Satellite Center Research Articles

Path Planning For Satellite Mounted Robots

One of the most important problems in space based robotics is the disturbance to the satellite attitude and to the satellite microgravity environment caused by satellite mounted robot operation. This paper reports on the development of algorithms for optimal path planning that minimizes these disturbances, and solve the inverse kinetics problem, i.e. with the satellite attitude control system off. Specific optimality criteria are studied, including minimum induced angular velocity of the satellite and minimizing the maximum acceleration of the satellite center of mass. In addition, the space based analog is generated for the common ground based linear interpolation in joint or Cartesian space, i.e. shortest distance paths. Some properties of the various types of optimal paths are developed analytically, and understanding of the typical nature of the optimal paths is obtained in numerical examples. The shortest paths in principal planes, seen in inertial space, are shown to be arcs of circles. The computation required to produce such optimized trajectories is 1 or 2 minutes on a workstation, and methods can be used to substantially decrease this number if necessary. Thus, it can be practical to make use of these optimized path plans in space.

SECTION OF PLANETARY SCIENCES: DATA UTILIZATION FROM METEOROLOGICAL SATELLITES*

Transactions of the New York Academy of SciencesVolume 31, Issue 8 Series II p. 1103-1105 SECTION OF PLANETARY SCIENCES: DATA UTILIZATION FROM METEOROLOGICAL SATELLITES* Clifford A. Spohn Sc.D., Clifford A. Spohn Sc.D. Director Office of Operations, National Environmental Satellite Center Suitland, Md.Search for more papers by this author Clifford A. Spohn Sc.D., Clifford A. Spohn Sc.D. Director Office of Operations, National Environmental Satellite Center Suitland, Md.Search for more papers by this author First published: December 1969 https://doi.org/10.1111/j.2164-0947.1969.tb02028.x † This paper was presented at a meeting of the Section on May 27, 1969. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume31, Issue8 Series IIDecember 1969Pages 1103-1105 RelatedInformation

Giant icebergs in the Weddell Sea, 1967–68

Two giant icebergs are moving westwards along the coast of Antarctica in the Weddell Sea. They were conspicuous throughout the 1967–68 season in ESSA-3 satellite photographs supplied by the United States National Environmental Satellite Center to the British Antarctic Survey. The two icebergs were first unmistakeably seen during orbit No 4699 on 11 October 1967 and last clearly seen before the winter during orbit No 6408 on 24 February 1968. The leading iceberg, which is roughly 45 km by 100 km, was last seen moving out to sea westwards from a position about 100 km north of Halley Bay station. The second, some 70 km by 100 km, was parallel with Riiser-Larsen Ice Front in long 21°W, and separated from it by only a few kilometres of open water. Although there were periods of weeks in which there was no movement, presumably owing to the grounding of the icebergs on shoals, both moved some 500 km along the coast in four months.

Report on the test and the calibration of a Tiros III five-channel radiometer : Roche, J. J., and A. J. Drummond, The Eppley Laboratory, Inc., and D. T. Hilleary, Meteorological Satellite Laboratory, (CWB10075), prepared for the National Weather Satellite Center, 6 April 1964, 48 pgs.

This paper describes a methodology used to evaluate pyranometers and reference cell performance in relation to solar overirradiance (OIR) events. By definition, these events are characterized when global horizontal irradiance (GHI) exceeds the extraterrestrial horizontal irradiance (ETH) due to cloud enhancement (CE) effects (e.g. scattering, reflection, cloud lense augmentation). Evaluation metrics are proposed to assess relevant features of the events such as uncertainty, event identification, and response time. The metrics were validated with high standard radiometers deployed at the Solar Energy Research Laboratory Fotovoltaica/UFSC in Florianópolis, Brazil. The results were checked against solar radiometers' specifications, and sensors were analyzed according to their performances. An ISO outdoor calibration, as well as a system uncertainty analysis and data response time evaluation, were performed, to assure results reliability. In addition, two extreme overirradiance (EOIR) events were evaluated separately, and seasonal occurrence of the energy fraction of overirradiance events was assessed and discussed.

Control of a synchronous satellite by continuous radial thrust

The motion of a satellite in an arbitrary circular orbit, resulting from the action of small, continuous forces acting circumferentially, radially, and normally to the orbit for short periods is discussed. A correlation is made between this motion and that of an equatorial synchronous satellite undergoing corrective orbital maneuvers by a single thruster, nominally pointing in a radial direction, but vectored to produce circumferential, normal, and incremental radial thrust components. A system is described employing such a single thruster for attitude and position control, and this system is shown to be competitive with a multiple-thruster system for long-life satellites. SYNCHRONOUS satellite is one that is launched in an easterly direction into a circular orbit having the same period as the rotational period of the earth. If this orbit lies in the equatorial plane, the satellite will appear to remain fixed in the sky, relative to an observer on earth. Over an extended period of time, the satellite, however, will not maintain its relative fixed position, owing to known perturbations from the moon, sun, and the earth's elliptical equatorial section (triaxiality). The conventional way of overcoming these perturbations is to have a multiple thruster system onboard the satellite which delivers a succession of impulses of appropriate magnitude and direction. Because of errors inherent in the control of thrust duration and thrust magnitude, and because of the impulsive nature of the corrective forces, the intermittent action of the thrusters will further perturb the position of the satellite. A simpler and presumably more reliable system to employ for position control consists of a single thruster (low thrust), operating continuously, and thrusting in a nominally radial direction. It is shown in this paper that a radial thruster of this type can maintain a satellite in a synchronous orbit at an altitude differing from that of the classical synchronous orbit. If the thruster is provided with the capability of vectoring in any direction about its nominal position, it will be able to correct the orbital errors caused by the sun, moon, and the earth's triaxiality. By mounting the thruster on an arm that is gimballed at the satellite center of mass, and again at a point close to the thruster, it will be possible to provide independent control of the position and attitude of the satellite. Ion propulsion is particularly suited for attitude and position control due to the anticipated long lifetime of the satellite. In comparing a multiple (9) ion thruster system with an equivalent single ion thruster, it is found that the total weights of both systems are quite similar.

Space Science

This fall, the University of Miami will set up a School of Environmental and Planetary Sciences, providing interdisciplinary programs leading to both master's and doctoral degrees. The School will consist of four cooperating divisions—new Institutes of Atmospheric Science, of Space Physics, and of Planetary Bioscience which will join Miami's Institute of Marine Science, established in 1942. Maximum enrollment is expected to be about 400, with some 100 graduate students in each institute. Named as dean of the complex is S. Fred Singer, who is resigning from his post as director of the National Weather Satellite Center in Washington, D.C.