DOCSLIB.ORG

What Grail Teaches Us About Error and Bias in Preliminary Gravity Fields

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
What Grail Teaches Us About Error and Bias in Preliminary Gravity Fields WHAT GRAIL TEACHES US ABOUT ERROR AND BIAS IN PRELIMINARY GRAVITY FIELDS Peter B. James1,2 J. C. Andrews-Hanna3, and M. T. Zuber4 ! LPSC 48 – March 2017! 1The Lunar and Planetary Institute, Houston, TX, 77058, USA ([email protected]); " 2Department of Geosciences, Baylor University, Waco, TX, 76798, USA; " 3Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, 85721, USA; " 4Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.! The problem: biased gravity fields Model A – White noise at orbit altitude What this method is, and what it is not ! The Gravity Recovery And Interior Laboratory mission (GRAIL) determined the Moon's The presence of noise increases the unfiltered gravity power by a factor nl:! !The described gravity enhancement technique (specifically Model B) relies on an gravity field to a high precision: the RMS amplitude of gravity exceeds that of the error by a factor ! extrapolation of the true gravity RMS to high spherical harmonic degrees using a power − 1 β 2(l−l ) 2 !!!!!!!!!s (5)! law, so this technique should be used cautiously for a low-resolution gravity field (l < of more than 10,000 at spherical harmonic degree l=180 [1,2]. The GRAIL gravity field may be ⎡ ⎛ l ⎞ ⎛ r ⎞ ⎤ max n ⎢1 s 0 ⎥ l = + ⎜ ⎟ ⎜ ⎟ treated as exact for all practical purposes, and this allows us to retrospectively analyze past ⎢ l a ⎥ 50). The technique also does not account for spatial variations in degree strength. ! ⎢ ⎝ ⎠ ⎝ ⎠ ⎥ gravity fields in light of the "true" gravity. In this study we analyze the LPE200 gravity field from ⎣ ⎦ !There is no trick that allows us to remove noise from a gravity dataset; note that Lunar Prospector (LP) [3]. We focus on the nearside using a bandwidth L=2 Slepian taper [4].! while we can improve admittance, we cannot improve the gravity/topography correlation. r0 – a! Error in LP gravity (i.e. the departure from GRAIL gravity) is positively correlated with GRAIL However, gravity enhancement allows us to reverse the biasing effect that results from gravity at high spherical harmonic degrees (Fig. 1). We call this "bias". Equivalently, the gravity/ data noise, an effect which hinders certain geophysical analyses. Additionally, topography admittance spectrum is biased toward zero. Such a bias in gravity/topography ratios enhancement is expected to come at a cost of higher RMS errors (since the field is detrimental to a variety of geophysical analyses, including determinations of compensation amplitude increases).! depth and crustal density.! 1 ! 0.9 An optimized gravity field is a 1 balance between minimized 0.8 0.5 error and unbiased estimation. “bias”! Minimized ! 0.7 Published gravity fields often Unbiased! 0 RMS Error! 0.6 GRAIL prioritize the reduction of RMS Estimation! −0.5 GRAIL + Noise error, but “enhanced” gravity Lunar Prospector 0.5 Lunar Prospector Error Correlation aims to minimize bias.! −1 0 20 40 60 80 100 120 140 160 180 Gravity/Topography Correlation 0.4 40 60 80 100 120 140 160 180 Spherical Harmonic Degree Spherical Harmonic Degree Figure 1. Correlation of Lunar Prospector error with true gravity! HOWEVER, even though the enhancement technique prioritizes unbiased estimation over Figure 2. Decline in LP correlation predicted using Model A! error reduction, Figure 5 shows that we can actually reduce RMS error in the Lunar Prospector gravity field by applying enhancement (Note that this is generally not expected to The solution: gravity “enhancement” Model B – Underestimation of power be the case):! ) 1 We will show that bias in the LP gravity field can largely be explained using two models: random 2 a) b) data noise and an underestimation of gravity power. Furthermore, we propose an analysis technique called "enhancement", the purpose of which is to reduce bias a gravity field. When applied to the LP gravity field, this technique reduces RMS error and improves the high-degree 0.1 admittance.! ! Gravity is detected at the altitude of the orbiting spacecraft (which, for simplicity, we GRAIL represent as a single radial position r=r0), and these detections are obscured by random noise I. Lunar Prospector If I is spectrally "white", the power spectral density is constant:! 0.01 Power Spectral Density (mgal 40 60 100 180 ! !!!!!!! !!!! (1)! Spherical Harmonic Degree I (r )2 ≈ N ! lm 0 l Figure 3. Comparison of GRAIL power and LP power! where Ilm(r0) is the spherical harmonic coefficient of I at r=r0, and angled brackets indicate expectation across spherical harmonic orders. The presence of noise in a gravity dataset Additionally, LP gravity power is underestimated by a factor pl:! 1 1 generally increases the power of an unconstrained gravity field, and the suppression of this !!!!!!!!!2 2 2 2 (6)! p = gobs gtrue 0 5 10 15 20 25 30 !!!!!l ( lm ) ! ( lm ) power (typically with a Kaula constraint) can be approximated as a degree-dependent filter nl. Error amplitude (mgal) The observed gravity gobs at the reference radius r=a is a downward continuation of the filtered We approximate pl for LP above l=120, where gravity power breaks from its Figure 5. a) Error in the LP gravity field expanded to l=140, with an RMS amplitude of 9.25 mgal across the lunar nearside; b) Error of the enhanced LP field, with an RMS amplitude of 8.59 mgal. ! gravity and noise from the spacecraft altitude:! log-linear trend. The denominator is an extrapolation of the best-fit power ! !!!!!!! l !!!! (2)! law for l=80–119, and the numerator is the power law fit for l=120–160.! gobs(a) gtrue(r ) I (r ) r a n lm = lm 0 + lm 0 ⋅ 0 ⋅ l Takeaways ! ( ) ( ) where n is:! l 1 Results (Model A + Model B) We’ve introduced a technique called “enhancement”, which improves gravity data ⎡ 2 2 2 ⎤ 2 ! !!!!!!n = gobs gtrue + I! !!!! (3)! for certain applications via a simple degree-wise scaling of the data.! l ⎢ ( ) ( ) ( ) ⎥ The enhanced gravity equals the observed gravity divided by n and p :! ! ⎣ ⎦ l l ! Here’s when to use it:! The observed gravity g typically has power comparable to g (see Model B for exceptions). obs true genhanced = gobs n ⋅ p !!!!!!!!! lm lm ( l l ) (7)! Gravity power may be approximated with a power law:! Do you want the most accurate estimate of Existing gravity fields are 120 ! !!!!!!2 ! !!!! (4)! gravity at an arbitrary point on the surface? generally acceptable! gtrue ≈ Al β ( lm ) 110 ! I.e., do you want to minimize RMS error?! (Fig. 5 notwithstanding) ! The Lunar Prospector spacecraft orbited with a mean altitude of 40 km at the end of its primary 100 mission and a mean altitude of 30 km during the extended mission, so we use an intermediate 90 Do you want an UNBIASED estimate of the value of r = 35 km. Error in the LP gravity approximately equals the amplitude of the gravity on An “enhanced” gravity ! 0 80 gravity amplitude such as for gravity/ field will be better! the lunar nearside at spherical harmonic degree 180, so we take this to be the degree strength ls. 70 topography comparisons?! For these parameter values, the filter nl nicely reproduces the high-degree decline in the Lunar GRAIL 60 Lunar Prospector Prospector gravity/topography correlation (Fig. 2). This demonstrates the efficacy of Model A. ! Admittance (mgal/km) Enhanced LP ! Noise amplifies the power of a gravity field, so the process of creating a gravity field 50 References typically involves suppression of high-degree power, often with a Kaula rule ($ = –2). However, 40 40 60 80 100 120 140 160 180 excessive or deficient suppression can cause the resulting gravity power to differ from the true Spherical Harmonic Degree [1] Goossens S. et al. (2014) LPSC, #1619. [2] Park R. S. et al. (2014) AGU, #G22A-01. [3] Han S.-C. power. The correction of gravity power is described by Model B.! Figure 4. GRAIL gravity, LP gravity, and the enhanced LP field! et al. (2011) Icarus 215, 455–459. [4] Wieczorek M. A. & Simons F. J (2007) J. Four. An. 15, 665–692.! .
Load more

Recommended publications
  • New Views of the Moon Enabled by Combined Remotely Sensed and Lunar Sample Data Sets, a Lunar Initiative
    New Views of the Moon Enabled by Combined Remotely Sensed and Lunar Sample Data Sets, A Lunar Initiative Using the hand tool on your Reader, click on the links below to view that particular section of the proposal. Proposal Summary Scientific/Technical/Management Objectives and Expected Significance Background and Impact Approach and Methodology: The Role of Integration in Fundamental Problems of Lunar Geoscience Workshop 2: New Views of the Moon II: Understanding the Moon Through the Integration of Diverse Datasets. Abstract Volume and Subsequent Publications Statement of Relevance Work Plan Potential Workshop (2000): Thermal and Magmatic Evolution of the Moon Potential Workshop (2001): Early Lunar Differentiation, Core Formation, Effects of Early Planetesimal Impacts, and the Origin of the Moon’s Global Asymmetry Potential Workshop (2002): Selection of Sites for Future Sample Return Capstone Publication Timeline for the New Views of the Moon Initiative Personnel: Initiative Management and Proposal Management References Facilities: The LPI Appendix 1. Workshop on New Views of the Moon: Integrated Remotely Sensed, Geophysical, and Sample Datasets. List of presentations Appendix 2. LPSC 30 (1999) special sessions related to the Lunar Initiative. List of presentations (oral and poster) Appendix 3. Lunar Initiative Steering Committee Web Note: This is the text of a proposal submitted on behalf of the Lunar Science Community to support ongoing workshops and activities associated with the CAPTEM Lunar Initiative. It was submitted in May, 1999, in response to the ROSS 99 NRA, which solicits such proposals to be submitted to the relevant research programs. This proposal was submitted jointly to Cosmo- chemistry and Planetary Geology and Geophysics.
    [Show full text]
  • Atlas V Launches LRO/LCROSS Mission Overview
    Atlas V Launches LRO/LCROSS Mission Overview Atlas V 401 Cape Canaveral Air Force Station, FL Space Launch Complex-41 AV-020/LRO/LCROSS United Launch Alliance is proud to be a part of the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater Observation and Sensing Satellite (LCROSS) mission with the National Aeronautics and Space Administration (NASA). The LRO/LCROSS mission marks the sixteenth Atlas V launch and the seventh flight of an Atlas V 401 configuration. LRO/LCROSS is a dual-spacecraft (SC) launch. LRO is a lunar orbiter that will investigate resources, landing sites, and the lunar radiation environment in preparation for future human missions to the Moon. LCROSS will search for the presence of water ice that may exist on the permanently shadowed floors of lunar polar craters. The LCROSS mission will use two Lunar Kinetic Impactors, the inert Centaur upper stage and the LCROSS SC itself, to produce debris plumes that may reveal the presence of water ice under spectroscopic analysis. My thanks to the entire Atlas team for its dedication in bringing LRO/LCROSS to launch, and to NASA for selecting Atlas for this ground-breaking mission. Go Atlas, Go Centaur, Go LRO/LCROSS! Mark Wilkins Vice President, Atlas Product Line Atlas V Launch History Flight Config. Mission Mission Date AV-001 401 Eutelsat Hotbird 6 21 Aug 2002 AV-002 401 HellasSat 13 May 2003 AV-003 521 Rainbow 1 17 Jul 2003 AV-005 521 AMC-16 17 Dec 2004 AV-004 431 Inmarsat 4-F1 11 Mar 2005 AV-007 401 Mars Reconnaissance Orbiter 12 Aug 2005 AV-010 551 Pluto New Horizons 19 Jan 2006 AV-008 411 Astra 1KR 20 Apr 2006 AV-013 401 STP-1 08 Mar 2007 AV-009 401 NROL-30 15 Jun 2007 AV-011 421 WGS SV-1 10 Oct 2007 AV-015 401 NROL-24 10 Dec 2007 AV-006 411 NROL-28 13 Mar 2008 AV-014 421 ICO G1 14 Apr 2008 AV-016 421 WGS-2 03 Apr 2009 Payload Fairing Number of Solid Atlas V Size (meters) Rocket Boosters Flight/Configuration Key AV-XXX ### Number of Centaur Engines 3-digit Tail Number 3-digit Configuration Number LRO Overview LRO is the first mission in NASA’s planned return to the Moon.
    [Show full text]
  • Protons in the Near Lunar Wake Observed by the SARA Instrument on Board Chandrayaan-1
    FUTAANA ET AL. PROTONS IN DEEP WAKE NEAR MOON 1 Protons in the Near Lunar Wake Observed by the SARA 2 Instrument on Board Chandrayaan-1 3 Y. Futaana, 1 S. Barabash, 1 M. Wieser, 1 M. Holmström, 1 A. Bhardwaj, 2 M. B. Dhanya, 2 R. 4 Sridharan, 2 P. Wurz, 3 A. Schaufelberger, 3 K. Asamura 4 5 --- 6 Y. Futaana, Swedish Institute of Space Physics, Box 812, Kiruna, SE-98128, Sweden. 7 ([email protected]) 8 9 10 1 Swedish Institute of Space Physics, Box 812, Kiruna, SE-98128, Sweden 11 2 Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum 695 022, India 12 3 Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland 13 4 Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Japan 14 Index Terms 15 6250 Moon 16 5421 Interactions with particles and fields 17 2780 Magnetospheric Physics: Solar wind interactions with unmagnetized bodies 18 7807 Space Plasma Physics: Charged particle motion and acceleration 19 Abstract 20 Significant proton fluxes were detected in the near wake region of the Moon by an ion mass 21 spectrometer on board Chandrayaan-1. The energy of these nightside protons is slightly higher than 22 the energy of the solar wind protons. The protons are detected close to the lunar equatorial plane at 23 a 140˚ solar zenith angle, i.e., ~50˚ behind the terminator at a height of 100 km. The protons come 24 from just above the local horizon, and move along the magnetic field in the solar wind reference 25 frame.
    [Show full text]
  • Global Mapping of Elemental Abundance on Lunar Surface by SELENE Gamma-Ray Spectrometer
    Lunar and Planetary Science XXXVI (2005) 2092.pdf Global Mapping of elemental abundance on lunar surface by SELENE gamma-ray spectrometer. 1M. -N. Kobayashi, 1A. A. Berezhnoy, 6C. d’Uston, 1M. Fujii, 1N. Hasebe, 3T. Hiroishi, 4H. Kaneko, 1T. Miyachi, 5K. Mori, 6S. Maurice, 4M. Nakazawa, 3K. Narasaki, 1O. Okudaira, 1E. Shibamura, 2T. Takashima, 1N. Yamashita, 1Advanced Research Institute of Sci.& Eng., Waseda Univ., 3-4-1, Okubo, Shinjuku-ku, Tokyo, 169-8555, Japan, (masa- [email protected]), 2Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510, 3Niihama Works, Sumitomo Heavy Industry Ltd., Niihama, Ehime, Japan, Moriya Works, 4Meisei Electric Co., Ltd., 3-249-1, Yuri-ga-oka, Moriya-shi, Ibaraki, 302-0192, 5Clear Pulse Co., 6-25-17, Chuo, Ohta-ku, Tokyo, Japan, 143-0024, 6Centre d’Etude Spatiale des Rayonnements, CNRS/UPS, Colonel Roche, B.P 4346, France. Introduction: Elemental composition on the sur- face of a planet is very important information for solv- ing the origin and the evolution of the planet and also very necessary for understanding the origin and the evolution of solar system. Planetary gamma-ray spec- troscopy is extremely powerful approach for the ele- mental composition measurement. Gamma-ray spec- trometer (GRS) will be on board SELENE, advanced lunar polar orbiter, and employ a large-volume Ge detector of 252cc as the main detector [1]. SELENE GRS is, therefore, approximately twice more sensitiv- ity than Lunar Prospector GRS, four times more sensi- Figure 1: The schematic drawing of SELENE Gamma- tive than APOLLO GRS.
    [Show full text]
  • Mission Design for the Lunar Reconnaissance Orbiter
    AAS 07-057 Mission Design for the Lunar Reconnaissance Orbiter Mark Beckman Goddard Space Flight Center, Code 595 29th ANNUAL AAS GUIDANCE AND CONTROL CONFERENCE February 4-8, 2006 Sponsored by Breckenridge, Colorado Rocky Mountain Section AAS Publications Office, P.O. Box 28130 - San Diego, California 92198 AAS-07-057 MISSION DESIGN FOR THE LUNAR RECONNAISSANCE ORBITER † Mark Beckman The Lunar Reconnaissance Orbiter (LRO) will be the first mission under NASA’s Vision for Space Exploration. LRO will fly in a low 50 km mean altitude lunar polar orbit. LRO will utilize a direct minimum energy lunar transfer and have a launch window of three days every two weeks. The launch window is defined by lunar orbit beta angle at times of extreme lighting conditions. This paper will define the LRO launch window and the science and engineering constraints that drive it. After lunar orbit insertion, LRO will be placed into a commissioning orbit for up to 60 days. This commissioning orbit will be a low altitude quasi-frozen orbit that minimizes stationkeeping costs during commissioning phase. LRO will use a repeating stationkeeping cycle with a pair of maneuvers every lunar sidereal period. The stationkeeping algorithm will bound LRO altitude, maintain ground station contact during maneuvers, and equally distribute periselene between northern and southern hemispheres. Orbit determination for LRO will be at the 50 m level with updated lunar gravity models. This paper will address the quasi-frozen orbit design, stationkeeping algorithms and low lunar orbit determination. INTRODUCTION The Lunar Reconnaissance Orbiter (LRO) is the first of the Lunar Precursor Robotic Program’s (LPRP) missions to the moon.
    [Show full text]
  • Planetary Science
    Mission Directorate: Science Theme: Planetary Science Theme Overview Planetary Science is a grand human enterprise that seeks to discover the nature and origin of the celestial bodies among which we live, and to explore whether life exists beyond Earth. The scientific imperative for Planetary Science, the quest to understand our origins, is universal. How did we get here? Are we alone? What does the future hold? These overarching questions lead to more focused, fundamental science questions about our solar system: How did the Sun's family of planets, satellites, and minor bodies originate and evolve? What are the characteristics of the solar system that lead to habitable environments? How and where could life begin and evolve in the solar system? What are the characteristics of small bodies and planetary environments and what potential hazards or resources do they hold? To address these science questions, NASA relies on various flight missions, research and analysis (R&A) and technology development. There are seven programs within the Planetary Science Theme: R&A, Lunar Quest, Discovery, New Frontiers, Mars Exploration, Outer Planets, and Technology. R&A supports two operating missions with international partners (Rosetta and Hayabusa), as well as sample curation, data archiving, dissemination and analysis, and Near Earth Object Observations. The Lunar Quest Program consists of small robotic spacecraft missions, Missions of Opportunity, Lunar Science Institute, and R&A. Discovery has two spacecraft in prime mission operations (MESSENGER and Dawn), an instrument operating on an ESA Mars Express mission (ASPERA-3), a mission in its development phase (GRAIL), three Missions of Opportunities (M3, Strofio, and LaRa), and three investigations using re-purposed spacecraft: EPOCh and DIXI hosted on the Deep Impact spacecraft and NExT hosted on the Stardust spacecraft.
    [Show full text]
  • The Lunar Dust-Plasma Environment Is Crucial
    TheThe LunarLunar DustDust --PlasmaPlasma EnvironmentEnvironment Timothy J. Stubbs 1,2 , William M. Farrell 2, Jasper S. Halekas 3, Michael R. Collier 2, Richard R. Vondrak 2, & Gregory T. Delory 3 [email protected] Lunar X-ray Observatory(LXO)/ Magnetosheath Explorer (MagEX) meeting, Hilton Garden Inn, October 25, 2007. 1 University of Maryland, Baltimore County 2 NASA Goddard Space Flight Center 3 University of California, Berkeley TheThe ApolloApollo AstronautAstronaut ExperienceExperience ofof thethe LunarLunar DustDust --PlasmaPlasma EnvironmentEnvironment “… one of the most aggravating, restricting facets of lunar surface exploration is the dust and its adherence to everything no matter what kind of material, whether it be skin, suit material, metal, no matter what it be and it’s restrictive friction-like action to everything it gets on. ” Eugene Cernan, Commander Apollo 17. EvidenceEvidence forfor DustDust AboveAbove thethe LunarLunar SurfaceSurface Horizon glow from forward scattered sunlight • Dust grains with radius of 5 – 6 m at about 10 to 30 cm from the surface, where electrostatic and gravitational forces balance. • Horizon glow ~10 7 too bright to be explained by micro-meteoroid- generated ejecta [Zook et al., 1995]. Composite image of morning and evening of local western horizon [Criswell, 1973]. DustDust ObservedObserved atat HighHigh AltitudesAltitudes fromfrom OrbitOrbit Schematic of situation consistent with Apollo 17 observations [McCoy, 1976]. Lunar dust at high altitudes (up to ~100 km). 0.1 m-scale dust present Gene Cernan sketches sporadically (~minutes). [McCoy and Criswell, 1974]. InIn --SituSitu EvidenceEvidence forfor DustDust TransportTransport Terminators Berg et al. [1976] Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment. PossiblePossible DustyDusty HorizonHorizon GlowGlow seenseen byby ClementineClementine StarStar Tracker?Tracker? Above: image of possible horizon glow above the lunar surface.
    [Show full text]
  • The Moon and Eclipses
    Lecture 10 The Moon and Eclipses Jiong Qiu, MSU Physics Department Guiding Questions 1. Why does the Moon keep the same face to us? 2. Is the Moon completely covered with craters? What is the difference between highlands and maria? 3. Does the Moon’s interior have a similar structure to the interior of the Earth? 4. Why does the Moon go through phases? At a given phase, when does the Moon rise or set with respect to the Sun? 5. What is the difference between a lunar eclipse and a solar eclipse? During what phases do they occur? 6. How often do lunar eclipses happen? When one is taking place, where do you have to be to see it? 7. How often do solar eclipses happen? Why are they visible only from certain special locations on Earth? 10.1 Introduction The moon looks 14% bigger at perigee than at apogee. The Moon wobbles. 59% of its surface can be seen from the Earth. The Moon can not hold the atmosphere The Moon does NOT have an atmosphere and the Moon does NOT have liquid water. Q: what factors determine the presence of an atmosphere? The Moon probably formed from debris cast into space when a huge planetesimal struck the proto-Earth. 10.2 Exploration of the Moon Unmanned exploration: 1950, Lunas 1-3 -- 1960s, Ranger -- 1966-67, Lunar Orbiters -- 1966-68, Surveyors (first soft landing) -- 1966-76, Lunas 9-24 (soft landing) -- 1989-93, Galileo -- 1994, Clementine -- 1998, Lunar Prospector Achievement: high-resolution lunar surface images; surface composition; evidence of ice patches around the south pole.
    [Show full text]
  • Lunar Occultation Observer (LOCO)
    Ex Luna, Scientia From the Moon, Knowledge Lunar Occultation Observer (LOCO) A Nuclear Astrophysics All-Sky Survey Mission Concept using the Moon as a Platform for Science A White Paper Submission to Planetary Science Decadal Survey April 1, 2009 Contact: RICHARD S. MILLER University of Alabama in Huntsville [email protected] (256) 824-2454 M. Bonamente, S. O’Brien, W. S. Paciesas University of Alabama in Huntsville D. J. Lawrence Johns Hopkins University/Applied Physics Laboratory C. A. Young ADNET Systems/NASA-GSFC D. Ebbets Ball Aerospace R.S. Miller, UAH Lunar Occultation Observer (LOCO) Ex Luna, Scientia From the Moon, Knowledge Summary The long-term goal of our program is the development of a next-generation mission capable of surveying the Cosmos in the nuclear regime (~0.02-10 MeV). The Lunar Occultation Observer (LOCO) [1-3] is a new γ-ray astrophysics mission concept having unprecedented flux sensitivity, high spectral resolution, excellent spatial resolution, and very uniform sky coverage. It meets or exceeds the capabilities required of the next-generation nuclear astrophysics mission, and is therefore capable of addressing multiple high-priority science goals. LOCO will be a pioneering mission in high-energy astrophysics: the first to utilize the moon as a scientific platform, and the first to successfully employ occultation imaging as the principle detec- tion method. This is a powerful, yet relatively simple, approach to imaging in regimes where traditional imaging approaches are inappropriate, complex, or cost prohibitive. Specifically, LOCO will utilize the Lunar Occultation Technique (LOT) - the temporal modulation of source fluxes as the are repeatedly occulted by the Moon - to detect and image both point- and extended-sources.
    [Show full text]
  • 02. Solar System (2001) 9/4/01 12:28 PM Page 2
    01. Solar System Cover 9/4/01 12:18 PM Page 1 National Aeronautics and Educational Product Space Administration Educators Grades K–12 LS-2001-08-002-HQ Solar System Lithograph Set for Space Science This set contains the following lithographs: • Our Solar System • Moon • Saturn • Our Star—The Sun • Mars • Uranus • Mercury • Asteroids • Neptune • Venus • Jupiter • Pluto and Charon • Earth • Moons of Jupiter • Comets 01. Solar System Cover 9/4/01 12:18 PM Page 2 NASA’s Central Operation of Resources for Educators Regional Educator Resource Centers offer more educators access (CORE) was established for the national and international distribution of to NASA educational materials. NASA has formed partnerships with universities, NASA-produced educational materials in audiovisual format. Educators can museums, and other educational institutions to serve as regional ERCs in many obtain a catalog and an order form by one of the following methods: States. A complete list of regional ERCs is available through CORE, or electroni- cally via NASA Spacelink at http://spacelink.nasa.gov/ercn NASA CORE Lorain County Joint Vocational School NASA’s Education Home Page serves as a cyber-gateway to informa- 15181 Route 58 South tion regarding educational programs and services offered by NASA for the Oberlin, OH 44074-9799 American education community. This high-level directory of information provides Toll-free Ordering Line: 1-866-776-CORE specific details and points of contact for all of NASA’s educational efforts, Field Toll-free FAX Line: 1-866-775-1460 Center offices, and points of presence within each State. Visit this resource at the E-mail: [email protected] following address: http://education.nasa.gov Home Page: http://core.nasa.gov NASA Spacelink is one of NASA’s electronic resources specifically devel- Educator Resource Center Network (ERCN) oped for the educational community.
    [Show full text]
  • Stationkeeping for the Lunar Reconnaissance Orbiter (Lro)
    https://ntrs.nasa.gov/search.jsp?R=20080012683 2019-08-29T19:07:49+00:00Z View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by NASA Technical Reports Server STATIONKEEPING FOR THE LUNAR RECONNAISSANCE ORBITER (LRO) Mark Beckman 1 and Rivers Lamb 2 The Lunar Reconnaissance Orbiter (LRO) is scheduled to launch in 2008 as the first mission under NASA’s Vision for Space Exploration. Following several weeks in a quasi-frozen commissioning orbit, LRO will fly in a 50 km mean altitude lunar polar orbit. During the one year mission duration, the orbital dynamics of a low lunar orbit force LRO to perform periodic sets of stationkeeping maneuvers. This paper explores the characteristics of low lunar orbits and explains how the LRO stationkeeping plan is designed to accommodate the dynamics in such an orbit. The stationkeeping algorithm used for LRO must meet five mission constraints. These five constraints are to maintain ground station contact during maneuvers, to control the altitude variation of the orbit, to distribute periselene equally between northern and southern hemispheres, to match eccentricity at the beginning and the end of the sidereal period, and to minimize stationkeeping ∆V. This paper addresses how the maneuver plan for LRO is designed to meet all of the above constraints. INTRODUCTION The Lunar Reconnaissance Orbiter (LRO) is the first mission under NASA’s Vision for Space Exploration. LRO will launch on an Atlas V launch vehicle in late 2008 using a direct minimum energy transfer to reach the moon. The spacecraft has a one year mission duration in a low lunar polar orbit.
    [Show full text]
  • Physics of Solar Wind and Terrestrial Magnetospheric Plasma Interactions with the Moon
    Physics of Solar Wind and Terrestrial Magnetospheric Plasma Interactions With the Moon R.P. Lin Physics Dept & Space Sciences Laboratory University of California, Berkeley with help from J. Halekas, M. Oieroset, & M. Fillingim Plasma Interaction with the Moon and Dust Plasma Physics of the Distant Magnetotail Plasma Interaction with Mini-Magnetospheres The Lunar Environment Dipolar E-Fields? Extreme Surface Charging Surface potentials of up to several kV (negative) found: • In the terrestrial plasmasheet, where 4 KeV Beam we encounter high plasma temperature. • During Solar Energetic Particle events Frequency of Extreme Charging Events During the Entire Lunar Prospector Mission • Green in color bar indicates magnetospheric tail passages, red indicates major SEP events The Earth’s magnetic shield DuringBefore reconnectionreconnection Dungey, Philos. Mag. 55, (1953) Wind observed 10 hours of reconnection flows at lunar distance (XGSE=-60 RE) lobe NP plasma Wind alternately inside plasma sheet sheet and lobe High speed reconnection flows always TP observed when the spacecraft was in the plasma sheet → 10 hours of continuous reconnection VX High speed Reconnection flows Bx Bz B (GSM) (Oieroset et al., 2000) By Wind satellite observations in distant magnetotail, 60RE • Measurements within the ion diffusion region reveal: Strong anisotropy in fe. Log(f) M. Øieroset et al. Nature 412, (2001) M. Øieroset et al. PRL 89, (2002) A trapped electron in the magnetotail mv 2 m(v2 - v 2 ) The magnetic moment: µ = ! = || 2B 2B Drift kinetic modeling of Wind data • Applying f(x0,v0) = f∞(|v1|) to an X-line geometry consistent with the Wind measurements • A potential,Φ∞ needed for trapping at low energies • Ion outflow: 400 km/s, consistent with acceleration in Φ ∞ ~ -300V Φ∞ Theory Wind Φ∞~ -800V Φ∞~ -1150V J.
    [Show full text]