To the surface of Mars via Titan: : Reuse of Huygens software components on Beagle 2

‘Beagle 2’ is a Mars lander, which will be flown in 2003 as part of ESA's Mars Express mission. Like the Huygens probe to Titan, it is critically dependent on the correct functioning of on-board software to control its descent. Beagle 2 is a much lower cost mission and cannot afford to develop all of its software from scratch. How has the Huygens software been given a new lease of life on-board Beagle 2?     

The Characterisation of Titan's Atmospheric Physical Properties by the Huygens Atmospheric Structure Instrument (Hasi)

The Huygens Atmospheric Structure Instrument (HASI) is a multi-sensor package which has been designed to measure the physical quantities characterising the atmosphere of Titan during the Huygens probe descent on Titan and at the surface. HASI sensors are devoted to the study of Titan's atmospheric structure and electric properties, and to provide information on its surface, whether solid or liquid. This revised version was published online in August 2006 with corrections to the Cover Date.     

ESA再入探测器的某些空气热动力问题

给出了两种不同的再入飞行器:充气的再入和下滑演示器(IRDT)和Huygens.两者的任务都涉及在靠近轨道的条件下再入并均已于2005年完成.概述了IRDT的使命和具体设计问题,综述了IRDT最近飞行的初步结果和ESTEC估计Huygens受到的辐射通量采用的方法.     

Huygens' Surface Science Package

The design and performance of the Surface Science Package (SSP) on the Huygens probe are discussed. This instrument consists of nine separate sensors that are designed to measure a wide range of physical properties of Titan's lower atmosphere, surface, and sub-surface. By measuring a number of physical properties of the surface it is expected that the SSP will be able to constrain the inferred composition and structure of the moon's near-surface environment. Although the SSP is primarily designed to sense properties of the surface, some of its sensors will also make measurements of the atmosphere along the probe's entry path and will complement the data gathered by other experiments on the Huygens probe. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Huygens Doppler Wind Experiment ' Titan Winds Derived from Probe Radio Frequency Measurements

A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m s⁻¹ from the start of mission at an altitude of ∼160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Touring the saturnian system: the atmospheres of titan and saturn

This report follows the presentation originally given in the ESA Phase A Study for the Cassini Huygens Mission. The combination of the Huygens atmospheric probe into Titan's atmosphere with the Cassini orbiter allows for both in-situ and remote-sensing observations of Titan. This not only provides a rich harvest of data about Saturn's famous satellite but will permit a useful calibration of the remote-sensing instruments which will also be used on Saturn itself. Composition, thermal structure, dynamics, aeronomy, magnetosphere interactions and origins will all be investigated for the two atmospheres, and the spacecraft will also deliver information on the interiors of both Titan and Saturn. As the surface of Titan is intimately linked with the atmosphere, we also discuss some of the surface studies that will be carried out by both probe and orbiter. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geology of the Icy Satellites

In the last 25 years, the explorations of the Voyager and Galileo missions have resulted in an entirely new view of the icy worlds orbiting the giant outer planets. These objects show a huge diversity in their characteristics, resulting from their formation histories, internal processes and interactions with their space environments. This paper will review the current state of knowledge about the icy satellites and discuss the exciting prospects for the upcoming Cassini/Huygens mission as it begins a new era of exploration of the Saturn satellite system.     

The Cassini/Huygens Mission to the Saturnian System

The international Cassini/Huygens mission consists of the Cassini Saturn Orbiter spacecraft and the Huygens Titan Probe that is targeted for entry into the atmosphere of Saturn's largest moon, Titan. From launch on October 15, 1997 to arrival at Saturn in July 2004, Cassini/Huygens will travel over three billion kilometers. Once in orbit about Saturn, Huygens is released from the orbiter and enters Titan's atmosphere. The Probe descends by parachute and measures the properties of the atmosphere. If the landing is gentle, the properties of the surface will be measured too. Then the orbiter commences a four-year tour of the Saturnian system with 45 flybys of Titan and multiple encounters with the icy moons. The rings, the magnetosphere and Saturn itself are all studied as well as the interactions among them. This revised version was published online in August 2006 with corrections to the Cover Date.     

激波后高温高速流场中的传热特性研究

激波后高温、高速流场中的热力学与传热特性分析是直接涉及到飞行器热防护设计与传热分析的关键问题之一,借助于多组分、考虑非平衡态气体的振动以及激波与热化学非平衡态效应的守恒积分型Navier-Stokes方程组,并用高分辨率总变差减小(TVD)格式进行求解,计算与研究了Apollo工程AS-202返回舱再入地球大气层的6个飞行工况(飞行马赫数15.52～22.63)以及Huygens飞行器再入土卫六大气层的6个工况(飞行马赫数17.29～24.47),分析了不同工况下弓形脱体激波后高温高速流场的热力学与传热特性,计算得到了沿壁面的热流密度分布、温度分布以及Stanton数分布,并与国外相关飞行数据进行了比较,两者吻合较好.相关计算可以指导有关飞行器的热防护设计.      

Autonomy architecture for aerobot exploration of Saturnian moon Titan

The Huygens probe arrived at Saturn's moon, Titan, January 14,2005, unveiling a world that is radically different from any other in the solar system. The data obtained, complemented by continuing observations from the Cassini spacecraft, show methane lakes, river channels and drainage basins, sand dunes, cryovolcanos and sierras. This has led to an enormous scientific interest in a follow-up mission to Titan, using a robotic lighter-than-air vehicle (or aerobot). Aerobots have modest power requirements, can fly missions with extended durations, and have very long distance traverse capabilities. They can execute regional surveys, transport and deploy scientific instruments and in-situ laboratory facilities over vast distances, and also provide surface sampling at strategic science sites. This describes our progress in the development of the autonomy technologies that will be required for exploration of Titan. We provide an overview of the autonomy architecture and some of its key components. We also show results obtained from autonomous flight tests conducted in the Mojave Desert.     

The Gas Chromatograph Mass Spectrometer for the Huygens Probe

The Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens Probe will measure the chemical composition of Titan's atmosphere from 170 km altitude (∼1 hPa) to the surface (∼1500 hPa) and determine the isotope ratios of the major gaseous constituents. The GCMS will also analyze gas samples from the Aerosol Collector Pyrolyser (ACP) and may be able to investigate the composition (including isotope ratios) of several candidate surface materials. The GCMS is a quadrupole mass filter with a secondary electron multiplier detection system and a gas sampling system providing continuous direct atmospheric composition measurements and batch sampling through three gas chromatographic (GC) columns. The mass spectrometer employs five ion sources sequentially feeding the mass analyzer. Three ion sources serve as detectors for the GC columns and two are dedicated to direct atmosphere sampling and ACP gas sampling respectively. The instrument is also equipped with a chemical scrubber cell for noble gas analysis and a sample enrichment cell for selective measurement of high boiling point carbon containing constituents. The mass range is 2 to 141 Dalton and the nominal detection threshold is at a mixing ratio of 10^{− 8}. The data rate available from the Probe system is 885 bit/s. The weight of the instrument is 17.3 kg and the energy required for warm up and 150 minutes of operation is 110 Watt-hours. This revised version was published online in August 2006 with corrections to the Cover Date.     

Astrobiology and habitability of Titan

Largest satellite of Saturn and the only in the solar system having a dense atmosphere, Titan is one of the key planetary bodies for astrobiological studies, due to several aspects. (i) Its analogies with planet Earth, in spite of much lower temperatures, with, in particular, a methane cycle on Titan analogous to the water cycle on Earth. (ii) The presence of an active organic chemistry, involving several of the key compounds of prebiotic chemistry. The recent data obtained from the Huygens instruments show that the complex organic matter in Titan’s low atmosphere is mainly concentrated in the aerosol particles. The formation of biologically interesting compounds may also occur in the deep water ocean, from the hydrolysis of complex organic material included in the chrondritic matter accreted during the formation of Titan. (iii) The possible emergence and persistence of Life on Titan. All ingredients which seem necessary for Life to appear and even develop – liquid water, organic matter and energy – are present on Titan. Consequently, it cannot be excluded that life may have emerged on or in Titan. In spite of the extreme conditions in this environment life may have been able to adapt and to persist. Many data are still expected from the Cassini-Huygens mission and future astrobiological exploration mission of Titan are now under consideration. Nevertheless, Titan already looks like another world, with an active organic chemistry, in the absence of permanent liquid water, on the surface: a natural laboratory for prebiotic-like chemistry.     

Organic Chemistry and Exobiology on Titan

Exobiology is not only the study of the origin, distribution and evolution of life in the universe, but also of structures — including at the molecular level, and processes — including organic chemical transformations — related to life. In that respect, with its dense nitrogen atmosphere, which includes a noticeable fraction of methane, and the many organic compounds which are present in the gas and aerosols phases, Titan appears to be a planetary object of prime interest for exobiology in the Solar system, allowing the study of chemical organic evolution in a planetary environment over a long time scale. We describe here some aspects of this extraterrestrial organic chemistry which involves many physical and chemical couplings in the different parts of what can be called ‘Titan's geofluid’ (gas phase, aerosol phases and surface solid and maybe liquid phases). The three complementary approaches which can be followed to study such chemistry of exobiological interest are considered. Those are experimental simulations in the laboratory, chemical and photochemical modeling and of course observation, using both remote sensing and in situ measurements, which is an essential approach. The Cassini-Huygens mission, that offers a unique opportunity to study in detail the many aspects of Titan's organic chemistry, is discussed and the many expected exobiological returns from the different instruments of the Cassini orbiter and the Huygens probe are considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Protein Microarrays-Based Strategies for Life Detection in Astrobiology

The detection of organic molecules of unambiguous biological origin is fundamental for the confirmation of present or past life. Planetary exploration requires the development of miniaturized apparatus for in situ life detection. Analytical techniques based on mass spectrometry have been traditionally used in space science. Following the Viking landers, gas chromatography-mass spectrometry (GC-MS) for organic detection has gained general acceptance and has been used successfully in the Cassini–Huygens mission to Titan. Microfluidics allows the development of miniaturized capillary electrophoresis devices for the detection of important molecules for life, like amino acids or nucleobases. Recently, a new approach is gaining acceptance in the space science community: the application of the well-known, highly specific, antibody–antigen affinity interaction for the detection and identification of organics and biochemical compounds. Antibodies can specifically bind a plethora of structurally different compounds of a broad range of molecular sizes, from amino acids level to whole cells. Antibody microarray technology allows us to look for the presence of thousands of different compounds in a single assay and in just one square centimeter. Herein, we discuss several important issues—most of which are common with other instruments dealing with life signature detection in the solar system—that must be addressed in order to use antibody microarrays for life detection and planetary exploration. These issues include (1) preservation of biomarkers, (2) the extraction techniques for biomarkers, (3) terrestrial analogues, (4) the antibody stability under space environments, (5) the selection of unequivocal biomarkers for the antibody production, or (6) the instrument design and implementation.     

Huygens Probe Aerosol Collector Pyrolyser Experiment

ACP's main objective is the chemical analysis of the aerosols in Titan's atmosphere. For this purpose, it will sample the aerosols during descent and prepare the collected matter (by evaporation, pyrolysis and gas products transfer) for analysis by the Huygens Gas Chromatograph Mass Spectrometer (GCMS). A sampling system is required for sampling the aerosols in the 135'32 km and 22'17 km altitude regions of Titan's atmosphere. A pump unit is used to force the gas flow through a filter. In its sampling position, the filter front face extends a few mm beyond the inlet tube. The oven is a pyrolysis furnace where a heating element can heat the filter and hence the sampled aerosols to 250 °C or 600 °C. The oven contains the filter, which has a thimble-like shape (height 28 mm). For transferring effluent gas and pyrolysis products to GCMS, the carrier gas is a labeled nitrogen ¹⁵N₂, to avoid unwanted secondary reactions with Titan's atmospheric nitrogen. Aeraulic tests under cold temperature conditions were conducted by using a cold gas test system developed by ONERA. The objective of the test was to demonstrate the functional ability of the instrument during the descent of the probe and to understand its thermal behavior, that is to test the performance of all its components, pump unit and mechanisms. In order to validate ACP's scientific performance, pyrolysis tests were conducted at LISA on solid phase material synthesized from experimental simulation. The chromatogram obtained by GCMS analysis shows many organic compounds. Some GC peaks appear clearly from the total mass spectra, with specific ions well identified thanks to the very high sensitivity of the mass spectrometer. The program selected for calibrating the flight model is directly linked to the GCMS calibration plan. In order not to pollute the two flight models with products of solid samples such as tholins, we excluded any direct pyrolysis tests through the ACP oven during the first phase of the calibration. Post probe descent simulation of flight results are planned, using the much representative GCMS and ACP spare models. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Descent Imager/Spectral Radiometer (DISR) Experiment on the Huygens Entry Probe of Titan

The payload of the Huygens Probe into the atmosphere of Titan includes the Descent Imager/Spectral Radiometer (DISR). This instrument includes an integrated package of several optical instruments built around a silicon charge coupled device (CCD) detector, a pair of linear InGaAs array detectors, and several individual silicon detectors. Fiber optics are used extensively to feed these detectors with light collected from three frame imagers, an upward and downward-looking visible spectrometer, an upward and downward looking near-infrared spectrometer, upward and downward looking violet phtotometers, a four-channel solar aerole camera, and a sun sensor that determines the azimuth and zenith angle of the sun and measures the flux in the direct solar beam at 940 nm. An onboard optical calibration system uses a small lamp and fiber optics to track the relative sensitivity of the different optical instruments relative to each other during the seven year cruise to Titan. A 20 watt lamp and collimator are used to provide spectrally continuous illumination of the surface during the last 100 m of the descent for measurements of the reflection spectrum of the surface. The instrument contains software and hardware data compressors to permit measurements of upward and downward direct and diffuse solar flux between 350 and 1700 nm in some 330 spectral bands at approximately 2 km vertical resolution from an alititude of 160 km to the surface. The solar aureole camera measures the brightness of a 6° wide strip of the sky from 25 to 75° zenith angle near and opposite the azimuth of the sun in two passbands near 500 and 935 nm using vertical and horizontal polarizers in each spectral channel at a similar vertical resolution. The downward-looking spectrometers provide the reflection spectrum of the surface at a total of some 600 locations between 850 and 1700 nm and at more than 3000 locations between 480 and 960 nm. Some 500 individual images of the surface are expected which can be assembled into about a dozen panoramic mosaics covering nadir angles from 6° to 96° at all azimuths. The spatial resolution of the images varies from 300 m at 160 km altitude to some 20 cm in the last frames. The scientific objectives of the experiment fall into four areas including (1) measurement of the solar heating profile for studies of the thermal balance of Titan; (2) imaging and spectral reflection measurements of the surface for studies of the composition, topography, and physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements of the extinction optical depth of the aerosols as a function of wavelength and altitude to study the size, shape, vertical distribution, optical properties, sources and sinks of aerosols in Titan's atmosphere; and (4) measurements of the spectrum of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout the descent. We briefly outline the methods by which the flight instrument was calibrated for absolute response, relative spectral response, and field of view over a very wide temperature range. We also give several examples of data collected in the Earth's atmosphere using a spare instrument including images obtained from a helicopter flight program, reflection spectra of various types of terrain, solar aureole measurements including the determination of aerosol size, and measurements of the downward flux of violet, visible, and near infrared sunlight. The extinction optical depths measured as a function of wavelength are compared to models of the Earth's atmosphere and are divided into contributions from molecular scattering, aerosol extinction, and molecular absorption. The test observations during simulated descents with mountain and rooftop venues in the Earth's atmosphere are very important for driving out problems in the calibration and interpretion of the observations to permit rapid analysis of the observations after Titan entry. This revised version was published online in August 2006 with corrections to the Cover Date.     

纳米碳酸盐对复合固体推进剂燃烧性能的影响

研究了纳米碳酸盐对丁羟三组元、丁羟四组元、低燃速NEPE推进剂燃烧性能的影响。结果表明:纳米碳酸盐使丁羟三组元推进剂在高压(10～18MPa)和低压(4～10MPa)段的压强指数降低到0.2以下,同时使燃速明显降低;使丁羟四组元推进剂在高压段(10～18MPa)的压强指数降低到0.26左右;使低燃速NEPE推进剂的的压强指数(4～9MPa)从0.77左右降至0.55以下。从研究结果可以看出,添加该纳米碳酸盐是降低复合推进剂压强指数行之有效的途径。     

样本量为2的极小样本相容性检验方法

在航空航天领域由于成本、时间周期等原因进行疲劳寿命及可靠性评估时样本量通常极少（m=1或2）,利用相容性检验方法可对样本量进行扩充。常规的Wilcoxon秩和检验和K-S（Kolmogorov-Smirnov）检验适用于小样本情形,而极小样本相容性检验方面研究较少,且缺乏对方法合理性的详细说明和对不同方法检验功效优劣的比较。航空航天产品疲劳寿命多服从正态分布,因此本文主要以正态分布作为研究对象。利用Monte Carlo仿真发现从某一正态分布N（μ,σ²）中随机抽取两个样本x₁、x₂计算均值μ₁和标准差σ₁后构建新正态分布N（μ₁,σ₁²）,其±σ₁、±2σ₁和±3σ₁范围内的点落在原正态分布N（μ,σ²）±3σ范围内的概率依次为99.80%、98.13%和97.37%。在此基础上针对现场试验数据样本量为2的情况,本文提出利用3σ原则对先验信息数据进行相容性检验从而扩充样本量的方法。将该方法与两种文献方法对比后发现其误差率明显更低并呈现出检验性能随先验数据增加而不断提高的优势。