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151.
NASA is moving into an era of Increasing spacecraft autonomy. However, before autonomy can be routinely utilized, we must develop techniques for providing assurance that the system will perform correctly in flight. We describe why autonomous systems require advanced verification techniques, and offer some management and technical techniques for addressing the differences. Autonomous goal-driven spacecraft require advances in verification techniques because optimization (e.g., planning and scheduling) algorithms are at the core of much of autonomy. It Is the nature of such algorithms that over much of the input space an intuitively "small" change in the input results in a correspondingly "small" change in the output: This type of response typically leads one to conclude, quite reasonably, that if the two responses are correct, those responses "between" them will probably also be correct. However, there are certain regions in the input space where a "small" change in the input will result in a radically different output: One is not so inclined to conclude that all responses in these transition zones are likely to be correct. We believe, for two reasons, that these transition zones are one place where autonomous systems are likely to fail. First, boundary conditions, often a rich source of faults, are highly exercised in the transition zones, and so increase the likelihood of faults. Second, within the transition zone the algorithm outputs are likely to appear unusual, and, since the outputs of the algorithm become inputs to the remainder of the system, the whole system is probably pushed outside of its nominal usage profile: historically shown to be another good source of faults. We close with a discussion of risk management. Autonomous systems have many well-known management risk factors. Risk management and quality concerns must be pervasive, throughout all team members and the whole life-cycle of the project. 相似文献
152.
P.T. Verronen S. Ceccherini U. Cortesi E. Kyrl J. Tamminen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1918-1925
GOMOS (Global Ozone Monitoring by Occultation of Stars) and MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) are remote sensing instruments on board the European Space Agency’s Envisat satellite. GOMOS and MIPAS have been designed for observations of stratospheric and mesospheric constituents, including ozone and nitrogen dioxide. Both instruments have a good global coverage of observations and can provide data also from the polar regions. In this paper, we compare night-time NO2 data from GOMOS with those from MIPAS. We present statistics of selected sets of data spanning from the year 2003 to 2006. The results for low-to-mid latitudes show that the two instruments are in a good agreement in the middle stratosphere, the differences being typically less than 5%. In the upper stratosphere, GOMOS observations generally show 15% higher values than those from MIPAS. The bias is in virtually all cases smaller than the combined systematic error of the measurements, giving great confidence in the GOMOS and MIPAS data quality. The result for high mesospheric NO2 mixing ratios observed in the polar regions during winter times indicate a good agreement between GOMOS and MIPAS. In the mesosphere, the difference is less than 35% and smaller than the systematic error. Due to the high mesospheric signal, MIPAS sensitivity decreases in the stratosphere which results in larger differences between the two instruments. 相似文献
153.
154.
Farzad Kamalabadi Jianqi Qin Brian J. Harding Dimitrios Iliou Jonathan J. Makela R. R. Meier Scott L. England Harald U. Frey Stephen B. Mende Thomas J. Immel 《Space Science Reviews》2018,214(4):70
The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.6 nm photons in the ionosphere including the mutual neutralization contribution as well as the effect of resonant scattering by atomic oxygen and pure absorption by oxygen molecules. This forward model is then used in conjunction with a constrained optimization algorithm to invert the anticipated ICON FUV line-of-sight integrated measurements. In this paper, we describe the connection between ICON FUV measurements and the nighttime ionosphere, along with the approach to inverting the measured emission profiles to derive the associated O+ profiles from 150–450 km in the nighttime ionosphere that directly reflect the electron density in the F-region of the ionosphere. 相似文献
155.
Angel O.U. Parentis Bruno S. Zossi Hagay Amit Ana G. Elias 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3228-3236
The geomagnetic field, modified by the solar wind, determines the shape, area and location of polar caps and auroral zones, among other magnetosphere and upper atmosphere characteristics. Since the field varies greatly with time it is of interest to analyze polar caps and auroral zones variations linked to magnetic field variations of intensity and pattern. Polar caps and auroral zones locations and areas for various single harmonic axial field configurations are obtained analytically assuming a simple magnetopause model. As the axial degree n increases, the polar caps and auroral zones total number, given by n + 1 and 2n respectively, also increase. However, their total areas decrease from a larger value in the case of an axial dipole to a minimum for an axial octupole (n = 3), and then increase for increasing degrees. The increasing rate is much higher in the auroral zones case to the point that it exceeds the dipolar value at n = 5 while in the polar caps case this occurs at n = 8. The absolute latitudes of the auroral zones and polar caps that reside around the geographical poles increase with axial degree. Our results represent an end-member case of the evolution of auroral zones and polar caps during polarity reversals if the transition involves axial dipole energy cascade to higher axial degrees. Evidence for such an energy transfer is found in the historical record of the geomagnetic secular variation. 相似文献
156.
C. Bianchi J.A. BaskaradasM. Pietrella U. SciaccaE. Zuccheretti 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
A series of Power Virtual Height measurements (PVH) of radio echoes reflected from the ionosphere were acquired at a given frequency during the period 3–22 January 2008 with the purpose of studying the slow fading variations through time of the ionospheric channel. To obtain PVH data, an ionospheric vertical sounding system was suitably adapted to work at a single fixed frequency. PVH measurements were recorded between two routine ionospheric vertical soundings, providing a data type that enables evaluation of fading fluctuation through time. The time stability of the ionospheric layers is determined by analyzing the level of the received signal power within a chosen threshold. In this paper the fading behaviour and its characteristics are described, considering only temporal periodicity above 0.5 s. In a further analysis a relation is demonstrated between the recorded fading and the time stability of the signal within a fixed interval of values. 相似文献
157.
H J Marthy G Gasset R Tixador B Eche P Schatt A Dessommes U Marthy R Bacchieri 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1151-1154
From many points of view, skeletogenesis in sea urchins has been well described. Based on this scientific background and considering practical aspects of sea urchin development (i.e. availability of material, size of larvae, etc.), we wanted to know whether orderly skeletogenesis requires the presence of gravity. The objective has been approached by three experiments successfully performed under genuine microgravity conditions (in the STS-65 IML-2 mission of 1994; in the Photon-10 IBIS mission of 1995 and in the STS-76 S/MM-03 mission of 1996). Larvae of the sea urchin Sphaerechinus granularis were allowed to develop in microgravity conditions for several days from blastula stage onwards (onset of skeletogenesis). At the end of the missions, the recovered skeletal structures were studied with respect to their mineral composition, architecture and size. Live larvae were also recovered for post-flight culture. The results obtained clearly show that the process of mineralisation is independent of gravity: that is, the skeletogenic cells differentiate correctly in microgravity. However, abnormal skeleton architectures were encountered, particularly in the IML-2 mission, indicating that the process of positioning of the skeletogenic cells may be affected, directly or indirectly, by environmental factors, including gravity. Larvae exposed to microgravity from blastula to prism/early pluteus stage for about 2 weeks (IBIS mission), developed on the ground over the next 2 months into normal metamorphosing individuals. 相似文献
158.
U.M. Leloglu E. Kocaoglan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Although it is generally agreed that the outer space should be used for the benefit of all mankind, only a fraction of the countries have the necessary technological base for accessing space. Space technology, with its implications on science, economy and well-being of citizens, is mostly chosen as one of the priority areas for technological development by developing countries. However, there is already an over-capacity in global space industry and there are doubts on necessity of additional capacity establishment by developing countries. In this study, the importance and benefits of capacity-building in these countries are emphasized and the advantages and disadvantages that developing countries have in the framework of space technology acquisition are briefly presented. The feasibility of certain levels of space technology is discussed and the necessity of combining existing indigenous capabilities with technology obtained from foreign sources in the optimal way is stressed. We have also mentioned various general mechanisms of technology transfer and argued the importance of licensing in catching-up developed countries. After considering the necessary conditions of efficiency of technology, such as establishment of regional centers of space science and technology education by United Nations, joint development of space systems, complete technology transfer packages, cooperative space projects within regional organizations, coordinated constellations and special agreements with large space agencies, which are specific mechanisms already in use, are reviewed. Some typical examples of mechanisms are also given with special emphasize on small satellite technology that makes access to space affordable for many countries. Through sharing and analyzing the experience of developing countries in their odyssey of space capacity-building, the difficulties can be negotiated and the vicious circles can be broken. This study, in our view, is a step to incite a general discussion of obstacles and opportunities for developing countries, that could help them in using their limited resources effectively, hence, enable them to offer better conditions to their citizens and to contribute space science to a larger extend. 相似文献
159.
W H Thiemann H Rosenbauer U J Meierhenrich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):323-328
In the last years extraterrestrial scenarios for the origin of homochirality in biological structures received considerable attention in the topical literature: Rubenstein and Bonner postulated a rapidly rotating neutron star emitting circularly polarised synchrotron radiation responsible for the first asymmetric synthesis; the group of Bailey published the observation of circular polarisation caused by Mie scattering from aligned dust grains in the Orion OMC-1 star-formation region that might provide an enantioselective effect on prochiral or racemic organic molecules. Rikken and Raupach observed a magnetochiral effect and considered extraterrestrial magnetic fields of sufficient strengths to introduce biomoleculars parity violation. With the aim to investigate these hypotheses among other theories describing the origin of biological asymmetry, our laboratory participates in the conception and development of ROSETTA's COSAC Experiment, that is designed to identify organic molecules in the cometary matter in situ. Within COSAC's 'Chirality Module' enantiomers will be separated gas chromatographically with the help of capillary columns coated with chirally active liquid films. This technique will allow the separation of specific chiral organic compounds out of the analysed cometary matter into their enantiomeric constituents. Both thermo conductivity and mass spectrometric detectors will be used to determine each enantiomer's amount and therefore the corresponding enantiomeric excesses. As a consequence of COSAC's 'Chirality-Experiment' far-reaching results are expected to investigate the various hypotheses about the first asymmetric synthesis. 相似文献
160.
Kallenbach R. Robert F. Geiss J. Herbst E. Lammer H. Marty B. Millar T.J. Ott U. Pepin R.O. 《Space Science Reviews》2003,106(1-4):319-376
Volatile isotope abundances are tracers for the evolutionary processes of the solar system. At the same time they carry information
on the galactic nucleosynthetic sources, from which solar matter originates. This working group report summarizes the present
knowledge and addresses unresolved issues regarding fractionation of isotopes of volatile elements in the solar system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献