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881.
The global positioning system (GPS) is a satellite-based radio navigation system to provide extremely accurate three-dimensional position fixes and system time to users anywhere on the Earth at any time regardless of weather conditions. The most significant performance parameter of the GPS is the degree of navigation accuracy which is strongly coupled to the choice of orbit configuration. The 3 X 8 orbit configuration has been considered as an operational GPS which consists of 24 satellites deployed in circular 63° inclined, subsynchronous 12-h orbits. In this paper, the geometric performance of several orbit configuration, including a 3 X 8 orbit configuration, is analyzed numerically by altering orbit period and elevation mask, respectively. It will be shown that 1) there are a few orbit configurations which are comparable to or better than the baseline 3 X 8 orbit configuration, and 2) for higher elevation mask, the geometric performance can be improved effectively by increasing orbit period to some extent. 相似文献
882.
B. Kirov K. Georgieva E. Apostolov M. Gusheva I. Kutiev S. Chapkunov Yu. Simeonova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):89-92
A Retarding Potential Analyzer (RPA) is designed using a micro-channel plate in front of the collector as a flow amplifier, which makes it possible to detect ion species with very low concentration (<0,5 cm.?3). A technique is described for using the micro-channel plate at abnormally high pressure (>0.01 N/m2). This allows the precise determination of the mass composition of the low ionosphere. An adaptive retarding potential consisting of 2048 steps is used to increase the sensitivity. This retarding potential is applied in the range where dI/dU ≠ 0. The sensor is hermetically sealed and opens on command. 相似文献
883.
A. Urban K.M. Torkar J. Bjordal J.A˚. Lundblad F. Søraas B. Grandal L.G. Smith J.C. Ulwick R.P. Vancour 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):77-80
Measurements of the precipitation of electrons and positive ions (in the keV to MeV range) detected aboard eight rockets launched from Northern Scandinavia are reported together with corresponding satellite data. The downgoing integral fluxes indicate the temporal fluctuations during each flight. Height profiles of the energy deposition into the atmosphere at different levels of geomagnetic disturbance are given. 相似文献
884.
Venkatesan S. Fetcenko M.A. Dhar S.K. Ovshinsky S.R. 《Aerospace and Electronic Systems Magazine, IEEE》1991,6(11):26-30
The environmental advantages of ovonic NiH2 batteries, due to the nontoxicity of ovonic alloys, are briefly discussed, and their general performance is described. Commercial progress in their development is summarized. Their use in electric vehicles is examined 相似文献
885.
886.
Active nutation damping generally requires a unique element to provide the necessary damping torques, plus a nutation-sensing system to properly monitor and control the active element by closed-loop action. This paper describes and analyzes, by computer- assisted mathematical techniques, a nutation damper for a dual-spin spacecraft which does not require an active ?element?. Damping is achieved through the inherent cross-axis torques generated by the spacecraft products of inertia and the existing motor controlling the relative spin rates of the two dynamic components comprising the spacecraft. 相似文献
887.
888.
Magnetic field experiment for Voyagers 1 and 2 总被引:1,自引:1,他引:0
K. W. Behannon M. H. Acuna L. F. Burlaga R. P. Lepping N. F. Ness F. M. Neubauer 《Space Science Reviews》1977,21(3):235-257
The magnetic field experiment to be carried on the Voyager 1 and 2 missions consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of ± 0.5 G for the LFM's and ± 20 G for the HFM's, low quantization uncertainty of ± 0.002 ( = 10–5 G) in the most sensitive (± 8 ) LFM range, low sensor RMS noise level of 0.006 , and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, and possibly Uranus; satellites of these planets; solar wind and satellite interactions with the planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic, field. The interstellar field may also be measured. 相似文献
889.
Kosta S.P. Lakshmeesha V.K. Nicholas L. 《IEEE transactions on aerospace and electronic systems》1978,(2):364-367
Calculations are made to obtain the raw electrical power that can be generated by using an ATS-6 type deployable parabolic dish as a surface for mounting solar cells without seriously interfering with its normal function as an antenna. A minimum of a few hundred watts to a maximum of a few kilowatts are generated during the apparent course of the Sun around the spacecraft. Academically, it seems that deployable solar cell panels along with their booms can be avoided. 相似文献
890.
Dramatic reductions in size and weight have been achieved in the area of signal and information processing. Power conditioning circuits have not kept pace, primarily due to the relatively slow proggress ress in the passive energy storage and transformation devices. A novel converter topology is described that minimizes the task these components must perform and thereby achieve a significant improvement in power supply density. 相似文献