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Agile Disturbance Free Payload
Abstract
The application of an advanced architecture in which the payload and the spacecraft bus are separate bodies that fly in close-proximity formation is considered for agile spacecraft. The proposed architecture provides a solution to the combined problems of payload pointing and isolation from spacecraft vibrations. The concept has far reaching implications to space borne missions with stringent pointing control and stability requirements allowing faster slews and uninterrupted mission during momentum dumping maneuvers. System level analysis is presented to assess the applicability of the proposed concept to missions requiring agility. Results from experimental demonstrations of agile maneuvering using a spacecraft hardware simulator are presented and demonstrate the feasibility of the concept. Results are presented for agile slewing, momentum dumping and isolation performance. Analysis and simulation results show good agreement with experimental data.
... The Disturbance-Free Payload(DFP) spacecraft, which consists of the payload module(PM) and the support module(SM) that fly in close-proximity formation, was proposed to address the needs of space payload with stringent pointing accuracy and stability requirements (Pedreiro 2003;Pedreiro et al. 2002Pedreiro et al. , 2005Gonzales et al. 2004;Zhou et al. 2019a). In the DFP spacecraft architecture, the vibration sources of the spacecraft, such as reaction wheels, cryocoolers, etc., are mounted on the support module, and equipment with high-precision pointing requirements, such as precision optical detection instruments, are installed on the payload module. ...
Disturbance-Free Payload (DFP) spacecraft is a novel spacecraft architecture consisting of the support module(SM) and the payload module(PM), which can provide an ultra-quiet vibration environment for sensitive payloads, but in practical applications, flexible cables used for the power supply and data transmission resulting in an additional vibration transmission path from the support module to the payload module. To address the problem that the flexible cable degrades the pointing performance of the payload module, one nonlinear model consisting of static and dynamic components of the flexible cable is established, and solved by a method of the differential quadrature based time integration. Separately applied the impulse disturbance to the support module, the dynamic transmission characteristics of flexible cable are analyzed. To suppress the micro-vibration caused by the flexible cable, a disturbance feedforward control compensation based on the established exact model is proposed, and the effectiveness of the disturbance feedforward compensation method is verified by numerical simulation.
In order to better meet the future high precision task requirements, the DFP(Disturbance-Free Payload) spacecraft composed of non-contact PM(Payload Module)and SM(Support Module)is taken as the object to study the relative motion dynamics modeling and control between the two modules and verify the system vibration isolation performance. Firstly, the force and torque expressions of the two modules are derived by simplifying the configuration and analyzing the stress. In view of that couple effect, the relative motion dynamics equations between two modules of DFP spacecraft with high model accuracy, and simple and uniform format are established with the dual quaternions. Based on this, the PD control law is designed, and the relative motion of PM and SM could meet DFP spacecraft working requirements when the measurability of control quantity and the measurement error of sensors were taken into account. Simulation results verify the advantage of vibration isolation and attitude maneuverability of DFP spacecraft.
The Disturbance-Free Payload (DFP) spacecraft, which includes the payload module (PM) and the support module (SM) connecting through voice coil motors (VCM), can provide unprecedented control and motion stability for the sensitive payload. The payload module and the support module have a high collision probability because of close proximity formation. In order to perform collision avoidance control on two modules, this paper establishes the dynamics model of the DFP spacecraft and proposes a collision avoidance control strategy based on the model predictive control (MPC). The established model synthesizes the back-Electromotive-Force (back-EMF) of the VCM and the stiffness and damping of the flexible cables. The MPC controller converts the collision avoidance problem into a quadratic programming problem. The control forces are obtained by solving the quadratic programming problem. The collision avoidance control simulation of the DFP spacecraft has performed while the payload module subjects to sudden disturbance. The simulation results verify the effectiveness of the proposed control strategy and show that the proposed MPC controller exhibits better collision avoidance capability than that of the PD controller.
A novel spacecraft architecture that provides a solution to the combined problems of payload pointing and isolation from spacecraft vibrations is demonstrated experimentally. In this architecture, known as Disturbance-Free Payload (DFP), the payload and the spacecraft are separate bodies that fly in close-proximity formation and interact through non-contact sensors and actuators to achieve precision payload control and isolation from spacecraft disturbances. Vibration isolation is provided down to zero frequency and isolation performance is not limited by sensor characteristics. A unique experimental apparatus consisting of an autonomous vehicle floating on air-bearings was built and used to demonstrate the DFP concept. The vehicle consists of the equivalent of a payload and a spacecraft, which are mechanically decoupled and contain a full set of sensors and actuators for real-time control implementation and performance assessment. The testbed was used to demonstrate operational capabilities, such as slew and momentum dump and assess performance. Test results validate earlier analysis that showed unprecedented isolation performance and the ability to continue the mission during momentum dump. Broadband isolation in excess of 50 dB has been demonstrated, which is well beyond the state-of-the-art.
Isolating a load from a source of vibrations includes detecting vibrations from that source, and controlling a displacement transducer stage with these detected vibrations through a feedforward loop. Isolation is increased with a resilient mount between the displacement transducer stage and the load. Residual movements of the load may be detected and the displacement transducer stage may additionally be controlled with these detected residual movements through a feedback loop.
The Terrestrial Planet Finder Coronagraph is a visible-light coronagraph to detect planets that are orbiting within the Habitable Zone of stars. The coronagraph instrument must achieve a contrast ratio stability of 2e-11 in order to achieve planet detection. This places stringent requirements on several spacecraft subsystems, such as pointing stability and structural vibration of the instrument in the presence of mechanical disturbance: for example, telescope pointing must be accurate to within 4 milli-arcseconds, and the jitter of optics must be less than 5 nm. This paper communicates the architecture and predicted performance of a precision pointing and vibration isolation approach for TPF-C called Disturbance Free Payload (DFP)* . In this architecture, the spacecraft and payload fly in close-proximity, and interact with forces and torques through a set of non-contact interface sensors and actuators. In contrast to other active vibration isolation approaches, this architecture allows for isolation down to zero frequency, and the performance of the isolation system is not limited by sensor characteristics. This paper describes the DFP architecture, interface hardware and technical maturity of the technology. In addition, an integrated model of TPF-C Flight Baseline 1 (FB1) is described that allows for explicit computation of performance metrics from system disturbance sources. Using this model, it is shown that the DFP pointing and isolation architecture meets all pointing and jitter stability requirements with substantial margin. This performance relative to requirements is presented, and several fruitful avenues for utilizing performance margin for system design simplification are identified.
A novel spacecraft architecture that provides a solution to the combined problems of payload pointing and isolation, from-spacecraft vibrations is presented. In this architecture, payload and spacecraft are separate bodies that fly in close-proximity formation and interact through noncontact sensors and actuators to achieve precision payload control and isolation from spacecraft disturbances. Vibration isolation is provided down to zero frequency and isolation performance is not limited by sensor characteristics. The proposed concept has far-reaching implications for space missions with stringent pointing control and stability requirements, allowing faster slews and uninterrupted missions during momentum dumping. The applicability of the proposed concept to future missions is discussed. Analysis and simulation results are presented for a large space telescope and provide a first demonstration of the concept. The results show more than two orders of magnitude performance improvement over state-of-the-art pointing and isolation systems.
The US Air Force Research Lab (AFRL) has integrated several technology development efforts together to form a cohesive approach for enabling deployable optical systems in the future. Aperture size dominates the cost/architecture trades for space based laser systems for missile defense and tactical imaging system pursuing broad area coverage with local access. Larger apertures allow both systems to consider higher orbits, offering greater fields of regard. However, large monolithic apertures quickly run into launch vehicle faring volumetric and throw mass constraints. Several technologies may enable space deployable of optical segments to form a large primary mirror at a reduced mass, circumventing the launch vehicle constraints. However, to produce an optically phased wavefront, a combination of technologies, deployment mechanisms, lightweight structures and mirrors, mirror mount isolators and actuators, adaptive optics, and processing techniques, must be applied in concert. While this paper concentrates on the hardware development activities under the UltraLITE program, namely the Precision Deployable Optical Structure ground demonstration and the brassboard Deployable Space Telescope, it will also briefly cover and provide references to related technology programs on-going at the AFRL.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
An overview is presented of the technology associated with the precision pointing of future spaceborne science instruments. High-level architectural options for dealing with the precision pointing problem are considered, and a representative NASA mission set for the 1990s is given. Pointing accuracy and stability requirements are extracted from the mission requirements, with the sub-0.1 arcsec stability requirement emerging as the primary driver. The state of the art of current technology is assessed, including an evaluation of gimbal systems, suspension systems, and actuator and sensor component technology. Areas where the technology needs to be pushed to satisfy future requirements are identified, and some promising design options are proposed.
StructuralControlofaFlexibleSatelliteBusforImprovedJitterPerformance
- J H Jacobs