The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission

The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced.     

Lunar Reconnaissance Orbiter (LRO): Observations for Lunar Exploration and Science

The Lunar Reconnaissance Orbiter (LRO) was implemented to facilitate scientific and engineering-driven mapping of the lunar surface at new spatial scales and with new remote sensing methods, identify safe landing sites, search for in situ resources, and measure the space radiation environment. After its successful launch on June 18, 2009, the LRO spacecraft and instruments were activated and calibrated in an eccentric polar lunar orbit until September 15, when LRO was moved to a circular polar orbit with a mean altitude of 50 km. LRO will operate for at least one year to support the goals of NASA’s Exploration Systems Mission Directorate (ESMD), and for at least two years of extended operations for additional lunar science measurements supported by NASA’s Science Mission Directorate (SMD). LRO carries six instruments with associated science and exploration investigations, and a telecommunications/radar technology demonstration. The LRO instruments are: Cosmic Ray Telescope for the Effects of Radiation (CRaTER), Diviner Lunar Radiometer Experiment (DLRE), Lyman-Alpha Mapping Project (LAMP), Lunar Exploration Neutron Detector (LEND), Lunar Orbiter Laser Altimeter (LOLA), and Lunar Reconnaissance Orbiter Camera (LROC). The technology demonstration is a compact, dual-frequency, hybrid polarity synthetic aperture radar instrument (Mini-RF). LRO observations also support the Lunar Crater Observation and Sensing Satellite (LCROSS), the lunar impact mission that was co-manifested with LRO on the Atlas V (401) launch vehicle. This paper describes the LRO objectives and measurements that support exploration of the Moon and that address the science objectives outlined by the National Academy of Science’s report on the Scientific Context for Exploration of the Moon (SCEM). We also describe data accessibility by the science and exploration community.     

Lunar Reconnaissance Orbiter Overview: The Instrument Suite and Mission

NASA’s Lunar Precursor Robotic Program (LPRP), formulated in response to the President’s Vision for Space Exploration, will execute a series of robotic missions that will pave the way for eventual permanent human presence on the Moon. The Lunar Reconnaissance Orbiter (LRO) is first in this series of LPRP missions, and plans to launch in October of 2008 for at least one year of operation. LRO will employ six individual instruments to produce accurate maps and high-resolution images of future landing sites, to assess potential lunar resources, and to characterize the radiation environment. LRO will also test the feasibility of one advanced technology demonstration package. The LRO payload includes: Lunar Orbiter Laser Altimeter (LOLA) which will determine the global topography of the lunar surface at high resolution, measure landing site slopes, surface roughness, and search for possible polar surface ice in shadowed regions, Lunar Reconnaissance Orbiter Camera (LROC) which will acquire targeted narrow angle images of the lunar surface capable of resolving meter-scale features to support landing site selection, as well as wide-angle images to characterize polar illumination conditions and to identify potential resources, Lunar Exploration Neutron Detector (LEND) which will map the flux of neutrons from the lunar surface to search for evidence of water ice, and will provide space radiation environment measurements that may be useful for future human exploration, Diviner Lunar Radiometer Experiment (DLRE) which will chart the temperature of the entire lunar surface at approximately 300 meter horizontal resolution to identify cold-traps and potential ice deposits, Lyman-Alpha Mapping Project (LAMP) which will map the entire lunar surface in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently shadowed regions illuminated only by starlight. Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation. The technology demonstration is an advanced radar (mini-RF) that will demonstrate X- and S-band radar imaging and interferometry using light weight synthetic aperture radar. This paper will give an introduction to each of these instruments and an overview of their objectives.     

Lunar Reconnaissance Orbiter Camera (LROC) Instrument Overview

The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) and Narrow Angle Cameras (NACs) are on the NASA Lunar Reconnaissance Orbiter (LRO). The WAC is a 7-color push-frame camera (100 and 400 m/pixel visible and UV, respectively), while the two NACs are monochrome narrow-angle linescan imagers (0.5 m/pixel). The primary mission of LRO is to obtain measurements of the Moon that will enable future lunar human exploration. The overarching goals of the LROC investigation include landing site identification and certification, mapping of permanently polar shadowed and sunlit regions, meter-scale mapping of polar regions, global multispectral imaging, a global morphology base map, characterization of regolith properties, and determination of current impact hazards.     

Lunar Exploration Neutron Detector for the NASA Lunar Reconnaissance Orbiter

The design of the Lunar Exploration Neutron Detector (LEND) experiment is presented, which was optimized to address several of the primary measurement requirements of NASA’s Lunar Reconnaissance Orbiter (LRO): high spatial resolution hydrogen mapping of the Moon’s upper-most surface, identification of putative deposits of appreciable near-surface water ice in the Moon’s polar cold traps, and characterization of the human-relevant space radiation environment in lunar orbit. A comprehensive program of LEND instrument physical calibrations is discussed and the baseline scenario of LEND observations from the primary LRO lunar orbit is presented. LEND data products will be useful for determining the next stages of the emerging global lunar exploration program, and they will facilitate the study of the physics of hydrogen implantation and diffusion in the regolith, test the presence of water ice deposits in lunar cold polar traps, and investigate the role of neutrons within the radiation environment of the shallow lunar surface.     

The Lunar Reconnaissance Orbiter Miniature Radio Frequency (Mini-RF) Technology Demonstration

The Miniature Radio Frequency (Mini-RF) system is manifested on the Lunar Reconnaissance Orbiter (LRO) as a technology demonstration and an extended mission science instrument. Mini-RF represents a significant step forward in spaceborne RF technology and architecture. It combines synthetic aperture radar (SAR) at two wavelengths (S-band and X-band) and two resolutions (150 m and 30 m) with interferometric and communications functionality in one lightweight (16 kg) package. Previous radar observations (Earth-based, and one bistatic data set from Clementine) of the permanently shadowed regions of the lunar poles seem to indicate areas of high circular polarization ratio (CPR) consistent with volume scattering from volatile deposits (e.g. water ice) buried at shallow (0.1–1 m) depth, but only at unfavorable viewing geometries, and with inconclusive results. The LRO Mini-RF utilizes new wideband hybrid polarization architecture to measure the Stokes parameters of the reflected signal. These data will help to differentiate “true” volumetric ice reflections from “false” returns due to angular surface regolith. Additional lunar science investigations (e.g. pyroclastic deposit characterization) will also be attempted during the LRO extended mission. LRO’s lunar operations will be contemporaneous with India’s Chandrayaan-1, which carries the Forerunner Mini-SAR (S-band wavelength and 150-m resolution), and bistatic radar (S-Band) measurements may be possible. On orbit calibration, procedures for LRO Mini-RF have been validated using Chandrayaan 1 and ground-based facilities (Arecibo and Greenbank Radio Observatories).     

The Lunar Gravity Ranging System for the Gravity Recovery and Interior Laboratory (GRAIL) Mission

The Lunar Gravity Ranging System (LGRS) flying on NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission measures fluctuations in the separation between the two GRAIL orbiters with sensitivity below 0.6 microns/Hz^1/2. GRAIL adapts the mission design and instrumentation from the Gravity Recovery and Climate Experiment (GRACE) to a make a precise gravitational map of Earth’s Moon. Phase measurements of Ka-band carrier signals transmitted between spacecraft with line-of-sight separations between 50 km to 225 km provide the primary observable. Measurements of time offsets between the orbiters, frequency calibrations, and precise orbit determination provided by the Global Positioning System on GRACE are replaced by an S-band time-transfer cross link and Deep Space Network Doppler tracking of an X-band radioscience beacon and the spacecraft telecommunications link. Lack of an atmosphere at the Moon allows use of a single-frequency link and elimination of the accelerometer compared to the GRACE instrumentation. This paper describes the implementation, testing and performance of the instrument complement flown on the two GRAIL orbiters.     

An Overview of the Lunar Crater Observation and Sensing Satellite (LCROSS)

The Lunar Crater Observation Sensing Satellite (LCROSS), an accompanying payload to the Lunar Reconnaissance Orbiter (LRO) mission (Vondrak et al. 2010), was launched with LRO on 18 June 2009. The principle goal of the LCROSS mission was to shed light on the nature of the materials contained within permanently shadowed lunar craters. These Permanently Shadowed Regions (PSRs) are of considerable interest due to the very low temperatures, <120?K, found within the shadowed regions (Paige et al. 2010a, 2010b) and the possibility of accumulated, cold-trapped volatiles contained therein. Two previous lunar missions, Clementine and Lunar Prospector, have made measurements that indicate the possibility of water ice associated with these PSRs. LCROSS used the spent LRO Earth-lunar transfer rocket stage, an Atlas V Centaur upper stage, as a kinetic impactor, impacting a PSR on 9 October 2009 and throwing ejecta up into sunlight where it was observed. This impactor was guided to its target by a Shepherding Spacecraft (SSC) which also contained a number of instruments that observed the lunar impact. A?campaign of terrestrial ground, Earth orbital and lunar orbital assets were also coordinated to observe the impact and subsequent crater and ejecta blanket. After observing the Centaur impact, the SSC became an impactor itself. The principal measurement goals of the LCROSS mission were to establish the form and concentration of the hydrogen-bearing material observed by Lunar Prospector, characterization of regolith within a PSR (including composition and physical properties), and the characterization of the perturbation to the lunar exosphere caused by the impact itself.     

The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment

The Diviner Lunar Radiometer Experiment on NASA’s Lunar Reconnaissance Orbiter will be the first instrument to systematically map the global thermal state of the Moon and its diurnal and seasonal variability. Diviner will measure reflected solar and emitted infrared radiation in nine spectral channels with wavelengths ranging from 0.3 to 400 microns. The resulting measurements will enable characterization of the lunar thermal environment, mapping surface properties such as thermal inertia, rock abundance and silicate mineralogy, and determination of the locations and temperatures of volatile cold traps in the lunar polar regions.     

The Mercury Laser Altimeter Instrument for the MESSENGER Mission

The Mercury Laser Altimeter (MLA) is one of the payload science instruments on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which launched on August 3, 2004. The altimeter will measure the round-trip time of flight of transmitted laser pulses reflected from the surface of the planet that, in combination with the spacecraft orbit position and pointing data, gives a high-precision measurement of surface topography referenced to Mercury’s center of mass. MLA will sample the planet’s surface to within a 1-m range error when the line-of-sight range to Mercury is less than 1,200 km under spacecraft nadir pointing or the slant range is less than 800 km. The altimeter measurements will be used to determine the planet’s forced physical librations by tracking the motion of large-scale topographic features as a function of time. MLA’s laser pulse energy monitor and the echo pulse energy estimate will provide an active measurement of the surface reflectivity at 1,064 nm. This paper describes the instrument design, prelaunch testing, calibration, and results of postlaunch testing.     

Gravity Recovery and Interior Laboratory (GRAIL): Mapping the Lunar Interior from Crust to Core

The Gravity Recovery and Interior Laboratory (GRAIL) is a spacecraft-to-spacecraft tracking mission that was developed to map the structure of the lunar interior by producing a detailed map of the gravity field. The resulting model of the interior will be used to address outstanding questions regarding the Moon’s thermal evolution, and will be applicable more generally to the evolution of all terrestrial planets. Each GRAIL orbiter contains a Lunar Gravity Ranging System instrument that conducts dual-one-way ranging measurements to measure precisely the relative motion between them, which in turn are used to develop the lunar gravity field map. Each orbiter also carries an Education/Public Outreach payload, Moon Knowledge Acquired by Middle-School Students (MoonKAM), in which middle school students target images of the Moon for subsequent classroom analysis. Subsequent to a successful launch on September 10, 2011, the twin GRAIL orbiters embarked on independent trajectories on a 3.5-month-long cruise to the Moon via the EL-1 Lagrange point. The spacecraft were inserted into polar orbits on December 31, 2011 and January 1, 2012. After a succession of 19 maneuvers the two orbiters settled into precision formation to begin science operations in March 1, 2012 with an average altitude of 55 km. The Primary Mission, which consisted of three 27.3-day mapping cycles, was successfully completed in June 2012. The extended mission will permit a second three-month mapping phase at an average altitude of 23 km. This paper provides an overview of the mission: science objectives and measurements, spacecraft and instruments, mission development and design, and data flow and data products.     

The Radio Frequency Subsystem and Radio Science on the MESSENGER Mission

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Radio Frequency (RF) Telecommunications Subsystem is used to send commands to the spacecraft, transmit information on the state of the spacecraft and science-related observations, and assist in navigating the spacecraft to and in orbit about Mercury by providing precise observations of the spacecraft’s Doppler velocity and range in the line of sight to Earth. The RF signal is transmitted and received at X-band frequencies (7.2 GHz uplink, 8.4 GHz downlink) by the NASA Deep Space Network. The tracking data from MESSENGER will contribute significantly to achieving the mission’s geophysics objectives. The RF subsystem, as the radio science instrument, will help determine Mercury’s gravitational field and, in conjunction with the Mercury Laser Altimeter instrument, help determine the topography of the planet. Further analysis of the data will improve the knowledge of the planet’s orbital ephemeris and rotation state. The rotational state determination includes refined measurements of the obliquity and forced physical libration, which are necessary to characterize Mercury’s core state.     

Galileo radio science investigations

The radio science investigations planned for Galileo's 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements will be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system used for these investigations is based on Voyager heritage but with several important additions and modifications that provide linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. Collaboration between the investigators and the space-craft communications engineers has resulted in the first highly-stable, dual-frequency, spacecraft radio system suitable for simultaneous measurements of all the parameters normally attributed to radio waves.     

Magnetic Cleanliness Program Under Control of Electromagnetic Compatibility for the SELENE (Kaguya) Spacecraft

To achieve the scientific objectives related to the lunar magnetic field measurements in a polar orbit at an altitude of 100 km, strict electromagnetic compatibility (EMC) requirements were applied to all components and subsystems of the SELENE (Kaguya) spacecraft. The magnetic cleanliness program was defined as one of the EMC control procedures, and magnetic tests were carried out for most of the engineering and flight models. The EMC performance of all components was systematically controlled and examined through a series of EMC tests. As a result, the Kaguya spacecraft was made to be very clean, magnetically. Hence reliable scientific data related to the magnetic field around the Moon were obtained by the LMAG (Lunar MAGnetometer) and the PACE (Plasma energy Angle and Composition Experiment) onboard the Kaguya spacecraft. These data have been available for lunar science use since November 2009.     

Towards a One Percent Measurement of Frame Dragging by Spin with Satellite Laser Ranging to LAGEOS, LAGEOS 2 and LARES and GRACE Gravity Models

During the past century Einstein’s theory of General Relativity gave rise to an experimental triumph; however, there are still aspects of this theory to be measured or more accurately tested. Today one of the main challenges in experimental gravitation, together with the direct detection of gravitational waves, is the accurate measurement of the gravitomagnetic field generated by the angular momentum of a body. Here, after a brief introduction on frame-dragging, gravitomagnetism and Lunar Laser Ranging tests, we describe the past measurements of frame-dragging by the Earth spin using the satellites LAGEOS, LAGEOS 2 and the Earth’s gravity models obtained by the GRACE project. We demonstrate that these measurements have an accuracy of approximately 10%. We then describe the LARES experiment to be launched in 2010 by the Italian Space Agency for a measurement of frame-dragging with an accuracy of a few percent. We finally demonstrate that a number of claims by a single individual, that the error budget of the frame-dragging measurements with LAGEOS-LAGEOS 2 and LARES has been underestimated, are indeed ill-founded.     

The Scientific Measurement System of the Gravity Recovery and Interior Laboratory (GRAIL) Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission that influenced and optimized the design, implementation, and testing of these elements. Because the two prime scientific observables, range between the two spacecraft and range rates between each spacecraft and ground stations, can be affected by the performance of any element of the mission, we treated every element as part of an extended science instrument, a science system. All simulations and modeling took into account the design and configuration of each element to compute the expected performance and error budgets. In the process, scientific requirements were converted to engineering specifications that became the primary drivers for development and testing. Extensive simulations demonstrated that the scientific objectives could in most cases be met with significant margin. Errors are grouped into dynamic or kinematic sources and the largest source of non-gravitational error comes from spacecraft thermal radiation. With all error models included, the baseline solution shows that estimation of the lunar gravity field is robust against both dynamic and kinematic errors and a nominal field of degree 300 or better could be achieved according to the scaled Kaula rule for the Moon. The core signature is more sensitive to modeling errors and can be recovered with a small margin.     

The Rosetta Lander (“Philae”) Investigations

The paper describes the Rosetta Lander named Philae and introduces its complement of scientific instruments. Philae was launched aboard the European Space Agency Rosetta spacecraft on 02 March 2004 and is expected to land and operate on the nucleus of 67P/Churyumov-Gerasimenko at a distance of about 3 AU from the Sun. Its overall mass is ~98 kg (plus the support systems remaining on the Orbiter), including its scientific payload of ~27 kg. It will operate autonomously, using the Rosetta Orbiter as a communication relay to Earth. The scientific goals of its experiments focus on elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus. In particular, surface and sub-surface samples will be acquired and sequentially analyzed by a suite of instruments. Measurements will be performed primarily during descent and along the first five days following touch-down. Philae is designed to also operate on a long time-scale, to monitor the evolution of the nucleus properties. Philae is a very integrated project at system, science and management levels, provided by an international consortium. The Philae experiments have the potential of providing unique scientific outcomes, complementing by in situ ground truth the Rosetta Orbiter investigations. Philae team members are listed in the acknowledgements     

Locating the LCROSS Impact Craters

The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated ～9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft’s trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of ?84.6796°, ?48.7093°, with a 1σ uncertainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is ?84.719°, ?49.61°, with a 1σ uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region.