A system of autonomous navigation and orientation for satellites based on virtual measurements of zenith distances of stars

An onboard astronomical system is suggested, based on the developed method using virtual measurements of zenith distances of stars. Two algorithms of the method are described, their theory is given, and statistical results of the system’s simulation are presented.     

Pose estimation using linearized rotations and quaternion algebra

In this paper we revisit the topic of how to formulate error terms for estimation problems that involve rotational state variables. We present a first-principles linearization approach that yields multiplicative error terms for unit-length quaternion representations of rotations, as well as for canonical rotation matrices. Quaternion algebra is employed throughout our derivations. We show the utility of our approach through two examples: (i) linearizing a sun sensor measurement error term, and (ii) weighted-least-squares point-cloud alignment.     

Laminar dust flames in a reduced-gravity environment

The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen–argon and oxygen–helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms.     

Tracking with classification-aided multiframe data association

In most conventional tracking systems, only the target kinematic information from, for example, a radar or sonar or an electro-optical sensor, is used in measurement-to-track association. Target class information, which is typically used in postprocessing, can also be used to improve data association to give better tracking accuracy. The use of target class information in data association can improve discrimination by yielding purer tracks and preserving their continuity. In this paper, we present the simultaneous use of target classification information and target kinematic information for target tracking. The approach presented integrates target class information into the data association process using the 2-D (one track list and one measurement list) as well as multiframe (one track list and multiple measurement lists) assignments. The multiframe association likelihood is developed to include the classification results based on the "confusion matrix" that specifies the accuracy of the target classifier. The objective is to improve association results using class information when the kinematic likelihoods are similar for different targets, i.e., there is ambiguity in using kinematic information alone. Performance comparisons with and without the use of class information in data association are presented on a ground target tracking problem. Simulation results quantify the benefits of classification-aided data association for improved target tracking, especially in the presence of association uncertainty in the kinematic measurements. Also, the benefit of 5-D (or multiframe) association versus 2-D association is investigated for different quality classifiers. The main contribution of this paper is the development of the methodology to incorporate exactly the classification information into multidimensional (multiframe) association.     

Contribution of secondaries to the radiation environment on space missions.

Calculations to predict the radiation environment for spacecraft in low earth orbit sometimes ignore the contribution from secondary radiation products. However, the contribution of secondaries, particularly neutrons, on heavy spacecraft or in planetary bodies can be of concern for biological systems. The Shuttle Activation Monitor (SAM) and Cosmic Radiation Effects and Activation Monitor (CREAM) experiments provide valuable data on secondary (as well as primary) radiation effects. Comparisons have been made between induced activity from flight-exposed samples, induced activity in a ground-irradiated sample, and Monte Carlo-derived predictions with and without secondaries. These comparisons show that for a flight-exposed sample, predictions which omit the secondary contribution result in a spectrum that is too low by a factor of 2. The addition of the secondaries results in a predicted spectrum that closely matches the measured data.     

Processor equivalence for daisy chain load sharing processors

A linear daisy chain of processors in which processor load is divisible and shared among the processors is examined. It is shown that two or more processors can be collapsed into a single equivalent processor. This equivalence allows a characterization of the nature of the minimal time solution, a simple method to determine when to distribute load for linear daisy chain networks of processors without front end communication subprocessors and closed form expressions for the equivalent processing speed of infinitely large daisy chains of processors     

Changes of vertical eye movements of goldfish for different otolith stimulation by linear acceleration.

Eye movements serves to hold the gaze steady or to shift the gaze to an object of interest. On Earth, signals from otoliths can be interpreted either as linear motion or as tilt with respect to gravity. In microgravity, static tilt will no longer give rise to changes in otolith activity. However, linear acceleration as well as angular acceleration stimulate the otolith organ. Therefore, during adaptation to microgravity, otolith-mediated response such as eye movements alter. In this study, we analyzed the eye movements of goldfish during linear acceleration. The eye movements during rectangular linear acceleration along the different body axis were video-recorded. The vertical eye rotations were analyzed frame by frame. In normal fish, leftward lateral acceleration induced downward eye rotation in the left eye and upward eye rotation in the right eye. Acceleration from caudal to rostral evoked downward eye rotation in both eyes. When the direction of acceleration was shifted 15 degrees left, the responses in the left eye disappeared. These results suggested that otolith organs in each side were stimulated differently.     

Use of MOBITEX wireless wide area networks as a solution toland-based positioning and navigation

The emergence of land-based positioning and navigation systems is the direct result of advancements in technologies relating to geographic information, wireless data communication, and navigation. The increasing demand for these systems has stimulated their rapid development. This paper identifies the wide variety of land-based positioning and navigation systems and classifies them into five groups. The basic system elements that are required in all land-based positioning and navigation systems are also discussed. A proposed system infrastructure that supports the five types of land-based positioning and navigation systems is described. The specific technologies integrated in this proposed infrastructure include the Global Positioning System (GPS), differential GPS, and the MOBITEX wireless wide area packet data networks. Real-time wireless mobile data communication is a key component of any land-based positioning and navigation system. Finally, the evaluation criteria necessary for field testing a pilot land-based positioning and navigation system are presented. This pilot system is used to determine the feasibility and effectiveness of the proposed system design     

Experimental evaluation of the processes resulting from the introduction of the transgenic microorganism Escherichia coli Z905/pPHL7 (lux+) into aquatic microcosms.

The processes resulting from the introduction of the tranagenic microorganism (TM) E. coli Z905/pPHL7 into aquatic microcosms have been modeled experimentally. It has been shown that the TM E. coli is able to adapt to a long co-existence with indigenous heterotrophic microflora in variously structured microcosms. In more complex microcosms the numerical dynamics of the introduced E. coli Z905/pPHL7 population is more stable. In the TM populations staying in the microcosms for a prolonged time, changes are recorded in the phenotypic expression of plasmid genes (ampicillin resistance and the luminescence level) and chromosome genes (morphological and physiological traits). However, in our study microcosms, the recombinant plasmid persisted in the TM cells for 6 years after the introduction, and as the population adapts to the conditions of the microcosms, the efficiency of the cloned gene expression in the cells is restored. In the microcosms with high microalgal counts (10(7) cells/ml), cells with a high threshold of sensitivity to ampicillin dominate in the population of the TM E. coli Z905/pPHL7.