On-orbit Servicing Operations Research Articles

Optimal Pose Design for Close-Proximity On-Orbit Inspection

Close-proximity on-orbit inspection is a critical ability to initiate on-orbit servicing operations, required technology for space exploration missions. It is challenging to solve an optimal inspection trajectory planning problem that provides a complete target observation due to major difficulties. First, the inspection requirements must be defined and imposed on the problem as a set of path constraints that result in a nondeterministic-polynomial-time-hard problem. Second, the optimization problem, including highly nonconvex constraints, is very difficult to solve directly using an optimal control solver. Additionally, it requires proper initialization of states and control variables, which is critical in such problems. To overcome these difficulties, this paper proposes a novel formulation and method of solution for a full six-degrees-of-freedom optimal inspection motion planning problem. Optimal inspection trajectories are designed for a rigid-body spacecraft, which performs close, continuous, and complete observation of rigid, nonrotating, and nonaccelerating known targets. The inspection and collision avoidance constraints are defined in explicit forms that rectify the nondifferentiability of the problem and satisfy the inspection requirements. A pseudospectral optimal control solver is implemented to numerically solve the trajectory optimization problem. The proposed methodology is applicable to any robotic inspection mission. Simulations are presented as a validation of the proposed methodology and the achieved optimality.

Task space control for on-orbit space robotics using a new ROS-based framework

This paper proposes several task space control approaches for complex on-orbit high degrees of freedom robots. These approaches include redundancy resolution and take the non-linear dynamic model of the on-orbit robotic systems into account. The suitability of the proposed task space control approaches is explored in several on-orbit servicing operations requiring visual servoing tasks of complex humanoid robots. A unified open-source framework for space-robotics simulations, called OnOrbitROS, is used to evaluate the proposed control systems and compare their behaviour with state-of-the-art existing ones. The adopted framework is based on ROS and includes and reproduces the principal environmental conditions that eventual space robots and manipulators could experience in an on-orbit servicing scenario. The architecture of the different software modules developed and their application on complex space robotic systems is presented. Efficient real-time implementations are achieved using the proposed OnOrbitROS framework. The proposed controllers are applied to perform the guidance of a humanoid robot. The robot dynamics are integrated into the definition of the controllers and an analysis of the results and practical properties are described in the results section.

Force control of a space robot in on-orbit servicing operations

Force control provided by a small-scaled free-flying space robot on a floating or spinning target will be required for future on-orbit servicing missions, such as detumbling a target, performing an assembly or a maintenance operation. Regarding to different contact geometries for a space robot interacting with a spinning target, this paper addresses the contact model considering its multi-dimensional characteristics. A hybrid motion and force controller is developed to acquire desired contact forces and space robot configuration despite the floating feature of the system. On this basis, the control strategy to implement the operations of three typical phases, namely approaching phase, contact phase and post-contact phase, is proposed. The simulations have been performed to verify the control approaches and visualize the contact scenarios.

Direct visual servoing and interaction control for a two-arms on-orbit servicing spacecraft

A direct visual-servoing algorithm for control of a space-based two-arm manipulator is proposed in this paper. The algorithm can be utilized in a two-arm manipulators configuration, where one of the arms performs the manipulation and the second arm is dedicated to the observation of the target zone of manipulation. The algorithm utilizes both visual features extracted from onboard cameras and force and torque measured at the manipulator's end-effector to control the movements of the manipulator during on-orbit servicing operations. The algorithm takes into account the relative dynamics of the bodies involved, it relies on images taken independently from de-localized cameras, e.g. at the end-effector of a second manipulator, and it integrates an impedance control for the compensation of eventual contact reactions when the end effector touches and operates the target body. The analytical derivations demonstrate the stability of the algorithm and incorporate an impedance compliance strategy into an optimal framework formulation. Simulations results in two different scenarios have been presented to show the adequate behavior of the presented approach in on-orbit-servicing operations.

Framework for Modeling and Optimization of On-Orbit Servicing Operations Under Demand Uncertainties

This paper develops a framework that models and optimizes the operations of complex on-orbit servicing infrastructures involving one or more servicers and orbital depots to provide multiple types of services to a fleet of geostationary satellites. The proposed method extends the state-of-the-art space logistics technique by addressing the unique challenges in on-orbit servicing applications and integrates it with the Rolling Horizon decision-making approach. The space logistics technique enables modeling of the on-orbit servicing logistical operations as a Mixed-Integer Linear Program whose optimal solutions can efficiently be found. The Rolling Horizon approach enables the assessment of the long-term value of an on-orbit servicing infrastructure by accounting for the uncertain service needs that arise over time among the geostationary satellites. Two case studies successfully demonstrate the effectiveness of the framework for 1) short-term operational scheduling and 2) long-term strategic decision making for on-orbit servicing architectures under diverse market conditions.

Про вибір орбіти базування сервісного космічного апарата

At present, the requirements for increasing spacecraft active life and operational reliability and reducing spacecraft operation costs become more and more stringent. Because of this, on-orbit servicing becomes more and more attractive. One of the most promising ways to increase the efficiency of transport operations in space is to carry out on-orbit servicing using reusable spacecraft with low-thrust solar electrojet engines. The aim of this paper is to develop a mathematical model for the choice of an optimal low near-Earth parking orbit for a reusable service spacecraft. The case of noncoplanar near-circular orbits of spacecraft and a shuttle scenario of their servicing is considered. The solution of the problem of choosing an optimal parking orbit for a reusable service spacecraft involves repeated solutions of the problem of determining the delta-velocity of the service spacecraft’s orbital transfers between its parking orbit and the orbits of the serviced spacecraft. In this connection, using the averaging method, a mathematical model is developed for the analytical determination of orbital transfer program controls and trajectories and assessing orbital transfer energy expenditures. With its use, a mathematical model is developed for the choice of a service spacecraft’s optimal parking orbit. The objective function is the total delta-velocity of the service spacecraft’s orbital transfers from its parking orbit to the orbits of the serviced spacecraft and vice versa with the inclusion of the orbital transfer frequency. The optimizable parameters are the service spacecraft parking orbit parameters. The use of the proposed models is illustrated by an example of service spacecraft parking orbit optimization. What is new is the mathematical models developed. The results obtained may be used in the preliminary planning of on-orbit servicing operations.

On-orbit servicing ontology applied to recommended standards for satellites in earth orbit

The Consortium for Execution of Rendezvous and Servicing Operations (CONFERS) is an industry-led initiative with initial seed funding provided by the Defense Advanced Research Projects Agency (DARPA) that aims to leverage best practices from government and industry to research, develop, and publish non-binding, consensus-derived technical and operations standards for On-Orbit Servicing (OOS) and Rendezvous and Proximity Operations (RPO). As part of the CONFERS effort, the University of Southern California’s (USC) Space Engineering Research Center (SERC) conducted research into existing RPO methodologies and practices and OOS methodologies through literature review and interviews with practitioners. Following the first year of analytical input focused solely on RPO, the second year’s activities have focused further into the full extent of attributes for satellite servicing and in-space docking (OOS). USC’s focus was to develop a taxonomy of functions and attributes related to all aspects of technical elements and techniques required for past/current/anticipated OOS missions. A taxonomy database was created that allowed various key elements to be broken down into quantifiable data within common categories. Following the taxonomy creation, working with the Space Infrastructure Foundation (SIF) a review of existing standards in space along with other industries were analyzed and compared for possible matches. This standards gap analysis focused primarily from the end of the RPO maneuver to the point of physical contact or action between two spacecraft. These comparisons were then used to recommend where gaps in standards exist and where it might be most beneficial to create new ones, enabling spacecraft of various shapes and sizes to safely execute various OOS operations, and spur the industry between customers and providers. The field of space servicing is a rapidly growing field, with governments and numerous private entities developing robotic systems for mission extension vehicles and satellite repair. With an increased number of servicing missions forthcoming, a system of guidelines and standards on how to effectively and safely design on-orbit servicing activities is a next natural step to enable the expansion of this burgeoning industry.

Type synthesis of non-holonomic spherical constraint underactuated parallel robotics

Space robotics is taken as one of the most promising approaches for on-orbit servicing missions. The underactuated non-holonomic parallel mechanism is a new direction of parallel space robotics, with small volume, lightweight, low cost, low energy consumption, and high flexibility. The existing methods on type synthesis could not generate underactuated non-holonomic parallel mechanisms with the introduction of the non-holonomic spherical pairs in parallel mechanisms. This paper is devoted to type synthesis of underactuated parallel mechanisms with spherical motion pattern accompanied by the generation of the non-holonomic spherical pairs in parallel mechanisms with spherical motion pattern. After the introduction of the traditional roller-sphere contact, this paper proposes a novel roller-sphere contact. After this paper provides the type synthesis of parallel mechanisms with spherical motion pattern, it puts forward the generation method of non-holonomic spherical pairs in parallel underactuated mechanisms with spherical motion pattern. The non-holonomic underactuated joint mechanism of a space robot for on-orbit servicing operations is taken as an example to demonstrate the proposed method.

Promoting international co-operation in the age of global space governance – A study on on-orbit servicing operations

Outer space exploration has been an area where the international community demonstrated a significant level of co-operation, successfully transcending geographical, national and cultural boundaries. In the age of global governance, international co-operation has never been more important in resolving today's global challenges. One of such challenges is the growing amount of space debris in orbits, which, if unresolved, will not only undermine global information and communications technology (ICT) system, but will also hinder areas of sustainable development where outer space activities contribute to. (e.g. satellite imaging for disaster warning and management, satellite imaging for agricultural purpose) This paper proposes to conceptualize space orbit and radio frequency as essential global commons, whose governance requires international co-operation. In examining potentials and challenges in moving forward space orbit governance, the paper pays particular focus on ensuring space safety and sustainability through the introduction of on-orbit servicing (OOS) operations. The paper will identify aspects of OOS that warrant further collaborations, specifically, the standardization of docking and rendez-vous practices that could facilitate future space activities. Recognizing the potential of future commercialization of refueling, repairing and debris removal operations in orbits, this paper argues that standardization practices would be the first step towards enhancing international co-operation, as well as in strengthening the existing regime of peaceful use of outer space. Ultimately, it could play a role in addressing one of today's most imminent challenges – ensuring sustainable use of global commons.

The effects of parking orbit elements on designing of on-orbit servicing missions

Nowadays on-orbit servicing operations such as satellite refuelling, debris removal and visual inspection are considered as the most important issues in the space missions. Mission planning has a key role on the designation of such missions and it is strongly dependent on the required fuel. In this study, a new approach is proposed for the designing of the on-orbit operations with considering the parking orbit elements and location of the servicing satellites. The proposed method improves the previous mission planning process of the multiple servicing satellites in the terms of the reduction in the mission fuel consumption. Furthermore, a special rendezvous maneuver is considered for meeting the servicing satellites and the targets. Also, the transfer orbits are obtained through Lambert targeting. The optimisation of the problem is carried out by particle swarm optimisation algorithm and Taguchi technique is employed for the robust design of the control parameters of the optimisation algorithm. The results reveal that the proposed approach is an efficient way in the reduction of the fuel consumption in the on-orbit servicing missions rather than the conventional methods.

An approach to ground based space surveillance of geostationary on-orbit servicing operations

On Orbit Servicing (OOS) is a class of dual-use robotic space missions that could potentially extend the life of orbiting satellites by fuel replenishment, repair, inspection, orbital maintenance or satellite repurposing, and possibly reduce the rate of space debris generation. OOS performed in geostationary orbit poses a unique challenge for the optical space surveillance community. Both satellites would be performing proximity operations in tight formation flight with separations less than 500m making atmospheric seeing (turbulence) a challenge to resolving a geostationary satellite pair when viewed from the ground. The two objects would appear merged in an image as the resolving power of the telescope and detector, coupled with atmospheric seeing, limits the ability to resolve the two objects. This poses an issue for obtaining orbital data for conjunction flight safety or, in matters pertaining to space security, inferring the intent and trajectory of an unexpected object perched very close to one׳s satellite asset on orbit. In order to overcome this problem speckle interferometry using a cross spectrum approach is examined as a means to optically resolve the client and servicer׳s relative positions to enable a means to perform relative orbit determination of the two spacecraft. This paper explores cases where client and servicing satellites are in unforced relative motion flight and examines the observability of the objects. Tools are described that exploit cross-spectrum speckle interferometry to (1) determine the presence of a secondary in the vicinity of the client satellite and (2) estimate the servicing satellite׳s motion relative to the client. Experimental observations performed with the Mont Mégantic 1.6m telescope on co-located geostationary satellites (acting as OOS proxy objects) are described. Apparent angular separations between Anik G1 and Anik F1R from 5 to 1 arcsec were observed as the two satellites appeared to graze one another. Data reduction using differential angular measurements derived from speckle images collected by the 1.6m telescope produced relative orbit estimates with better than 90m accuracy in the cross-track and in-track directions but exhibited highly variable behavior in the radial component from 50 to 1800m. Simulations of synthetic tracking data indicated that the radial component requires approximately six hours of tracking data for an Extended Kalman Filter to converge on an relative orbit estimate with less than 100m overall uncertainty. The cross-spectrum approach takes advantage of the Fast Fourier Transform (FFT) permitting near real-time estimation of the relative orbit of the two satellites. This also enables the use of relatively larger detector arrays (>106 pixels) helping to ease acquisition process to acquire optical angular data.

On‐orbit servicing: a time‐dependent, moving‐target traveling salesman problem

AbstractThe robotic capability of maintaining and repairing space assets, on‐orbit servicing (OOS), has the potential to change the way spacecraft are designed, manufactured and operated. The most common OOS mission concept envisions an orbital “depot”, where consumables and spare parts for spacecraft will be stored. A “servicing platform”, based at this depot, will be used to service a number of client spacecraft and then return to the depot for resupply. We model OOS as a time‐dependent, moving‐target traveling salesman problem and present an algorithm for minimizing the total amount of energy or time required for OOS operations.