17,060 research outputs found
Attitude Determination of Unmanned Aerial Vehicle using Single Camera Vector Observations
Technological development in the fields of electrical and mechanical engineering as well as computer and communication sciences in the last decade, have dramatically increased the popularity and fields of application of Unmanned Aerial Vehicles (UAVs). Despite the technological advancements, there are still very important challenges related to the operation of UAVs. One of the main challenging task for UAVs is to accurately determine their attitude during the flight, using the onboard sensors. This paper presents a framework for attitude determination of an UAV from single camera vector observations in a known environment. The framework has been experimentally evaluated. The results from the conducted evaluation suggest that the proposed method is appropriate and that it can be used in the control proces
Locating the LCROSS Impact Craters
The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted
a spent Centaur rocket stage into a permanently shadowed region near the lunar
south pole. The Sheperding Spacecraft (SSC) separated \sim9 hours before impact
and performed a small braking maneuver in order to observe the Centaur impact
plume, looking for evidence of water and other volatiles, before impacting
itself. This paper describes the registration of imagery of the LCROSS impact
region from the mid- and near-infrared cameras onboard the SSC, as well as from
the Goldstone radar. We compare the Centaur impact features, positively
identified in the first two, and with a consistent feature in the third, which
are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta
region. The images are registered to Lunar Reconnaisance Orbiter (LRO)
topographical data which allows determination of the impact location. This
location is compared with the impact location derived from ground-based
tracking and propagation of the spacecraft's trajectory and with locations
derived from two hybrid imagery/trajectory methods. The four methods give a
weighted average Centaur impact location of -84.6796\circ, -48.7093\circ, with
a 1{\sigma} un- certainty of 115 m along latitude, and 44 m along longitude,
just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC
impact location is -84.719\circ, -49.61\circ, with a 1{\sigma} uncertainty of 3
m along the Earth vector and 75 m orthogonal to that, 766 m from the target
location and 2.803 km south-west of the Centaur impact. We also detail the
Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS
mission requirements are shown to be met by wide margins. We hope that these
results facilitate further analyses of the LCROSS experiment data and follow-up
observations of the impact region.Comment: Accepted for publication in Space Science Review. 24 pages, 9 figure
Algorithms for autonomous star identification
Algorithms for onboard autonomous star identification are presented. The algorithms are applicable to two types of spacecraft missions, those flown with nearly inertially fixed attitude (solar maximum mission type); and those flown with smoothly time varying attitude (LANDSAT-D type)
Mariner Mars 1971 optical navigation demonstration
The feasibility of using a combination of spacecraft-based optical data and earth-based Doppler data to perform near-real-time approach navigation was demonstrated by the Mariner Mars 71 Project. The important findings, conclusions, and recommendations are documented. A summary along with publications and papers giving additional details on the objectives of the demonstration are provided. Instrument calibration and performance as well as navigation and science results are reported
Video guidance, landing, and imaging systems
The adaptive potential of video guidance technology for earth orbital and interplanetary missions was explored. The application of video acquisition, pointing, tracking, and navigation technology was considered to three primary missions: planetary landing, earth resources satellite, and spacecraft rendezvous and docking. It was found that an imaging system can be mechanized to provide a spacecraft or satellite with a considerable amount of adaptability with respect to its environment. It also provides a level of autonomy essential to many future missions and enhances their data gathering ability. The feasibility of an autonomous video guidance system capable of observing a planetary surface during terminal descent and selecting the most acceptable landing site was successfully demonstrated in the laboratory. The techniques developed for acquisition, pointing, and tracking show promise for recognizing and tracking coastlines, rivers, and other constituents of interest. Routines were written and checked for rendezvous, docking, and station-keeping functions
The Pointing System of the Herschel Space Observatory. Description, Calibration, Performance and Improvements
We present the activities carried out to calibrate and characterise the
performance of the elements of attitude control and measurement on board the
Herschel spacecraft. The main calibration parameters and the evolution of the
indicators of the pointing performance are described, from the initial values
derived from the observations carried out in the performance verification phase
to those attained in the last year and half of mission, an absolute pointing
error around or even below 1 arcsec, a spatial relative pointing error of some
1 arcsec and a pointing stability below 0.2 arsec. The actions carried out at
the ground segment to improve the spacecraft pointing measurements are
outlined. On-going and future developments towards a final refinement of the
Herschel astrometry are also summarised. A brief description of the different
components of the attitude control and measurement system (both in the space
and in the ground segments) is also given for reference. We stress the
importance of the cooperation between the different actors (scientists, flight
dynamics and systems engineers, attitude control and measurement hardware
designers, star-tracker manufacturers, etc.) to attain the final level of
performance.Comment: 28 pages, 8 figures, accepted for publication in Experimental
Astronom
Orbit/attitude estimation for the GOES spacecraft using VAS landmark data
A software system is described which provides for batch least squares estimation of spacecraft orbit, attitude, and camera bias parameters using image data from the Geostationary Operational Environmental Satellites (GOES). The image data are obtained by the Visible and Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS). The resulting estimated parameters are used for absolute image registration. Operating in the Digital Equipment Corporation (DEC) PDP-11/70 computer, the FORTRAN system also includes the capabilities of image display and manipulations. An overview of the system is presented as well as some numerical results obtained from observations taken by the SMS-2 satellite over a 3 day interval in August 1975
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