End-to-end on-orbit services

Abstract

An on-orbit servicing spacecraft comprises an engagement system for engaging a space vehicle or object to be serviced or towed to form a space system; and an electronic reaction control system for rotating the spacecraft around a roll axis, a yaw axis and a pitch axis to control the attitude and displacement along a given trajectory, thereby enabling the spacecraft to perform a given maneuver. The electronic reaction control system comprises: a sensing system to directly sense physical quantities or to allow indirect calculation of physical quantities based on sensed physical quantities including one or more of position, attitude, angular rate, available fuel, geometrical characteristics and onboard system status; attitude control thrusters mounted to allow their position and orientation to be adjustable; and an attitude control computer in communication with the sensing system and the attitude control thrusters and programmed to receive data from the sensing system and to control the position, orientation and operational state of the attitude control thrusters based on the received data, thereby controlling the attitude and position of the spacecraft, the attitude control computer being programmed to cause the spacecraft to perform a given mission including an engagement step, wherein the engagement system and the attitude control thrusters are controlled by the attitude control computer to engage a space vehicle or object to be serviced or towed, and one or more operation steps, in each of which the attitude control thrusters are controlled by the attitude control computer to meet one or more requirements established for the operation step. Each operation step may include at least one stabilization substep during which the attitude of the space system is stabilized according to the requirements of the operation step and a given optimization criterion, followed by a stabilization operation substep that begins at the end of the stabilization substep of the attitude of the space system. In each operational step, the attitude control computer is also programmed to optimize the configuration of the attitude control thrusters according to the requirements of the operational step by implementing an iterative process for optimizing the configuration of the attitude control thrusters.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000019322 filed on October 18, 2019. Technical Field

[0003] The present invention generally relates to end-to-end on-orbit servicing, and more particularly to on-orbit servicing of spacecraft for on-orbit inspection and / or maintenance of spacecraft, and for towing of spacecraft or other space objects. Background Art

[0004] It is well known that in the space landscape, end-to-end on-orbit servicing services are revolutionizing space transportation and the way space is used.

[0005] In general, end-to-end on-orbit servicing services can be divided into two broad categories: spacecraft inspection and / or maintenance services and towing services, which are used to tow space vehicles or space objects of other nature (such as space debris).

[0006] Spacecraft inspection and / or maintenance services can be further subdivided into spacecraft inspection services, spacecraft life extension services, including refueling and spacecraft repositioning services; and spacecraft update services to adapt the spacecraft to its mission throughout its service life.

[0007] Spacecraft towing services can be further subdivided into geosynchronous orbit spacecraft towing services, including spacecraft delivery, and low Earth orbit (LEO) spacecraft towing services, including satellite constellation deployment. For example, these are provided to satellites that failed to reach their operating orbits due to launch failures.

[0008] On the other hand, towing services or more precisely space object removal services essentially consist of cleanup services aimed at actively removing space debris.

[0009] On-orbit servicing services are provided by on-orbit servicing spacecraft. When the on-orbit servicing spacecraft is designed to provide inspection and / or maintenance services to a spacecraft, the on-orbit servicing spacecraft is distinguished as an inspection spacecraft and / or a maintenance spacecraft, and when the on-orbit servicing spacecraft is designed to provide towing services for a space vehicle / object, the on-orbit servicing spacecraft is distinguished as a space tugcraft.

[0010] Space object towing services can also be provided to space objects that failed to cooperate during service provision, and spacecraft inspection and / or maintenance services and spacecraft towing services are provided to spacecraft that can or cannot cooperate during service provision.

[0011] When spacecraft tugs are used to provide spacecraft towing services, the spacecraft tugs can be connected to the spacecraft to be towed before being launched and directly enter the launch facility for launch together with the spacecraft to be towed, or they can be launched separately from the spacecraft to be towed into a so-called rendezvous orbit (LEO or NRHO - near rectilinear halo orbit) waiting for the spacecraft to be towed, and the spacecraft is launched into the rendezvous orbit after space towing.

[0012] When they are used to tow individually launched spacecraft, the spacecraft tugs are controlled to autonomously approach and dock with the spacecraft via an appropriate docking system (usually in the form of a robotic arm), and possibly propel the docked spacecraft until they reach a desired orbit from which the spacecraft can be operated or maintained / refueled, repairs or other operations can be performed.

[0013] When a space tug is used to tow a space object, the space tug is controlled to autonomously approach and capture the space object with the help of an appropriate capture system (e.g., a net, fork or other system), and to deviate or raise the orbit of the captured space object, simply changing their orbit in order to bring them to a place where there is no longer a risk to operating satellites.

[0014] US2018 / 148197A1 discloses a service satellite having a body, a controller and a docking unit. The docking unit includes at least two foldable and adjustable gripping arms, which are pivotally mounted on the satellite body. Each gripping arm can pivot relative to the satellite body and includes a gripping end at each free end of the gripping arm. The gripping end is suitable for and configured to capture and grasp the target portion of the orbiting satellite. Each gripping arm is independently controlled by a controller, which coordinates the movement of the gripping arm. The service satellite also includes a propulsion unit, which includes a first thruster installed at the nadir end of the adjacent service satellite body and a balancing thruster spaced apart from the first thruster and facing a direction different from the first thruster, and a propellant for the thruster and the balancing thruster. The service satellite also includes a device for aligning the thrusters so that the propulsion vector passes through the joint center of gravity of the service satellite and the serviced satellite.

[0015] US6017000A discloses apparatus and methods for performing satellite proximity operations such as inspection, recovery and life extension of a target satellite through the operation of a "Satellite Inspection Recovery and Extension" ("SIRE") spacecraft, which can operate in a remote operation mode, an automatic mode and an autonomous mode. The SIRE concept also includes those methods and techniques for performing certain on-orbit operations, including but not limited to inspection, service, recovery and life extension of satellites, spacecraft, space systems, space platforms and other aircraft and objects in space (collectively referred to as "target satellites"). The three basic types of SIRE proximity missions are defined as "life extension", "recovery" and "utility". A remote cockpit system is provided to allow manual control of the SIRE spacecraft during proximity operations.

[0016] James Jillian, in “Adaptive control for post-dockmanoeuvres with an unknown semi-cooperative object,” 2016 IEEE Aerospace Conference, IEEE, March 5, 2016 (2016-03-05), pp. 1-10, explores the trade space in which adaptive controllers can maintain attitude control authority when a spacecraft is engaged with an object with limited physical parameter information, with the goal of charting a path for controller validation through future spaceflight experiments. A baseline attitude and position proportional-integral-derivative (PID) control system is compared to an adaptive PID control approach. The inertia, mass, and center of mass position of the attached spacecraft are varied to evaluate the limitations, performance, and robustness of these controllers.

[0017] US9115662B1 discloses a method and apparatus for managing multiple thrusters in a platform, comprising operating multiple thrusters in the platform using a thruster control system, estimating an aircraft response resulting from the operation of the multiple thrusters to form an estimated aircraft response, and comparing the estimated aircraft response with a desired aircraft response to produce a target function error.

[0018] CN110110342A discloses a data-driven control method for a combined spacecraft based on a proximity algorithm. The method includes the following steps: establishing a combined spacecraft motion model; designing a data-driven attitude controller based on a proximity algorithm; initializing controller parameters and establishing a database; calculating the predicted value of the system by using a formula and calculating the predicted output of the system by using a formula; calculating the controller; updating the data in the database; and iterating to adjust the output of the controller.

[0019] CN109625333A discloses a method for capturing non-cooperative targets in space based on deep reinforcement learning. The method includes two steps. Interaction can be achieved through this method. The method includes step 1, using three-dimensional visualization software to build a three-dimensional visualization environment for a service aircraft and a target aircraft, the input of the visualization environment is the control force and control torque of the service aircraft, and the output is the state of the service aircraft and the target aircraft; step 2, constructing a convolutional neural network model, and performing intelligent autonomous space non-cooperative target capture training on the service aircraft in a three-dimensional visualization environment. The convolutional neural network model uses the state of the service aircraft and the target aircraft as input, uses the weight parameters of the convolutional neural network model to output the control force and control torque required to control the service aircraft, and sends the control force and control torque to the visualization environment, and continuously inputs the state of the two aircraft into the neural network for continuous deep reinforcement training. Summary of the invention

[0020] Applicants have experienced that one of the key technical issues that the servicing spacecraft must face when servicing client spacecraft, especially satellites, is to optimize (i.e., reduce) fuel consumption to ensure the proper attitude, especially when the center of mass of the gathering spacecraft is located at a position (usually unknown in advance) midway between the two spacecraft when docking with the client satellite.

[0021] The Applicant has found that, to the best of its knowledge, the techniques currently used or proposed for solving the above-mentioned technical problem are essentially based on providing, by appropriate mechanisms, attitude control thrusters that move in two or more predetermined discrete positions, typically a stowed or undeployed position and a deployed position, wherein, to the best of the Applicant's knowledge, the deployed position is calculated on the ground based on an estimate of the position that can be assumed by the center of mass of the gathering spacecraft in all possible a priori predictable missions that the gathering spacecraft must perform.

[0022] As a result, the applicant has demonstrated that the above-described technology, while satisfactory in many respects, leaves significant room for improvement in terms of optimizing the efficiency of fuel consumption by servicing spacecraft throughout their useful life, particularly in situations where interaction with the servicing spacecraft from the ground is difficult due to their distance from the Earth, and in terms of the number and total mass of attitude control thrusters necessary to control the attitude of the servicing spacecraft and the gathering spacecraft throughout the useful life of the servicing spacecraft.

[0023] The object of the present invention is therefore to provide a technique that allows improvements to be obtained in terms of optimized efficiency of fuel consumption and in terms of the number of attitude control thrusters required to control the attitude of the service and aggregation spacecraft, taking into account the necessary redundancies.

[0024] According to the present invention, and as described in the accompanying claims, there is provided an on-orbit servicing spacecraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is an on-orbit servicing spacecraft.

[0026] Figure 2 Shown by Figure 1 A space system formed by an on-orbit servicing spacecraft, which is responsible for receiving the spacecraft to be serviced or towed;

[0027] Figure 3 Show Figure 1 Positioning and orientation systems for attitude control thrusters of on-orbit servicing spacecraft;

[0028] Figure 4 Show Figure 1 A block diagram of the electronic response control system for an on-orbit servicing spacecraft; and

[0029] Figure 5 Shown by Figure 4 A flow chart of the operations performed by the attitude control computer of the electronic reaction control system. DETAILED DESCRIPTION

[0030] The invention will now be described in detail with reference to the accompanying drawings to allow those skilled in the art to make and use it. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles described may be applied to other embodiments and applications without thereby departing from the scope of protection as defined in the appended claims of the present invention. Therefore, the present invention should not be considered limited to the described and illustrated embodiments, but should conform to the broadest scope of protection consistent with the described and claimed features.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly used by those of ordinary skill in the art of the present invention. In the event of any conflict, this specification (including the definitions provided) shall be binding. In addition, the embodiments provided are for illustrative purposes only and are therefore not to be considered restrictive.

[0032] In particular, the block diagrams contained in the accompanying drawings and described below are not intended to represent structural features, i.e. construction limitations, but they must be interpreted as representing functional characteristics, i.e. inherent characteristics of the device defined by the effect obtained, i.e. functional characteristics are functional limitations and can be implemented in different ways, therefore in order to protect their functionality (possibility of implementing the functionality).

[0033] To facilitate understanding of the embodiments described herein, reference will be made to some specific embodiments and specific language will be used to describe these embodiments. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of the invention.

[0034] In addition, for ease of description, the following description will, without loss of generality, relate to a mission in which an on-orbit servicing spacecraft in the form of a space tug must dock (not necessarily cooperatively) with a spacecraft in the form of a satellite, thereby forming a rigid space system consisting of the space tug and the satellite rigidly coupled to each other.

[0035] In summary, the basic idea of ​​the present invention is essentially to provide an artificial intelligence (AI) based attitude control that is able to output the best solutions regarding the positioning, orientation and operation of the attitude control thrusters of the space tug vessel based on the information provided by the sensing system of the space tug vessel, whether it is engaging a satellite or when it is still separating from the satellite.

[0036] The artificial intelligence based attitude control is also designed to adapt to changes over time, such as, for example, displacement of the center of mass position of the space system due to progressive fuel consumption on the space system.

[0037] This makes it possible to reduce fuel consumption on the one hand and to reduce the total number of necessary attitude control thrusters (including redundancy) on the other hand, thereby reducing the weight of the attitude control system, while also providing greater capacity to absorb any failure of the attitude control thrusters and increasing the maneuverability of the space system.

[0038] Figure 1 , Figure 2 and Figure 3 A space tug vessel according to the invention is shown, generally indicated by reference numeral 1 .

[0039] Space Tug 1 includes:

[0040] - a body or structure or platform 2; and

[0041] - Airborne equipment carried by the body 2, including:

[0042] ○ Solar panels 3, used to power the onboard electrical systems;

[0043] o an electronically controllable engagement system 4 of known type and therefore not described in detail, and shown by way of example in the form of a ring to which an engagement mechanism according to the prior art (not shown) is fixed for docking / capturing the towed satellite 5, thereby forming a space system 6 with the satellite 5; and

[0044] ○ Electronic Reaction Control System (RCS)7( Figure 4 ) is used to rotate the space tug 1 around the roll axis, yaw axis and pitch axis to control its attitude and displacement along a given trajectory, so that the spacecraft 1 performs given maneuvers, such as rendezvous and docking maneuvers between spacecraft (using displacement control to control the speed of approaching the target and aligning with the docking point) and orbit change maneuvers.

[0045] like Figure 4 As shown in the block diagram, the electronic reaction control system 7 includes:

[0046] a sensing system 8 of known type, therefore not described in detail, allowing direct sensing of physical quantities or indirect calculation of physical quantities based on sensed physical quantities such as position, attitude, angular rate, available fuel, geometrical characteristics and onboard system states;

[0047] - electronically controllable actuators / motors in the form of attitude control thrusters 9 mounted to allow their position and orientation to be adjustable; and

[0048] - an attitude control computer 10, which communicates with the sensing system 8 and the attitude control thrusters 9, and is programmed to receive data from the sensing system 8 and control the position, orientation and operating state of the attitude control thrusters 9 based on the received data, thereby controlling the attitude and position of the space tug vessel 1.

[0049] Reference again Figure 1 , Figure 2 and Figure 3 In order to allow their position and orientation to be adjustable, the attitude control thrusters 9 are mounted on the body 2 of the space tug vessel 1 by means of an electronically controllable deployable motion system 11, which is designed to allow the position and orientation of the attitude control thrusters 9 to be adjustable in response to electrical commands from an attitude control computer 10.

[0050] like Figure 2 As shown in more detail by way of non-limiting example, for each individual attitude control thruster 9, its orientation will be adjusted individually, or for each group of attitude control thrusters 9, their orientation will be adjusted collectively, referred to as an RCS cluster 9 hereinafter for simplicity, the motion system 11 includes an electronically controllable orientation structure 12, which is designed to support the RCS cluster 9 to allow the RCS cluster 9 to rotate about at least two orthogonal rotation axes A and B in response to electrical commands from the attitude control computer 10, thereby allowing the orientation of the RCS cluster 9 to be adjusted on the space tug vessel 1 as needed.

[0051] For each individual directional structure 12, whose position is desired to be adjusted individually, or for a group of directional structures 12, whose positions are desired to be adjusted collectively, the motion system 11 also includes an electronically controllable positioning structure 13, which is designed to support the directional structure 12 or a group of directional structures 12 so as to allow the directional structure 12 or a group of directional structures 12 to be displaced along a straight or curved displacement direction, thereby allowing the position of the directional structure 12 or a group of directional structures 12 to be adjusted on the space tugboat 1.

[0052] Figure 1 , Figure 2 and Figure 3 A guide slider type positioning structure 13 is shown by way of example, wherein the orienting structure 12 is anchored on a slider slidably mounted on a linear guide so as to move in a linear direction C in response to electrical commands from the attitude control computer 10, thereby allowing the position of the RCS cluster 9 carried by the orienting structure 12 to be adjusted.

[0053] Finally, for each positioning structure 13, the motion system 11 also includes an electronically controllable deployment structure 14, which connects the positioning structure 13 to the body 2 of the space tugboat 1 and is designed to respond to electrical commands from the attitude control computer 10 to present an undeployed configuration and a deployed configuration relative to the body 2. In the undeployed configuration, the positioning structure 13 remains close to the body 2, and in the deployed configuration, the positioning structure 13 moves away from the body 2 and is in a position close to the satellite 5.

[0054] Figure 1 , Figure 2 and Figure 3 By way of example, a deployment structure 14 of the type having a lever articulated between the body 2 and a linear guide of the positioning structure 13 is shown.

[0055] exist Figure 1 , Figure 2 and Figure 3 In the example shown, the motion system 11 is formed by two motion subsystems having the same architecture, and each motion subsystem is formed by a directional structure 12 carrying an RCS cluster 9 having two attitude control thrusters 9, a positioning structure 13 carrying a single directional structure 12, and a deployment structure 14 between the positioning structure 13 and the body 2 of the space tug vessel 1.

[0056] The two kinematic subsystems are arranged radially symmetrically on the body 2 so as to maintain a neutral behavior relative to the centre of mass of the space system and to allow full management of the position and orientation of the attitude control thrusters 9 so as to maximize the efficiency of the thrust generated.

[0057] Figure 5A flow chart of the operations performed by the attitude control computer 8 is shown to control the position, direction and operating state of the attitude control thrusters 9 to adjust and maintain the attitude of the space tug vessel 1 and change its trajectory.

[0058] To this end, the mission of the space tug vessel 1, known a priori, can be conceptually divided into operational steps, which include a preparation step for receiving the towed satellite 5, followed by one or more operational steps for achieving the mission objectives, such as maintaining the pre-assigned pointing direction of the possibly scattered satellite 5 through orbit transfer and attitude stabilization steps, depending on the specific mission.

[0059] The attitude control computer 10 is programmed to carry out the tasks assigned to the space tug 1 and to optimize the medium and long term operating steps, assuming that the orbit transfer steps are optimized based on criteria established a priori, depending on the specific mission, or during the mission, for example using one or different dedicated neural networks, appropriately trained on the ground.

[0060] Since extension to more complex scenarios is straightforward, for simplicity the following description is based on the assumption that the mission of the space tug vessel 1 consists only of a preparatory step for docking / capturing a satellite 5 and a single operational step following the preparatory step. It is also assumed that once the space tug vessel 1 has docked or captured a satellite 5, the space system 6 thus formed behaves as a rigid body, thereby allowing a reference system that is a priori integrated with the space system 6 to be considered for controlling the space system 6.

[0061] First, an operation step consists in stabilizing the attitude of the space system 6 according to the mission requirements (e.g. pointing) and the selected optimization criteria (e.g. minimization of fuel consumption, pointing error, etc.). For ease of description, hereinafter, the acronym FS will be used to refer to the attitude stabilization substep, and the acronym FR will be used to refer to the stabilization operation substep, which starts at the end of the attitude stabilization substep (i.e. when the space system 6 has reached stability) and which is maintained by the attitude control computer 10 throughout the duration of the substep FR by executing attitude control steps of known type (and therefore not described in detail).

[0062] According to an aspect of the invention, the implementation of sub-step FS is controlled by the attitude control computer 10 based on a neural network previously trained on the ground. For this purpose, already available techniques can be adopted, such as those described in CN109625333A, which relates to the stabilization of the space system 6 without considering further objectives, such as minimizing fuel consumption. In sub-step FS, the attitude control thrusters 9 are positioned and oriented according to a pre-established default configuration.

[0063] In the considered case, the use of a neural network as an alternative to conventional control methods may be particularly advantageous, since both the center of mass and the relative moments of inertia of the spatial system 6 are not known a priori.

[0064] During substep FS, the neural network is designed to efficiently solve the standard control problem, which can be mathematically described as follows:

[0065]

[0066]

[0067] g(x(t),u(t),t)≤0 (3)

[0068]

[0069] where expression (1) is the optimization objective, such as minimization of fuel consumption, pointing error, etc.; vector equation (2) represents the dynamic state x(t) of the considered space system 6 (position and angular velocity relative to a specified reference system) at each time instant t, as its time derivative (angular velocity and acceleration of the space system 6) and a control vector u(t), which is formed by the forces and torques applied to the space system 6 as a whole at any time t.

[0070] Expressions (3) and (4) are defined at time t0 and t f Constraints on state / control variables and on the initial and final states (if required) of the space system 6.

[0071] The solution to the problem defined by equations (1)-(4) output by the neural network is optimized with respect to a specified (default) configuration of the attitude control thrusters 9. However, since, according to the present invention, the configuration of the attitude control thrusters 9 is adjustable, the parameters of the space system 6, namely the position and orientation of the attitude control thrusters 9, are considered in terms of additional (albeit time-independent) control variables. In this way, the scope of the solution is extended, resulting in the following new optimization problem:

[0072]

[0073]

[0074] g(x(t),u(t),P,γ,t)≤0 (7)

[0075]

[0076] where the vectors P and γ (implicit in equations (1)-(4)) represent the position and orientation of the attitude control thruster 9, respectively (no longer considered as constants, but as structural parameters of the space system 6, which can be defined in the context of the corresponding domain, as indicated by condition (7)). In the following, the optimization problem defined by (1)-(4) is denoted as the "simplified optimization problem" (PR), while the optimization problem defined by (5)-(8) is denoted as the "extended optimization problem" (PE).

[0077] The optimal solution of the extended optimization problem PE is, in general, better than the optimal solution of the simplified optimization problem PR, regardless of the specific objective function chosen. In the formula:

[0078]

[0079] Since the spacecraft 1 is equipped with a kinematic system 11 to pattern the attitude control thrusters 9, the attitude control computer 10 is programmed to calculate the allowed positions and orientations for each attitude control thruster 9 after docking (extending the domain of P and γ in the optimization problem PE).

[0080] It is also worth noting that the simple (tout court) solution of the extended optimization problem PE is significantly more complex than the simple solution of the simplified optimization problem PR. Therefore, it would be unrealistic to optimize the stability of the space system 6 and the configuration of the attitude control thrusters 9 at the same time, and for this reason, a sub-step of reconfiguring (RC) the attitude control thrusters 9 is introduced, and the following is proposed and described for optimizing Figure 4 The iterative process of configuration of the attitude control thrusters 9 is shown in the flow chart.

[0081] like Figure 4 As shown, the process for optimizing the configuration of the attitude control thruster 9 basically includes the following operations, which will be described in detail below:

[0082] 1. Get / update input for an operation step; (block 100),

[0083] 2. Stabilizing the space system 6 (block 110),

[0084] 3. Obtain / update input for optimizing the placement of attitude control thrusters 9 (block 120).

[0085] 4. Optimizing the position and orientation of the attitude control thrusters 9 (block 130), and

[0086] 5. (Physically) adjust the position and orientation of the attitude control thrusters 9 (block 140).

[0087] Operations 1 to 5 are performed only in the operation step of the space system 6, and therefore, as indicated by the dotted line in the flowchart, the exit of the space system 6 from the operation step results in the immediate termination of the execution of the steps being executed at that moment (general stop rule).

[0088] Operation 1

[0089] Get / update input for an action step

[0090] The purpose of operation 1 is to acquire the operating scenario of the spatial system 6 in an operating step or to update it during the optimization process.

[0091] Operation 1 includes performing the following steps:

[0092] 1.1 Requirements for obtaining / updating operational procedures, such as maintaining a given pointing angle of the onboard optical system of Satellite 5, and requirements for optimization criteria, such as minimization of fuel consumption;

[0093] 1.2 Acquiring / updating (available) data of the initial / current state of the space system 6, such as the position, orientation and angular velocity of the space system 6 in a reference system integrated with the space system 6;

[0094] 1.3 Determine the position and orientation of the satellite 5 relative to the space tug vessel 1 to determine the geometric configuration of the space system 6;

[0095] 1.4 Get the current position and orientation of the attitude control thrusters 7 (at the initial step of the optimization process, design nominal / default).

[0096] For step 1.1, the requirements of the operating steps and the requirements of the optimization criteria are known when the optimization process is started. They may change later if an update is determined to be necessary, for example due to changes in conditions sensed by the sensing system 8 or due to the occurrence of other unforeseen conditions.

[0097] The updates defined for the operation steps, i.e. obtaining updated data to perform (or re-perform, if necessary) operations 2 and 3, are conveniently performed by a dedicated neural network previously trained on the ground.

[0098] If necessary, after docking, step 1.3 is performed with the aid of a sensing system in the form of, for example, optical sensors, image capture and recognition sensors, etc. This is, for example, the case where the pointing function of the optical instrument on board the captured satellite is to be restored.

[0099] Operation 1 is performed at the start of the optimization process and thereafter only when condition 1 described below occurs. Steps 1.1), 1.2), 1.3) and 1.4) have the purpose of initializing (or reinitializing, if necessary) operation 2 and / or transferring the input of operation 3.

[0100] Operation 2

[0101] Space system stability

[0102] The purpose of operation 2 is to perform sub-step FS, namely to stabilize the attitude of the space system 6 according to the requirements of the operation step and the selected optimization criterion (i.e. the solution of the simplified optimization problem PR), wherein the current orientation and position of the attitude control thrusters 9 are considered constant.

[0103] Operation 2 is conveniently performed with the help of a neural network previously trained on the ground.

[0104] The neural network is operated by importing the information obtained from operation 1 via steps 1.1, 1.2, 1.3 and 1.4.

[0105] Then, when the space system 6 is able to satisfy the requirements of the operational step and the selected optimization criteria (eg, minimization of fuel consumption), operation 3 is performed.

[0106] Operation 3

[0107] Get / update input for optimizing the placement of attitude control thrusters

[0108] The purpose of operation 3 is to prepare input data that can be updated during the optimization process necessary to perform sub-step RC (ie, optimizing the position and orientation of the attitude control thrusters 9 ).

[0109] Operation 3 includes performing the following steps:

[0110] 3.1 extracting a subset of attitude control forces and torques applied to the space system 6 during the control step of the stabilization operation step FR; and

[0111] 3.2 Determine the allowed position and orientation domain of the attitude control thrusters 9 and any updates.

[0112] The subset of attitude control forces and torques required to perform step 3.1 is obtained after appropriate statistical sampling of the attitude control forces and torques applied to the space system 6 during a sufficiently extended sampling period during sub-step FR (i.e., stable operation of the space system 6).

[0113] To this end, the attitude control computer 10 is programmed to extract a subset of predetermined magnitudes of the resulting forces and torques acting on the space system during attitude control of a sufficiently extended sampling period during sub-step FR.

[0114] Conveniently, the attitude control computer 10 can be programmed to extract the attitude control forces and torques acting on the space system 6 during the most critical attitude control steps of sub-step FR, and the attitude control forces and torques correspond to, for example, the maximum and minimum values ​​of the modules of attitude control forces and torques, the maximum required consumption, etc., as well as the attitude control forces and torques acting most frequently on the space system 6 during sub-step FR.

[0115] In order to ensure that the subset of extracted attitude control forces and torques is as representative as possible of those attitude control forces and torques that actually acted on the space system 6 during the attitude control steps that occurred during substep FR, the attitude control computer 10 can be conveniently programmed to select attitude control steps that maximize the "total difference" of attitude control forces and likewise maximize the "total difference" of torques. For this purpose, different formulas can be used, such as maximizing, by means of selected weights, the standard deviation of forces and torques, the sum of the corresponding distances expressed by the L1 and L2 norms, etc. Useful techniques and algorithms are available for this purpose, such as "K-means clustering".

[0116] The main purpose of step 3.2 is to determine the allowed position and orientation of each attitude control thruster 9, which defines the domain of vectors P and γ in the extended optimization problem PE. Since this information is unknown a priori and the exact position and orientation of the satellite 5 relative to the space tug 1 cannot be predicted, the allowed position and orientation of each attitude control thruster 9 is conveniently determined by image recognition technology.

[0117] A further purpose of step 3.2 is to determine any updates on the availability of the attitude control thrusters 9, this information being necessary for the execution of operation 4. In practice, it may happen, for example, that an attitude control thruster 9 signals a possible failure and, in this case, it should be replaced appropriately by one or a different attitude control thruster 9 operating under more reliable conditions. Another example may involve the need to redistribute the use of the attitude control thrusters 9 to avoid overloading some of them. Step 3.2 is also conveniently performed by a neural network previously trained on the ground.

[0118] The attitude control forces and torques selected in step 3.1, the determination of the available attitude control thrusters 9 and the definition of the corresponding position domain and orientation domain calculated in step 3.2 are the basic elements for the discrete (small) formulation of the extended optimization problem PE, which is used in sub-step RC described in operation 4 thereafter.

[0119] At the end of the execution of operation 3, the attitude control computer 10 is programmed to check the occurrence of the operating condition defined by the execution of operation 3, represented in the flowchart by the term condition 1 (box 150), with or without the execution of operation 3 resulting in a change in the operating scenario of the space system 6, in particular a different subset of attitude control forces and torques has been determined, or one or more attitude control thrusters 9 have been excluded during the optimization process compared to the operating scenario existing before the execution of operation 3.

[0120] If condition 1 is determined to occur, the attitude control computer 10 is programmed to perform operation 4 described below, otherwise it is designed to repeat operation 1 after a given period of time has passed (block 160).

[0121] During the first execution of operation 3, condition 1 is always determined to have occurred, while in subsequent iterations, condition 1 may not occur, in which case there is no reason to re-execute operation 4, as it will fall into an already considered operation scenario, creating a possible loop. Therefore, operation 4 is activated only when condition 1 occurs.

[0122] Operation 4

[0123] Optimizing the position and orientation of attitude control thrusters

[0124] The purpose of operation 4 is to optimize the available attitude control thruster 9 position and orientation determined in operation 3, ie the calculation aspect of sub-step RC, while the output of sub-step RC, ie the movement of the attitude control thruster 9, is implemented in operation 5 described subsequently.

[0125] In operation 4 , the extended optimization problem PE is solved, in which the vectors P and γ representing the position and orientation of each attitude control thruster 9 are no longer considered to be constants, but system parameters (time-independent) that can vary within the correlation domain determined in operation 3 .

[0126] The optimization model / algorithm employed (starting from operation 3) inputs a representative subset of attitude control forces and torques, the available attitude control thrusters 9, the thrust constraints for each of the available attitude control thrusters 9, and any constraints on the time of use or thrust provided and / or additional conditions.

[0127] It is worth noting that a representative subset of attitude control forces and torques is conveniently employed, rather than a subset of attitude control forces and torques comprising all control steps actually sampled, in order to significantly reduce the size (and therefore difficulty) of the extended optimization problem PE.

[0128] The extended optimization problem PE (discrete according to the selected subset of forces and torques) can be expressed as a mathematical program using a nonlinear model or a mixed integer programming (MIP) model and solved using a global optimizer (GO) or MIP. Alternatively, the extended optimization problem PE can be solved by a dedicated neural network pre-trained on the ground (using a dedicated model, algorithm and optimizer). In this case, operations 3 and 4 can be merged into a single operation performed by a dedicated neural network pre-trained on the ground.

[0129] When operation 4 has been completed, the attitude control computer 10 is programmed to check the occurrence of the operating condition defined by the solution determined in operation 4, represented in the flowchart by the term condition 2 (box 170), and based on the optimization criteria considered, the operating condition defined by the solution determined in operation 4 is considered better or not better than the operating condition defined by the solution determined in the same operation 4 in the previous iteration of the optimization process of the configuration of the attitude control thrusters 9.

[0130] For example, if the optimization criterion is minimization of fuel consumption, condition 2 is defined by the configuration of the attitude control thrusters 9 determined in operation 4, thereby allowing fuel savings to be obtained compared to the configuration of the attitude control thrusters 9 determined in the same operation 4 in a previous iteration of the optimization process of the configuration of the attitude control thrusters 9.

[0131] If condition 1 is determined to occur, the attitude control computer 10 is programmed to perform operation 5 described below, otherwise it is designed to repeat operation 1 after a predetermined period of time has passed (block 160).

[0132] Operation 5

[0133] (Physically) modify the position and orientation of attitude control thrusters

[0134] The purpose of operation 5 is to modify the position and orientation of the attitude control thrusters 9 based on the output of operation 4 .

[0135] For this purpose, the attitude control computer 10 is programmed to control the kinematic system 11 so that the attitude control thrusters 9 assume the position and orientation calculated in operation 4 .

[0136] Based on the above description, it can be understood that the advantages that the present invention allows to be achieved.

[0137] In particular, the present invention allows to provide an electronic reaction control system which allows to optimize the efficiency of the fuel consumption of the on-orbit servicing spacecraft and to obtain improvements in the number of attitude control thrusters required to control the attitude of the on-orbit servicing spacecraft and in the space system formed by the on-orbit servicing spacecraft and the docked or captured space vehicle or object.

[0138] Electronic reaction control systems can also be used, for example, in individual spacecraft such as satellites in order to optimize fuel consumption during different use steps or to optimally redefine the configuration of attitude control thrusters in the event of a failure in one or more spacecraft.

[0139] Furthermore, the neural network used may be capable of self-learning by improving its responsiveness over time. At the current state of the art, it is assumed that the neural network used can be retrained from the ground using data sensed during onboard use and re-updated via an uplink connection.

Claims

1. An on-orbit servicing spacecraft (1), comprising: - a coupling system (4) for coupling a space vehicle or object (5) to be serviced or towed to form a space system (6); and - an electronic reaction control system (7) for rotating the spacecraft (1) about the roll, yaw and pitch axes to control the attitude and displacement of the spacecraft (1) along a given trajectory, so that the spacecraft (1) performs a given maneuver; The electronic reaction control system (7) comprises: - a sensing system (8) allowing direct sensing of physical quantities or indirect calculation of physical quantities based on sensed physical quantities including one or more of position, attitude, angular rate, available fuel, geometrical characteristics and onboard system status; - attitude control thrusters (9) mounted so as to allow their position and orientation to be adjustable; and - an attitude control computer (10) in communication with the sensing system (8) and the attitude control thrusters (9) and programmed to receive data from the sensing system (8) and to control the position, orientation and operational state of the attitude control thrusters (9) based on the received data, thereby controlling the attitude and position of the spacecraft (1); The attitude control computer (10) is programmed to cause the spacecraft (1) to perform a given mission, the given mission comprising an engagement step and one or more operating steps, in which the engagement system (4) and the attitude control thrusters (9) are controlled by the attitude control computer (10) to engage a space vehicle or object (5) to be serviced or towed, and in each of the operating steps, the attitude control thrusters (9) are controlled by the attitude control computer (10) to meet one or more requirements established for the operating step; Each operating step comprises at least one stabilization sub-step (FS), during which the attitude of the space system (6) is stabilized according to the requirements of the operating step and according to a given optimization criterion; characterised in that each stabilisation sub-step (FS) is followed by a stabilisation operation sub-step (FR), said stabilisation operation sub-step (FR) starting at the end of said stabilisation sub-step (FS) of said attitude of said space system (6); and Wherein, in each operating step, the attitude control computer (10) is further programmed to optimize the configuration of the attitude control thruster (9) by implementing an iterative process of optimizing the configuration of the attitude control thruster (9) according to the requirements of the operating step, the operating step comprising:

1. Operation 1, including: 1.1 Obtain / update the requirements of the operation steps and the requirements of the optimization criteria; 1.2 obtaining / updating the current state of the space system (6) defined by the position, orientation and angular velocity of the space system (6) in the reference system of the space system (6); 1.3 determining the position and orientation of the engaged space vehicle or object (5) relative to the spacecraft (1) to allow determination of the geometrical configuration of the space system (6); as well as 1.4 determining the current position and orientation of the attitude control thruster (9); 2. Operation 2, including: Based on the current state and geometric configuration of the space system (6) and the current position and orientation of the attitude control thruster (9) determined in step 1.4, stabilizing the attitude of the space system (6) according to the requirements of the operation step and the optimization criterion; 3. Operation 3, including: 3.1 During the sufficiently extended sampling period of the stable operation sub-step (FR), determining attitude control forces and torques acting on the space system (6); and 3.2 determining the permissible position domain and orientation domain of the attitude control thruster (9) and the availability of the attitude control thruster (9); 4. Operation 4, including: Optimizing the position and orientation of the available attitude control thrusters (9) based on the optimization criteria and considering the position and orientation of the attitude control thrusters (9) as system variables that can vary within the associated allowed domain determined in step 3.2; 5. Operation 5, including: The position and orientation of the attitude control thrusters (9) are modified so that the attitude control thrusters (9) assume the optimized position and orientation calculated in step 4.

1.

2. The on-orbit servicing spacecraft (1) according to claim 1, wherein: The attitude control computer (10) is also programmed to: - when operation 3 has been completed, checking (150) the occurrence of a first operating condition defined by the execution of operation 3, the execution of operation 3 having or not having resulted in a change of an operating scenario of the space system (6) defined by a set of attitude control forces and torques applied to the space system (6) and / or the availability, with or without the presence or absence of one or more attitude control thrusters (9) compared to the operating scenario before the execution of operation 3 in an iterative process of optimization of the configuration of the attitude control thrusters (9); - If it is determined that the first operating condition has occurred, perform operation 4 (130); and - If it is determined that the first operating condition has not occurred, repeating operation 1 after a given period of time (160) has elapsed.

3. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The posture control computer (10) is also configured as: - when operation 4 has been completed, checking the occurrence (170) of a second operating condition defined by the execution of operation 4, said second operating condition having or not having resulted in an improvement determined based on said optimization criterion compared to a previous execution of operation 4 during an iterative process of optimization of the configuration of said attitude control thrusters (9); - If it is determined that the second operating condition has occurred, perform operation 5 (140); as well as - If it is determined that the second operating condition has not occurred, repeating operation 1 after a given period of time (160) has elapsed.

4. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The attitude control computer (10) is also programmed to implement one or more of the stabilization sub-step (FS), determining the update requirements according to step 1.1 in operation 1, operation 2 and step 3.2 in operation 3 through a same or different neural network previously trained on the ground.

5. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The attitude control computer (10) is also programmed to determine, according to step 1.3 of operation 1, the position and orientation of the space vehicle or object (5) to be serviced or towed relative to the spacecraft (1), and the geometric configuration of the space system (6) based on the data output by the sensing system (8).

6. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The attitude control computer (10) is also programmed to perform operation 3 when the space system (6) meets the requirements of the operation step and the optimization criteria.

7. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The attitude control computer (10) is also programmed to perform step 3.1 of operation 3 by extracting a subset of attitude control forces and torques applied to the space system (6), wherein the subset of attitude control forces and torques represents the attitude control forces and torques applied to the space system (6) during the control steps that have occurred during the stabilization operation sub-step (FR).

8. The on-orbit servicing spacecraft (1) according to claim 7, wherein: The attitude control computer (10) is also programmed to extract a subset of attitude control forces and torques applied to the space system (6), the subset of attitude control forces and torques comprising attitude control forces and torques applied to the space system (6) during critical attitude control steps that have occurred during the stabilization operation sub-step (FR) and / or attitude control forces and torques applied to the space system (6) more frequently during the stabilization operation sub-step (FR).

9. The on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein: The electronic reaction control system (7) further comprises an electronically controllable motion system (11) operable to move the attitude control thruster (9), and the electronically controllable motion system (11) comprises: - an electronically controllable orientation structure (12) designed to support one or different attitude control thrusters (9) to allow said attitude control thrusters (9) to rotate about at least two orthogonal rotation axes (A, B) in response to electrical commands from said attitude control computer (10), thereby allowing the orientation of said attitude control thrusters (9) to be adjustable; - an electronically controllable positioning structure (13) designed to support one or a different orientation structure (12) to allow said orientation structure (12) to translate along a displacement direction in response to electrical commands from said attitude control computer (10), thereby allowing the position of said orientation structure (12) to be adjustable; and - for each positioning structure (13), an electronically controllable deployment structure (14) is designed to connect the positioning structure (13) to the spacecraft (1) and, in response to electrical commands from the attitude control computer (10), to assume an undeployed configuration in which the positioning structure (13) is close to the spacecraft (1) and a deployed configuration in which the positioning structure (13) is moved away from the spacecraft (1) and is brought to the location of the spacecraft or object (5) to be serviced or towed.

10. A computer program product, comprising a computer program that can be loaded into an attitude control computer (10) of an electronic reaction control system (7) of an on-orbit servicing spacecraft (1) according to claim 1 or 2, wherein when the computer program is executed, the attitude control computer (10) is changed into the configuration according to claim 1 or 2.

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