Simulation study for the determination of the lunar gravity field from PRARE-L tracking onboard the German LEO mission

A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment – Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2–3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth–Moon system.     

NEO scientific and policy developments, 1995–2000

Scientific and policy developments in the field of Near-Earth Objects (NEOs) since the UN NEO conference in 1995 are briefly outlined. Some areas of research and discovery have exhibited considerable progress while others have languished. In particular, facilities in the southern hemisphere for discovery and tracking of NEOs are inadequate. Suggestions are made both at the scientific and technical levels as well as at the policy level to provide coordinated and coherent progress in developing a long-term approach to NEO hazard mitigation. The next step should be the establishment of a panel of international scientific experts on the subject.     

Distribution and stable isotopic composition of amino acids from fungal peptaibiotics: assessing the potential for meteoritic contamination

The presence of nonprotein α-dialkyl-amino acids such as α-aminoisobutyric acid (α-AIB) and isovaline (Iva), which are considered to be relatively rare in the terrestrial biosphere, has long been used as an indication of the indigeneity of meteoritic amino acids. However, recent work showing the presence of α-AIB and Iva in peptides produced by a widespread group of filamentous fungi indicates the possibility of a terrestrial biotic source for the α-AIB observed in some meteorites. We measured the amino acid distribution and stable carbon and nitrogen isotopic composition of four α-AIB-containing fungal peptides and compared this data to similar meteoritic measurements. We show that the relatively simple distribution of the C(4) and C(5) amino acids in fungal peptides is distinct from the complex distribution observed in many carbonaceous chondrites. We also identify potentially diagnostic relationships between the stable isotopic compositions of pairs of amino acids from the fungal peptides that may aid in ruling out fungal contamination as a source of meteoritic amino acids.     

未来机载雷达中具有高精度测距能力的新HPRF模式

已研究了一种新的雷达模式，它可以不模糊地估算目标速度并能通过IPRF模式中的脉冲时间延迟估算距离。要实现这点，距离门宽度要减至近乎机载目标（比如战斗机）的距离向长度。与普通HPRF模式不同的是，在不模糊距离中要有多个可辨别的距离门。距离模糊的分辨则由脉冲串至脉冲串间的脉冲重复频率变化来进行。模糊分辨的算法要考虑到这样一个事实，即在PRF变化期间，目标能移至下一个距离门或跨过一个或更多的相邻距离门。此外，可以在算法中采用不模糊速度测量来补偿目标距离徙动以减少虚警率。