共查询到20条相似文献,搜索用时 31 毫秒
1.
Peter H. Schultz Carolyn M. Ernst Jennifer L. B. Anderson 《Space Science Reviews》2005,117(1-2):207-239
The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the
surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet
9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will
provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments
performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes
for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key
scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded
particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation
applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse
of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters
could indicate unusually low density (< 0.3 g cm−3) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical
nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this
ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying
DI flyby instruments should provide critical data that will further resolve ambiguities. 相似文献
2.
Nikos Mastrodemos Daniel G. Kubitschek Stephen P. Synnott 《Space Science Reviews》2005,117(1-2):95-121
The engineering goal of the Deep Impact mission is to impact comet Tempel 1 on July 4, 2005, with a 370 kg active Impactor
spacecraft (s/c). The impact velocity will be just over 10 km/s and is expected to excavate a crater approximately 20 m deep
and 100 m wide. The Impactor s/c will be delivered to the vicinity of Tempel 1 by the Flyby s/c, which is also the key observing
platform for the event. Following Impactor release, the Flyby will change course to pass the nucleus at an altitude of 500
km and at the same time slow down in order to allow approximately 800 s of observation of the impact event, ejecta plume expansion,
and crater formation. Deep Impact will use the autonomous optical navigation (AutoNav) software system to guide the Impactor
s/c to intercept the nucleus of Tempel 1 at a location that is illuminated and viewable from the Flyby. The Flyby s/c uses
identical software to determine its comet-relative trajectory and provide the attitude determination and control system (ADCS)
with the relative position information necessary to point the High Resolution Imager (HRI) and Medium Resolution Imager (MRI)
instruments at the impact site during the encounter. This paper describes the Impactor s/c autonomous targeting design and
the Flyby s/c autonomous tracking design, including image processing and navigation (trajectory estimation and maneuver computation).
We also discuss the analysis that led to the current design, the expected system performance as compared to the key mission
requirements and the sensitivity to various s/c subsystems and Tempel 1 environmental factors. 相似文献
3.
K. J. Meech M. F. A’Hearn Y. R. Fernández C. M. Lisse H. A. Weaver N. Biver L. M. Woodney 《Space Science Reviews》2005,117(1-2):297-334
Prior to the selection of the comet 9P/Tempel 1 as the Deep Impact mission target, the comet was not well observed. From 1999 through the present there has been an intensive world-wide observing
campaign designed to obtain mission critical information about the target nucleus, including the nucleus size, albedo, rotation
rate, rotation state, phase function, and the development of the dust and gas coma. The specific observing schemes used to
obtain this information and the resources needed are presented here. The Deep Impact mission is unique in that part of the mission observations will rely on an Earth-based (ground and orbital) suite of complementary
observations of the comet just prior to impact and in the weeks following. While the impact should result in new cometary
activity, the actual physical outcome is uncertain, and the Earth-based observations must allow for a wide range of post-impact
phenomena. A world-wide coordinated effort for these observations is described. 相似文献
4.
Jessica M. Sunshine Michael F. A’Hearn Olivier Groussin Lucy A. McFadden Kenneth P. Klaasen Peter H. Schultz Carey M. Lisse 《Space Science Reviews》2005,117(1-2):269-295
The science payload on the Deep Impact mission includes a 1.05–4.8 μm infrared spectrometer with a spectral resolution ranging
from R∼200–900. The Deep Impact IR spectrometer was designed to optimize, within engineering and cost constraints, observations
of the dust, gas, and nucleus of 9P/Tempel 1. The wavelength range includes absorption and emission features from ices, silicates,
organics, and many gases that are known to be, or anticipated to be, present on comets. The expected data will provide measurements
at previously unseen spatial resolution before, during, and after our cratering experiment at the comet 9P/Tempel 1. This
article explores the unique aspects of the Deep Impact IR spectrometer experiment, presents a range of expectations for spectral
data of 9P/Tempel 1, and summarizes the specific science objectives at each phase of the mission. 相似文献
5.
Michael F. A’Hearn Michael J. S. Belton Alan Delamere William H. Blume 《Space Science Reviews》2005,117(1-2):1-21
The Deep Impact mission will provide the first data on the interior of a cometary nucleus and a comparison of those data with
data on the surface. Two spacecraft, an impactor and a flyby spacecraft, will arrive at comet 9P/Tempel 1 on 4 July 2005 to
create and observe the formation and final properties of a large crater that is predicted to be approximately 30-m deep with
the dimensions of a football stadium. The flyby and impactor instruments will yield images and near infrared spectra (1–5
μm) of the surface at unprecedented spatial resolutions both before and after the impact of a 350-kg spacecraft at 10.2 km/s.
These data will provide unique information on the structure of the nucleus near the surface and its chemical composition.
They will also used to interpret the evolutionary effects on remote sensing data and will indicate how those data can be used
to better constrain conditions in the early solar system. 相似文献
6.
Michael F. A’Hearn 《Space Science Reviews》2008,138(1-4):237-246
The Deep Impact mission revealed many properties of comet Tempel 1, a typical comet from the Jupiter family in so far as any comet can be considered typical. In addition to the properties revealed by the impact itself, numerous properties were also discovered from observations prior to the impact just because they were the types of observations that had never been made before. The impact showed that the cometary nucleus was very weak at scales from the impactor diameter (~1 m) to the crater diameter (~100 m) and suggested that the strength was low at much smaller scales as well. The impact also showed that the cometary nucleus is extremely porous and that the ice was close to the surface but below a devolatilized layer with thickness of order the impactor diameter. The ambient observations showed a huge range of topography, implying ubiquitous layering on many spatial scales, frequent (more than once a week) natural outbursts, many of them correlated with rotational phase, a nuclear surface with many features that are best interpreted as impact craters, and clear chemical heterogeneity in the outgassing from the nucleus. 相似文献
7.
Deep Impact Mission Design 总被引:1,自引:0,他引:1
William H. Blume 《Space Science Reviews》2005,117(1-2):23-42
The Deep Impact mission is designed to provide the first opportunity to probe below the surface of a comet nucleus by a high-speed
impact. This requires finding a suitable comet with launch and encounter conditions that allow a meaningful scientific experiment.
The overall design requires the consideration of many factors ranging from environmental characteristics of the comet (nucleus
size, dust levels, etc.), to launch dates fitting within the NASA Discovery program opportunities, to launch vehicle capability
for a large impactor, to the observational conditions for the two approaching spacecraft and for telescopes on Earth. 相似文献
8.
Kenneth P. Klaasen Brian Carcich Gemma Carcich Edwin J. Grayzeck Stephanie Mclaughlin 《Space Science Reviews》2005,117(1-2):335-372
A comprehensive observational sequence using the Deep Impact (DI) spacecraft instruments (consisting of cameras with two different
focal lengths and an infrared spectrometer) will yield data that will permit characterization of the nucleus and coma of comet
Tempel 1, both before and after impact by the DI Impactor. Within the constraints of the mission system, the planned data
return has been optimized. A subset of the most valuable data is planned for return in near-real time to ensure that the DI
mission success criteria will be met even if the spacecraft should not survive the comet’s closest approach. The remaining
prime science data will be played back during the first day after the closest approach. The flight data set will include approach
observations spanning the 60 days prior to encounter, pre-impact data to characterize the comet at high resolution just prior
to impact, photos from the Impactor as it plunges toward the nucleus surface (including resolutions exceeding 1 m), sub-second
time sampling of the impact event itself from the Flyby spacecraft, monitoring of the crater formation process and ejecta
outflow for over 10 min after impact, observations of the interior of the fully formed crater at spatial resolutions down
to a few meters, and high-phase lookback observations of the nucleus and coma for 60 h after closest approach. An inflight
calibration data set to accurately characterize the instruments’ performance is also planned. A ground data processing pipeline
is under development at Cornell University that will efficiently convert the raw flight data files into calibrated images
and spectral maps as well as produce validated archival data sets for delivery to NASA’s Planetary Data System within 6 months
after the Earth receipt for use by researchers world-wide. 相似文献
9.
Peter C. Thomas Joseph Veverka Michael F. A’Hearn Lucy Mcfadden Michael J. S. Belton Jessica M. Sunshine 《Space Science Reviews》2005,117(1-2):193-205
The Deep Impact mission will provide the highest resolution images yet of a comet nucleus. Our knowledge of the makeup and
structure of cometary nuclei, and the processes shaping their surfaces, is extremely limited, thus use of the Deep Impact
data to show the geological context of the cratering experiment is crucial. This article briefly discusses some of the geological
issues of cometary nuclei. 相似文献
10.
L. A. Mcfadden M. K. Rountree-Brown E. M. Warner S. A. M Claughlin J. M. Behne J. D. Ristvey S. Baird-Wilkerson D. K. Duncan S. D. Gillam G. H. Walker K. J. Meech 《Space Science Reviews》2005,117(1-2):373-396
The Deep Impact mission’s Education and Public Outreach (E/PO) program brings the principles of physics relating to the properties
of matter, motions and forces and transfer of energy to school-aged and public audiences. Materials and information on the
project web site convey the excitement of the mission, the principles of the process of scientific inquiry and science in
a personal and social perspective. Members of the E/PO team and project scientists and engineers, share their experiences
in public presentations and via interviews on the web. Programs and opportunities to observe the comet before, during and
after impact contribute scientific data to the mission and engage audiences in the mission, which is truly an experiment. 相似文献
11.
Donald L. Hampton James W. Baer Martin A. Huisjen Chris C. Varner Alan Delamere Dennis D. Wellnitz Michael F. A’Hearn Kenneth P. Klaasen 《Space Science Reviews》2005,117(1-2):43-93
A suite of three optical instruments has been developed to observe Comet 9P/Tempel 1, the impact of a dedicated impactor spacecraft,
and the resulting crater formation for the Deep Impact mission. The high-resolution instrument (HRI) consists of an f/35 telescope with 10.5 m focal length, and a combined filtered CCD camera and IR spectrometer. The medium-resolution instrument
(MRI) consists of an f/17.5 telescope with a 2.1 m focal length feeding a filtered CCD camera. The HRI and MRI are mounted on an instrument platform
on the flyby spacecraft, along with the spacecraft star trackers and inertial reference unit. The third instrument is a simple
unfiltered CCD camera with the same telescope as MRI, mounted within the impactor spacecraft. All three instruments use a
Fairchild split-frame-transfer CCD with 1,024× 1,024 active pixels. The IR spectrometer is a two-prism (CaF2 and ZnSe) imaging spectrometer imaged on a Rockwell HAWAII-1R HgCdTe MWIR array. The CCDs and IR FPA are read out and digitized
to 14 bits by a set of dedicated instrument electronics, one set per instrument. Each electronics box is controlled by a radiation-hard
TSC695F microprocessor. Software running on the microprocessor executes imaging commands from a sequence engine on the spacecraft.
Commands and telemetry are transmitted via a MIL-STD-1553 interface, while image data are transmitted to the spacecraft via a low-voltage differential signaling (LVDS) interface standard. The instruments are used as the science instruments and are
used for the optical navigation of both spacecraft. This paper presents an overview of the instrument suite designs, functionality,
calibration and operational considerations. 相似文献
12.
K. C. Hansen T. Bagdonat U. Motschmann C. Alexander M. R. Combi T. E. Cravens T. I. Gombosi Y.-D. Jia I. P. Robertson 《Space Science Reviews》2007,128(1-4):133-166
The plasma environment of comet 67P/Churyumov-Gerasimenko, the Rosetta mission target comet, is explored over a range of heliocentric
distances throughout the mission: 3.25 AU (Rosetta instruments on), 2.7 AU (Lander down), 2.0 AU, and 1.3 AU (perihelion).
Because of the large range of gas production rates, we have used both a fluid-based magnetohydrodynamic (MHD) model as well
as a semi-kinetic hybrid particle model to study the plasma distribution. We describe the variation in plasma environs over
the mission as well as the differences between the two modeling approaches under different conditions. In addition, we present
results from a field aligned, two-stream transport electron model of the suprathermal electron flux when the comet is near
perihelion. 相似文献
13.
A Coradini F. Capaccioni P. Drossart G. Arnold E. Ammannito F. Angrilli A. Barucci G. Bellucci J. Benkhoff G. Bianchini J. P. Bibring M. Blecka D. Bockelee-Morvan M. T. Capria R. Carlson U. Carsenty P. Cerroni L. Colangeli M. Combes M. Combi J. Crovisier M. C. Desanctis E. T. Encrenaz S. Erard C. Federico G. Filacchione U. Fink S. Fonti V. Formisano W. H. Ip R. Jaumann E. Kuehrt Y. Langevin G. Magni T. Mccord V. Mennella S. Mottola G. Neukum P. Palumbo G. Piccioni H. Rauer B. Saggin B. Schmitt D. Tiphene G. Tozzi 《Space Science Reviews》2007,128(1-4):529-559
The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe
for Planetary Exploration. VIRTIS, developed in cooperation among Italy, France and Germany, has been already selected as
a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus
Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully
observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars
in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison
– using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative
of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship
with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed
to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the
comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will
be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload
of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral
bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification
of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent
of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied. 相似文献
14.
鸟体撞击结构过程的相似律研究(英文) 总被引:2,自引:0,他引:2
Li Yulong* Zhang Yongkang Xue Pu School of Aeronautics Northwestern Polytechnical University Xi’an China 《中国航空学报》2008,21(6):512-517
With dimensional analysis and similarity theory, the model similarity law of aircraft structures trader bird impact load is investigated. Numerical calculations by means of nonlinear dynamic software ANSYS/LS-DYNA are conducted on the finite element models constructed with different scaling factors. The influence of strain rate on the model similarity law is found to be dependent on the strain rate sensitivity of materials and scale factors. Specifically, materials that are not sensitive to strain rate obey the model similarity law in the bird impact process. The conclusions obtained are supposed to provide a theoretical basis for the experimental work of bird impact on aircraft structure. 相似文献
15.
Cratering Records in the Inner Solar System in Relation to the Lunar Reference System 总被引:5,自引:0,他引:5
The well investigated size-frequency distributions (SFD) for lunar craters is used to estimate the SFD for projectiles which formed craters on terrestrial planets and on asteroids. The result shows the relative stability of these distributions during the past 4 Gyr. The derived projectile size-frequency distribution is found to be very close to the size-frequency distribution of Main-Belt asteroids as compared with the recent Spacewatch asteroid data and astronomical observations (Palomar-Leiden survey, IRAS data) as well as data from close-up imagery by space missions. It means that asteroids (or, more generally, collisionally evolved bodies) are the main component of the impactor family. Lunar crater chronology models of the authors published elsewhere are reviewed and refined by making use of refinements in the interpretation of radiometric ages and the improved lunar SFD. In this way, a unified cratering chronology model is established which can be used as a safe basis for modeling the impact chronology of other terrestrial planets, especially Mars. 相似文献
16.
S. A. Stern D. C. Slater J. Scherrer J. Stone M. Versteeg M. F. A’hearn J. L. Bertaux P. D. Feldman M. C. Festou Joel Wm. Parker O. H. W. Siegmund 《Space Science Reviews》2007,128(1-4):507-527
We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700–2050 Å spectral band with a spectral resolution between 8 Å and 12 Å for extended sources that fill its ~0.05^ × 6.0^ field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a toroidal concave holographic reflection grating. The microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a two-dimensional delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating well in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet C/2002 T7 (LINEAR) in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaign. 相似文献
17.
G. Klingelhöfer J. Brückner C. D’uston R. Gellert R. Rieder 《Space Science Reviews》2007,128(1-4):383-396
The Alpha Particle X-Ray Spectrometer (APXS) is a small instrument to determine the elemental composition of a given sample.
For the ESA Rosetta mission, the periodical comet 67P/Churyumov-Gerasimenko was selected as the target comet, where the lander
PHILAE (after landing) will carry out in-situ observations. One of the instruments onboard is the APXS to make measurements
on the landing site. The APXS science goal is to provide basic compositional data of the comet surface. As comets consist
of a mixture of ice and dust, the dust component can be characterized and compared with known meteoritic compositions. Various
element ratios can be used to evaluate whether chemical fractionations occurred in cometary material by comparing them with
known chondritic material. To enable observations of the local environment, APXS measurements of several spots on the surface
and one spot as function of temperature can be made. Repetitive measurements as function of heliocentric distance can elucidate
thermal processes at work. By measuring samples that were obtained by drilling subsurface material can be analyzed. The accumulated
APXS data can be used to shed light on state, evolution, and origin of 67P/Churyumov- Gerasimenko. 相似文献
18.
L. Colangeli J. J. Lopez-Moreno P. Palumbo J. Rodriguez M. Cosi V. Della Corte F. Esposito M. Fulle M. Herranz J. M. Jeronimo A. Lopez-Jimenez E. Mazzotta Epifani R. Morales F. Moreno E. Palomba A. Rotundi 《Space Science Reviews》2007,128(1-4):803-821
The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted
to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the
dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and
time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation
or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The
coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma
evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure
mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10−10 ÷ 4.0 × 10−4 kg m s−1 for velocities up to about 300 m s−1. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10−10 g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties
in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts
demonstrate that GIADA is behaving as expected according to the design specifications.
The International GIADA Consortium (I, E, UK, F, D, USA). 相似文献
19.
Boris A. Ivanov 《Space Science Reviews》2001,96(1-4):87-104
This article presents a method to adapt the lunar production function, i.e. the frequency of impacts with a given size of a formed crater as discussed by Neukum et al. (2001), to Mars. This requires to study the nature of crater-forming projectiles, the impact rate difference, and the scaling laws for the impact crater formation. These old-standing questions are reviewed, and examples for the re-calculation of the production function from the moon to Mars are given. 相似文献
20.
Since its discovery in 1867, periodic comet 9P/Tempel 1 has been observed at 10 returns to perihelion, including all its returns
since 1967. The observations for the seven apparitions beginning in 1967 have been fit with an orbit that includes only radial
and transverse nongravitational accelerations that model the rocket-like thrusting introduced by the outgassing of the cometary
nucleus. The successful nongravitational acceleration model did not assume any change in the comet’s ability to outgas from
one apparition to the next and the outgassing was assumed to reach a maximum at perihelion. The success of this model over
the 1967–2003 interval suggests that the comet’s spin axis is currently stable. Rough calculations suggest that the collision
of the impactor released by the Deep Impact spacecraft will not provide a noticeable perturbation on the comet’s orbit nor
will any new vent that is opened as a result of the impact provide a noticeable change in the comet’s nongravitational acceleration
history. The observing geometries prior to, and during, the impact will allow extensive Earth based observations to complement
the in situ observations from the impactor and flyby spacecraft. 相似文献