In-space Assembly Research Articles

Thruster-Pointing-Constrained Optimal Control for Satellite Servicing Using Indirect Optimization

Future space missions such as in-space assembly of telescopes and on-orbit servicing require rendezvous and proximity operations trajectories that avoid thruster-induced contamination of delicate components onboard the client spacecraft. We present a novel technique to incorporate a hard thruster pointing constraint into the indirect optimal control formulation and solve the problem using a single-shooting method. A thruster pointing constraint is an inequality constraint that imposes a limit on the angular range over which a spacecraft thruster is permitted to operate, thus mitigating plume contamination during rendezvous and proximity operations. Through novel incorporation of the constraint directly into the dynamic model, the problem can be easily solved with no a priori knowledge of the burn sequence or information about when the constraint is active or inactive. Our formulation is capable of handling a constant thruster pointing constraint as well as one that varies as a function of distance from the target spacecraft. Results are presented under Clohessy–Wiltshire dynamics; however, the method can be easily extended to handle nonlinear dynamic systems. As expected, we see an increase in fuel consumption with increasing constraint angle for the solution of problems with the same boundary conditions and time of flight. To validate our method, we compare the performance and results to those of a direct method, sequential convex optimization, utilizing the CVX MATLAB plug-in and the MOSEK solver. We found that our approach converged more easily and required no hand-tuning of parameters. It also converged to solutions that satisfy the pointing constraints to a stricter tolerance. We anticipate that our novel approach to generating thruster-pointing-constrained fuel-optimal trajectories will be enabling to a host of future servicing space missions.

Simulation on Flexible Multibody System with Topology Changes for In-space Assembly

Simulation on Flexible Multibody System with Topology Changes for In-space Assembly

A hybrid soft material robotic end-effector for reversible in-space assembly of strut components.

Based on the NASA in-Space Assembled Telescope (iSAT) study (Bulletin of the American Astronomical Society, 2019, 51, 50) which details the design and requirements for a 20-m parabolic in-space telescope, NASA Langley Research Center (LaRC) has been developing structural and robotic solutions to address the needs of building larger in-space assets. One of the structural methods studied involves stackable and collapsible modular solutions to address launch vehicle volume constraints. This solution uses a packing method that stacks struts in a dixie-cup like manner and a chemical composite bonding technique that reduces weight of the structure, adds strength, and offers the ability to de-bond the components for structural modifications. We present in this paper work towards a soft material robot end-effector, capable of suppling the manipulability, pressure, and temperature requirements for the bonding/de-bonding of these conical structural components. This work is done to investigate the feasibility of a hybrid soft robotic end-effector actuated by Twisted and Coiled Artificial Muscles (TCAMs) for in-space assembly tasks. TCAMs are a class of actuator which have garnered significant recent research interest due to their allowance for high force to weight ratio when compared to other popular methods of actuation within the field of soft robotics, and a muscle-tendon actuation design using TCAMs leads to a compact and lightweight system with controllable and tunable behavior. In addition to the muscle-tendon design, this paper also details the early investigation of an induction system for adhesive bonding/de-bonding and the sensors used for benchtop design and testing. Additionally, we discuss the viability of Robotic Operating System 2 (ROS2) and Gazebo modeling environments for soft robotics as they pertain to larger simulation efforts at LaRC. We show real world test results against simulation results for a method which divides the soft, continuous material of the end-effector into discrete links connected by spring-like joints.

Built On-orbit Robotically assembled Gigatruss (BORG): A mixed assembly architecture trade study.

This paper explores a mixed assembly architecture trade study for a Built On-orbit Robotically assembled Gigatruss (BORG). Robotic in-space assembly (ISA) and servicing is a crucial field to expand endeavors in space. Currently, large structures in space are commonly only deployable and must be efficiently folded and packed into a launch vehicle (LV) and then deployed perfectly for operational status to be achieved. To actualize being able to build increasingly large structures in space, this scheme becomes less feasible, being constrained by LV volume and mass requirements. ISA allows the use of multiple launches to create even larger structures. The common ISA proposals consist of either strut-by-strut or multiple deployable module construction methodologies. In this paper, a mixed assembly scheme is explored and a trade study is conducted on its possible advantages with respect to many phases of a mission: 1) manufacturing, 2) stowage and transport, 3) ISA, and 4) servicing. Finally, a weighted decision matrix was created to help compare the various advantages and disadvantages of different architectural schemes.

Design engineering a walking robotic manipulator for in-space assembly missions.

In-Space Services aim to introduce sustainable futuristic technology to support the current and growing orbital ecosystem. As the scale of space missions grows, there is a need for more extensive infrastructures in orbit. In-Space Assembly missions would hold one of the key responsibilities in meeting the increasing demand. In the forthcoming decades, newer infrastructures in the Earth’s orbits, which are much more advanced than the International Space Station are needed for in-situ manufacturing, servicing, and astronomical and observational stations. The prospect of in-orbit commissioning a Large Aperture Space Telescope (LAST) has fuelled scientific and commercial interests in deep-space astronomy and Earth Observation. However, the in-situ assembly of such large-scale, high-value assets in extreme environments, like space, is highly challenging and requires advanced robotic solutions. This paper introduces an innovative dexterous walking robotic system for in-orbit assembly missions and considers the Large Aperture Space Telescope system with an aperture of 25 m as the use case. The top-level assembly requirements are identified with a deep insight into the critical functionalities and challenges to overcome while assembling the modular LAST. The design and sizing of an End-over-end Walking Robot (E-Walker) are discussed based on the design of the LAST and the specifications of the spacecraft platform. The E-Walker’s detailed design engineering includes the structural finite element analysis results for space and earth-analogue design and the corresponding actuator selection methods. Results of the modal analysis demonstrate the deflections in the E-Walker links and end-effector in the open-loop due to the extremities present in the space environment. The design and structural analysis of E-Walker’s scaled-down prototype is also presented to showcase its feasibility in supporting both in-orbit and terrestrial activities requiring robotic capabilities over an enhanced workspace. Further, the mission concept of operations is presented based on two E-Walkers that carry out the assembly of the mirror modules. The mission discussed was shortlisted after conducting an extensive trade-off study in the literature. Simulated results prove the dual E-Walker robotic system’s efficacy for accomplishing complex in-situ assembly operations through task-sharing.

SpaceDrones 2.0—Hardware-in-the-Loop Simulation and Validation for Orbital and Deep Space Computer Vision and Machine Learning Tasking Using Free-Flying Drone Platforms

The proliferation of reusable space vehicles has fundamentally changed how assets are injected into the low earth orbit and beyond, increasing both the reliability and frequency of launches. Consequently, it has led to the rapid development and adoption of new technologies in the aerospace sector, including computer vision (CV), machine learning (ML)/artificial intelligence (AI), and distributed networking. All these technologies are necessary to enable truly autonomous “Human-out-of-the-loop” mission tasking for spaceborne applications as spacecrafts travel further into the solar system and our missions become more ambitious. This paper proposes a novel approach for space-based computer vision sensing and machine learning simulation and validation using synthetically trained models to generate the large amounts of space-based imagery needed to train computer vision models. We also introduce a method of image data augmentation known as domain randomization to enhance machine learning performance in the dynamic domain of spaceborne computer vision to tackle unique space-based challenges such as orientation and lighting variations. These synthetically trained computer vision models then apply that capability for hardware-in-the-loop testing and evaluation via free-flying robotic platforms, thus enabling sensor-based orbital vehicle control, onboard decision making, and mobile manipulation similar to air-bearing table methods. Given the current energy constraints of space vehicles using solar-based power plants, cameras provide an energy-efficient means of situational awareness when compared to active sensing instruments. When coupled with computationally efficient machine learning algorithms and methods, it can enable space systems proficient in classifying, tracking, capturing, and ultimately manipulating objects for orbital/planetary assembly and maintenance (tasks commonly referred to as In-Space Assembly and On-Orbit Servicing). Given the inherent dangers of manned spaceflight/extravehicular activities (EVAs) currently employed to perform spacecraft maintenance and the current limitation of long-duration human spaceflight outside the low earth orbit, space robotics armed with generalized sensing and control and machine learning architecture have a unique automation potential. However, the tools and methodologies required for hardware-in-the-loop simulation, testing, and validation at a large scale and at an affordable price point are in developmental stages. By leveraging a drone’s free-flight maneuvering capability, theater projection technology, synthetically generated orbital and celestial environments, and machine learning, this work strives to build a robust hardware-in-the-loop testing suite. While the focus of the specific computer vision models in this paper is narrowed down to solving visual sensing problems in orbit, this work can very well be extended to solve any problem set that requires a robust onboard computer vision, robotic manipulation, and free-flight capabilities.

Comparing Multi-Arm Robotics for In-Space Assembly

Robotic In-space assembly (ISA) is the next step to building larger and more permanent structures in orbit. Determining the best robot for ISA is difficult as it will not only depend on the structure being assembled but on how it is assembled. This analysis shows how changing some key design parameters can influence different robotic systems for ISA. This study focuses on the construction of a 20 m linear truss structure but also expands to a 10 and 50 m truss. Two categories of robots are included in this study: a stationary robot and a mobile robot which crawls along the structure. Both the stationary and crawling robotic systems utilize two planar dexterous manipulators to assemble individual truss pieces into a linear truss. In the case of the stationary robotic system a single long positioning leg is used to move the two dexterous arms into position. The crawling robotic system uses two planar manipulators to crawl along the truss. A systems level analysis is presented which details how the forces from the robotic systems drive the mass of the truss and also how the size of the truss segments drive the requirements of the robotic system. This analysis shows how changing some key design parameters can influence each of the different robotic systems and the truss design itself. The estimated masses of the robotic systems and the truss and the assembly time are presented. There are trade-offs to every robot design and understanding those trade-offs is essential to building a system that is not only efficient but also cost-effective.

An Autonomous Task Assignment Paradigm for Autonomous Robotic In-Space Assembly.

The development of autonomous robotic systems is a key component in the expansion of space exploration and the development of infrastructures for in-space applications. An important capability for these robotic systems is the ability to maintain and repair structures in the absence of human input by autonomously generating valid task sequences and task to robot allocations. To this end, a novel stochastic problem formulation paired with a mixed integer programming assembly schedule generator has been developed to articulate the elements, constraints, and state of an assembly project and solve for an optimal assembly schedule. The developed formulations were tested with a set of hardware experiments that included generating an optimal schedule for an assembly and rescheduling during an assembly to plan a repair. This formulation and validation work provides a path forward for future research in the development of an autonomous system capable of building and maintaining in-space infrastructures.

Toward the Autonomous Assembly of Large Telescopes Using CubeSat Rendezvous and Docking

This paper describes the results of a system study for the in-space assembly of large optical telescopes using a building block approach involving multiple mirror segments. Such an approach is enabled by CubeSat rendezvous and docking and mirror steering technologies for compensating misalignment of the assembly. This concept thus removes the constraints imposed by the limited volume of launchers’ fairing, and hence larger telescope dimensions can be envisaged, leading to new observation capabilities. Each mirror segment is mounted on top of a small satellite, containing the miniaturized subsystems to achieve autonomous docking to either the service module containing the science instruments or other segments to build up the primary mirror. A systems’ design of all the elements constituting the assembly is provided, including tradeoffs, optimization, as well as mass and power budgets. The proposed solution scales with the size of the telescope and can be used to build primary mirrors as large as 20 m in diameter. The critical guidance, navigation, and control function is introduced, and related docking performances are presented. The results indicate that the in-space assembly of such large telescopes is feasible once these two key technologies are demonstrated in flight in the coming years.

State of the Profession: NASA Langley Research Center Capabilities/Technologies for Autonomous In-Space Assembly and Modular Persistent Assets

State of the Profession: NASA Langley Research Center Capabilities/Technologies for Autonomous In-Space Assembly and Modular Persistent Assets

Which Jurisdiction for Private In-space Assembled Autonomous Platforms?

This article builds a model for determining the law applicable to in-space assembled autonomous platforms and the services they are likely to provide. It makes a comprehensive inventory of the new challenges and emerging industry trends in the field of in-space assembly. It identifies some of the most significant industrial projects, which are currently engaged or contemplated. It then examines the status of such private platforms assembled in space in terms of both international rules and state jurisdiction. It suggests an approach that distinguishes the service provided from the physical platform itself, which would enable States to regulate service operation. The conclusion sets out a series of practical recommendations that could be implemented at different levels.

Reversible bonding via exchange reactions following atomic oxygen and proton exposure

Future space structures have several design concerns, among them are larger physical scale and changes in mission profile over their potentially multi-decade operational lifetimes. A reversible adhesive suitable for in-space assembly could simplify these efforts. Key requirements for such applications are that: (1) the reversible adhesive has a sufficiently high glass transition temperature (Tg) to provide mechanical strength throughout the day/night cycle, (2) the adhesive schema is truly reversible in a vacuum environment and can be executed in space, and (3) the reversible adhesive can survive significant durations under the elevated radiation flux of low earth orbit (LEO) and mission locations. This study examines a high Tg vitrimer-type reversible adhesive known as aromatic thermosetting copolyester (ATSP) under two radiation species (atomic oxygen and protons) at flux levels intended to represent equivalent exposure in LEO for 1, 10, and 50 years. Surface morphology studies were conducted via 3 D laser profilometry and found no change in morphology following exposure. Reversible adhesive experiments were conducted and found consistent performance after atomic oxygen and proton exposures up to 50 years. Raman spectroscopy likewise found no obvious changes in surface chemistry. A consistent activation energy for bond exchange was observed between unexposed films and films exposed to 1 and 10 years of LEO-equivalent proton exposure. Similarly, thermogravimetry found consistent performance in the thermal stability of ATSP polymer films before and after 1 and 10 years of LEO-equivalent proton exposure. Results suggest that ATSP represents a viable option for a reversible adhesive for in-space assembly.

In-space structural assembly using predefined performance based method

PurposeThe purpose of this paper is to propose a pre-defined performance robust control method for pre-assembly configuration establishment of in-space assembly missions, and collision avoidance is considered during the configuration establishment process.Design/methodology/approachFirst, six-degrees-of-freedom error kinematic and dynamic models of relative translational and rotational motion between transportation systems are developed. Second, the prescribed transient-state performance bounds of tracking errors are designed. In addition, based on the backstepping, combining the pre-defined performance control method with a robust control method, a pre-defined performance robust controller is designed.FindingsBy designing prescribed transient-state performance bounds of tracking errors to guarantee that there is no overshoot, collision-avoidance can be achieved. Combining the pre-defined performance control method with a robust control method, robustness to disturbance is guaranteed.Originality/valueThis paper proposed a pre-defined performance robust control method. Simulation results demonstrate that the proposed controller can achieve a pre-assembly configuration establishment with collision avoidance in the existence of external disturbances.

Dynamics and control for in-space assembly robots with large translational and rotational maneuvers

There are two major characteristics of in-space structure assembly missions. First, in order to improve the transport efficiency of assembly robot and reduce the number of structural modules, the size of each structural module is usually designed as large as possible. Second, it is necessary for autonomous assembly robot to quickly transport such large-sized flexible structural modules to the desired locations for integration. However, the coupling effect between the deformation of structural module and large-scale maneuver of robot is inevitably involved during transportation. In this paper, a dynamics modeling method for in-space assembly (ISA) robot with large translational and rotational maneuvers was proposed. The descriptions of dual quaternions were expanded, and a general expression for the dynamics model of rigid-flex system was derived to describe motion of the assembly robot. Innovation of this method is that it considered the complex coupling effect among deformation of structural modules, translational and rotational maneuvers of the assembly robot during transportation in ISA missions. On this basis, the proportional-derivative (PD) controllers were adopted as the in-space structural module assembly method. Finally, taking the ISA of antenna as an example, successful application of the proposed dynamics model and controller to the assembly mission was verified.

Cooperative Orbital Control of Multiple Satellites via Consensus

In space systems consisting of a large number of satellites, coordinating orbits among satellites is necessary throughout the entire mission lifetime. Although previous works mainly focused on the boundedness of relative motion between satellites in the group, in this paper, an extra degree of freedom is also addressed in order to manipulate an arbitrary number of orbital elements, which is represented as coordinating a general orbital transfer and an in-space assembly. The underlying concept is using consensus theory to characterize the properties of the control objective as in a multiagent system. To that end, this paper assumes that the communication in the networked satellite system is represented as an undirected graph, and then implements the governing system dynamics in a control-affine form as described by the Gauss's variational equations. For the general orbital transfer problem, an edge-error-based controller is developed and proven asymptotically stable. Definitions of error functions are also investigated to understand the behavior of developed controllers. Several strategies for assembly control are discussed, namely, via changing of variables or in a two-phase control process based on the dynamical structure. Numerical simulations are performed to validate the analysis and demonstrate the results.

Infrastructure for large space telescopes

It is generally recognized (e.g., in the National Aeronautics and Space Administration response to recent congressional appropriations) that future space observatories must be serviceable, even if they are orbiting in deep space (e.g., around the Sun–Earth libration point, SEL2). On the basis of this legislation, we believe that budgetary considerations throughout the foreseeable future will require that large, long-lived astrophysics missions must be designed as evolvable semipermanent observatories that will be serviced using an operational, in-space infrastructure. We believe that the development of this infrastructure will include the design and development of a small to mid-sized servicing vehicle (MiniServ) as a key element of an affordable infrastructure for in-space assembly and servicing of future space vehicles. This can be accomplished by the adaptation of technology developed over the past half-century into a vehicle approximately the size of the ascent stage of the Apollo Lunar Module to provide some of the servicing capabilities that will be needed by very large telescopes located in deep space in the near future (2020s and 2030s). We specifically address the need for a detailed study of these servicing requirements and the current proposals for using presently available technologies to provide the appropriate infrastructure.

Exploration Technology Program plans and directions

During the first part of the next century, the United States will return to the Moon to create a permanent lunar base, and, before the year 2019, we will send a human mission to Mars. In addition to these human operations, the Space Exploration Initiative will integrally incorporate robotic lunar and Mars missions. In achieving these efforts to expand human presence and activity in space and also exerted and frontiers of human knowledge, the SEI will require an array of new technologies. Mission architecture definition is still underway, but previous studies indicate that the SEI will require developments in areas such as advanced engines for space transportation, in-space assembly and construction to support permanent basing of exploration systems in space, and advanced surface operations capabilities including adequate levels of power and surface roving vehicles, and technologies to support safely long-duration human operations in space. Plans are now being put into place to implement an Exploration Technology Program (ETP) which will develop the major technologies needed for SEI. In close coordination with other ongoing U.S. government research and development efforts, the ETP will provide in the near term clear demonstrations of potential exploration technologies, research results to support SEI architecture decisions, and a foundation of mature technology that is ready to be applied in the first round of SEI missions. In addition to the technology needed for the first round of SEI missions, the ETP will also put in place a foundation of research for longer-term technology needs—ultimately leading the human missions to Mars. The Space Exploration Initiative and the Exploration Technology Program will challenge the best and the brightest minds across government, industry and academia, inspiring students of all ages and making possible future terrestial applications of SEI technologies that may create whole new industries for the future.

In-Space Assembly and Maintenance of Unmanned Spacecraft

Possible future space operations, such as building a large platform using ground integrated modules launched separately or maintenance of satellites, require basically the same major subsystems as concerns Rendez-vous and Docking, Manipulation and Connections capabilities, at least in their unmanned implementation. The geostationary orbit (GEO) provides good conditions for the feasibility evaluation and cost efficiency assessment of the unmanned operations in orbit related to assembly and maintenance.This paper is a synthesis of the related design concepts considered by MATRA (**) and discusses the performance limitations for assembly, repair and maintenance in GEO.