Autonomous flight and navigation of VTOL UAVs: from autonomy demonstrations to out-of-sight flights

Future applications of UAV systems will depend on the aircraft autonomous behavior and decision capabilities. Search and Rescue is one complex possible mission and is here taken as a case study. The ReSSAC project is a multidisciplinary project at ONERA. Its main challenges are related to the architectures and algorithms for autonomous decision and information processing onboard UAVs that perform their mission in cooperation with operators. The feasibility demonstrations and results of the project are intended to be reused and extended in further studies, projects and collaborations. A first step of the project was to develop an autonomous control architecture for our two rotorcraft. In this paper, we present the current status and preliminary achievements of the ReSSAC project, especially some records of past experimental flights with our autonomous aircraft. We further discuss ongoing studies and research perspectives.     

Time variations of dynamical processes in the midlatitude upper mesosphere — lower thermosphere

Complex studies with the use of spectrum and harmonic analysis allow determination of wave disturbances in the prevailing and tidal wind, and also mesoscale short period oscillation intensity per unit mass. We particularly find enhanced periods of 4–6, 9–12, 15–20, 25–30 days, which are typical for planetary waves in the lower and middle atmosphere of the Earth. We also reveal the non-linear character of vertical amplitude and phase profiles for wave disturbances with planetary wave scales in the prevailing, tidal and short period oscillation intensity. This non-linearity is interpreted as a consequence of the non-linear interaction of waves such as internal gravity waves, tides and planetary waves among themselves and with background movements.     

Variations of the ground-level ultraviolet radiation in East Siberia

Daily measurements of the ground-level ultraviolet radiation (UVR) for the years 1998–2000 were used to investigate the seasonal UVR variation in the East Siberian region. The study revealed the asymmetry of the seasonal UVR variation with respect to the angular altitudes of the Sun, caused by the seasonal variation of the total ozone content (TOC), and possibly by the presence of the snow cover. Characteristics of the occurrence of short-lasting increases in UVR are considered, which are associated with TOC anomalies and with high atmospheric transparency. Fluctuations of the ground-level UVR with periods of 2.8, 6–13 and 26 days are identified. A study is made of the dependence of the ground-level UVR on solar activity. Statistically significant correlation coefficients with solar activity indices are obtained.     

Selenodetic experiments of SELENE: Relay subsatellite,differential VLBI,and laser altimeter

Since 1960s, the gravitational potential of the Moon has been extensively studied from Doppler tracking data between a ground station and spacecraft orbiting in front of the Moon (e. g., Lorell and Sjogren, 1968; Bills and Ferrari, 1980; Konopliv et al., 1993; Lemoine et al., 1997). Because direct radio communication is interrupted while spacecraft is orbiting behind the Moon, however, the coverage of tracking data has been limited mostly to the nearside of the Moon so far. In order to compensate for such lack of tracking data, we propose satellite-to-satellite Doppler measurement by using a relay subsatellite in Japanese mission to the Moon in 2003. A complete coverage of Doppler tracking from an orbiter at sufficiently low altitude will significantly improve lunar gravity model and will contribute for future geophysical study of interior and tectonics on the Moon. Further, we propose differential VLBI experiment between the subsatellite and a propulsion module landed on the surface of the Moon. The differential VLBI is about 10 times more accurate than conventional Doppler measurement for long-wavelength gravity field. Besides, differential VLBI is sensitive to the displacement perpendicular to the line of sight. Thus the VLBI experiment provides precise estimates of the lunar gravity potential at low degree. The last proposal for selenodetic experiments is a laser altimeter. Global topography model has been already developed from the analysis of Clementine LIDAR data (Zuber et al., 1994), but it is suggested that the model includes appreciable anisotropy between NS and E-W directions due to highly eccentric orbit of Clementine spacecraft (Bills and Lemoine, 1995). The laser altimeter experiment from an orbiter in nearly circular orbit will provide a new reference for the isotropic lunar topography model.     

空间碎片超高速碰撞数值模拟的SPH方法

利用光滑质点动力学SPH(Smoothed Particle Hydrodynamics)方法对Whipple防护结构在空间碎片超高速碰撞下的物理过程进行了数值模拟.在数值模拟中,为了充分发挥SPH方法和有限元方法FEM(Finite Element Method)的优点,利用有限元单元和SPH节点混合建模,将有限元单元和SPH节点(SPH nodes)通过定义接触条件相结合,在大变形和飞溅区域采用SPH节点建模,而小变形区域则采用有限元单元建模,从而大大节省求解时间,提高计算效率.计算结果表明,弹丸在穿透前板后,形成二次碎片,碎片云经膨胀和拉长,对后板造成轻微的损伤,这和文献的相关试验数据是符合的.利用SPH方法对空间碎片的超高速碰撞过程进行数值模拟,不仅很好地预测了Whipple防护结构的破坏情况,而且对整个碰撞过程,包括碎片云的形成、膨胀和拉长过程都有形象的描述,符合超高速碰撞的试验测试结果.     

基于应力循环特征的裂纹萌生寿命预测方法

以两种镍基高温合金的应力循环特征为基础,即粉末高温合金FGH95的循环硬化继而软化及变形高温合金GH4169的循环软化特性,寻求载荷历程相关的损伤参量,进而建立应力弱化损伤模型,以考虑载荷历程对疲劳寿命的影响.建立的应力弱化损伤模型可以较好地预测不同循环载荷条件下的疲劳寿命,其预测精度不低于传统方法,且优势在于使建立模型所需要的试样数量大大减少.      

基于气动热力模型的FADEC系统FHA方法

从适航规章对全权限数字发动机控制(full authority digital engine control,简称FADEC)系统的安全要求出发,结合功能危险分析(functional hazard assessment,简称FHA)的一般原则和FADEC系统的特点,得到了FADEC系统FHA的分析要素.根据分析要素中的工具与数据需求,将航空发动机气动热力模型用于可调放气活门(variable bleed valve,简称VBV)控制功能失效危险分析,结果表明:①该模型能够辅助确定FADEC系统功能失效的发动机影响;②FADEC系统功能危险的模型分析方法通过定量分析确定发动机影响的危险等级,为FHA提供直观的参考依据,可作为对专家经验的补充.      

大功率狭缝式活塞激励器流场测量与分析

研制了一种大功率活塞射流激励器,出口瞬时速度峰值可达0.3Hz,通过对活塞激励器射流流场测量,得到激励器出口流场速度、涡量分布,分析得到激励器合成射流流动结构与特征,通过采用活塞激励器控制同轴射流掺混,实验结果证明此种活塞激励器可以用于相对较高的速度流场的主动流动控制.利用提出的设计方法设计合成射流激励器可以在激励器出口形成稳定的对涡结构,采用一定的激励频率即可对喷管气流掺混进行有效控制.研究表明,合成射流激励器作为主动流动的执行机构,在航空动力排气系统具有潜在的重要价值.     

某型航空发动机喷管红外辐射特征数值模拟和试验研究

基于N-S方程建立了某型发动机喷管及其喷流流场的数值计算模型,利用辐射传输方程(RTE)积分法编制了红外辐射特征计算程序,得到了此喷管在非加力状态下工作时的红外辐射特征分布,同时利用模型试验测量得到该喷管的红外辐射特征分布。给出了在3.0～5.0μm光谱范围内的红外辐射特征数值模拟结果和试验测量结果,经比较表明:数值模拟结果和试验测量结果吻合良好。     

Responsibility,capability, and Active SETI: Policy,law, ethics,and communication with extraterrestrial intelligence

With recently growing interest in the Active Search for Extraterrestrial Intelligence (SETI), in which humankind would send intentional signals to extraterrestrial civilizations, there have been increased concerns about appropriate policy, as well as the role of space law and ethics in guiding such activities. Implicit in these discussions are notions of responsibility and capability that affect judgments about whether humans or other civilizations should initiate transmissions. Existing protocols that guide SETI research address transmissions from Earth, but there is debate over whether these guidelines should inform de novo transmissions as well. Relevant responsibilities to address include (1) looking out for the interests of humankind as a whole, (2) being truthful in interstellar messages, and (3) benefiting extraterrestrial civilizations. Our capabilities as a species and a civilization affect how well we can fulfill responsibilities, as seen when we consider whether we will be able to reach consensus about message contents (and whether that would be desirable), and whether we have the capacity to decode messages from beings that rely on different sensory modalities. The interplay of these responsibilities and capabilities suggests that humankind should place increased emphasis on Active SETI.