排序方式: 共有44条查询结果,搜索用时 25 毫秒
31.
The aim of this paper is to study, from a mission analysis point of view, the performance of a hybrid propulsion concept for a two-dimensional transfer towards a planet of the Solar System. The propulsion system is obtained by combining a chemical thruster, used for the phases of Earth escape and/or target planet capture, with an electric sail, which provides a continuous thrust during the heliocentric transfer. Two possible mission scenarios are investigated: in the first case the sailcraft reaches the target planet with zero hyperbolic excess velocity, thus performing a classical rendezvous mission in a heliocentric framework. In the second mission scenario, a given final hyperbolic excess velocity relative to the planet is tolerated in order to decrease the mission flight time. The amount of final hyperbolic excess velocity is used as a simulation parameter for a tradeoff study in which the minimum flight time is related to the total velocity variation required by the chemical thruster to accomplish the mission, that is, for Earth escape and planetary capture. 相似文献
32.
33.
Paulino-Lima IG Janot-Pacheco E Galante D Cockell C Olsson-Francis K Brucato JR Baratta GA Strazzulla G Merrigan T McCullough R Mason N Lage C 《Astrobiology》2011,11(9):875-882
In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD(10)) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4?keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200?keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD(10) increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study. 相似文献
34.
Optical data taken in January 1987 from La Silla, when compared with the discovery plate of 1975.2 show no proper motion for PSR 0833-45, while a very significant one was expected if the pulsar originated in the center of the Vela SNR, which has so far been associated with it. If such an association is to be retained, either an extreme asymmetry of the SNR is required, or both objects are much older than has so far been thought. Both alternatives have their difficulties, thus possibly casting doubts on the reality of this classic SNR/pulsar association.Based on observations collected at the European Southern Observatory, La Silla, Chile. 相似文献
35.
R. Monti G. Mannara 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):121-132
Potential application of non invasive surface temperature measurements in Material Science and Fluid Science microgravity experiments is reviewed by analyzing the experiments that can benefit of thermographic techniques and by identifying the parameters that can be directly or indirectly measured. The hardware and software requirements of a thermographic equipment are indicated for a system of use in space.
The capabilities and the relevant features are described of a computerized system, conceived and breadboarded in connection to ESA activities related to Fluid Science Facilities. 相似文献
36.
Preliminary validation of computational procedures for a new atmospheric ionizing radiation (AIR) model. 总被引:1,自引:0,他引:1
John M Clem Giovanni De Angelis Paul Goldhagen John W Wilson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(1):27-33
A new computational procedure to determine particle fluxes in the Earth's atmosphere is presented. The primary cosmic ray spectrum has been modeled through an analysis of simultaneous proton and helium measurements made on high altitude balloon flights and spacecraft. An improved global fit to the data was achieved through applying a unique technique utilizing the Fokker-Plank equation with a non-linear rigidity-dependent diffusion coefficient. The propagation of primary particles through the Earth's atmosphere is calculated with a three-dimensional Monte Carlo transport program called FLUKA. Primary protons and helium nuclei (alphas) are generated within the rigidity range of 0.5 GV-20 TV uniform in cos2 theta. For a given location, primaries above the effective cutoff rigidity are transported through the atmosphere. Alpha particles are initially transported with a separate package called HEAVY to simulate fragmentation. This package interfaces with FLUKA to provide interaction starting points for each nucleon originating from a helium nucleus. Results from this calculation are presented and compared to measurements. 相似文献
37.
A free floating platform is realized with a pneumatic suspension system which enables a two-dimensional test of complex space operations, such as rendezvous and docking. The platform is equipped with a IMU and actuated via cold gas thrusters. In addition, an on-board camera is used to acquire a target and its image is processed for evaluating the control actions needed to reach it. A technique for determining the relative position and velocity with respect to target using the same visual device is proposed and realized. The novel algorithms and relevant experimental results are presented. The tested accuracy of the relative navigation system is not very high, but the guidance algorithm, which is image based and has just a weak dependence on the position information, is robust enough to perform a successful maneuver. The error between the final acquired target image and the desired final target image is of the order of one pixel, notwithstanding all the testbed disturbances. 相似文献
38.
39.
Riccardo Notarpietro Manuela Cucca Marco Gabella Giovanna Venuti Giovanni Perona 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
One of the most attractive scientific issues in the use of GNSS (Global Navigation Satellite System) signals, from a meteorological point of view, is the retrieval of high resolution tropospheric water vapour maps. The real-time (or quasi real-time) knowledge of such distributions could be very useful for several applications, from operative meteorology to atmospheric modelling. Moreover, the exploitation of wet refractivity field reconstruction techniques can be used for atmospheric delay compensation purposes and, as a very promising activity, it could be applied for example to calibrate SAR or Interferometric-SAR (In-SAR) observations for land remote sensing. This is in fact one of the objectives of the European Space Agency project METAWAVE (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water vapour Effects), in which several techniques are investigated and results were compared to identify a strategy to remove the contribution of water vapour induced propagation delays in In-SAR products. Within this project, the tomographic reconstruction of three dimensional wet refractivity fields from tropospheric delays observed by a local GNSS network (9 dual frequency GPS receivers) deployed over Como area (Italy), during 12–18 October, 2008, was performed. Despite limitations due to the network design, internal consistency tests prove the efficiency of the adopted tomographic approach: the rms of the difference between reconstructed and GNSS observed Zenith Wet Delays (ZWD) are in the order of 4 mm. A good agreement is also observed between our ZWDs and corresponding delays obtained by vertically integrating independent wet refractivity fields, taken by co-located meteorological analysis. Finally, during the observing period, reconstructed vertical wet refractivity profiles evolution reveals water vapour variations induced by simple cloud covering. Even if our main goal was to demonstrate the effectiveness in adopting tomographic reconstruction procedures for the evaluation of propagation delays inside water vapour fields, the actual water vapour vertical variability and its evolution with time is well reproduced, demonstrating also the effectiveness of the inferred 3D wet refractivity fields. 相似文献
40.