Onboard control, tracking and navigation for autonomous systems

To operate effectively and safely, autonomous systems must be able to navigate complex environments, precisely control their attitude, accurately estimate their own states and make real-time decisions. A new adaptive controller is designed for attitude tracking control of rigid spacecraft with inertia uncertainties and full state feedback of attitude and angular rate. The controller preserves the proportional-derivative plus feedforward (PD+) structure but introduces time varying feedback gains, wherein the desired attitude state is represented by quaternions. Stable asymptotic tracking of the desired reference trajectories is guaranteed without any further restrictions upon the initial conditions, reference trajectories or any requirement for a priori availability of bounds upon the inertia matrix. The onboard estimation of the angular velocity of a spacecraft using Rate-integrating Gyroscopes (RIGs) is considered next. RIGs provide measurements of angular displacement which need to a low pass filter or observer to obtain angular velocity of the system. A continuous time observer is proposed which estimates angular velocity using the RIG measurements and achieves exponential convergence, while asymptotic convergence is guaranteed for the adaptive inertia observer. Unlike conventional certainty equivalence methods, a novel adaptation update law is proposed with additional control knobs changing with the attitude states. The final part of the dissertation deals with the Simultaneous Localization and Mapping (SLAM) problem. Estimating the location of a robot along with the position of the surrounding features on a map can be done onboard recursively with a simple Extended Kalman Filter (EKF-SLAM), but has higher chances of divergence and inconsistency. The robocentric SLAM method transforms the map of features to a local reference frame centered at the robot's position, leading to reduced inconsistency due to lower linearization errors in the update function. Improvements to the robocentric SLAM methods are suggested in the form of addition of second order terms to the linear propagation step and elimination of the composition step by transforming the feature maps before every update step. These modifications provide better filter consistency and prevent divergence in cases which were previously not possible.Aerospace Engineerin

Precision Attitude Stabilization with Intermittent External Torque

The attitude stabilization of a micro-satellite employing a variable-amplitude cold gas thruster which reflects as a time varying gain on the control input is considered. Existing literature uses a persistence filter based approach that typically leads to large control gains and torque inputs during specific time intervals corresponding to the 'on' phase of the external actuation. This work aims at reducing the transient spikes placed upon the torque commands by the judicious introduction of an additional time varying scaling signal as part of the control law. The time update mechanism for the new scaling factor and overall closed-loop stability are established through a Lyapunov-like analysis. Numerical simulations highlight the various features of this new control algorithm for spacecraft attitude stabilization subject to torque intermittence.Comment: Presented as paper AAS 21-402 at the 31st AAS/AIAA Space Flight Mechanics Meeting, Virtual, February 1-4 202

Uniform exponential stability result for the rigid-body attitude tracking control problem

This work proves that uniform exponential stability is achieved for the attitude control problem by adopting a PD+ control law that retains the classical proportional-derivative (PD) structure plus feedforward terms associated with tracking the desired attitude state. Previously, this controller was only known to offer the weaker result of uniform asymptotic stability. This thesis parameterizes the kinematics through the three-dimensional Modified Rodrigues Parameter (MRP), assumes perfect measurement of the full-state (i.e., both orientation and angular rate signals) and guarantees a stronger uniform exponential stability (UES) result. It should be emphasized that no additional restrictions on the reference trajectory or high-gain feedback assumptions are placed in achieving this new exponential stability result for the closed loop system. The design of a new Lyapunov function permits this stronger UES result which further allows facilitating robustness analysis in the possible presence of bounded unknown external disturbance torques. Saliently, this new Lyapunov function naturally extends to the classical Gibbs-Rodrigues parameterization of the attitude kinematicsAerospace Engineerin

OVRL-V2: A simple state-of-art baseline for ImageNav and ObjectNav

We present a single neural network architecture composed of task-agnostic components (ViTs, convolutions, and LSTMs) that achieves state-of-art results on both the ImageNav ("go to location in ") and ObjectNav ("find a chair") tasks without any task-specific modules like object detection, segmentation, mapping, or planning modules. Such general-purpose methods offer advantages of simplicity in design, positive scaling with available compute, and versatile applicability to multiple tasks. Our work builds upon the recent success of self-supervised learning (SSL) for pre-training vision transformers (ViT). However, while the training recipes for convolutional networks are mature and robust, the recipes for ViTs are contingent and brittle, and in the case of ViTs for visual navigation, yet to be fully discovered. Specifically, we find that vanilla ViTs do not outperform ResNets on visual navigation. We propose the use of a compression layer operating over ViT patch representations to preserve spatial information along with policy training improvements. These improvements allow us to demonstrate positive scaling laws for the first time in visual navigation tasks. Consequently, our model advances state-of-the-art performance on ImageNav from 54.2% to 82.0% success and performs competitively against concurrent state-of-art on ObjectNav with success rate of 64.0% vs. 65.0%. Overall, this work does not present a fundamentally new approach, but rather recommendations for training a general-purpose architecture that achieves state-of-art performance today and could serve as a strong baseline for future methods.Comment: 15 pages, 7 figures, 9 table

COMPARATIVE STUDIES ON COMPOSTING EFFICIENCY OF Eisenia foetida (SAVIGNY) AND Perionyx excavatus (PERRIER)

KEYWORDS Agrowaste Vermicomposting P. excavatus E. foetida Epigeic earthworms ABSTRACT The potential of two epigeic earthworms (Perionyx excavatus and Eisenia foetida) was studied for composting of crop residues (wheat straw and paddy straw) amended with farm yard manure. At the end of vermicomposting significant increase in total nitrogen (71 -150%), phosphorus (49 %-116%) and potassium (26.3-142%), along with decrease in organic carbon was recorded in different experimental vermibeds. Maximum total nitrogen as well as available phosphorous concentration was observed from vermibeds inoculated with E. foetida, whereas increased exchangeable potassium and reduction in organic carbon was shown in vermicompost produced by P. excavatus. Enhanced hydrolytic enzyme activities of CMCases (1.51 folds), Fpases (2.11 folds) and β-glucosidases (1.38 folds) were recorded in treatments vermicomposted with P. excavatus. Microbial activity parameters such as dehydrogenase, FDA hydrolase, alkaline phophatase, were also monitored during decomposition process and gradual increase was recorded in vermibeds up to 90 days of experimentation. The mean individual live weight, growth rate (mg wt. worm -1 day -1 ) of earthworm were higher for P. excavatus as compared to E. foetida. Overall, P. excavatus exhibited better growth and mineralization efficiency, which further support the suitability of the species for large scale vermiculture operations

Assessment of Groundwater Quality using Water Quality Index (WQI) in Kulpahar watershed, District Mahoba, Uttar Pradesh, India

The continuous stress on groundwater due to its overexploitation and rampant use which is indispensable to the quality of life on the earth. The study area is occupied by Precambrian basement comprised of Bundelkhand massif unconformably overlain by Quaternary sediments consisting of alluvium, clay, silt, sand and gravel. The present study deals with the various geochemical characteristic of groundwater and henceforth assess the water quality index (WQI) which is an important criterion for the determination of drinking water quality of the area. The WQI is significant unique digital rating expression to decipher the overall quality of groundwater viz. excellent, good, poor, etc. that is helpful for selecting appropriate and economically feasible treatment process to cope up with the concerned quality issues. It is one of the most relevant and effective tool for educating the people residing in the area concerned and policy-makers about water quality. An attempt has been made to understand the suitability of groundwater for human consumption in hard rock terrain of Bundelkhand region particularly in Kulpahar watershed, district Mahoba, Uttar Pradesh using WQI. The WQI has been calculated considering twenty parameters of twenty-two groundwater samples of different locations of the study area. These parameters pH, EC, TDS, alkalinity, total hardness, Ca2+, Mg2+, Na+, K+, HCOᶾ⁻, SO₄2⁻, Cl⁻, F⁻, NO₃⁻, Ag, Cu, Fe,  Mn, Ni, Zn. The WQI in the study area ranges from 4.75 to 115.93.  The extreme southern part of the Kulpahar watershed, district Mahoba of Bundelkhand region is dominant with poor groundwater quality. The higher value of WQI indicative of poor quality has been observed which is mainly due to the higher values of EC, fluoride, nitrate, manganese, and nickel in the groundwater. The study suggests that groundwater quality in Panwari Block mainly belongs to excellent and good categories. A remarkable portion in the southern part of Jaitpur block is affected by poor to unsuitable category and needs sincere effort for a detailed zonation at micro-level to understand properly and provide accurate information to the residents as well as policy makers

Determinants of agriculture biodiversity in Western Terai landscape complex of Nepal

The study explored agriculture biodiversity around protected areas and identified factors affecting diversity of agriculture biodiversity in farming households. The study analyzed the data collected from household survey of about 907 farmers from Western-Terai Landscape Complex of Nepal. Intra-species and inter-species richness and evenness in agriculture landscape were estimated and compared across a spectrum of land-uses. The study identified different social, economic, technological and ecological factors affecting the richness of intra-species and inter-species diversity of agriculture biodiversity using generalized linear regression models. Technology index, information index, food security, animal holding, ethnicity, irrigation facility and land-use were found as major variables affecting agriculture. The results also indicated that buffer zones had higher diversity than other land-uses, indicating positive effects of protected-land on surrounding agriculture biodiversity. Results supported need of coordinated efforts to mainstream agriculture biodiversity conservation with landscape conservation plans and socio-economic developments of the region

Determinants of agriculture biodiversity in Western Terai landscape complex of Nepal

The study explored agriculture biodiversity around protected areas and identified factors affecting diversity of agriculture biodiversity in farming households. The study analyzed the data collected from household survey of about 907 farmers from Western-Terai Landscape Complex of Nepal. Intra-species and inter-species richness and evenness in agriculture landscape were estimated and compared across a spectrum of land-uses. The study identified different social, economic, technological and ecological factors affecting the richness of intra-species and inter-species diversity of agriculture biodiversity using generalized linear regression models. Technology index, information index, food security, animal holding, ethnicity, irrigation facility and land-use were found as major variables affecting agriculture. The results also indicated that buffer zones had higher diversity than other land-uses, indicating positive effects of protected-land on surrounding agriculture biodiversity. Results supported need of coordinated efforts to mainstream agriculture biodiversity conservation with landscape conservation plans and socio-economic developments of the region