Nuclear space—an indispensable option?

There is renewed interest in using nuclear power in a variety of ways in space, as well as in disposing of terrestrial nuclear waste aloft. While the benefits of such use to space exploration might be high, the potential costs to Earth and its inhabitants are currently too dear. Accidents have already occurred which, despite official denials, have spread radiation worldwide. Such denials are characteristic of the closed and secretive nature of the nuclear ‘debate’. This viewpoint calls for the involvement of all those concerned with space nuclear power—lay, professional, government and NGO—in decisions on whether to proceed with it and suggests that maybe we should wait for safer scientific discoveries before we attempt further planetary exploration.     

CTD MTI Radar Filter with Charge-Transfer Inefficiency Compensation

The design and implementation of a second-order nonrecursive moving target indication (MTI) radar filter using commercially available charge-transfer devices as delay lines are described. A simple technique is included to compensate for the device charge-transfer in-efficiency and its sensitivity is analyzed. Experimental laboratory tests and results in an operating radar system are reported showing the good performance of the realized MTI radar filter.     

A numerical model to calculate the wake structure of a spacecraft under ionospheric conditions

A spacecraft, that travels at mesothermal speeds, disturbs the plasma in its surroundings. Due to the fade out of the ions an extended negative potential structure is formed behind the probe. A numerical model based on the Vlasov-Poisson system to describe the wake structure of a spacecraft under ionospheric conditions is presented. The dependence of the wake structure on the streaming velocity of the plasma and on the ratio of electron to ion temperature is discussed.     

Symmetric model of spacecraft charging and plasma emission effects

The electrostatic charging of satellites in space and the interactions with the plasma in the near surroundings are investigated by making use of symmetric models. In this case, the Vlasov-Poisson system describing the ambient plasma disturbances and the plasma emitted from the surface can be integrated self-consistently within a numerical iteration scheme, and the current balance yields the floating potential of the probe. The spacecraft charging and the potentials in its surroundings are investigated for the following plasma and emission conditions: (1) in the ionosphere in the case of very negative surface potentials, (2) in the solar wind with regard to the HELIOS mission and (3) in the near vicinity of the comet Halley, where a very strong plasma emission due to the impact of neutral gases onto the surface must be regarded. Finally, the importance of the shielding due to the ambient plasma is discussed.     

Orbit determination for the GOCE satellite

Precise Orbit Determination (POD) for the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first core explorer mission by the European Space Agency (ESA), forms an integrated part of the so-called High-Level Processing Facility (HPF). Two POD chains have been set up referred to as quick-look Rapid and Precise Science Orbit determination or RSO and PSO, respectively. These chains make use of different software systems and have latencies of 1 day and 2 weeks, respectively, after tracking data availability. The RSO and PSO solutions have to meet a 3-dimensional (3D) position precision requirement of 50 cm and a few cm, respectively. The tracking data will be collected by the new Lagrange GPS receiver and the predicted characteristics of this receiver have been taken into account during the implementation phase of the two chains.     

Characterization of lunar soils through spectral features extraction in the NIR

Recently launched hyper-spectral instrumentation with ever-increasing data return capabilities deliver the remote-sensing data to characterize planetary soils with increased precision, thus generating the need to classify the returned data in an efficient way for further specialized analysis and detection of features of interest. This paper investigates how lunar near-infrared spectra generated by the SIR-2 on Chandrayaan-1 can be classified into distinctive groups of similar spectra with automated feature extraction algorithms. As common spectral parameters for the SIR-2 spectra, two absorption features near 1300 nm and 2000 and their characteristics provide 10 variables which are used in two different unsupervised clustering methods, the mean-shift clustering algorithm and the recently developed graph cut-based clustering algorithm by Müller et al. (2012). The spectra used in this paper were taken on the lunar near side centering around the Imbrium region of the Moon. More than 100,000 spectra were analyzed.     

先进焊接技术在航空航天领域中的应用

先进飞机的研制与生产对焊接技术的发展具有强大的推动作用,在解决航空制造技术关键问题时,焊接的优势越来越明显,如减轻结构重量、提高结构性能等,焊接技术已由原来的辅助制造工艺演变成为飞机制造中的关键技术;另一方面,焊接技术自身的发展和完善,也为新型先进飞机的结构设计和制造提供了技术保证。     

Effects of space weather on the ionosphere and LEO satellites’ orbital trajectory in equatorial,low and middle latitude

We study the effects of space weather on the ionosphere and low Earth orbit (LEO) satellites’ orbital trajectory in equatorial, low- and mid-latitude (EQL, LLT and MLT) regions during (and around) the notable storms of October/November, 2003. We briefly review space weather effects on the thermosphere and ionosphere to demonstrate that such effects are also latitude-dependent and well established. Following the review we simulate the trend in variation of satellite’s orbital radius (r), mean height (h) and orbit decay rate (ODR) during 15 October–14 November 2003 in EQL, LLT and MLT. Nominal atmospheric drag on LEO satellite is usually enhanced by space weather or solar-induced variations in thermospheric temperature and density profile. To separate nominal orbit decay from solar-induced accelerated orbit decay, we compute $r\text{,}h$ and ODR in three regimes viz. (i) excluding solar indices (or effect), where $r=r_0\text{,}h=h_0$ and $\mathit{ODR}={\mathit{ODR}}_0$ (ii) with mean value of solar indices for the interval, where $r=r_m\text{,}h=h_m$ and $\mathit{ODR}={\mathit{ODR}}_m$ and (iii) with actual daily values of solar indices for the interval ($r\text{,}h$ and ODR). For a typical LEO satellite at h?=?450?km, we show that the total decay in r during the period is about 4.20?km, 3.90?km and 3.20?km in EQL, LLT and MLT respectively; the respective nominal decay ($r_0$) is 0.40?km, 0.34?km and 0.22?km, while solar-induced orbital decay ($r_m$) is about 3.80?km, 3.55?km and 2.95?km. h also varied in like manner. The respective nominal ${\mathit{ODR}}_0$ is about 13.5?m/day, 11.2?m/day and 7.2?m/day, while solar-induced ${\mathit{ODR}}_m$ is about 124.3?m/day, 116.9?m/day and 97.3?m/day. We also show that severe geomagnetic storms can increase ODR by up to 117% (from daily mean value). However, the extent of space weather effects on LEO Satellite’s trajectory significantly depends on the ballistic co-efficient and orbit of the satellite, and phase of solar cycles, intensity and duration of driving (or influencing) solar event.