国外火星飞机及火星风洞研究

在简述火星与地球大气飞行环境差异的基础上,分析研究了火星飞机主要布局特征和动力推进问题;阐述了国外开展火星飞机研究发展的地面模拟设备--火星风洞的情况,意在跟踪国外新技术走向,为国内航空航天未来发展提供参考.     

火星探测需要"勇气"与"机遇"

人类在40多年火星探测中,经历了无数次失败.但为了进一步探测这颗红色星球的奥秘,美国于今年6、7月又分别发射了"勇气"号和"机遇"号探测器,这两个探测器上安装了许多用于科研的测试仪器和设备,并采用了许多关键技术     

X-Rays From Mars

X-rays from Mars were first detected in July 2001 with the satellite Chandra. The main source of this radiation was fluorescent scattering of solar X-rays in its upper atmosphere. In addition, the presence of an extended X-ray halo was indicated, probably resulting from charge exchange interactions between highly charged heavy ions in the solar wind and neutrals in the Martian exosphere. The statistical significance of the X-ray halo, however, was very low. In November 2003, Mars was observed again in X-rays, this time with the satellite XMM-Newton. This observation, characterized by a considerably higher sensitivity, confirmed the presence of the X-ray halo and proved that charge exchange is indeed the origin of the emission. This was the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet. Previously, this kind of emission had been detected from comets (which are largely exospheres) and from the terrestrial exosphere. Because charge exchange interactions between atmospheric constituents and solar wind ions are considered as an important nonthermal escape mechanism, probably responsible for a significant loss of the Martian atmosphere, X-ray observations may lead to a better understanding of the present state of the Martian atmosphere and its evolution. X-ray images of the Martian exosphere in specific emission lines exhibited a highly anisotropic morphology, varying with individual ions and ionization states. With its capability to trace the X-ray emission out to at least 8 Mars radii, XMM-Newton can explore exospheric regions far beyond those that have been observationally explored to date. Thus, X-ray observations provide a novel method for studying processes in the Martian exosphere on a global scale.     

Mars Crustal Magnetism

Mars lacks a detectable magnetic field of global scale, but boasts a rich spectrum of magnetic fields at smaller spatial scales attributed to the spatial variation of remanent magnetism in the crust. On average the Mars crust is 10 times more intensely magnetized than that of the Earth. It appears likely that the Mars crust acquired its remanence in the first few hundred million years of evolution when an active dynamo sustained an intense global field. An early dynamo era, ending in the Noachian, or earliest period of Mars chronology, would likely be driven by thermal convection in an early, hot, fluid core. If crustal remanence was acquired later in Mars history, a dynamo driven by chemical convection associated with the solidification of an inner core is likely. Thermal evolution models cannot yet distinguish between these two possibilities. The magnetic record contains a wealth of information on the thermal evolution of Mars and the Mars dynamo, but we have just begun to decipher its message.     

Mars Global Surveyor Observations of Solar Wind Magnetic Field Draping Around Mars

We examine the magnetic field in the martian magnetosheath due to solar wind draping. Mars Global Surveyor provided 3-D vector magnetic field measurements at a large range of altitudes, local times, and solar zenith angles as the spacecraft orbit evolved. We choose orbits with very clean signatures of draping to establish the nominal morphology of the magnetic field lines at local times of near-subsolar and near-terminator. Next, using a compilation of data from Mars Global Surveyor, we determine the average magnetic field morphology in the martian magnetosheath due to the solar wind interaction. The topology of the field is as expected from previous observations and predictions. The magnetic field magnitude peaks at low altitude and noon magnetic local time and decreases away from that point. The magnetic field has an inclination from the local horizontal of 5.6° on average in the dayside magnetosheath and 12.5° on the nightside. The inclination angle is closest to zero at noon magnetic local time and low altitude. It increases both upward and to later local times. The magnetic field in the induced magnetotail flares out from the Mars—Sun direction by 21°. Finally, we compare the observations to gasdynamic model predictions and find that the shocked solar wind flow in the martian magnetosheath can be treated as a gasdynamic flow with the magnetic pileup boundary as the inner boundary to the flow.     

Mars Express and MARSIS

Space Science Reviews - The Mars Express mission to be launched in 2003 will provide high resolution measurements of the Martian atmosphere and ionosphere. The neutral density, temperature, and...     

Geophysical Constraints on the Evolution of Mars

The evolution of Mars is discussed using results from the recent Mars Global Surveyor (MGS) and Mars Pathfinder missions together with results from mantle convection and thermal history models and the chemistry of Martian meteorites. The new MGS topography and gravity data and the data on the rotation of Mars from Mars Pathfinder constrain models of the present interior structure and allow estimates of present crust thickness and thickness variations. The data also allow estimates of lithosphere thickness variation and heat flow assuming that the base of the lithosphere is an isotherm. Although the interpretation is not unambiguous, it can be concluded that Mars has a substantial crust. It may be about 50 km thick on average with thickness variations of another ±50 km. Alternatively, the crust may be substantially thicker with smaller thickness variations. The former estimate of crust thickness can be shown to be in agreement with estimates of volcanic production rates from geologic mapping using data from the camera on MGS and previous missions. According to these estimates most of the crust was produced in the Noachian, roughly the first Gyr of evolution. A substantial part of the lava generated during this time apparently poured onto the surface to produce the Tharsis bulge, the largest tectonic unit in the solar system and the major volcanic center of Mars. Models of crust growth that couple crust growth to mantle convection and thermal evolution are consistent with an early 1 Gyr long phase of vigorous volcanic activity. The simplest explanation for the remnant magnetization of crustal units of mostly the southern hemisphere calls for an active dynamo in the Noachian, again consistent with thermal history calculations that predict the core to become stably stratified after some hundred Myr of convective cooling and dynamo action. The isotope record of the Martian meteorites suggest that the core formed early and rapidly within a few tens of Myr. These data also suggest that the silicate rock component of the planet was partially molten during that time. The isotope data suggest that heterogeneity resulted from core formation and early differentiation and persisted to the recent past. This is often taken as evidence against vigorous mantle convection and early plate tectonics on Mars although the latter assumption can most easily explain the early magnetic field. The physics of mantle convection suggests that there may be a few hundred km thick stagnant, near surface layer in the mantle that would have formed rapidly and may have provided the reservoirs required to explain the isotope data. The relation between the planform of mantle convection and the tectonic features on the surface is difficult to entangle. Models call for long wavelength forms of flow and possibly a few strong plumes in the very early evolution. These plumes may have dissolved with time as the core cooled and may have died off by the end of the Noachian.     

Radar observations of Mars

Radar observations in the past were used to investigate the astronomical properties of the planet and its reflectivity in radar frequencies. Because of the difficulties in signal detection and processing due to the low level of return signal, the data were published only in the form of Doppler spectrograms. In view of the increasing interest in Mars and the practicability of missions to Mars this paper uses the published data to evaluate the angular behavior of the radar backscattering characteristics of Mars; a required information for the design of radar equipment of spacecrafts. In addition, results of past observations are summarized, analyzed and discussed in terms of a general interpretation of the Martian surface. It is found that the generally accepted suggestion that Mars is a relatively smooth planet, smoother than the Moon, is confirmed by most of the results, but not all observations agree with this hypothesis. A surface model of relief and composition based on radar information in conjunction with other observations is reviewed. The processing methods of radar return signals are compared for a better understanding of the handling of the Doppler spectrogram, a form which is most widely used for the presentation of processed data.An extensive bibliography of available papers and reports relevant to radar observations and the surface and lower atmosphere of Mars is included. The literature is concerned mainly with post-Mariner IV experiment, the mission which changed considerably many conceptions of Mars.     

Cratering Chronology and the Evolution of Mars

Results by Neukum et al. (2001) and Ivanov (2001) are combined with crater counts to estimate ages of Martian surfaces. These results are combined with studies of Martian meteorites (Nyquist et al., 2001) to establish a rough chronology of Martian history. High crater densities in some areas, together with the existence of a 4.5 Gyr rock from Mars (ALH84001), which was weathered at about 4.0 Gyr, affirm that some of the oldest surfaces involve primordial crustal materials, degraded by various processes including megaregolith formation and cementing of debris. Small craters have been lost by these processes, as shown by comparison with Phobos and with the production function, and by crater morphology distributions. Crater loss rates and survival lifetimes are estimated as a measure of average depositional/erosional rate of activity.We use our results to date the Martian epochs defined by Tanaka (1986). The high crater densities of the Noachian confine the entire Noachian Period to before about 3.5 Gyr. The Hesperian/Amazonian boundary is estimated to be about 2.9 to 3.3 Gyr ago, but with less probability could range from 2.0 to 3.4 Gyr. Mid-age dates are less well constrained due to uncertainties in the Martian cratering rate. Comparison of our ages with resurfacing data of Tanaka et al. (1987) gives a strong indication that volcanic, fluvial, and periglacial resurfacing rates were all much higher in approximately the first third of Martian history. We estimate that the Late Amazonian Epoch began a few hundred Myr ago (formal solutions 300 to 600 Myr ago). Our work supports Mariner 9 era suggestions of very young lavas on Mars, and is consistent with meteorite evidence for Martian igneous rocks 1.3 and 0.2 – 0.3 Gyr old. The youngest detected Martian lava flows give formal crater retention ages of the order 10 Myr or less. We note also that certain Martian meteorites indicate fluvial activity younger than the rock themselves, 700 Myr in one case, and this is supported by evidence of youthful water seeps. The evidence of youthful volcanic and aqueous activity, from both crater-count and meteorite evidence, places important constraints on Martian geological evolution and suggests a more active, complex Mars than has been visualized by some researchers.     

目标:火星极区美国"凤凰"号火星着陆探测器

8月4日,美国"凤凰"号火星着陆探测器从卡纳维拉尔角肯尼迪航天中心发射升空,开始了它历时近10个月的飞向火星的旅程。在火星北极地区着陆后,"凤凰"号将通过挖掘并分析火星极区土壤样本以确定当地环境是否适合生物生存。     

Flexible piloted Mars missions using the TIHTUS engine

The present investigation points out the potential of continuously propelled spacecraft for piloted Mars missions and compares them to impulsive propulsion (chemical and nuclear thermal) and ballistic trajectories. Although the results are related to piloted Mars missions, the stated issues raised hold true for a broad range of space missions. It is demonstrated that the use of impulsive propulsion leads to inflexible missions and may result in long total mission durations. Meanwhile, the use of continuous electric propulsion not only guarantees short total mission durations of Mars missions with moderate masses but also results in highly flexible missions. These criteria can be met with a continuous electric propulsion system that provides a thrust level of 100 N and 3000 s of specific impulse. Great potential lies in electric hybrid thrusters. The high-power, two-stage hybrid plasma thruster TIHTUS is currently being developed at the Institute of Space Systems (IRS). Its technology including preliminary laboratory testing results are presented.     

Mars navigation system utilizes GPS

Tasks envisioned for future generation Mars rovers - sample collection, area survey, resource mining, habitat construction, etc. - will require greatly enhanced navigational capabilities over those possessed by the Mars Sojourner rover. Many of these tasks will involve cooperative efforts by multiple rovers and other agents, adding further requirements both for accuracy and commonality between users. This paper presents a new navigation system a "Self-Calibrating Pseudolite Array" (SCPA) that can provide centimeter-level, drift-free localization to multiple rovers within a local area by utilizing GPS-based transceivers deployed in a ground-based array. Such a system of localized beacons can replace or augment a system based on orbiting satellite transmitters, and is capable of fully autonomous operations and calibration. This paper describes the prototype SCPA developed at Stanford to demonstrate these capabilities and then presents results from a set of field trials performed at NASA Ames Research Center. These experiments, which utilize the K9 Mars rover research platform, validate both the navigation and self-calibration capabilities of the system. By carrying an on-board GPS transceiver, K9 was successfully able to calibrate the system using no a priori position information and localized the pseudolite beacons to under 5 cm RMS.     

First Mars outpost power systems

Research into potential power systems for the First Mars Outpost (FMO) was performed. The author examined a representative mission architecture which was developed by NASA to determine power system requirements. Power system options including nuclear, isotope, photovoltaic (PV), chemical heat engine, and regenerative fuel cell (RFC) concepts were identified for potential Mars surface applications. A top-level characterization study was conducted to determine power system mass and area for each application. It is seen that PV systems are generally not suited for Mars surface applications due to the large surface area required and higher mass than a closed Brayton cycle SP100 reactor system. A reactor is currently being considered by NASA Lewis Research Center to provide power for base architectures including an ISRU (in situ resource utilization). An oxygen/methane powered heat engine would provide 40 kWe of emergency power for the habitat. A dynamic isotope power system (DIPS) is the current choice for a long-duration pressurized rover due to the excessive size of a PV/RFC system and higher mass of a heat engine system. DIPS has advantages for other low power systems due to its neatly immediate availability and flexibility (night or day power; no recharging required)     

Selection of the Mars Science Laboratory Landing Site

The selection of Gale crater as the Mars Science Laboratory landing site took over five years, involved broad participation of the science community via five open workshops, and narrowed an initial >50 sites (25 by 20?km) to four finalists (Eberswalde, Gale, Holden and Mawrth) based on science and safety. Engineering constraints important to the selection included: (1)?latitude (±30°) for thermal management of the rover and instruments, (2)?elevation (<?1?km) for sufficient atmosphere to slow the spacecraft, (3)?relief of <100–130?m at baselines of 1–1000?m for control authority and sufficient fuel during powered descent, (4)?slopes of <30° at baselines of 2–5?m for rover stability at touchdown, (5)?moderate rock abundance to avoid impacting the belly pan during touchdown, and (6)?a?radar-reflective, load-bearing, and trafficable surface that is safe for landing and roving and not dominated by fine-grained dust. Science criteria important for the selection include the ability to assess past habitable environments, which include diversity, context, and biosignature (including organics) preservation. Sites were evaluated in detail using targeted data from instruments on all active orbiters, and especially Mars Reconnaissance Orbiter. All of the final four sites have layered sedimentary rocks with spectral evidence for phyllosilicates that clearly address the science objectives of the mission. Sophisticated entry, descent and landing simulations that include detailed information on all of the engineering constraints indicate all of the final four sites are safe for landing. Evaluation of the traversabilty of the landing sites and target “go to” areas outside of the ellipse using slope and material properties information indicates that all are trafficable and “go to” sites can be accessed within the lifetime of the mission. In the final selection, Gale crater was favored over Eberswalde based on its greater diversity and potential habitability.     

Biological implications of the Viking mission to Mars

A central purpose of Viking was to search for evidence that life exists on Mars or may have existed in the past. The missions carried three biology experiments the prime purpose of which was to seek for existing microbial life. In addition the results of a number of the other experiments have biological implications: (1) The elemental analyses of the atmosphere and the regolith showed or implied that the elements generally considered essential to terrestrial biology are present. (2) But unexpectedly, no organic compounds were detected in Martian samples by an instrument that easily detected organic materials in the most barren of terrestrial soils. (3) Liquid water is believed to be an absolute requisite for life. Viking obtained direct evidence for the presence of water vapor and water ice, and it obtained strong inferential evidence for the existence of large amounts of subsurface permafrost now and in the Martain past. However it obtained no evidence for the current existence of liquid water possessing the high chemical potential required for at least terrestrial life, a result that is consistent with the known pressure-temperature relations on the planet's surface. On the other hand, the mission did obtain strong indications from both atmospheric analyses and orbital photographs that large quantities of liquid water flowed episodically on the Martian surface 0.5 to 2.5 G years ago.The three biology experiments produced clear evidence of chemical reactivity in soil samples, but it is becoming increasingly clear that the chemical reactions were nonbiological in origin. The unexpected release of oxygen by soil moistened with water vapor in the Gas Exchange experiment together with the negative findings of the organic analysis experiment lead to the conclusion that the surface contains powerful oxidants. This conclusion is consistent with models of the atmosphere. The oxidants appear also to have been responsible for the decarboxylation of the organic nutrients that were introduced in the Label Release experiment. The major results of the GEX and LR experiments have been simulated at least qualitatively on Earth. The third, Pyrolytic Release, experiment obtained evidence for organic synthesis by soil samples. Although the mechanism of the synthesis is obscure, the thermal stability of the reaction makes a biological explanation most unlikely. Furthermore, the response of soil samples in all three experiments to the addition of water is not consistent with a biological interpretation.The conditions now known to exist at and below the Martian surface are such that no known terrestrial organism could grow and function. Although the evidence does not absolutely rule out the existence of favourable oases, it renders their existence extremely unlikely. The limiting conditions for the functioning of terrestrial organisms are not the limits for conceivable life elsewhere, and accordingly one cannot exclude the possibility that indigenous life forms may currently exist somewhere on Mars or may have existed sometime in the past. Nevertheless, the available information about the present Martian environment puts severe constraints and presents formidable challenges to any putative Martian organisms. The Martian environment in the past, on the other hand, appears to have been considerably less hostile biologically, and it might possibly have permitted the origin and transient establishment of a biota.     

火星探测器飞行轨道设计

在一些基本假设的基础上,初步设计了从地球停泊轨道发射探测器到达火星的飞行轨道。运用圆锥曲线拼接法,设计了采用双共切和单共切两种不同的日心段转移方式时,探测器日心段、地心段和火星中心段的飞行轨道,并分析比较了这两种设计方法的特点。根据限制性二体问题动力学模型,仿真计算了探测器在不同轨道段的飞行轨迹,结果表明,探测器可以按照所设计的轨道飞行到达火星,并被其捕获,成为环绕火星飞行的卫星。     

2001 Mars Odyssey Mission Summary

The 2001 Mars Odyssey spacecraft, now in orbit at Mars, will observe the Martian surface at infrared and visible wavelengths to determine surface mineralogy and morphology, acquire global gamma ray and neutron observations for a full Martian year, and study the Mars radiation environment from orbit. The science objectives of this mission are to: (1) globally map the elemental composition of the surface, (2) determine the abundance of hydrogen in the shallow subsurface, (3) acquire high spatial and spectral resolution images of the surface mineralogy, (4) provide information on the morphology of the surface, and (5) characterize the Martian near-space radiation environment as related to radiation-induced risk to human explorers. To accomplish these objectives, the 2001 Mars Odyssey science payload includes a Gamma Ray Spectrometer (GRS), a multi-spectral Thermal Emission Imaging System (THEMIS), and a radiation detector, the Martian Radiation Environment Experiment (MARIE). THEMIS and MARIE are mounted on the spacecraft with THEMIS pointed at nadir. GRS is a suite of three instruments: a Gamma Subsystem (GSS), a Neutron Spectrometer (NS) and a High-Energy Neutron Detector (HEND). The HEND and NS instruments are mounted on the spacecraft body while the GSS is on a 6-m boom. Some science data were collected during the cruise and aerobraking phases of the mission before the prime mission started. THEMIS acquired infrared and visible images of the Earth-Moon system and of the southern hemisphere of Mars. MARIE monitored the radiation environment during cruise. The GRS collected calibration data during cruise and aerobraking. Early GRS observations in Mars orbit indicated a hydrogen-rich layer in the upper meter of the subsurface in the Southern Hemisphere. Also, atmospheric densities, scale heights, temperatures, and pressures were observed by spacecraft accelerometers during aerobraking as the spacecraft skimmed the upper portions of the Martian atmosphere. This provided the first in-situ evidence of winter polar warming in the Mars upper atmosphere. The prime mission for 2001 Mars Odyssey began in February 2002 and will continue until August 2004. During this prime mission, the 2001 Mars Odyssey spacecraft will also provide radio relays for the National Aeronautics and Space Administration (NASA) and European landers in early 2004. Science data from 2001 Mars Odyssey instruments will be provided to the science community via NASA’s Planetary Data System (PDS). The first PDS release of Odyssey data was in October 2002; subsequent releases occur every 3 months.