香京julia种子在线播放

The evolution of robotics and artificial intelligence has revolutionised state-of-the-art space systems. Robotics, Automation and Autonomous Systems (RAAS) solutions have helped the space community conduct ground-breaking research in various planetary missions and on the International Space Station (ISS). Building upon these substantial achievements, the next few decades would unfold new chapters in orbital missions. Over the years, Extra-Vehicular Activities (EVA) have proven beneficial for servicing and maintenance missions on the ISS (Culbertson 2003). The installation of corrective optics on the Hubble Space Telescope (HST) is another explicit example of the success of EVA (Burrows 1991). However, the unfavourable space environment constantly risks EVA operations (Thirsk et al., 2009; Fazekas 2020). With future missions involving large-scale high-value infrastructures, assembly and maintenance would be much beyond human capabilities, requiring autonomous robots. Advancements in RAAS have resulted in a paradigm shift in space exploration as it would facilitate a multitude of In-Space services. In support of the plans to be a dominant candidate in the In Orbit Services and Manufacturing (IOSM) market, the UK Space Agency, along with multiple enterprises, are in plans to invest in relevant futuristic space technologies (Catapult 2020). In-Space services can facilitate numerous missions such as manufacturing, assembly, servicing, debris removal, astronomy, and Earth Observation (EO), to list a few (Alondra Nelson et al., 2022). Amongst the innumerable tasks which In-Space services can expedite, this paper focuses on assembling a Large Aperture Space Telescope (LAST) in orbit. LAST would promote a series of astronomical and EO missions (Baiocchi and Stahl 2009, Catapult 2020).

The move towards LAST commenced ever since the successful launch of the HST. Launched in 1990, the HST with a 2.4 m monolithic Primary Mirror (PM), became the ‘eye in the sky’ for any astronomer. It has helped mankind pin down the age of our cosmos, prove the existence of supermassive black holes and other numerous contributions (Hubble 2020). Thereafter, its successor, the James Webb Space Telescope (JWST) mission, was launched in December 2021. The JWST has a folded-wing design to incorporate the 6.5 m PM, with capabilities to visualise a hundred million years after the Big Bang (Lockwood Optics 2020). As understood, there exists a constant scientific and commercial clamour to upgrade the telescope sizing for a better resolution and signal-to-noise ratio. Addressing these requirements, the space community is moving towards deploying telescopes with a much larger aperture in orbit. Assembling a LAST on the ground is not practical given the limited fairing size of current and planned launch vehicles (Nelson, Mast and Chanan 2013; Garzón et al., 2017). Much like the trend for planned futuristic space designs, LAST would facilitate a modular design approach for the mirror units to fit well within the fairing limits of the launcher. The modules of the LAST system are to be autonomously assembled in orbit using RAAS. Existing literature provides conceptual models of various approaches to carry out in-situ assembly missions of LAST. These include a hexbot, robots inspired by the Special Purpose Dexterous Manipulator, a fixed-to-base robotic manipulator concept and mobile robotic manipulators, to enlist a few (Oegerle et al., 2006; Lee et al., 2016; Nanjangud et al., 2019; Rognant et al., 2019). However, a wide knowledge gap exists in design engineering autonomous space robotic systems. Therefore, it is of utmost importance to shift from concepts to simulations and eventually realise large-scale robotic assembly in orbit. Previous studies presented a five Degrees-of-Freedom (DoF) End-Over-End Walking Robot (E-Walker) as a potential candidate for efficiently assembling a LAST in-orbit (Nair et al., 2020a; Nair et al., 2020b; Nair et al., 2020c). The initial design, kinematic and dynamical modelling of the E-Walker integrated with an industrially proven Proportional-Integral-Derivative Computed-Torque Controller (PID-CTC) to successfully track the joint parameters within its limits was discussed in (Nair et al., 2020a). A detailed feasibility analysis on a series of mission concepts and a potential mission concept was presented in (Nair et al., 2020b; Nair et al., 2020c).

This paper presents an updated design of the E-Walker for efficiently assembling a 25 m LAST in orbit. Initially, this paper elicits the top-level assembly requirements of LAST, the robotic system and the spacecraft platform. To meet the mission requirements, a seven Degrees-of-Freedom (DoF) fully dexterous E-Walker is introduced. The E-Walker draws inspiration from the Canadarm2 and the European Robotic Arm (ERA) on the ISS. The two links of the Canadarm2 are separated by a joint offset in the elbow, making it complicated for the robot arm to walk around connector ports placed in a straight line. On the other hand, the ERA has both its links attached to the side of its elbow joint, limiting the complete rotation of its the elbow joint like the Canadarm2 to an end-to-end motion. In comparison to Canadarm2 and ERA, the E-Walker has both its links in line about its elbow joint, allowing it to walk end-over-end like Canadarm2 without an offset. Either end of the E-Walker is equipped with a Latching End-Effector (LEE) to latch onto the static connector ports on LAST and the spacecraft platform. The proposed E-Walker’s redundant design and mobility features offer access to a much larger workspace than conventional fixed-to-base robotic manipulators. Also, the LAST design presented can be considered as a baseline for futuristic LAST designs, which can be scaled up for PMs up to 100 m aperture.

An in-depth design engineering exercise has been carried out for the E-Walker according to the system and mission requirements for 1) optimising the link and LEE parameters 2) actuator selection. Initially, different link shapes of a given link length were compared to analyse the mass and area moment of inertia. Thereafter, to evaluate deflection, stress and strain, and open-loop performance under external disturbances in orbit, Finite Element Analysis (FEA) was carried out for the E-Walker components through Static Structural Analysis (SSA) and Modal analysis. The torque requirements for joint actuators were obtained using E-Walker’s dynamic equation formulation, which eventually helped in selecting the electrical actuators for the system. Additionally, a scaled-down prototype for the Earth-analogue testing is introduced, which underwent a similar FEA analysis. The E-Walker prototyping work is now in progress at the University of Lincoln; therefore, the experimental verification and validation will be published separately. Figure 1 presents an overview of various applications of the E-Walker along with its configuration. Finally, this paper discusses a potential mission concept of operations (ConOps) to carry out a sequential assembly of the 25 m LAST. The presented mission concept is chosen based on an extensive feasibility study carried out in (Nair et al., 2020b). The ConOps utilise two E-Walkers to assemble the PM, showcasing the extensive cooperative task-sharing capabilities of a dual robotic system, much required in futuristic robotic space missions.

The rest of the paper is organised into five sections. Top-level assembly requirements discusses the LAST mission’s top-level assembly requirements, including the robot and spacecraft system requirements. The Space grade E-Walker’s extensive design engineering is presented in End-over-end walking robot, where the full-scale system is optimised and analysed using SSA and Modal analysis under microgravity conditions. E-walker scaled-down Earth analogue design introduces the scaled-down Earth-analogue E-Walker prototype design. Mission concept of operations discusses a mission concept involving a dual E-Walker system to carry out the assembly. A flowchart is presented to depict the execution of this mission. In Conclusion and future research, the main inferences are covered, including an insight into planned experimental testing and further research.

The top-level system architecture of the 25 m LAST mission comprises the robotic system (E-Walker), the 25 m LAST and the spacecraft platform. The spacecraft platform is a composite system inclusive of the B_sc, S_sc and truss modules. Throughout the paper, it is assumed that the components of the spacecraft platform remain docked. To carry out the assembly tasks in orbit, each system should meet certain requirements for a safe and precise assembly. The E-Walker has to meet certain mission-oriented goals to carry out the assembly of the 25m LAST, i.e., in terms of mobility, and pick and place operations. Table 1 presents the top-level requirements of the E-Walker.

In this paper, the robotic architecture presented to facilitate the autonomous assembly of the 25 m LAST in orbit is an End-Over-End Walking Robot (E-Walker). The choice is conclusive evidence of the extensive review by (Nanjangud et al., 2019a) and the proposed architecture in (Brooks et al., 2016; Nanjangud et al., 2019b; Letier et al., 2019; Rognant et al., 2019). The E-Walker’s space design is symmetric and draws inspiration from the Candarm2 and the ERA onboard the ISS and the robotic manipulator presented in the Modular and Re-Configurable Spacecraft (MOSAR) project (Cruijssen et al., 2014; Glen Gook, 2015; Deremetz et al., 2021). The symmetric feature was also introduced in a five DoF earth-based walking robot manipulator—the Climbot (Guan et al., 2011). This section compares the E-Walker design with the other identified walking robotic manipulators and identifies the key differences to propose a novel robotic solution for the upcoming in orbit missions.

A top-level comparison between the state-of-the-art walking robot manipulators in space and the E-Walker space design is shown in Table 2. In terms of design comparison, the Canadarm2 has an offset around the elbow joint, which provides it with the capability to walk end-over-end, however, the connector ports have to be placed in a spacing equal to the joint offset to enable a straight-line motion. In comparison, the ERA and MOSAR have in-line elbow joint without an offset. However, as the two links are clamped onto the elbow joint on the sides, both the arms are limited of a full rotation around the elbow and end up in end-to-end walking. This results in an increased dependency on the roll joints of these robot manipulators, which is not recommended for a space mission. The E-Walker is an amalgamation of all the key features of the above-mentioned robotic arms, i.e., achieving end-over-end walking with an in-line elbow joint to achieve easy motion along a straight line without joint offset. For the earth-based design, the Climbot is a walking robot manipulator which has a similar elbow joint feature as the E-Walker. However, its workspace, redundancy and dexterity are limited due to the reduced number of joints (5 DoF).

In comparison, the E-Walker prototype is dexterous with seven DoF and facilitates a modular design with customisable end-effectors. A comparison between Climbot and the E-Walker prototype design is enlisted in Table 3.

The E-Walker’s capability to connect to static connector ports onboard the B_sc and Truss helps to cover a workspace much larger than its span. This enhanced reachability is an added benefit for assembly missions. In this paper, the E-Walker is assigned two key operations throughout the mission. These operations involve assembling PMSs using PMUs, thereafter, performing pick-and-place operations of the assembled PMSs onto their respective truss locations. The E-Walker would facilitate mobility around an attitude-stabilised B_sc, with a predefined motion that will not alter the attitude of the B_sc. This is contrary to the state-of-the-art concept of a space robot which requires additional effort in the Guidance, Navigation and Control unit. This is due to the complexities involved in maintaining attitude due to the non-linear dynamic coupling effects between the spacecraft platform and the fixed-to-base robotic manipulator (Flores-Abad et al., 2014).

The seven DoF E-Walker has three revolute joints, each in the shoulder and the wrist, and one DoF in the elbow joint. The dexterous symmetric design provides access to any part of the workspace (see Figure 1), satisfying the requirement R 3 completely. The seven DoF E-Walker can use either of its two LEEs to latch on to the B_sc. During each phase, the LEE on either side of the E-Walker, attached to J₁ or J₇, is locked to the spacecraft platform. A fixed-to-base robot manipulator would require a full-length span of ∼ 12 m to assist with the assembly when placed at the centre of the 25 m LAST system (Nanjangud et al., 2019a). On the contrary, the E-Walker’s dimensions can be reduced subject to the availability of the connector points and the payload sizing.

The initial design of the E-Walker considered a five DoF model, which included two revolute joints, each in the shoulder and wrist, one revolute joint in the elbow and two LEE on either end (Nair et al., 2020a). The five DoF E-Walker provided an insight into the minimum DoF required to realise the cyclic motion dynamics; this was a baseline design to carry out an end-over-end motion. This design met the requirement R 4 partly. However, for space-based operations, both redundancy and dexterity are essential (Dalla and Pathak 2019). Redundancy offers enhanced reachability and acts as a significant backup in case of a joint failure. Therefore, to overcome the challenges of the five DoF E-Walker’s limitations, the seven DoF E-Walker design was introduced as an upgrade. The enhanced mobility feature of the seven DoF E-Walker can also help satisfy the requirement R 5 post the assembly.

Verifying the large-scale model of the E-Walker is near to impossible under Earth analogue conditions, given the high torque demands due to Earth’s gravitational pull and the limited microgravity environment test facility on the ground. Due to these reasons, a scaled-down prototype of the E-Walker is considered for fabrication to verify and validate tasks involving mobility and pick-and-place operations. The design engineering exercise similar to the one carried out in End-over-end walking robot is repeated for the prototype in Sections 4.1–4.4. The comparison of the full-scale E-Walker and its scaled-down Earth-analogue design helps understand the issues with scalability and the impact of Earth’s gravitational acceleration. Table 7 presents a summary of the design trade-offs of the full-scale E-Walker and its prototype. Detailed SSA and actuator selection methods are presented in the following subsections. Similar to the full-scale space design, it is significant to identify the design requirements specific to the E-Walker’s scaled-down prototype ( R P i ) to carry out operations under Earth’s gravity. Table 8 presents the list of requirements.

A detailed feasibility analysis was carried out in a previous publication (Nair et al., 2020b), where a potential mission scenario, namely Mission Scenario 2b, was shortlisted after a trade-off analysis of eleven mission scenarios. A maximum of four E-Walkers were considered to carry out the assembly of the 25 m LAST. The analysis took into consideration the mission cost, lifting mass, net power requirements, control and motion planning complexity. This paper presents Mission Scenario 2b, which involves only two E-Walkers, namely EW₁ and EW₂ to carry out the in-orbit assembly of the 25 m LAST (Figure 14A). The mission ConOps provide an insight into task-sharing and co-manipulation with the collaborative operation between the two E-Walkers. This mission concept facilitated by two E-Walkers could facilitate futuristic LAST assembly missions with much larger apertures of 50 m or 100 m.

Mission Scenario 2b involves both the E-Walkers sharing equal responsibilities in the assembly process. The tasks are split into assembling the PMS using the PMUs and performing pick-and-place operations to place the assembled PMSs to assemble the 25 m PM. To undertake the assembly, each of the E-Walkers is initially assigned one-half of the truss. This paper considers EW₁ to take up the responsibility of the left half of the truss, whereas EW₂ is responsible for the right half. The E-Walker’s reach is considered large enough to attend to the inner-ring assembly (positions 1–6) by staying on the B_sc. For the outer-ring assembly (positions 7–18), the E-Walkers will move to pre-designed connector points on the truss.

For a quick and efficient assembly, the operation is carried out in two modes. In Mode 1, both the E-Walkers collaborate to assemble a PMS, using the PMUs stored in the S_sc, in the inner ring of the truss. Once a PMS is assembled, one E-Walker steps onto the respective connector point on the truss (EW₁ for the left-half and EW₂ for the right-half) to pick and place the assembled PMS onto the respective outer-ring positions. Considering an operation where EW₁ moves onto a left-half connector point on the truss to place a PMS, EW₂ will begin assembling a new PMS while EW₁ is away. Once EW₁ places the PMS, it climbs back onto the B_sc to assist EW₂ with the ongoing PMS assembly. For the right-half assembly, the roles of the E-Walkers are switched. Mode 1 of operation sees a majority of the outer ring being assembled.

Mode two of the assembly operation involves both the E-Walkers taking up individual responsibilities to assemble the PMS and to perform the pick-and-place operation in their respective halves. This is with the intent to utilise the E-Walker’s walking capability and reduce the overall sizing of the E-Walker. Additionally, each of the E-Walker will assemble PMSs simultaneously in the inner ring. The E-Walkers can attend to their respective halves in the inner ring from the B_sc itself. In Mode 2, both the E-Walkers collaborate to work independently and simultaneously, resulting in a faster assembly.

This paper introduced the design and feasibility of a walking space manipulator for in-situ robotic assembly of a 25 m Large Aperture Space Telescope (LAST). It captured the critical challenges of in-space robotic assembly mission, elicited the mission and system-level requirements and provided a deeper understanding of the design engineering of the E-Walker. The seven DoF End-over-End Walking Robot (E-Walker) selected for this mission provides the modularity, dexterity features alongside manoeuvring capabilities over an enhanced workspace. Detailed design engineering helped identify an optimised design for the E-Walker to carry out the assembly of LAST. These included static structural and modal analysis of the full-scale space design of the E-Walker. This provided an insight into understanding the dynamical behaviour of the intercoupled links and the end-effectors of the E-Walker while carrying a payload under different environmental conditions.

The E-Walker presented would be able to extend the mission lifecycle by carrying out routine maintenance and servicing missions post assembly. The E-Walker design shown is versatile, and it is a candidate robot for future planetary and orbital missions. In addition to the full-scale design, a scaled-down ( 1 : 6 ) prototype design of the E-Walker is also presented, along with its detailed structural analysis. The optimised design analysis (considering a payload) identifies the E-Walker prototype to also be an ideal candidate for servicing, maintenance, and assembly operations on the ground. An example could be the E-Walker carrying out regular maintenance checks on a wind turbine, given its capability to manoeuvre anywhere in a 3D space. Once the detailed design engineering for the E-Walker was discussed, a mission concept, namely Mission Scenario 2b, was presented to carry out the assembly of the 25 m LAST. The assembly flow presented using the dual-agent system (two E-Walkers) realises robotic task-sharing capabilities in orbit. The mission serves as a baseline study for large-scale future missions requiring multiple agents. Overall, this paper presents the top-level system design to assemble a 25 m telescope in orbit, with a detailed analysis of the E-Walker design to be integrated into future in-orbit and terrestrial operations. This paper is a useful case study for future LAST missions with Primary Mirrors of apertures planned up to 100 m .

Future research includes finalising the design specifications of the true-scale E-Walker for the 25 m LAST mission. Additionally, an Earth-based small-scale E-Walker prototype is under development for further hardware-in-loop experimentation. This prototype can then be tested with space-qualified robust controllers, like the Proportional-Integral-Derivative-Computed-Torque-Controller or the H_∞ controller for precise joint tracking under external disturbances and parametric uncertainties. Given the huge commercial interest in this topic, Space agencies and industries have developed their road maps for orbital robotics missions. The LAST mission and the E-Walker model have also drawn commercial and scientific attention. Over the next 5–10 years, it is envisaged that researchers and industries will carry out further development to assess E-Walker’s feasibility. These include prototyping an E-Walker for a precursor mission involving a 2.5m/5 m LAST. The E-Walker’s capability for assembling the secondary mirror, truss modules and baffles is not yet realised.