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41.
I. Yoshikawa A. Yamazaki T. Murachi S. Kameda H. Sagawa S. Okano T. Okada M. Nakamura 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(12):2195-2199
Extreme and far ultraviolet imaging spectrometers are proposed for the low-altitude orbiter of the BepiColombo mission. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring (1) emission lines from molecules, atoms and ions present in the Mercury’s tenuous atmosphere and (2) the reflectance spectrum of Mercury’s surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30–150 nm with the field of view of 5.0°, and the spectrum from 130 to 430 nm is obtained by the far UV spectrometer. The extreme UV spectrometer employs multi-layer coating technology to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signatures such as He II (30.4 nm) and Na II (37.2 nm), which could not be detected with conventional optics. 相似文献
42.
The Mercury Dual Imaging System on the MESSENGER Spacecraft 总被引:1,自引:0,他引:1
S. Edward Hawkins III John D. Boldt Edward H. Darlington Raymond Espiritu Robert E. Gold Bruce Gotwols Matthew P. Grey Christopher D. Hash John R. Hayes Steven E. Jaskulek Charles J. Kardian Jr. Mary R. Keller Erick R. Malaret Scott L. Murchie Patricia K. Murphy Keith Peacock Louise M. Prockter R. Alan Reiter Mark S. Robinson Edward D. Schaefer Richard G. Shelton Raymond E. Sterner II Howard W. Taylor Thomas R. Watters Bruce D. Williams 《Space Science Reviews》2007,131(1-4):247-338
The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin
and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC
is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color
filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled
device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and
the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward
from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel
binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at
Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission
angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor
images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct
a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips.
Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement
history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper
summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing
units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated
from MDIS data. 相似文献
43.
James V. McAdams Robert W. Farquhar Anthony H. Taylor Bobby G. Williams 《Space Science Reviews》2007,131(1-4):219-246
Nearly three decades after the Mariner 10 spacecraft’s third and final targeted Mercury flyby, the 3 August 2004 launch of
the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft began a new phase of exploration
of the closest planet to our Sun. In order to ensure that the spacecraft had sufficient time for pre-launch testing, the NASA
Discovery Program mission to orbit Mercury experienced launch delays that required utilization of the most complex of three
possible mission profiles in 2004. During the 7.6-year mission, the spacecraft’s trajectory will include six planetary flybys
(including three of Mercury between January 2008 and September 2009), dozens of trajectory-correction maneuvers (TCMs), and
a year in orbit around Mercury. Members of the mission design and navigation teams optimize the spacecraft’s trajectory, specify
TCM requirements, and predict and reconstruct the spacecraft’s orbit. These primary mission design and navigation responsibilities
are closely coordinated with spacecraft design limitations, operational constraints, availability of ground-based tracking
stations, and science objectives. A few days after the spacecraft enters Mercury orbit in mid-March 2011, the orbit will have
an 80° inclination relative to Mercury’s equator, a 200-km minimum altitude over 60°N latitude, and a 12-hour period. In order
to accommodate science goals that require long durations during Mercury orbit without trajectory adjustments, pairs of orbit-correction
maneuvers are scheduled every 88 days (once per Mercury year). 相似文献
44.
Dipak K. Srinivasan Mark E. Perry Karl B. Fielhauer David E. Smith Maria T. Zuber 《Space Science Reviews》2007,131(1-4):557-571
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. 相似文献
45.
H. Hayakawa Y. Kasaba H. Yamakawa H. Ogawa T. Mukai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(12):2142-2146
The Institute of Space and Astronautical Science (ISAS) of Japan plans to contribute the Mercury Magnetospheric Orbiter (MMO) to the BepiColombo program, the ESA Cornerstone mission to the planet Mercury. The principal objective of the MMO is to study the magnetic field and magnetosphere of Mercury. The ISAS Mercury exploration working group has performed the definition study of the MMO mission in cooperation with the ESA/ESTEC BepiColombo project team. This paper briefly reviews the scientific objectives, and describes the model payload and its operation plan. 相似文献
46.
Doris Breuer Steven A. Hauck II Monika Buske Martin Pauer Tilman Spohn 《Space Science Reviews》2007,132(2-4):229-260
The interior evolution of Mercury—the innermost planet in the solar system, with its exceptional high density—is poorly known.
Our current knowledge of Mercury is based on observations from Mariner 10’s three flybys. That knowledge includes the important
discoveries of a weak, active magnetic field and a system of lobate scarps that suggests limited radial contraction of the
planet during the last 4 billion years. We review existing models of Mercury’s interior evolution and further present new
2D and 3D convection models that consider both a strongly temperature-dependent viscosity and core cooling. These studies
provide a framework for understanding the basic characteristics of the planet’s internal evolution as well as the role of
the amount and distribution of radiogenic heat production, mantle viscosity, and sulfur content of the core have had on the
history of Mercury’s interior.
The existence of a dynamo-generated magnetic field suggests a growing inner core, as model calculations show that a thermally
driven dynamo for Mercury is unlikely. Thermal evolution models suggest a range of possible upper limits for the sulfur content
in the core. For large sulfur contents the model cores would be entirely fluid. The observation of limited planetary contraction
(∼1–2 km)—if confirmed by future missions—may provide a lower limit for the core sulfur content. For smaller sulfur contents,
the planetary contraction obtained after the end of the heavy bombardment due to inner core growth is larger than the observed
value. Due to the present poor knowledge of various parameters, for example, the mantle rheology, the thermal conductivity
of mantle and crust, and the amount and distribution of radiogenic heat production, it is not possible to constrain the core
sulfur content nor the present state of the mantle. Therefore, it is difficult to robustly predict whether or not the mantle
is conductive or in the convective regime. For instance, in the case of very inefficient planetary cooling—for example, as
a consequence of a strong thermal insulation by a low conductivity crust and a stiff Newtonian mantle rheology—the predicted
sulfur content can be as low as 1 wt% to match current estimates of planetary contraction, making deep mantle convection likely.
Efficient cooling—for example, caused by the growth of a crust strongly in enriched in radiogenic elements—requires more than
6.5 wt% S. These latter models also predict a transition from a convective to a conductive mantle during the planet’s history.
Data from future missions to Mercury will aid considerably our understanding of the evolution of its interior. 相似文献
47.
John F. Cavanaugh James C. Smith Xiaoli Sun Arlin E. Bartels Luis Ramos-Izquierdo Danny J. Krebs Jan F. McGarry Raymond Trunzo Anne Marie Novo-Gradac Jamie L. Britt Jerry Karsh Richard B. Katz Alan T. Lukemire Richard Szymkiewicz Daniel L. Berry Joseph P. Swinski Gregory A. Neumann Maria T. Zuber David E. Smith 《Space Science Reviews》2007,131(1-4):451-479
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. 相似文献
48.
John O. Goldsten Edgar A. Rhodes William V. Boynton William C. Feldman David J. Lawrence Jacob I. Trombka David M. Smith Larry G. Evans Jack White Norman W. Madden Peter C. Berg Graham A. Murphy Reid S. Gurnee Kim Strohbehn Bruce D. Williams Edward D. Schaefer Christopher A. Monaco Christopher P. Cork J. Del Eckels Wayne O. Miller Morgan T. Burks Lisle B. Hagler Steve J. DeTeresa Monika C. Witte 《Space Science Reviews》2007,131(1-4):339-391
A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery
Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched
successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation.
The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet
surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects
gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum
for 60Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide
the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the
intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft,
but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron
Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of
ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help
resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer
and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort,
and a look at some early in-flight data. 相似文献
49.
G. Cremonese A. Sprague J. Warell N. Thomas L. Ksamfomality 《Space Science Reviews》2007,132(2-4):291-306
The Mariner 10 spacecraft made three flyby passes of Mercury in 1974 and 1975. It imaged a little less than half of the surface
and discovered Mercury had an intrinsic magnetic field. This paper briefly describes the surface of Mercury as seen by Mariner
10 as a backdrop to the discoveries made since then by ground-based observations and the optimistic anticipation of new discoveries
by MESSENGER and BepiColombo spacecraft that are scheduled for encounter in the next decade. 相似文献
50.
A. Milillo P. Wurz S. Orsini D. Delcourt E. Kallio R. M. KILLEN H. Lammer S. Massetti A. Mura S. Barabash G. Cremonese I. A. Daglis E. De Angelis A. M. Di Lellis S. Livi V. Mangano K. Torkar 《Space Science Reviews》2005,117(3-4):397-443
Mercury is a poorly known planet, since the only space-based information comes from the three fly-bys performed in 1974 by
the Mariner 10 spacecraft. Ground-based observations also provided some interesting results, but they are particularly difficult
to obtain due to the planet’s proximity to the Sun. Nevertheless, the fact that the planet’s orbit is so close to the Sun
makes Mercury a particularly interesting subject for extreme environmental conditions. Among a number of crucial scientific
topics to be addressed, Mercury’s exosphere, its interaction with the solar wind and its origin from the surface of the planet,
can provide important clues about planetary evolution. In fact, the Hermean exosphere is continuously eroded and refilled
by these interactions, so that it would be more proper to consider the Hermean environment as a single, unified system – surface-exosphere-magnetosphere.
These three parts are indeed strongly linked to each other. In recent years, the two missions scheduled to explore the iron
planet, the NASA MESSENGER mission (launched in March 2004) and the ESA cornerstone mission (jointly with JAXA) BepiColombo
(to be launched in 2012), have stimulated new interest in the many unresolved mysteries related to it. New ground-based observations,
made possible by new technologies, have been obtained, and new simulation studies have been performed. In this paper some
old as well as the very latest observations and studies related to the surface-exosphere-magnetosphere system are reviewed,
outlining the investigations achievable by the planned space-based observations. This review intends to support the studies,
in preparation of future data, and the definition of specific instrumentation. 相似文献