Rudranarayan Mukherjee

Architecture for in-space robotic assembly of a modular space telescope

Abstract. An architecture and conceptual design for a robotically assembled, modular space telescope (RAMST) that enables extremely large space telescopes to be conceived is presented. The distinguishing features of the RAMST architecture compared with prior concepts include the use of a modular deployable structure, a general-purpose robot, and advanced metrology, with the option of formation flying. To demonstrate the feasibility of the robotic assembly concept, we present a reference design using the RAMST architecture for a formation flying 100-m telescope that is assembled in Earth orbit and operated at the Sun–Earth Lagrange Point 2.

Efficient Approach for Constraint Enforcement in Constrained Multibody System Dynamics

We present an efficient and robust approach for enforcing the loop closure constraint at acceleration, velocity and position level in modeling multi-rigid body system dynamics. Our approach builds on the seminal ideas of the Divide and Conquer Algorithm (DCA) and the Augmented Lagrangian Method (ALM). The order-independent hierarchic assembly-disassembly process of the DCA provides an excellent opportunity for modularizing the system topology such that the loop closure constraints can be elegantly handled using constraint enforcement ideas motivated by the ALM. We present a non-iterative, user controlled constraint enforcement approach that enables robust constraint enforcement within the DCA. This approach eliminates the need for the iterative scheme found in many ALM motivated approaches. Similarly, it enables the use of relative or internal coordinates to model kinematic joint constraints not involved in the loop closure, thereby enforcing the constraints exactly for these joints. The approach also enables computationally very efficient serial and parallel implementations. Results from a number of test cases with single and couple closed loops are presented to demonstrate verification of the algorithm.Copyright

A Lunar Surface Operations Simulator

The Lunar Surface Operations Simulator (LSOS) is being developed to support planning and design of space missions to return astronauts to the moon. Vehicles, habitats, dynamic and physical processes and related environment systems are modeled and simulated in LSOS to assist in the visualization and design optimization of systems for lunar surface operations. A parametric analysis tool and a data browser were also implemented to provide an intuitive interface to run multiple simulations and review their results. The simulator and parametric analysis capability are described in this paper.

Integrated Ground Reaction Force Sensing and Terrain Classification for Small Legged Robots

We present the design and implementation of a miniature tactile sensing array for ground reaction force measurements in small legged robots. Dynamic ground pressure data from the sensors were collected using a small two-legged runner and used to train a support vector machine (SVM) terrain classifier. Results show that tactile sensing data, in combination with information about the motor torque and robot gait, are sufficient to distinguish among hard, slippery, grassy and granular terrain types with >90% accuracy in a single stride. The most useful classifier features include stride frequency, peak motor torque, and peak and average tactile sensor readings.

Recent Developments on a Simulator for Lunar Surface Operations

New models and capabilities in the Jet Propulsion Laboratory’s (JPL) Lunar Surface Operations Simulator (LSOS) are reported in this paper. LSOS is a simulator built to support surface operations design and planning for future lunar missions. LSOS models surface systems, their mechanical properties, and operations. In addition to simulating the dynamic interactions during operations, for example, wheel-soil interaction or component motion, LSOS also models associated environmental, and system mechanical and physical processes. These include thermal, radiation and power transients, and terrain. Lighting models are used to generate material textures, reflectance and shadows. LSOS’s integrated architecture allows use of common models and enables interactions between components operating in different domains to be easily modeled. Models used in LSOS simulations and results from the simulation of two traverses are reported. The first is a replication of a traverse conducted during a field trial of prototype systems. The second is a traverse from a lunar outpost site near Shackleton Crater to Malapert Mountain. LSOS simulations and analyses will provide data to help in the optimization of mission plans.

M3tk: A Robot Mobility and Manipulation Modeling Toolkit

In this brief paper, we present an overview of the M3tk software for modeling robotic systems. M3tk contains basic kinematics, inverse kinematics, dynamics and inverse dynamics capabilities for articulated multi-rigid body systems. Written in C++, the software features a core kinematics and dynamics library, a linear algebra library specialized for use with the algorithms in M3tk, and a Graphical User Interface with full 3D visualization. It contains implementations of multiple contact mechanics models and the ability to model terrain through heightfields. M3tk also features an ability to model terrains with spatially distributed properties. There is also an ability to manipulate objects using a joystick. This paper summarizes M3tk without delving into the details of the code.Copyright

Modeling and Testing of Phase Transition-Based Deployable Systems for Small Body Sample Capture

This paper summarizes the modeling, simulation, and testing work related to the development of technology to investigate the potential that shape memory actuation has to provide mechanically simple and affordable solutions for delivering assets to a surface and for sample capture and return. We investigate the structural dynamics and controllability aspects of an adaptive beam carrying an end-effector which, by changing equilibrium phases is able to actively decouple the end-effector dynamics from the spacecraft dynamics during the surface contact phase. Asset delivery and sample capture and return are at the heart of several emerging potential missions to small bodies, such as asteroids and comets, and to the surface of large bodies, such as Titan.

Parallel Algorithm for Modeling Multi-Rigid Body System Dynamics With Nonholonomic Constraints

This paper presents a new algorithm for serial or parallel implementation of computer simulations of the dynamics of multi-rigid body systems subject to nonholonomic and holonomic constraints. The algorithm presents an elegant approach for eliminating the nonholonomic constraints explicitly from the equations of motion and implicitly expressing them in terms of nonlinear coupling in the operational inertias of the bodies subject to these constraints. The resulting equations are in the same form as those of a body subject to kinematic joint constraints. This enables the nonholohomic constraints to be seamlessly treated in either a (i) recursive or (ii) hierarchic assembly-disassembly process for solving the equations of motion of generalized multi-rigid body systems in serial or parallel implementations. The algorithm is non-iterative and although the nonholonomic constraints are imposed at the acceleration level, constraint satisfaction is excellent as demonstrated by the numerical test case implemented to verify the algorithm. The paper presents procedures for handling both cases where the nonholonomic constraints are imposed between terminal bodies of a system and the environment as well as when the constraints are imposed between bodies in the interior of the system topology. The algorithm uses a mixed set of coordinates and is built on the central idea of eliminating either constraint loads or relative accelerations from the equations of motion by projecting the equations of motion into the motion subspaces or their orthogonal complements.© 2013 ASME

Massively Parallel Granular Media Modeling of Robot-Terrain Interactions

This paper presents select results that demonstrate the feasibility of modeling the interactions of robotic systems with granular terrain through Discrete Element Modeling (DEM) using massively parallel computing systems. We report numerical simulation results of full 3D DEM simulations with the granular material modeled as a deformable bed of spherical granules. The mobility systems of the robots retain their CAD geometry and are represented as triangular meshes. The inter-granular interactions and the interactions between the CAD mesh triangles with the granules are modeled explicitly using a deformation-damping force field. The parameters of the force field are derived from physically measurable properties. We model friction, cohesion, and shearing and other interactions among the granules, and between the CAD mesh and the granules. The simulations involve granular beds with number of granules in the order of several hundred thousand to several millions. Temporally, we report simulations in the order of several seconds. These simulations were run on parallel clusters with number of processors ranging from 100 to 256. We present the findings from a number of simulations ranging including wheeled and legged mobility systems, and robotic tools in micro-gravity environments.Copyright

Development of miniature robotic manipulators to enable SmallSat clusters

This paper presents the concept to provide a robust and scalable robotic solution to enable SmallSat clusters via Cluster Forming On-board Robotic Manipulators (C-FORM). Instead of dedicated launches of large science instruments, small science satellites could be piggybacked as secondary payloads. After deployment, the SmallSats will rendezvous. Miniature robot arms will deploy and perform docking to a second SmallSat, similar to robotic docking on the ISS or space shuttle. This docking method accommodates uncertainty in GNC while reducing risk of spacecraft collision through increased separation distance. Docking will be repeated until the cluster is completely formed, amplifying their capabilities. These clusters would be scalable in both the number and size of the cluster elements. The formation will be maintained without expending energy or fuel. This work addresses technology development areas of creating large, scalable structures in space. This assembly method allows for very small packing volumes that reduces mass and cost. Increased separation distance between cluster elements provide larger aperture per SmallSat, reducing number of total elements. It also enables scalable large structures that can be reconfigurable. Precise relative repositioning can accommodate alignment errors or thermal drift in addition to enabling variable baseline instruments. Individual cluster elements could be grossly repositioned to provide hardware reconfiguration. Applications include large, scalable RF and optical apertures, interferometry, in-space assembly, close formation flying, scanning and fixed “stare” imagers, and mother-daughter spacecraft. Four aspects addressed in this paper include the robotic arm, end effector, SmallSat bus, and rendezvous. The robotic arm is designed to meet SmallSat size (< 0.5U), weight (< kg), actuation, and power (∼ 15 W) (SWAP) constraints. The actuators can be driven using SmallSat processing and motor drivers. Manipulator position can be held without use of power. By maintaining these constraints, the miniature robotic arm can be used as a payload of a variety of science SmallSats. Accounting for general SmallSat bus trends, capabilities, and interfaces help to provide minimal integration efforts across different platforms. The compact end effector is designed to accommodate any positioning uncertainty and relative spacecraft motion during docking. After docking, the end effector remains engaged without the use of power. Docking can be released to allow for gross hardware reconfiguration. Modularity was another important aspect of the end effector design. While the focus of this work is on docking, modularity allows for a wide range of potential applications. A representative SmallSat bus was designed using COTS components. Finally, rendezvous and relative control of two SmallSats was investigated.