Free-flying Platform Research Articles

A Comprehensive Review of UAV-Assisted FSO Relay Systems

The evolving requirements of next-generation mobile communications networks can be met by leveraging vertically deployed Unmanned Aerial Vehicle (UAV) platforms integrated with Free Space Optical communications (FSO). This integration offers a flexible and scalable architecture capable of delivering high-rate communication without requiring licenses while aligning with the multi-gigabit paradigm. In recent times, the increasing availability of commercial aerial platforms has facilitated experimental demonstrations of UAV-enabled FSO systems, which play a crucial role in proposed backhaul networks and point-to-point communications by overcoming Line-of-Sight (LOS) challenges. These systems can be rapidly deployed to meet sudden demand scenarios. This document provides a comprehensive review of relevant field demonstrations of UAV-enabled FSO relay systems, with a particular focus on commercially available, free-flying platforms that are driving advancements in this domain. It categorizes the different platforms by considering the operational altitudes of these systems and their payload actuation capacity, which determines their adaptability to variables. The analysis aims to distill the design considerations that lead to optimal performance regarding communications throughput and other relevant metrics. Moreover, it also attempts to highlight areas where design choices have fallen short, indicating gaps in current research efforts toward the widespread adoption of UAV-enabled FSO relay systems. Finally, this work endeavors to outline effective design considerations, guidelines, and recommendations to bridge these identified gaps. It serves as a valuable reference guide for researchers involved in developing UAV-enabled FSO relay systems, enabling them to make informed decisions and pave the way for the successful implementation of such systems.

Unleashing the Potential of Networked Tethered Flying Platforms: Prospects, Challenges, and Applications

Networked Tethered Flying Platforms (NTFPs) have gained growing interest in recent years due to their versatility and cost-efficiency. These aerial platforms are linked to ground stations via tethers that supply them with continuous power and data. The main advantages of NTFPs include endurance, broad coverage, and robust backhaul capacity, allowing them to carry various types of applications. This survey provides a comprehensive overview of NTFPs from a general and wireless communication perspective. We start with a general overview of this solution by reviewing all the existing types of NTFPs, including their components, characteristics, applications, advantages, and regulations. We also describe several case studies in various fields. Then, we investigate the role of NTFPs in wireless communications and their integration in Non-Terrestrial Networks (NTNs) alongside free-flying platforms and satellites in Sixth Generation (6G) cellular technology. We present NTFPs system models and emerging works on NTFPs performance. We show how 6G key technologies will be integrated into NTFPs and discuss how NTFPs will enable 6G use cases. The related channel models to NTFPs deployment are also covered. For completeness, we provide an economic analysis of the use of NTFPs. Finally, we discuss the challenges and open problems.

Maneuver and vibration control of flexible manipulators using variable-speed control moment gyros

In this paper, the variable-speed control moment gyros (VS-CMGs) are adopted as actuators for vibration suppression of space flexible manipulators. They are directly mounted on the flexible links of the manipulator. Such system can be viewed as a flexible multibody system in chain topology actuated by both joint motors and VS-CMGs. We first develop a general approach for establishing the system equations of motion through Kane׳s method. Then, two controllers are designed for trajectory tracking and vibration suppression: one is an inverse dynamics control, whereas the other is based on the singular perturbation method. The proposed two control strategies are applied to a free-flying platform with a flexible manipulator. Sample numerical results show that the VS-CMGs can significantly suppress the induced vibration of the flexible links during the large angle maneuver.

Dynamical Modeling of Cooperating Underactuated Manipulators for Space Manipulation

Underactuation may arise when a manipulator includes at least one passive joint. Free-flying platforms fall under passive systems since they can be considered as linked to a fixed base by 6-d.o.f. free joints with no friction. Dynamics of underactuated cooperating manipulators have become a bigger challenge when underactuation is encountered by the combination of free, flexible and/or active joints in the context of a free-flying platform. This paper demonstrates the presented methodology on the dynamical modeling and simulation of underactuated manipulators cooperating to perform a common task on a free-flying space platform.

Issues and solutions for testing free-flying robots

Space robotics currently has an important role in space operations and scientists and engineers are designing new robotic systems for space servicing missions and extra-vehicular activities. In particular, free-flying robots with extended arms have compelling applications and several prototypes have recently been developed. Testing on Earth free-flying robots is a main issue as the unconstrained environment of free space must be simulated. From the experience acquired by testing a free-flying robot prototype both in a tethered facility and during a parabolic flight campaign, and after several years of experiments using air-bearing planar systems, the authors describe and discuss methods to test free-flying robots. A recent study aimed at designing a free-flying platform suitable for an under-water environment is also presented and discussed.

Solutal-thermo-diffusion convection in a vibrating rectangular cavity

Diffusion-dominated experiments on-board the International Space Station and other free-flying platforms are affected by the convective flow due to the residual acceleration field and/or to the oscillatory accelerations ( g-jitters) caused by several external sources. We are interested in investigating these effects on the solutal-thermo-diffusion for a binary fluid mixture. We considered a rectangular rigid cavity filled with methane (20%) and normal butane (80%), subject to a temperature difference on its lateral walls and radiation heat transfer on the horizontal walls. The full transient Navier–Stokes equations, accounting for a unique mode of oscillatory acceleration, coupled with the mass and heat transfer formulations and the equation of state of the fluid were solved numerically using the control volume technique. The species transport equation accounts for varying diffusion coefficients with the temperature and the fluid composition and their effect is analysed as compared to that of their average constant values. Results revealed that convection is enhanced and temperature and species profiles distortion from purely diffusive (zero-gravity) condition increases in a buoyancy-destabilizing configuration. The numerical study shows that by elimination both the residual gravity and the g-jitter levels are essential to achieve nearly purely diffusive conditions when their direction is orthogonal to that of the temperature gradient. For the configuration investigated, the g-jitter is found to reduce compositional variation. When quasi-steady state conditions are attained, thermal and compositional quantities fluctuate following a mode whose fundamental (primary) frequency is equal to that of the initially imposed vibration.

Why Doing Fundamental Physics on the ISS?—The Experimental Conditions

The International Space Station (ISS) already serves as a laboratory for experiments in fundamental physics. It could be used for a much wider range of experiments if the operational concept of the ISS will be changed. Operational constraints set limits for the precision level of experiments. Free-flying platforms with high precision attitude and orbit control (drag-free control) could co-orbit with the ISS and improve the experimental conditions. The paper summarizes the main constraints and discusses concepts for improvement.

An engineering approach to the dynamic control of space robotic on-orbit servicers

Robotic on-orbit servicing is the key to the commercial development of a space robotics infrastructure. A major technical difficulty has been the problem of control of the robotic manipulators mounted onto a freeflying platform in space. The problem of control is directly related to the fact that manipulator motions exert reaction effects on the mounting spacecraft. A solution to this problem is outlined-one in which no fuel is expended and that demands no excessive computational resources that would otherwise preclude real-time performance.

Advanced thin-film materials processing in the ultra-vacuum of space

The utilization of the vacuum of space for thin-film materials development has been pioneered by the Wake Shield Facility (WSF) program. The WSF is a 4 m diameter disc-shaped free-flying platform designed to generate an ultra-vacuum in low earth orbit (LEO) space, and to utilize that ultra-vacuum for the fabrication of thin-film materials by epitaxial growth. In the three flights of WSF, high-quality GaAs-based epitaxial thin films were grown, vacuum quality was assessed, and cooperative experiments were activated. The promising results on high-purity film growth indicate future benefits of thin-film materials fabrication in LEO for terrestrial applications in high-performance electronic devices.

Orbit demonstration of two-dimensional deployable array including high voltage photovoltaic power generation

The Institute of Space and Astronautical Science is developing a Two-dimensional Deployable High Voltage (2D/HV) Solar Array Experiment, which will demonstrate repetitive deployment/retraction of a plane structure and high voltage photovoltaic power generation in space. The flight operation of 2D/HV experiment will be executed on the free-flying platform, Space Flyer Unit in early 1994.

The flight telerobotic servicer (FTS): A focus for automation and robotics on the space station

NASA has committed to the design and implementation of a robotic device to assist the astronauts in assembly, maintenance, servicing and inspection tasks in the unpressurized environment of the Space Station, substantially reducing the time required for crew extra vehicular activity (EVA). This system introduces into the Space Station program a “telerobot” adaptable to a variety of tasks and worksites. The term “telerobot” is used to indicate the combined attributes of an autonomous robot and a teleoperated manipulator. Design requirements for the telerobot are driven by a detailed analysis of the tasks which are required on the Space Station and its associated free-flying platforms. The Space Station will have several kilometers of truss structure to which are attached numerous scientific payloads, as well as functional elements and utilities of the Space Station itself. Scientific payloads require servicing of different levels of complexity. Free-flying spacecraft will be brought into the hangar-like servicing facility for repair. There will be maintenance and inspection tasks of the Space Station elements, as well as initial Space Station assembly tasks. A step-by-step analysis of candidate tasks has led to a design envelope for the telerobot. Since the telerobot is an extension or telepresence of the astronaut at the remote worksite, design of the workstation in the pressurized module has to give careful consideration to the man/machine interface, as well as the constrained volume in the pressurized modules. The flight telerobotic servicer (FTS) is designed for future growth toward more autonomy. By a careful selection of the functional architecture, and a modular approach to the hardware and software design, the FTS can accept developments in artificial intelligence and newer, more advanced sensors, such as machine vision and collision avoidance. The FTS is a focus for automation and robotics on the Space Station, as well as a baseline from which visionary projections of future space exploration with robots can be developed.

Design and economics of a free-flying platform for space manufacturing

This paper reviews the feasibility of materials processing in a microgravity environment using existing space platforms. The feasibility is described in terms of cost, payload mass, carrier mass, quality of the microgravity environment, and spacecraft subsystem requirements. The results indicate that the optimum platform is the free-flying space platform since it is the cheapest and provides the best microgravity environment.

Satellite Servicing by Teleoperators

The Teleoperator Maneuvering System (TMS) will initially be a Shuttle-launched ground-based, satellite servicing vehicle controlled by man-in-the-loop. During Space Station implementation, it will be used to assist the assembly and placement of the various Space Station elements as well as to provide logistics module transportation from the Shuttle to the Space Station. It will eventually be based at the Space Station to support satellite viewing, spacecraft and payload placement and retrieval functions, and to provide support of science or materials processing free-flying platforms. Various satellite servicing examples with the use of the TMS from the Space Station and/or the Space Shuttle are provided in this paper. Concepts for the number of TMS and the type of basing required at the Space Station are also reviewed. Specific station accommodations must await definition of the emerging station configurations.

Utilisation of the European Retrieval Carrier Eureca for life science research

Eureca, the European Retrieval Carrier, is a reusable free-flying platform, which will be launched to 500 km altitude and retrieved by the Shuttle, up to 6 months later at 300 km. The first mission of Eureca is dedicated to research in the fields of life sciences and material sciences. The experimental hardware of the first mission will consist of a variety of processing chambers for crystal growth and equipment for biological investigations viz plant growth and protein crystallization, and there is the possibility to perform experiments in the field of exobiology. The Eureca mission offers the opportunity for long time exposure of material and of terrestrial origin to the unique environment of space or to selected factors of it, such as the radiation environment, the space vacuum, extreme temperatures and microgravity conditions.

The pinhole/occulter facility

The Pinhole/Occulter Facility concept uses a remote occulting mask to provide high resolution observations of the solar corona and of astronomical X-ray sources. With coded-aperture and Fourier-transform techniques, the Pinhole/Occulter makes images at a resolution of 0.2 arc sec for 2 - 120 keV X-rays, using a 50-m boom erected from the payload bay of the Space Shuttle or mounted on a free-flying platform. The remote occulter also creates a large shadow area for solar coronal observations; the Pinhole/Occulter concept includes separate optical and ultraviolet telescopes with 50-cm apertures. These large telescopes will provide a new order of resolution and sensitivity for diagnostic observations of faint structures in the solar corona. The Pinhole/Occulter is a powerful and versatile tool for general-purpose X-ray astronomy, with excellent performance in a broad spectral band complementary to that accessible with AXAF. The large collecting area of 1.5 m2 results in a 5σ detection threshold of about 0.02 μJy for the 2 - 10 keV band, or about 10−5 ph(cm2sec keV)−1 at 20 keV.