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201.
The plasma produced by a Kaufman (UK-25) ion thruster possesses four distinct regions. The interaction of two of these regions, the coupling and discharge plasmas, is important for thruster design and efficiency, since it controls the production of the primary electrons responsible for most of the ionisation in the thruster. This paper details the measurement and analysis techniques used to obtain two-dimensional experimental plasma parameter maps across a plasma double layer in the baffle aperture region of this type of ion thruster. This plasma-interaction region was mapped experimentally using Langmuir probes.The Langmuir probe data were collected and analysed to produce maps of plasma potential, Maxwellian and primary electron energy and number density. Detailed static magnetic field measurements using Hall-effect probes were also obtained. A number of derived plasma parameter maps were then made possible, such as electron pressure. The application of the analysis techniques used here allowed ion thruster plasma property maps to be constructed of a spatial extent and resolution previously unseen. Two-dimensional maps of the spatial location of primary electrons are presented, as effected by applied magnetic field changes, along with the detection of regions showing depletion of primary electron energies. 相似文献
202.
203.
Yuriy Sumin Sergey F. Kostromin Nikolai Panichkin Yves Prel Mikhail Osin David Iranzo-Greus Marco Prampolini 《Acta Astronautica》2009,65(7-8):943-948
This paper presents the study of a concept of Ariane-5 evolution by means of replacement of two solid-propellant boosters EAP with two liquid-propellant reusable fly-back boosters (RFBBs) called “Bargouzine”. The main design feature of the reference RFBB is LOX/LH2 propellant, the canard aerodynamic configuration with delta wings and rocket engines derived from Vulcain-2 identical to that of the central core except for the nozzle length. After separation RFBBs return back by use of air breathing engines mounted in the aft part and then landing on a runway.The aim of the study is a more detailed investigation of critical technology issues concerning reliability, re-usability and maintenance requirements. The study was performed in three main phases: system trade-off, technical consolidation, and programmatic synthesis. The system trade-off includes comparative analysis of two systems with three and four engines on each RFBB and determination of the necessary thrust level taking into account thrust reservation for emergency situations. Besides, this phase contains trade-off on booster aerodynamic configurations and abort scenario analysis.The second phase includes studying of controllability during the ascent phase and separation, thermo-mechanical design, development of ground interfaces and attachment means, and turbojets engine analysis taking into account reusability. 相似文献
204.
Interplanetary transfer of photosynthesis: an experimental demonstration of a selective dispersal filter in planetary island biogeography 总被引:2,自引:0,他引:2
Cockell CS Brack A Wynn-Williams DD Baglioni P Brandstätter F Demets R Edwards HG Gronstal AL Kurat G Lee P Osinski GR Pearce DA Pillinger JM Roten CA Sancisi-Frey S 《Astrobiology》2007,7(1):1-9
We launched a cryptoendolithic habitat, made of a gneissic impactite inoculated with Chroococcidiopsis sp., into Earth orbit. After orbiting the Earth for 16 days, the rock entered the Earth's atmosphere and was recovered in Kazakhstan. The heat of entry ablated and heated the rock to a temperature well above the upper temperature limit for life to below the depth at which light levels are insufficient for photosynthetic organisms ( approximately 5 mm), thus killing all of its photosynthetic inhabitants. This experiment shows that atmospheric transit acts as a strong biogeographical dispersal filter to the interplanetary transfer of photosynthesis. Following atmospheric entry we found that a transparent, glassy fusion crust had formed on the outside of the rock. Re-inoculated Chroococcidiopsis grew preferentially under the fusion crust in the relatively unaltered gneiss beneath. Organisms under the fusion grew approximately twice as fast as the organisms on the control rock. Thus, the biologically destructive effects of atmospheric transit can generate entirely novel and improved endolithic habitats for organisms on the destination planetary body that survive the dispersal filter. The experiment advances our understanding of how island biogeography works on the interplanetary scale. 相似文献
205.
David J. McComas 《Space Science Reviews》2009,143(1-4):125-138
The Voyager 1 and 2 spacecraft recently crossed the termination shock and are currently sending back groundbreaking and detailed observations at two locations in the inner heliosheath. Complementary global observations will soon be provided by the Interstellar Boundary Explorer—IBEX, which measures energetic neutral atoms (ENAs) produced via charge exchange with energetic protons in this region. While several data sets from instruments on other spacecraft have provided tantalizing observations that might be heliosheath ENAs, none has definitively shown that they are observing this source. In contrast, IBEX has been specifically designed and developed to make all-sky observations of inner heliosheath ENAs with very high sensitivity and signal to noise. These observations will provide the critical global perspective required to understand the three-dimensional heliospheric interaction with the Circum-Heliospheric Interstellar Medium (CHISM). This paper, written prior to the launch of IBEX, reviews previous observations and provides background on this important new mission. 相似文献
206.
Koji Matsumoto Hideo Hanada Noriyuki Namiki Takahiro Iwata Sander Goossens Seiitsu Tsuruta Nobuyuki Kawano David D. Rowlands 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Results of numerical simulations are presented to examine the global gravity field recovery capability of the Japanese lunar exploration project SELENE (SELenological and ENgineering Explorer) which will be launched in 2007. New characteristics of the SELENE lunar gravimetry include 4-way satellite-to-satellite Doppler tracking of main orbiter and differential VLBI tracking of two small free-flier satellites. It is shown that the proposed satellite constellation will provide the first truly global satellite tracking data coverage. The expected results from these data are; (1) drastic reduction in far-side gravity error, (2) estimation of many gravity coefficients by the observation, not by a priori information, and (3) one order of magnitude improvement over existing gravity models for low-degree field. 相似文献
207.
CUTTINGTEMPERATUREOFCBNTOOLSWHENMACHININGSTEELOFMEDIUMHARDNESSChenWuyi1(陈五一),DavidK.Aspinwal2,HanShuwen3(韩书文)1BeijingUniversi... 相似文献
208.
A.B. Burgess A. Dudhia R.G. Grainger D. Stevenson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,37(12):2218-II
The Michelson Interferometer for Passive Atmospheric Sounding is a polar orbiting high resolution mid-infrared emission limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of routinely retrieved species led to the examination of ammonia, NH3. In this paper, we explore the feasibility of upper tropospheric retrievals around 6-km altitude, discussing appropriate methods. We demonstrate a weak north to south gradient outside the error bars, using co-addition to improve signal-to-noise and compare these first results with a model. 相似文献
209.
A lunar L2-Farside exploration and science mission concept with the Orion Multi-Purpose Crew Vehicle and a teleoperated lander/rover 总被引:1,自引:0,他引:1
Jack O. Burns David A. Kring Joshua B. Hopkins Scott Norris T. Joseph W. Lazio Justin Kasper 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
A novel concept is presented in this paper for a human mission to the lunar L2 (Lagrange) point that would be a proving ground for future exploration missions to deep space while also overseeing scientifically important investigations. In an L2 halo orbit above the lunar farside, the astronauts aboard the Orion Crew Vehicle would travel 15% farther from Earth than did the Apollo astronauts and spend almost three times longer in deep space. Such a mission would serve as a first step beyond low Earth orbit and prove out operational spaceflight capabilities such as life support, communication, high speed re-entry, and radiation protection prior to more difficult human exploration missions. On this proposed mission, the crew would teleoperate landers/rovers on the unexplored lunar farside, which would obtain samples from the geologically interesting farside and deploy a low radio frequency telescope. Sampling the South Pole-Aitken basin, one of the oldest impact basins in the solar system, is a key science objective of the 2011 Planetary Science Decadal Survey. Observations at low radio frequencies to track the effects of the Universe’s first stars/galaxies on the intergalactic medium are a priority of the 2010 Astronomy and Astrophysics Decadal Survey. Such telerobotic oversight would also demonstrate capability for human and robotic cooperation on future, more complex deep space missions such as exploring Mars. 相似文献
210.
Maria T. Zuber Oded Aharonson Jonathan M. Aurnou Andrew F. Cheng Steven A. Hauck II Moritz H. Heimpel Gregory A. Neumann Stanton J. Peale Roger J. Phillips David E. Smith Sean C. Solomon Sabine Stanley 《Space Science Reviews》2007,131(1-4):105-132
Current geophysical knowledge of the planet Mercury is based upon observations from ground-based astronomy and flybys of the
Mariner 10 spacecraft, along with theoretical and computational studies. Mercury has the highest uncompressed density of the
terrestrial planets and by implication has a metallic core with a radius approximately 75% of the planetary radius. Mercury’s
spin rate is stably locked at 1.5 times the orbital mean motion. Capture into this state is the natural result of tidal evolution
if this is the only dissipative process affecting the spin, but the capture probability is enhanced if Mercury’s core were
molten at the time of capture. The discovery of Mercury’s magnetic field by Mariner 10 suggests the possibility that the core
is partially molten to the present, a result that is surprising given the planet’s size and a surface crater density indicative
of early cessation of significant volcanic activity. A present-day liquid outer core within Mercury would require either a
core sulfur content of at least several weight percent or an unusual history of heat loss from the planet’s core and silicate
fraction. A crustal remanent contribution to Mercury’s observed magnetic field cannot be ruled out on the basis of current
knowledge. Measurements from the MESSENGER orbiter, in combination with continued ground-based observations, hold the promise
of setting on a firmer basis our understanding of the structure and evolution of Mercury’s interior and the relationship of
that evolution to the planet’s geological history. 相似文献