Retroreflector Array for Lunar Landers (LRALL) is a small optical instrument designed to provide a target for precision laser ranging from a spacecraft in lunar orbit, enabling geolocation of the lander and its instrument suite and establishing a fiducial maker on the lunar surface. Here we describe the optical performance of LRALL at visible and near-infrared wavelengths. Individual corner cube reflectors (CCRs) within LRALL were tested for surface flatness and dihedral angle values. We also imaged the far-field diffraction patterns of individual CCRs as well as the entire retroreflector array over the range of possible incident angles to extract the optical cross section as a function of viewing angle. We also measured the optical properties of one of the CCRs over the lunar temperature range (100-380 K) and found no significant temperature-dependent variance. The test results show LRALL meets the design criteria and can be ranged to elevation angles above 30° with respect to the instrument base from an orbital laser altimeter such as the Lunar Orbiter Laser Altimeter on the Lunar Reconnaissance Orbiter. This work summarizes the test data and serves as a guide for future laser ranging to these retroreflector arrays.

Global classification of lunar reflectance spectra obtained by Kaguya (SELENE): Implication for hidden basaltic materials

A global classification map of lunar absorption spectra is developed under unified classification criteria by applying the K-means and ISODATA unsupervised classification methods. The spectra were obtained by the Spectral Profiler (SP) onboard the Kaguya (SELENE) lunar orbiter spacecraft. The spectra are mostly categorized into seven spectral groups by the K-means method: K1, K2, K3, K4, K5, K6, and K7. Then, each K-means group is divided into 66 total classes by the ISODATA method. The K1 and K3 groups are classified into 21 and 14 classes, respectively, for which the average spectra are high-calcium pyroxene (HCP)-abundant compared to the other groups. Both groups are mainly located on maria and pyroclastic deposits. However, while the K1 group can be found primarily near the center of large maria, the K3 group can be found mainly at small maria and the margins of large maria. The K2 group contains eight classes and shows average spectra, such as low-calcium pyroxene (LCP), in abundance, which are found mainly on the South Pole-Aitken (SPA) basin and on the coast of Mare Frigoris. The K5 (eight classes), K6 (two classes) and K7 (three classes) groups indicate average spectra with shallower absorption (between 0.9 µm and 1.2 µm wavelength) than those of the K1, K2, and K3 groups. These groups are located in highland regions, and the K5 group is located in high-albedo regions, such as fresh craters. The K6 group is found on nearside highland areas and the K7 group is found on farside highland areas. The K4 group with nine classes shows average spectra, such as mixtures of K1/K2/K3 and K5/K6/K7, and these classes are located around boundaries between mare/SPA and highland. In addition, one class is independently defined without using K-means and ISODATA because its spectra are unsuitable for automatic unsupervised classification. However, this class is still geologically meaningful.The average spectra of the ISODATA classes show not only the characteristics of the major host material belonging to a spectral group, but they also show the small influence of materials from other groups in nearby regions on that host material. This influence is considered to be caused by horizontal material mixing of materials in that location with the ejecta from nearby regions. However, occasionally the ISODATA classes of the K4, K5, and K6 groups influenced by the K1/K3 groups are clustered geographically in regions far from the K1/K3 regions. Some locations of the clusters correspond to locations of the well-known cryptomaria and small pyroclastic deposits. On the other hand, some locations of them also contain candidates of hidden subterranean basaltic materials, such as undiscovered cryptomare, dike, and sill estimated based on recent lunar gravitational anomalies. This agreement suggests to be appeared hidden basaltic materials by the material mixing occurring vertically. The total area of the clusters except for known cryptomaria is approximately two times larger than that of the known cryptomaria, and this area reaches approximately 20% of the total area of exposed maria. The total volume of hidden basaltic materials, except for the known cryptomaria, is estimated to be 104 to 106 km3, depending on assumptions of the relative abundance between cryptomare and dike/sill. This volume is comparable to that of the known cryptomaria and approximately 10% of that of the exposed mare.

Mapping of the lunar surface by average atomic number based on positron annihilation radiation from Chang’e-1

A map of the average atomic number of lunar rock and soil can be used to differentiate lithology and soil type on the lunar surface. This paper establishes a linear relationship between the average atomic number of lunar rock or soil and the flux of position annihilation radiation (0.512-MeV gamma-ray) from the lunar surface. The relationship is confirmed by Monte Carlo simulation with data from lunar rock or soil samples collected by Luna (Russia) and Apollo (USA) missions. A map of the average atomic number of the lunar rock and soil on the lunar surface has been derived from the Gamma-Ray Spectrometer data collected by Chang’e-1, an unmanned Chinese lunar-orbiting spacecraft. In the map, the higher average atomic numbers (ZA > 12.5), which are related to different types of basalt, are in the maria region; the highest ZA (13.2) readings are associated with Sinus Aestuum. The middle ZA (~12.1) regions, in the shape of irregular oval rings, are in West Oceanus Procellarum and Mare Frigoris, which seems to be consistent with the distribution of potassium, rare earth elements, and phosphorus as a unique feature on the lunar surface. The lower average atomic numbers (ZA < 11.5) are found to be correlated with the anorthosite on the far side of the Moon.

Ranger and Apollo S-IVB spacecraft impact craters

Numerous spacecraft have impacted the surface of Moon during the last several decades of lunar exploration. These impacts fall into two categories: relatively high-angle impacts formed by spacecraft on direct trajectories from the Earth and low-angle impacts formed by spacecraft in lunar orbit. The craters produced by the Ranger spacecraft and the Apollo S-IVB boosters are discussed here. The Ranger spacecraft had a mass of ~370kg (816lb.), impacted at 2600kms−1 and formed craters ~14–15m in diameter. The S-IVB boosters had masses of ~14,000kg (30865lb.), impacted at ~2600kms−1 and formed craters ~35m in diameter. These impacts are relatively unique due to the low bulk-density of the impactor (28 and 700kgm−3, respectively the S-IVB and Ranger spacecraft). Craters produced by the impact of the Ranger spacecraft are similar to other lunar mare craters in which the excavation process was impeded by the underlying solid basalt. Craters produced by the S-IVB impacts are non-circular and exhibit an elongate central mound. It appears that the S-IVB crater excavation also interacted with the basalt but in a more complicated manner than for the Ranger craters. Ejecta and rays associated with these craters are asymmetric and indicate that the excavation flow field varied with time and was not symmetric about the trajectory direction.

Statistical study of the properties of the magnetic field and plasma in the earth’s magnetotail near lunar orbit

Based on the magnetic field and plasma data obtained by GEOTAIL in 1992–1995 and WIND in1994–2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the superposed epoch analysis. The results showed that near the 0° sector the plasma density was negatively correlated with Dst index while the temperature was positively correlated with Dst index. The plasma velocity and magnetic field strength had little correlation with Dst index. Around the current sheet near the lunar orbit, the Bx varied between −15-15 nT, the plasma density was less than 0.4 cm−3, the median of plasma density for all events was less than 0.1 cm−3, the temperature varied from 0.016 to 8.98 keV, the median of the plasma temperature for all the events was ∼3 keV, the median of speed was about 200 km/s and the maximum speed was up to 1500 km/s. The tailward and earthward flows could be observed accompanied with the current sheet. For the current sheet cases with tailward flow, the Bx varied from −15 to 15 nT, the upper quartile of plasma velocity was more than 400 km/s, the maximum speed was up to 1500 km/s. For the current sheet cases with tailward flow, the Bx varied from −10 to 10 nT, the upper quartile of plasma velocity was less than 400 km/s, the maximum speed was up to 1200 km/s. The median of plasma density, temperature and velocity were similar for the two categories. This paper discussed the relationship between above results and magnetic reconnection at magnetic tail, compared the above results with the observation in the far magnetotail. We fitted the statistical results according to the Harris current sheet model, and the observation was consistent with Harris current sheet model. The above results can provide useful information for the design and protection of lunar-orbiting spacecraft and can be used as the background magnetic field and plasma parameters in the numerical simulation of mid-magnetotail reconnection.

Autonomous navigation and rendezvous of spacecraft in lunar orbit

The task of autonomous navigation of a spacecraft in a lunar orbit on optical measurements of the star tracker and Moon horizon sensor is considered. A method to carry out the measurements is proposed, and a recurrent algorithm for definition of a current estimate of an orbit by earlier measurements is developed. The accuracy of problem solution is investigated. It is shown that the accuracy of the orbit estimation is essentially influenced by errors in knowledge of topography of the lunar surface, as well as by errors of the gravitational field of the Moon. A possibility to use the topographic map of the Moon CLEM-L-LIDAR-TOPO-VI.0 received by the results of measurements performed on the spacecraft CLEMENTINE in 1994 and a model of the gravitational field of the Moon GLGM-2 of 70 × 70 to solve the navigation problem is considered. The results of modeling of the proposed method efficiency with regard to the topographic map of the Moon and the model of the gravitational field with the accuracy of navigation measurements of the star tracker and horizon sensor of ∼5″ have shown a possibility to maintain the positional accuracy of navigation in a lunar orbit of ∼50 m, which is commensurable with the accuracy of the US radionavigation system Deep Space Network including a network of antenna complexes with antenna diameters from 26 to 70 m. It is also shown that on the basis of the proposed method of absolute navigation a system of relative navigation providing rendezvous of two spacecrafts in a lunar orbit can be realized, which differs from the existing systems of rendezvous by simplicity of realization, low weight, power consumption and cost.

Nonthermal galactic emission below 10 megahertz

The Radio Astronomy Explorer 2 (RAE 2) lunar-orbiting satellite has provided measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low-frequency Galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-m traveling-wave V antenna on this lunar-orbiting spacecraft. The improved frequency coverage offers additional insights into the structure of the local Galactic neighborhood.

Lunar dynamics and selenodesy: Results from analysis of VLBI and laser data

Very-long-baseline interferometry (VLBI) observations of lunar radio transmitters have been combined with data from laser ranging to lunar retroreflectors to estimate simultaneously (i) parameters in models of the lunar orbit and libration; and (ii) the selenodetic coordinates of the radio transmitters and retroreflectors. For the ratio of the mass of the sun to that of the earth plus moon, we obtain 328,900.50 ± 0.03. For the lunar moment-of-inertia ratios we find β[Ξ(C-A)/B] = (631.27 ± 0.03) x 10-6 and ϒ[Ξ(B-A)/C] = (227.7 ± 0.7) x 10-6. The value implied for C/MR2 is 0.392 ± 0.003, with the uncertainty being dominated by that of the coefficient, J2, of the second zonal gravity harmonic, obtained by Gapcynski et al. from analysis of Explorer spacecraft orbital data. The values and most of the uncertainties that we obtain for the third-degree harmonics of the moon’s gravity field are comparable to those which have been obtained by others from observations of lunar-orbiting spacecraft. However, our determination of β appears to be the best available, and our results for two third-degree gravity coefficients, C31 = (26 ± 4) x 10-6 and C33 = (2 ± 2) x 10-6, have much less uncertainty than determinations based on laser data alone. For the relative-position vectors of both the lunar radio transmitters and the retroreflectors our estimates have uncertainties of about 30 m along the earth-moon direction and about 10 m in each of the two transverse coordinates.

Source location measurements of terrestrial kilometric radiation obtained from lunar orbit

Two‐dimensional source locations of individual terrestrial kilometric radiation (TKR) events have been measured by the Radio Astronomy Explorer‐2 (RAE‐2) spacecraft in lunar orbit. Although the average source location at 250 kHz is above the polar regions near the Earth (r ∼ 2‐3 RE), approximately 10% of the events occur at &gt; 7 RE from the Earth. Furthermore, there is considerable evidence for multiple sources and source motion over the time scale of tens of minutes. Recent TKR mechanism theories which assume that the emission occurs at or near the local electron plasma or gyrofrequency would predict generation much closer to the Earth's surface. We therefore suggest that alternative emission mechanisms or special propagation conditions are required to explain many TKR events.

Spectral reflectance of highland rock types at Apollo 17: Evidence from Boulder 1, Station 2

Many of the non-mare rock types at Apollo 17 can be identified uniquely by their spectral reflectance properties. Mineralogical and textural information is present in the spectral curves of samples from Boulder 1, Station 2. It should be possible to determine the regional extent of rocks similar to the boulder using reflectance spectra from a spacecraft in lunar orbit.

Dual-frequency bistatic-radar investigations of the Moon with Apollos 14 and 15

Dual-frequency bistatic-radar observations of the moon have been made using Apollo 14 and 15 spacecraft in lunar orbit. Simultaneous 13- and 116-cm wavelength radio transmissions from the spacecraft were received on the earth after reflection from the lunar surface. The received data were processed to obtain complete polarization and power spectra of the echo signal; the ellipticity, orientation, and magnitude of the deterministically polarized part were obtained as a function of frequency. The polarized parts of the echo spectra were then reduced according to the theory of quasispecular scattering from a gently undulating surface. The unpolarized portions of the echo spectra were associated with a diffuse scattering mechanism. When adjusted to normal incidence, the ratio of polarized to unpolarized power is 8(+l, −3) db at the 13-cm wavelength. Variations in the 13-cm unpolarized power are on the order of 1 db. At 116 cm, variations in the ratio of polarized to unpolarized power are considerably larger, on the order of 5 db. In two regions, near Lalande δ and the northern portions of Hipparchus, the unpolarized power apparently exceeds the polarized power. The craters Lansberg, Bessel, and Euler are not detectable in their effects on the orientation and eccentricity of the polarization ellipse or on the unpolarized component. Within Mare Serenitatis and Oceanus Procellarum, the 13-cm data follow a classical Fresnel reflection curve corresponding to relative dielectric constant ϵ = 3.1 ± 0.1. Over most of these same areas, the 116-cm data are consistent with this value of relative dielectric constant. In some areas, however, notably between Reiner and Hevelius, there are marked deviations from the reflectivities predicted for ϵ = 3.1. These results cannot be explained on the basis of simple models employing contiguous, semi-infinite, dielectric interfaces. In the highlands to the south and southwest of Mare Crisium, the relative dielectric constant obtained at 116 cm wavelength is ϵ = 2.8 ± 0.1. In this region, the 13-cm data depart from the reflectivities predicted for simple dielectric interface. These departures may be explained in terms of models employing layered dielectric structures. In Oceanus Procellarum, a model that has a local minimum in density at depth of 2 to 4 meters is consistent with the data. Lunar rms slopes, as determined by the Gaussian equivalent method from the polarized frequency spectra, show systematic differences with respect to mare and highland units. Within the highlands, the rms slopes obtained at the two wavelengths are nearly equal and vary between tan 6° and tan 8°. Within mare units, rms slopes inferred from the 116-cm data vary between tan 1° and tan 2°. Mare rms slopes at 13 cm are in the range of tan 2° to tan 4°. At the same location, the slopes obtained at the 116-cm wavelengths are typically one-half as large as those obtained at 13 cm. Using Hagfors' (1966) model for wavelength dependence, we conclude that on a 0.2- to 2-meter surface scale, the mare are rougher than the highlands, albeit overall, on larger scales, the opposite is true.

Lunar orbiter gravity analysis

This paper presents the results to date of the Jet Propulsion Laboratory (JPL) effort at analyzing the tracking data from the five Lunar Orbiter spacecraft. Emphasis is placed on the long-arc evaluation, to which most of the work was directed, rather than on the mascon analysis, which will be reported separately. The model of the Moon's gravity field that has been derived from the long-arc analysis is interpreted in terms of the Moon's mass distribution. The results are evaluated from the point of view of consistency and of statistical significance. In particular, the various factors contributing to the uncertainty in the estimation process are discussed.

Lunar gravitational field as determined from Lunar Orbiter tracking data

Lunar gravitational field determination from analysis of Lunar Orbiter spacecraft tracking data

A Description of the Lunar Orbiter Spacecraft

The U.S. Lunar Orbiter Spacecraft Program was conceived to search out potential Apollo landing sites, and to return detailed photographic coverage of the lunar surface for scientific study. The first flight was launched in August 1966, and the successful launch of the fifth orbiter was in August 1967. All five were successful and returned to Earth a large amount of photographic data.Presented in this paper is a short description of the spacecraft system with particular emphasis on the photographic system. The intent is to supply information which will permit a better understanding of the photographic data to be presented by Dr. William Brunk in the following paper.

Apollo Lunar Landing Site Selection Process

The selection of potential lunar landing sites for the Apollo Program poses some unusual problems. Among the factors to be considered are geographic location on the moon, surface topography, and mechanical properties. Data from Ranger, Surveyor, and Lunar Orbiter spacecraft are analyzed in detail to determine which sites are more suitable for lunar landings. Some of the methods used to reduce photographic data differ greatly from normal photogrammetric procedures. Monoscopic photography is reduced to produce topographic information in high-speed digital computers, and the resulting data is analyzed statistically for topographic suitability for landings.

Lunar Orbiter Ranging Data: Initial Results

Data from two Lunar Orbiter spacecraft have been used to test the significance of corrections to the lunar ephemeris. Range residuals of up to 1700 meters were reduced by an order of magnitude by application of the corrections, with most of the residuals reduced to less than 100 meters. Removal of gross errors in the ephemeris reveals residual patterns that may indicate errors in location of observing stations, as well as the expected effects of Lunar nonsphericity.

High Reliability PCM Telemeter System for Lunar Orbiter Spacecraft

The PCM Telemeter System described in this paper was designed and developed specifically for the Lunar Orbiter Spacecraft (LOS). Its functional capabilities are those of a good general-purpose PCM Telemeter. Reliability of the PCM System was the most important design consideration. The system reliability of Ps 0.986 for a 30-day mission was endeavored to be met through the use of Hi-Rel piece - parts qualified to existing Minuteman/Gemini/Apollo/LEM high reliability specifications. The Reliability Program was based on NPC 250-1. In operation, the PCM Telemeter accepts three types of input signals, (1) high level analog, (2) parallel digital (bilevel), and (3) serial digital data. The analog signals are multiplexed and encoded with an accuracy of 0.2% including over-all linearity of 0.1%. Digital data is interlaced into the output word format by the system as it is received. System timing is normally synchronized with an external clock. However, if the external clock fails, timing is automatically switched to an internal clock source and thus the PCM System will continue to function. The basic output bit rate for the PCM System is 50 bits per second. The PCM Telemeter supplies "read-in" pulses to other external equipment as timing commands for reading serial digital data into the PCM. The PCM also provides a 50 PPS shift pulse to an external 26-bit serial digital channel register. The PCM Telemeter can be divided, for purposes of exolanation, into six subunits: •Analog Multiplexer •Analog-to-Digital Converter •Digital Multiplexer •Programmer •Output Shift Register & Formatter •Power Supply.