Orbital Maneuvering Vehicle Research Articles

Time-Optimal Detumbling Control of Spacecraft

T HE problem of designing fast detumbling maneuvers for a spacecraft with restricted actuation torques arises inmany space applications. Satellites are often equipped with an attitude control system (ACS), which usually has two modes of operation: detumbling and stabilization. In detumbling mode, the ACS controller is responsible for dumping the initial angular velocity from when the satellite was in the idle mode; this situation occurs when the satellite is released from the launch vehicle or when power is so low that ACS has to be turned off to save power [1]. Only after this phase can the stabilization mode be activated to control the orientation of the satellite to align antennas toward the Earth. Reaction wheels are commonly used as the actuators of the ACSs. Satellites frequently need fast maneuvers [2], minimum time maneuvers, while the speed is restricted owing to a low level capacity of the actuators. Hence, planning optimal maneuvers is highly desired. Alternatively, spin-stabilized spacecraft allow simple attitude maneuvers without the need for complex control systems. The spacecraft can be spun up around its axisymmetric axis to stabilize the orientation of the vehicle axis through the gyroscopic effect. This method is also widely used to stabilize the final stage of a launch vehicle [3]. However, when a spacecraft is in the tumblingmotion, its angular velocity is not parallel to the axisymmetric axis. Therefore, the objective in deployment of a spin-stabilized spacecraft [4] is to bring the spacecraft form the tumblingmotion to the statewherein the spacecraft spins around a single axis. The detumbling or passivation of a satellite is also required before on-orbit servicing of the satellite or its retrieval [5]. For such a mission, an orbital maneuvering vehicle can be used to apply torques to the target satellite for removing any relative velocity [5,6]. Also, the vehicle can be equipped by an articulating arm with a grappling device on it that could be driven to capture a tumbling target satellite and then detumble it [7,8]. After capture of an uncontrolled tumbling satellite by a spacemanipulator, the satellite should be brought to rest in minimum time. Again, the restriction of the manipulator end effector to provide “braking torques” for the fast maneuvers motivates an optimal trajectory planning. Optimal detumbling ofmultibody systems has been considered for spacecraft possessing appendages, such as a robotic manipulator, with well-controlled motion relative to the spacecraft to achieve detumbling [9–13].However, because of the complexity of dynamics of space manipulators, only a numerical solution or intensive trialand-error procedures have been found for the optimization problem. The problem of time-optimal detumbling control of rigid spacecraft is formulated as a nonlinear programming and solved numerically by using an iterative procedure in [14], while nonoptimal control approaches have been reported in [15–17]. There also exists a fair amount of research done on the time-optimal reorientation control, rest to rest, of rigid spacecraft [18–20] and a survey, for example, can be found in [21]. This paper presents a closed-form solution for time-optimal detumbling control of a rigid spacecraft with the constraint on maintaining the Euclidean norm of the braking torques below a prescribed value. Thefinal angular rate can be specified as zero or any vector parallel to the eigenaxis. The optimal control theory and Pontryagin’s principle are applied to derive the optimal solution, which is not only easy to implement but also gives a great deal of insight. First, it will be shown that for our particular optimal control problem, the system costates and states are related by a nonlinear but static function. Subsequently, the optimal control law is explicitly derived in the form of a nonlinear state feedback. The magnitude of the system angular momentum is found to be linearly deceasing with time, leading to a simple expression for the terminal time needed for control implementation. Furthermore, the time-optimal controller is extended for the case of nonzero terminal velocity. To this end, the time-optimal control technique is applied to derive a nonlinear feedback control law which can drive a tumbling axisymmertic spacecraft to a final spin-stabilized state. Finally, the time-optimal detumbling technique is illustrated through numerical examples.

Position and Attitude Control of a Spacecraft by Sliding Mode Control.

Future spacecraft such as Orbital Maneuvering Vehicle or "Remover" which tries to capture and remove large space debris objects in orbit are supposed to do large angle and complicated position maneuver in space. The equation of motion of the rigid body which performs attitude and translational motion (six degrees of freedom motion) is a nonlinear equation. This paper applies Sliding Mode Control which can handle a nonlinear plant to the six degrees of freedom control for such a vehicle. Through a numerical simulation of proximity flight around a tumbling target object, its feasibility is investigated.

Alternative solution of power supply for new spacecraft generation

The power supply for new generation of the long life spacecraft is one of the complicated problem staying in front of designers within practically all the space vehicle life phases. Up to day the most widespread solution consists of the own on board power supply system for each spacecraft including main (usually solar arrays or radioisotope thermal electric units) and redundant (usually chemical accumulating batteries) power sources. The technical and cost efficiency aspects of an advanced scheme of spacecraft power supply by the directional power beams from board of several Space Power Plants is analyzed. Practically all possible spacecraft types are included into the study: systems of communication satellites in the LEO and GEO, navigation and remote sensing satellites operated in the orbits with altitudes to 25000 km, surveillance and technology space platforms into LEO, as well as orbital maneuvering vehicle equipped with electrical propulsion to transport payloads from LEO into operational orbit. The preliminary evaluation of PowerSat's and servicing spacecraft systems orbital configuration is presented. Side by side with some characteristics of the power generation units (on base of solar arrays, solar thermal dynamics facilities, nuclear power plants) the brief discussion of electric thrusters and power transmission system is provided. The perspectives and ways of the further studies for all of main PowerSat's subsystems are nominated.

Optimal spacecraft attitude control using collocation and nonlinear programming

Introduction I N recent years, NASA has been able to retrieve disabled satellites from orbit and has even repaired one satellite, the Solar Maximum satellite, while in orbit. However, there are many satellites in orbits too high for the shuttle to reach. If such a satellite fails to deploy properly or malfunctions after some use is made of it, there is currently no way of retrieving it. A remotely operated satellite [or orbital maneuvering vehicle (OMV)] is needed for retrieval of such satellites. A prerequisite for retrieval is the detumbling of the satellite. Optimal open-loop controls for detumbling of a satellite were developed by Con way and Widhalm. A nonlinear feedback control for the same problem was developed by Widhalm and Conway. Webber improved the nonlinear feedback controller of Ref. 2 and was able to make the cost comparable to that of the open-loop control formulation. Here, a new method, direct collocation with nonlinear programming (DCNLP), is employed to find the optimal openloop control histories for detumbling a disabled satellite. The satellite system is assumed to have docked in such a way that the tumbling motion of the disabled satellite is not disturbed. The controls are torques and forces applied to the docking arm and joint and torques applied about the body axes of the OMV. The results of Ref. 1 have been reproduced, verifying the solution, but the method used for this work is simpler to implement and more robust. Solutions have been obtained for cases in which various constraints are placed on the controls and in which the number of controls is reduced or increased from that considered in Ref. 1.

Unmanned servicing of Earth observation systems in sunsynchronous orbits

This paper addresses the feasibility of servicing or reboosting Earth observation spacecraft that are in or near sunsynchronous orbits through the use of an unmanned servicing vehicle. The term sunsynchronous (SS) as used here pertains to any retrograde orbit which exhibits a nodal regression rate of 360° per year, so that the orbit plane maintains a constant angle to the sun. The paper addresses both quantitatively and qualitatively how future Earth observation systems in inclinations between 96 and 100° may be periodically serviced using a transfer vehicle and other components needed to carry out the support mission. Two operational concepts are considered for the employment of the transfer vehicle. In one case, the vehicle is based at a Space Based Support Platform (SBSP) which remains at a lower altitude and higher inclination than the assets to be serviced. Consideration is also given to servicing from a transfer vehicle which is a free flyer (i.e. not based at an SBSP). The design requirements of the servicer are discussed quantitiatively and sample calculations of ΔV and propellant expenditure are given. Consideration is given to the NASA developed Orbital Maneuvering Vehicle (OMV), and other transfer vehicles which use electrical or other advanced propulsion. In addition, a quantitative assessment is made of the subsystem redundancy requirements in the design for an Earth observation satellite that is periodically serviced as compared with design requirements for an unserviceable spacecraft. The benefits of servicing with respect to Pre-planned Product Improvements (P 3I) are discussed.

United States orbital transfer vehicle programs

The United States will rely on five orbital transfer vehicles to carry spacecraft to higher energy orbits than achievable by the Space Shuttle or various Expendable Launch Vehicles (ELV). These vehicles are the Payload Assist Module-Delta (PAM-D), an upgraded version designated PAM-DII, the Inertial Upper Stage (IUS), the Transfer Orbit Stage (TOS), and the Orbital Maneuvering Vehicle (OMV). Development of these vehicles have evolved through contrasting cultures of government and commercial management. The spectrum of their capabilities range from providing spacecraft with only a preprogrammed perigee velocity additions to man-in-the-loop remote controlled spacecraft rendezvous, docking, retrieval and return to a space base; either the Shuttle or the Space Station Freedom. The PAM-D, PAM-DII, and IUS are now nearing maturity. Their characteristics, flight record, costs, and projected future uses are defined. The TOS and OMV are currently in development with first uses scheduled in 1992 and 1993, respectively. The TOS is being commercially developed while the OMV is government developed. The TOS and OMV capabilities, constraints, and costs are reviewed.

EivaN - An interactive orbital trajectory planning tool

EivaN is an interactive orbital trajectory planning tool that runs on a desktop computer with commercially available software. Orbital operations at any altitude around any celestial body can be planned and plotted on one's desktop with eivaN. After inputting the initial position of an object, such as an orbital maneuvering vehicle, with respect to a stationary object, such as a space station in a circular orbit, the operator enters the parameters of thruster firings in four dimensions (three spatial, one temporal) in order to simulate a particular mission, such as a docking maneuver. EivaN then plots the resulting trajectory. Currently, up to 5 burns may be used with 21 points plotted for each burn at a user-specified time interval. However, both the number of points and the number of burns may be modified. EivaN has successfully been used in several studies. One demonstrated the ability of naive subjects to plan docking maneuvers; the other determined velocity increment requirements for the self-rescue of a stranded extra-vehicular activity crewperson. EivaN is being used by researchers both domestic and international. NASA's computer database, COSMIC, has evaluated eivaN and is in charge of its distribution.

Effect of an anomalous thruster input during a simulated docking maneuver

An experiment was performed in the Space Station Proximity Operations Simulator at the NASA Ames Research Center. Five test subjects were instructed to perform 20 simulated remote docking maneuvers of an orbital maneuvering vehicle (OMV) to the space station in which they were located. The OMV started from an initial range of 304.8 m (1000 ft) on the space station's negative velocity vector (V-bar). Anomalous out-of-plane thruster firings of various magnitudes (simulating a faulty thruster) occurred at one of five ranges from the target. Initial velocity, range of anomalous burn, and magnitude of anomalous burn were the factors varied. In addition to whether the trial was successful, time and fuel to return to a nominal trajectory, total mission duration, total fuel consumption (delta K), failure rate, and time histories of commanded burns were recorded. Analyses of the results added support to the hypothesis that slow approach velocities are not inherently safer than their more rapid counterparts. Naive subjects were capable of docking successfully at velocities faster than those prescribed by the 0.1% rule even when a simulated faulty thruster disturbed the nominal trajectory. Little to no justification for slow approach velocities remains from a human-factors standpoint.

自律型宇宙ロボット地上実験装置ＡＳＲＯＴの開発

We developed a two dimensional operation testbed for an autonomous free-flying space robot such as an orbital maneuvering vehicle. This system is named ASROT (Autonomous space robot operation testbed) . Basically, ASROT consists of a satellite robot, a target, a host computer and a planar base. A host computer is only used for observation and data gathering of the system. A satellite robot is a satellite which can establish various tasks with a manipulator. A satellite is 620mm (W) ×805mm (H) ×620mm (L) . Its weight is 120 kg. This system is floating on a planar base using air bearings, and is able to fly around using thrusters for position control and a control moment gyro for attitude control. A manipulator is a flexible arm and 1.4m long. This paper proposes an operating system which is needed for real time autonomous control. A satellite robot installs hardware systems such as vision systems, board computers, image processing units, and software systems such as algorithms for path planning.

Nuclear-electric reusable orbital transfer vehicle

To help determine the systems requirements for a 300-kWe space nuclear reactor power system, a mission and spacecraft have been examined that utilize electric propulsion supported by the nuclear reactor's power for multiple transfers of cargo between low earth orbit (LEO) and geosynchronous earth orbit (GEO). A propulsion system employing ion thrusters and xenon propellant was selected. Propellant and thrusters are replaced after each sortie to GEO. The mass of the orbital transfer vehicle (OTV), empty and dry, is 11,000 kg; nominal propellant load is 5000 kg. The OTV operates between a circular orbit at 925-km altitude, 28.5-deg inclination, and GEO. Cargo is brought to the OTV by Shuttle and an orbital maneuvering vehicle (OMV); the OTV then takes it to GEO. The OTV can also bring cargo back from GEO for transfer by OMV to the Shuttle. OTV propellant is resupplied, and the ion thrusters are replaced, by the OMV before each sortie to GEO. At the end of mission life, the OTV's electric propulsion is used to place it in a heliocentric orbit so that the reactor will not return to earth. The nominal cargo capability to GEO is 6000 kg, with a transit time of 120 days; 1350 kg can be transferred in 90 days, and 14,300 kg in 240 days. These capabilities can be considerably increased by using separate Shuttle launches to bring up propellant and cargo or by changing to mercury propellant.

Orbital maneuvering vehicle: A new capability

The Orbital Maneuvering Vehicle (OMV) is a reusable, remotely controlled, free-flying vehicle being developed by NASA to perform a wide range of on-orbit missions and services in support of orbiting spacecraft. The OMV is capable of satellite delivery, retrieval, reboost, controlled deorbit, viewing, and subsatellite support missions. It is an important extension to the Space Transportation System and a key element of the Space Station operational scenario. The OMV can operate from the Shuttle, the Space Station, or can be space based. The OMV, being 15 ft in diameter and approximately 4 1 2 thick, mounts directly into the Shuttle payload bay. The vehicle design is highly modular, consisting of a Short Range Vehicle containing both hydrazine and cold gas RCS systems and all the avionics systems for electrical power, communications, data management, guidance, navigation, and 6-degree of freedom control. This vehicle weighs approximately 6,500 lb and can accomplish a high percentage of the project missions. For high delta-velocity missions, a bipropellant Propulsion Module (approximately 11,000lb) is added, giving a total weight of 17,500 lb. This module can be exchanged on orbit to effect bipropellant refueling. All the RCS and avionics modules are replaceable on orbit for maintenance. The OMV development program was initiated in 1986 with the selection of TRW as the prime contractor. The first flight is projected for 1991. An early planned use of OMV is to reboost the Hubble Space Telescope when required because of atmospheric drag. This paper contains details of the program status, vehicle description, and mission capabilities. The purpose of the paper is to acquaint the international space community with OMV capabilities and to stimulate the identification of new and unique mission applications.

An overview of the office of space flight satellite servicing program plan

The NASA Office of Space Flight has established a comprehensive program for the development of satellite servicing tools and techniques. It is founded upon a satellite servicing infrastructure, formulated by analyzing satellite servicing requirements. In addition, this program is Shuttle-based, compatible with the Orbital Maneuvering Vehicle (OMV) and the Space Station, and is capable of meeting the needs of NASA, the Department of Defense, and commercial users of space. The satellite servicing program encompasses four main types of servicing: (1) refueling (or consumable resupply); (2) repairing; (3) retrieving; and (4) retrofitting (or pre-planned product improvement). Innovative studies and development work are being pursued in all of these areas, and flight readiness schedules for satellite servicing hardware and advanced development flight experiments have been established. The purpose of this paper is to provide an overview of the satellite servicing program's evolution, basic assumptions, and content, as well as the current status of its activities.

The use of computer graphic simulation in the development of robotic systems

This paper describes the use of computer graphic simulation techniques to resolve critical design and operational issues for robotic systems. Use of this technology will result in greatly improved systems and reduced development costs. The major design issues in developing effective robotic systems are discussed and the use of ROBOSIM, a NASA developed simulation tool, to address these issues is presented. Three representative simulation case studies are reviewed: off-line programming of the robotic welding development cell for the Space Shuttle Main Engine (SSME); the integration of a sensor to control the robot used for removing the Thermal Protection System (TPS) from the Solid Rocket Booster (SRB); and the development of a teleoperator/robot mechanism for the Orbital Maneuvering Vehicle (OMV).

A mathematical model of the orbital maneuvering vehicle

A mathematical model was designed and developed of the Or bital Maneuvering Vehicle (OMV), a critical part of the OMV man-in-the-loop simulation at Marshall Space Flight Center, Huntsville, Alabama. The OMV evaluator is a full-scale, six- degree-of-freedom simulator that can replicate the motion of the actual OMV spacecraft in orbit. Translational and rotational equa tions of motion that model the OMV are presented. Simulation results that verify the correctness of the model are also given. This high-fidelity simulator is valuable for crew training, develop ing and testing new teleoperated equipment, and verification of the OMV final design. The evaluator also serves as an impor tant test ground for determining the capabilities of the OMV in performing orbital operations.

Nonlinear feedback control for remote orbital capture

The problem of detumbling a freely spinning and precessing axisymmetric target satellite with feedback control by an axisymmetric retriever spacecraft or orbital maneuvering vehicle is considered. Equations of motion for the two-body system are derived using Euler's dynamical equations in conjunction with the methodology developed by Hooker and Margulies. A Liapunov technique is employed to derive a nonlinear feedback control law for the thruster torques applied by the orbital maneuvering vehicle and the motor torques applied at the joint to drive the two-body system to a final spin-stabilized state asymptotically. State and control histories are presented to illustrate that the detumbling process is quite benign and that the required control magnitudes are small. The loads at the joint are determined and found to be within acceptable bounds during detumbling.

Capture of Satellites having Rotational Motion

This paper describes the results of system development simulations conducted to resolve key human factors issues involved in the capture of satellites having rotational motion, using both manned and remotely piloted vehicles. These man-in-the-loop simulations of remotely piloted Orbital Maneuvering Vehicle (OMV) spacecraft, combined with recent on-orbit experience from Manned Maneuvering Unit (MMU) capture and retrieval missions, have provided results related to many of the human factors issues inherent in such piloting tasks. The results discussed relate to control authority, piloting techniques, communications time delays, plume impingement, contact dynamics, controls, and displays. The paper concludes with a summary table of knowledge established through simulations and mission experience that is applicable to capture and retrieval of dynamic satellites.

Optimal continuous control for remote orbital capture

Optimal control histories are presented for the problem of detumbling (passivating) a satellite. It is proposed that this be done remotely by a robot spacecraft, sometimes referred to as a teleoperator or orbital maneuvering vehicle, in preparation for the return of both vehicles to low-Earth orbit. The dynamics of the coupled two-body system are described with equations of motion derived from an Eulerian formulation (the Hooker-Margulies equations). Two degrees of rotational freedom and one of translation are allowed at the joint that connects the orbital maneuvering vehicle and target spacecraft. The initial condition of the target satellite is free spin and precession. Representative masses and inertias are assumed for both bodies. Application of optimal control theory results in a nonsingular, two-point-boundary-value problem that is solved numerically for the controls, which are principally the external (thruster) and internal (joint) torques to be applied by the orbital maneuvering vehicle. Control histories and vehicle motion are found for both constrained and unconstrained fixed-time optimization. Constraint forces and torques at the joint are determined.

Speech Recognition, Speech Synthesis and Touch-Panel Technology Applied to the Control of Remotely Piloted Spacecraft

A permanent Space Station (SS) is under development which will be serviced by remotely piloted spacecraft such as the Orbital Maneuvering Vehicle (OMV). When arriving or departing the SS, the OMV will be controlled from a pilot station in the SS. This study describes continuing research in progress at the Martin Marietta Space Operations Simulator Laboratory which is contributing to the design of a prototype pilot station. Speech recognition, speech synthesis and touch-panel technology are being examined as means for data display and control operation. Where appropriate, speech recognition is experimentally compared with touch-screen as a means of entering commands, using a measure of subjective workload. Selected technologies will be incorporated in an evolving prototype pilot station and used to drive simulations of operations near the SS. Simulation will provide an empirical test of the selected technologies, in concert with tests of operating scenarios and engineering design. This research will contribute to the literature on human aspects of control system design and eventually to the design of the SS - OMV operating interface.

Benefits of a reusable upper stage orbital maneuvering vehicle

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Integratable propulsion systems for the Space Station

Oxygen/hydrogen propulsion system options for space station orbit maintenance and attitude control were developed and evaluated relative to monopropellant and storable bipropellant propulsion systems. Space station propulsion requirements were analyzed with reference to such considerations as station size, altitude, power, crew size, and orbit transfer vehicle and orbital maneuvering vehicle servicing requirements. The evolutionary growth of oxygen/hydrogen bipropellant propulsion as an integral part of several interrelated space station functions, e.g., life support, power, and thermal management was considered. Propellant resupply evolves from resupply based on transport of liquid oxygen and liquid hydrogen to water. The advantages of the operation of the space station based on an oxygen/hydrogen economy are presented and discussed.