Onboard Computer Memory Research Articles

КОМБІНОВАНИЙ МЕТОД ВИЗНАЧЕННЯ ПОТОЧНОГО ЗНАЧЕННЯ КООРДИНАТ НАВІГАЦІЙНОЮ СИСТЕМОЮ З ФІЛЬТРОМ ЧАСТИН РАО-БЛЕКВЕЛЛА

Modern trends in the development of information technology and robotics, sets before us the task of adapting obsolete navigation systems of military equipment to the requirements of our time. Existing navigation systems are widely used in both military and civilian spheres The analysis of existing navigation systems showed a number of negative problems, which became the reason for work to create a navigation system that could meet the following requirements: low financial costs for production, mobility, small overall dimensions, accuracy in determining coordinates and the most important - autonomy. The most effective methods for positioning autonomous moving objects is the method for calculating the coordinates of the EKF-SLAM with the Rao-Blackwell parts filter. This article presents a combined method for determining the current coordinate value by a navigation system with a Rao-Blackwell parts filter. The Rao-Blackwell filter for mapping progressively processes observation and odometer evidence as they become available. This process is accomplished by resuming a set of samples that represent the posterior on the map and the vehicle’s path. The proposed way of modifying the well-known mathematical relations of Kalman filters from the point of view of their adaptation to the peculiarities of algorithmic and software implementation in onboard computers provides savings in onboard computer memory and reduces the required computing resource. It is noticed that the algorithms for the implementation of SLAM navigation are changed in the proposed way using a smaller number of particles than methods based only on the frequency filter. The error in the initial calculation of the coordinates of landmarks is minimized and does not accumulate over time in a mathematical sense. Keywords: Autonomous mobile object, Simultaneous Localization And Mapping, EKF-SLAM, Gmapping, Rao-Blackwell particle filter, covariance, parameter prediction, positioning, orientation algorithm, Kalman filter.

Быстрый алгоритм идентификации кадра звездного датчика по звездным конфигурациям, не требующий перебора. Вариант бортовой реализации

The paper presents a method for identifying the frame of a star sensor (SS), based on determination of the star local features allowing its unique recognition. The star identifiers are located in a multidimensional integer feature space, and the relevant feature catalog presents a disperse array, which provides search-free star determination. Examples of onboard implementation of feature catalog are presented, containing the stars up to magnitude of six. The required memory is estimated, and a method is proposed for compressing the feature catalog to be recorded in the onboard computer memory. The frame identification algorithm using the reduced feature catalog is described in detail. The algorithm was tested on real sky frames.

Calibration of Model Parameters in Navigation Devices Based on Fiber-Optic Gyroscopes

The features of navigation devices based on fiber-optic gyroscopes cause problems in their practical applications and require calibration prior to being used. The algorithms for accumulating and processing the information of strapdown inertial blocks (SIBs) based on fiber-optic gyroscopes and units determining the stars’ coordinates (UDSC) are given. The calibration algorithms are modified to reduce the onboard computer memory and take into account the time limitations of the program execution. The results of the modeling prove the efficiency of the proposed solutions.

SEFI Protection for Nanosat 16-Bit Chip Onboard Computer Memories

Plans to launch miniaturized satellite missions have been increasing in the last few years. Space missions like these are exposed to radiation, which is a cause of errors in electronic systems. Memories are one of the electronic systems that need special attention. Radiation effects in memories include single-event upsets (SEUs), multiple cell upsets, and single-event functional interrupts (SEFIs). In this paper, two solutions are presented to protect a nano/pico satellite onboard computer memory prototype with 16-bit data words against SEFIs and SEUs. The prototype uses a 32-bit memory interface, organized in two 16-bit chips. The approach to provide the error-correction capabilities is based on orthogonal latin square codes. The results show that the area and delay introduced by the solutions are acceptable. When a SEFI affects one of the chips, the solutions are able to recover the information using the remaining data.

Buoy pitch and roll computed using three angular rate sensors

The National Data Buoy Center (NDBC), a part of the US National Weather Service (NWS), operates networks of data buoys. Each buoy measures, and reports to shore each hour, air temperature, water temperature, barometric pressure, wind speed, wind direction, and nondirectional wave data. Some 15 discus-type buoys report directional wave data each hour. The systems aboard these buoys apply measurement and analysis techniques that require time-series records of hull east and north slopes, which are, in turn, based on measurements of hull bow azimuth, pitch, and roll. Pitch and roll are normally measured on NDBC hulls using the Datawell (Netherlands) Hippy 40 model sensor. Time-series records of pitch and roll thus measured are stored in the onboard computer memory of a wave processing module. These pitch and roll records are used in conjunction with hull azimuth and heave acceleration time series to compute directional wave data. The Hippy 40 heave, pitch, roll sensor consumes little power, is reliable when handled correctly, and provides sufficiently accurate measurements of pitch and roll. On the other hand, it is heavy, large, requires special handling, and is expensive. Thus, NDBC needs an alternative basis for the measurement of hull pitch and roll. In recent years, low-cost, solid-state angular rate sensors have become available. Three of these small, inexpensive sensors, when mounted orthogonally in a buoy, can produce estimates of the body-fixed components of the angular velocity vector. From the time-series outputs of these sensors aboard a discus hull, there are mathematical means to produce time-series records of wave-frequency pitch and roll relative to mean pitch and roll. Other sensors provide mean values of pitch and roll, so that by summing, instantaneous total hull pitch and roll records can be produced. The NDBC existing onboard-buoy wave processing module (WPM) system can process these total pitch and roll records just as if they had come from a Hippy 40, so that little change to NDBC's existing WPM hardware/software, or to the shore-based supporting software, is necessary to produce a new directional wave measurement system based on angular rate sensors. This paper describes the techniques NDBC is employing to produce wave-frequency pitch and roll relative to mean pitch and roll, and the necessary additional sensors needed to determine mean pitch and mean roll. The validity of these techniques is demonstrated by comparing pitch and roll records resulting from their application to pitch and roll records taken directly from the Hippy 40. NDBC's plans for the employment of this new pitch-roll measuring technique in a modified WPM system are summarized.

Correction of Spacecraft Autonomous Navigation System Using Terrain Image Processing and Analysis

Structures of on-board autonomous navigation systems that spacecraft coordinates estimation by analysis of on-board camera data without receiving extra data from earth ground stations or other external sources are considered. Various approaches to correct the autonomous navigation system (ANS) of a spacecraft based on comparison of current images (CI) of the earth&s surface obtained on board, for example in optical wave band, and digital terrain maps (Reference Images, RI) stored in on-board computer memory are considered. Recommendations for increasing the efficiency of image processing (from the point of view of algorithm speed) are suggested. Results concerning potential accuracy of such systems are cited.

THE FRACTION OF CLOSE BINARIES AMONG HUBBLE SPACE TELESCOPE GUIDE STARS - OPERATIONAL CONSEQUENCES, WORKAROUNDS, AND SUGGESTIONS FOR DESIGNERS OF FUTURE SPACE OBSERVATORIES

ABSTRACT It is observationally determined that a significant number of guide stars which will be used by the Hubble Space Telescope are close binaries which can prevent a Fine-Guidance-Sensor fine lock. This is because the Fine Guidance Sensors (FGSs) operate as white-light interferometers, and the fringe patterns of binaries will result in a reduction in the loop gain in the FGS control system. Consequently, multiple guide stars must be attempted to ensure a successful acquisition. The limited HST on-board computer memory may restrict the number of guide stars which can be attempted, resulting in a possible loss of several hundred hours per year of observing time. The FGSs of the next-generation (and presumably larger) space-telescopes would be even more susceptible to the binary problem. Other types of guidance systems (such as quadrant detectors) deserve serious consideration for future space observatories.

Guidance and Control System Design of the Viking Planetary Lander

This paper describes the salient features and unique problem solutions for the Viking lander guidance and control system design. Because of the following design requirements imposed, the lander guidance and control function presented stringent design challenges. These requirements were as follows: 1) a completely autonomous operation was required although the onboard computer memory size was limited to solve the descent problem; 2) the lander deorbit maneuver had to be very accurate to achieve a satisfactory planet atmospheric entry and an accurate touchdown at the predicted landing site; 3) the landers had to descend through an unknown atmosphere with a large variation in predicted characteristics, and they had to land at an unknown terrain height; and 4) they had to be as fuel-efficient as possible, particularly in the terminal descent phase. This paper describes how a safe and accurate landing on the surface of Mars while meeting these design requirements was achieved by the guidance and control systems of both Viking landers.