ABSTRACT The frequency function of a linear dynamical system can be estimated using spectral esti... more ABSTRACT The frequency function of a linear dynamical system can be estimated using spectral estimation techniques. Traditionally, this is done by smoothing in the frequency domain or windowing in the lag domain. These methods are successful in most cases but sometimes they yield estimates that suffer from poor resolution. Typically, this happens when fine details are estimated. In this paper an alternative method is proposed. The method combines traditional windowing with results in adaptive time-frequency analysis. In simulations concerning systems which are difficult for the traditional approach, this method gives better better estimates of the frequency function
This paper deals with the problem of enhancement of speech signals in slowly varying background n... more This paper deals with the problem of enhancement of speech signals in slowly varying background noise. The method suggested uses the wavelet packet transform together with a simple statistical model of the noise. As in spectral subtraction, information about the background is collected during non-speech intervals. The signal estimate is obtained with spectral subtraction in the time-frequency domain and a rule for choosing the most favorable time-frequency decomposition is suggested. The method is demonstrated with a real-data example
The PRISMA project for autonomous formation flying and rendezvous has passed its critical design ... more The PRISMA project for autonomous formation flying and rendezvous has passed its critical design review in February–March 2007. The project comprises two satellites which are an in-orbit testbed for Guidance, Navigation and Control (GNC) algorithms and sensors for advanced formation flying and rendezvous. Several experiments involving GNC algorithms, sensors and thrusters will be performed during a 10 month mission with launch planned for the second half of 2009.The project is run by the Swedish Space Corporation (SSC) in close cooperation with the German Aerospace Center (DLR), the French Space Agency (CNES) and the Technical University of Denmark (DTU). Additionally, the project also will demonstrate flight worthiness of two novel motor technologies: one that uses environmentally clean and non-hazardous propellant, and one that consists of a microthruster system based on MEMS technology.The project will demonstrate autonomous formation flying and rendezvous based on several sensors—GPS, RF-based and vision based—with different objectives and in different combinations. The GPS-based onboard navigation system, contributed by DLR, offers relative orbit information in real-time in decimetre range. The RF-based navigation instrument intended for DARWIN, under CNES development, will be tested for the first time on PRISMA, both for instrument performance, but also in closed loop as main sensor for formation flying. Several rendezvous and proximity manoeuvre experiments will be demonstrated using only vision based sensor information coming from the modified star camera provided by DTU. Semi-autonomous operations ranging from 200 km to 1 m separation between the satellites will be demonstrated.With the project now in the verification phase particular attention is given to the specific formation flying and rendezvous functionality on instrument, GNC-software and system level.
This paper presents the Attitude and Orbit Control System (AOCS) on SMART-1. The paper first summ... more This paper presents the Attitude and Orbit Control System (AOCS) on SMART-1. The paper first summarizes the phases of the mission and gives an overview of the main requirements and constraints that have been fundamental for the control system design solution. This is followed by a presentation of all the AOCS-related sensors and actuators and their configuration. A presentation of the different operational modes is then given and finally, the structure and development strategy for the on-board application software is presented.
SMART-1 is the first of the small missions for advanced research and technology as part of ESA's ... more SMART-1 is the first of the small missions for advanced research and technology as part of ESA's science programme “Cosmic vision”. It was successfully launched on September 27, 2003 and is presently traveling towards its destination, the Moon. The main objective of the mission, to demonstrate solar electric primary propulsion for future Cornerstones (such as Bepi-Colombo), has already been achieved. At the time of writing the electric propulsion system has been working already for more than 3400 h and has provided a Delta-V to the spacecraft of more than 2500 m/s. The other technology objectives are also being fulfilled by the verification of the proper functioning of such on-board experiments like the X-Ka band transponder, the X-ray spectrometer, the near IR spectrometer, the laser link, etc. The scientific objectives are related to lunar science and will be fulfilled once the spacecraft enters its operational lunar orbit, currently expected for January 2005. SMART-1 lunar science investigations will include studies of the chemical composition of the Moon, of geophysical processes, environment and high-resolution studies in preparation for future steps of lunar exploration.SMART-1 has been an innovative mission in many aspects and we are now drawing some preliminary conclusions about the lessons to be learnt. The paper describes the spacecraft and the technology elements with particular emphasis to the technology nature of the mission. The on-board avionics employs many novel designs for spacecraft, including a serial CAN bus for data communication, autonomous star trackers and extensive use of auto-code generation for implementing the attitude control system and the failure, detection, isolation and recovery (FDIR). Finally, the orbital operation phase currently ongoing, including the routine electric propulsion operations and the instrument commissioning, is providing a wealth of data and lesson-learnt useful for future autonomous planetary missions.
This paper focuses on the technical challenges that arise when electric propulsion is used on a s... more This paper focuses on the technical challenges that arise when electric propulsion is used on a small spacecraft such as SMART-1. The choice of electric propulsion influences not only the attitude control system and the power system, but also the thermal control as well as the spacecraft structure. A description is given on how the design of the attitude control system uses the possibility to control the alignment of the thrust vector in order to reduce the momentum build-up. An outline is made of the philosophy of power generation and distribution and shows how the thermal interfaces to highly dissipating units have been solved.Areas unique for electric propulsion are the added value of a thrust vector orientation mechanism and the special consideration given to the electromagnetic compatibility. SMART-1 is equipped with a thruster gimbal mechanism providing a 10° cone in which the thrust vector can be pointed. Concerning the electromagnetic compatibility, a discussion on how to evaluate the available test results is given keeping in mind that one of the main objectives of the SMART-1 mission is to assess the impact of electric propulsion on the scientific instruments and on other spacecraft systems.Finally, the assembly, integration and test of the spacecraft is described. Compared to traditional propulsion systems, electric propulsion puts different requirements on the integration sequence and limits the possibilities to verify the correct function of the thruster since it needs high quality vacuum in order to operate.Prime contractor for SMART-1 is the Swedish Space Corporation (SSC). The electric propulsion subsystem is procured directly by ESA from SNECMA, France and is delivered to SSC as a customer furnished item.The conclusion of this paper is that electric propulsion is possible on a small spacecraft, which opens up possibilities for a new range of missions for which a large velocity increment is needed. The paper will also present SMART-1 and show how the problems related to the accommodation of electric propulsion have been solved during design and planning of the project.
ABSTRACT This paper deals with the problem of structure determination for generalized orthonormal... more ABSTRACT This paper deals with the problem of structure determination for generalized orthonormal basis models used in system identification. The model structure is parametrized by a pre-specified set of poles. Given this structure and experimental data a model can be estimated using linear regression techniques. Since the variance of the estimated model increases with the number of estimated parameters, the objective is to find structures that are as compact/parsimonious as possible. A natural approach would be to estimate the poles, but this leads to nonlinear optimization with possible local minima. In this paper, a best basis algorithm is derived for the generalized orthonormal rational bases. Combined with linear regression and thresholding this leads to compact transfer function representations
ABSTRACT A problem in prediction error system identification methods is estimation of pole locati... more ABSTRACT A problem in prediction error system identification methods is estimation of pole locations. Typically, iterative numerical optimization methods are used. Reliable initial values are then necessary for good results. The parameterization is often done in the coefficients of transfer function polynomials or some canonical form. In this contribution we discuss a couple of issues related to the above problem. First, we study how all-pass systems can be used to generate suitable model structures. This analysis is based on the relation between balanced realizations of all-pass filters and orthonormal basis transfer functions. Next, we investigate the effects of a priori fixed pole locations, such as in Laguerre and Kautz models. One idea is to use very flexible high-order models. However, the corresponding estimation problem has to be regularized in order to reduce the variance errors due to noise. We will discuss how this can be done by using thresholding of the estimated coefficients
Title: PRISMA: An In-Orbit Test Bed for Guidance, Navigation, and Control Experiments. Authors: B... more Title: PRISMA: An In-Orbit Test Bed for Guidance, Navigation, and Control Experiments. Authors: Bodin, Per; Larsson, Robin; Nilsson, Fredrik; Chasset, Camille; Noteborn, Ron; Nylund, Matti. Publication: Journal of Spacecraft and Rockets, vol. 46, issue 3, pp. 615-623. ...
SMART-1 was launched in September 2003 and impacted the Moon 3 years later. It was the first of E... more SMART-1 was launched in September 2003 and impacted the Moon 3 years later. It was the first of ESA's Small Missions for Advanced Research in Technology, with the main goal of testing electric propulsion. Following a spectacular navigation strategy, the craft reached the Moon, where its orbit was optimised for scientific observations. The instruments provided data throughout the mission, interrupted only by manoeuvres. The last of these had to be done with the attitude thrusters after exhausting the ion thruster's xenon fuel. The impact was observed from Earth by radio and infrared telescopes worldwide in an international campaign.
SMART-1 is the first of a series of ESA Small Missions for Advance Research and Technology where ... more SMART-1 is the first of a series of ESA Small Missions for Advance Research and Technology where elements of the platform and the payload technology have been conceived as a demonstration for future cornerstone missions and an early opportunity for science. SMART-1 has also been an opportunity to experiment with new ways of conducting ground operations taking advantage of both increased satellite autonomy and ground automation tools. The paper will focus on three areas:The accumulated performance of the technology demonstration components since launch as the electrical propulsion engine, the triple-junction solar cells, the lithium-ion batteries, the 32 bit CPU ERC32 Single Chip, the CAN bus, the DTU Star Trackers and the complex on-board autonomy.The changes implemented on-board and on the ground during the lunar phase to increase the data return.The pros and contras in some of the choices made for SMART-1, the developments and solutions implemented to mitigate the problems, the tools developed to automate the operations and the distribution of data.
ABSTRACT The frequency function of a linear dynamical system can be estimated using spectral esti... more ABSTRACT The frequency function of a linear dynamical system can be estimated using spectral estimation techniques. Traditionally, this is done by smoothing in the frequency domain or windowing in the lag domain. These methods are successful in most cases but sometimes they yield estimates that suffer from poor resolution. Typically, this happens when fine details are estimated. In this paper an alternative method is proposed. The method combines traditional windowing with results in adaptive time-frequency analysis. In simulations concerning systems which are difficult for the traditional approach, this method gives better better estimates of the frequency function
This paper deals with the problem of enhancement of speech signals in slowly varying background n... more This paper deals with the problem of enhancement of speech signals in slowly varying background noise. The method suggested uses the wavelet packet transform together with a simple statistical model of the noise. As in spectral subtraction, information about the background is collected during non-speech intervals. The signal estimate is obtained with spectral subtraction in the time-frequency domain and a rule for choosing the most favorable time-frequency decomposition is suggested. The method is demonstrated with a real-data example
The PRISMA project for autonomous formation flying and rendezvous has passed its critical design ... more The PRISMA project for autonomous formation flying and rendezvous has passed its critical design review in February–March 2007. The project comprises two satellites which are an in-orbit testbed for Guidance, Navigation and Control (GNC) algorithms and sensors for advanced formation flying and rendezvous. Several experiments involving GNC algorithms, sensors and thrusters will be performed during a 10 month mission with launch planned for the second half of 2009.The project is run by the Swedish Space Corporation (SSC) in close cooperation with the German Aerospace Center (DLR), the French Space Agency (CNES) and the Technical University of Denmark (DTU). Additionally, the project also will demonstrate flight worthiness of two novel motor technologies: one that uses environmentally clean and non-hazardous propellant, and one that consists of a microthruster system based on MEMS technology.The project will demonstrate autonomous formation flying and rendezvous based on several sensors—GPS, RF-based and vision based—with different objectives and in different combinations. The GPS-based onboard navigation system, contributed by DLR, offers relative orbit information in real-time in decimetre range. The RF-based navigation instrument intended for DARWIN, under CNES development, will be tested for the first time on PRISMA, both for instrument performance, but also in closed loop as main sensor for formation flying. Several rendezvous and proximity manoeuvre experiments will be demonstrated using only vision based sensor information coming from the modified star camera provided by DTU. Semi-autonomous operations ranging from 200 km to 1 m separation between the satellites will be demonstrated.With the project now in the verification phase particular attention is given to the specific formation flying and rendezvous functionality on instrument, GNC-software and system level.
This paper presents the Attitude and Orbit Control System (AOCS) on SMART-1. The paper first summ... more This paper presents the Attitude and Orbit Control System (AOCS) on SMART-1. The paper first summarizes the phases of the mission and gives an overview of the main requirements and constraints that have been fundamental for the control system design solution. This is followed by a presentation of all the AOCS-related sensors and actuators and their configuration. A presentation of the different operational modes is then given and finally, the structure and development strategy for the on-board application software is presented.
SMART-1 is the first of the small missions for advanced research and technology as part of ESA's ... more SMART-1 is the first of the small missions for advanced research and technology as part of ESA's science programme “Cosmic vision”. It was successfully launched on September 27, 2003 and is presently traveling towards its destination, the Moon. The main objective of the mission, to demonstrate solar electric primary propulsion for future Cornerstones (such as Bepi-Colombo), has already been achieved. At the time of writing the electric propulsion system has been working already for more than 3400 h and has provided a Delta-V to the spacecraft of more than 2500 m/s. The other technology objectives are also being fulfilled by the verification of the proper functioning of such on-board experiments like the X-Ka band transponder, the X-ray spectrometer, the near IR spectrometer, the laser link, etc. The scientific objectives are related to lunar science and will be fulfilled once the spacecraft enters its operational lunar orbit, currently expected for January 2005. SMART-1 lunar science investigations will include studies of the chemical composition of the Moon, of geophysical processes, environment and high-resolution studies in preparation for future steps of lunar exploration.SMART-1 has been an innovative mission in many aspects and we are now drawing some preliminary conclusions about the lessons to be learnt. The paper describes the spacecraft and the technology elements with particular emphasis to the technology nature of the mission. The on-board avionics employs many novel designs for spacecraft, including a serial CAN bus for data communication, autonomous star trackers and extensive use of auto-code generation for implementing the attitude control system and the failure, detection, isolation and recovery (FDIR). Finally, the orbital operation phase currently ongoing, including the routine electric propulsion operations and the instrument commissioning, is providing a wealth of data and lesson-learnt useful for future autonomous planetary missions.
This paper focuses on the technical challenges that arise when electric propulsion is used on a s... more This paper focuses on the technical challenges that arise when electric propulsion is used on a small spacecraft such as SMART-1. The choice of electric propulsion influences not only the attitude control system and the power system, but also the thermal control as well as the spacecraft structure. A description is given on how the design of the attitude control system uses the possibility to control the alignment of the thrust vector in order to reduce the momentum build-up. An outline is made of the philosophy of power generation and distribution and shows how the thermal interfaces to highly dissipating units have been solved.Areas unique for electric propulsion are the added value of a thrust vector orientation mechanism and the special consideration given to the electromagnetic compatibility. SMART-1 is equipped with a thruster gimbal mechanism providing a 10° cone in which the thrust vector can be pointed. Concerning the electromagnetic compatibility, a discussion on how to evaluate the available test results is given keeping in mind that one of the main objectives of the SMART-1 mission is to assess the impact of electric propulsion on the scientific instruments and on other spacecraft systems.Finally, the assembly, integration and test of the spacecraft is described. Compared to traditional propulsion systems, electric propulsion puts different requirements on the integration sequence and limits the possibilities to verify the correct function of the thruster since it needs high quality vacuum in order to operate.Prime contractor for SMART-1 is the Swedish Space Corporation (SSC). The electric propulsion subsystem is procured directly by ESA from SNECMA, France and is delivered to SSC as a customer furnished item.The conclusion of this paper is that electric propulsion is possible on a small spacecraft, which opens up possibilities for a new range of missions for which a large velocity increment is needed. The paper will also present SMART-1 and show how the problems related to the accommodation of electric propulsion have been solved during design and planning of the project.
ABSTRACT This paper deals with the problem of structure determination for generalized orthonormal... more ABSTRACT This paper deals with the problem of structure determination for generalized orthonormal basis models used in system identification. The model structure is parametrized by a pre-specified set of poles. Given this structure and experimental data a model can be estimated using linear regression techniques. Since the variance of the estimated model increases with the number of estimated parameters, the objective is to find structures that are as compact/parsimonious as possible. A natural approach would be to estimate the poles, but this leads to nonlinear optimization with possible local minima. In this paper, a best basis algorithm is derived for the generalized orthonormal rational bases. Combined with linear regression and thresholding this leads to compact transfer function representations
ABSTRACT A problem in prediction error system identification methods is estimation of pole locati... more ABSTRACT A problem in prediction error system identification methods is estimation of pole locations. Typically, iterative numerical optimization methods are used. Reliable initial values are then necessary for good results. The parameterization is often done in the coefficients of transfer function polynomials or some canonical form. In this contribution we discuss a couple of issues related to the above problem. First, we study how all-pass systems can be used to generate suitable model structures. This analysis is based on the relation between balanced realizations of all-pass filters and orthonormal basis transfer functions. Next, we investigate the effects of a priori fixed pole locations, such as in Laguerre and Kautz models. One idea is to use very flexible high-order models. However, the corresponding estimation problem has to be regularized in order to reduce the variance errors due to noise. We will discuss how this can be done by using thresholding of the estimated coefficients
Title: PRISMA: An In-Orbit Test Bed for Guidance, Navigation, and Control Experiments. Authors: B... more Title: PRISMA: An In-Orbit Test Bed for Guidance, Navigation, and Control Experiments. Authors: Bodin, Per; Larsson, Robin; Nilsson, Fredrik; Chasset, Camille; Noteborn, Ron; Nylund, Matti. Publication: Journal of Spacecraft and Rockets, vol. 46, issue 3, pp. 615-623. ...
SMART-1 was launched in September 2003 and impacted the Moon 3 years later. It was the first of E... more SMART-1 was launched in September 2003 and impacted the Moon 3 years later. It was the first of ESA's Small Missions for Advanced Research in Technology, with the main goal of testing electric propulsion. Following a spectacular navigation strategy, the craft reached the Moon, where its orbit was optimised for scientific observations. The instruments provided data throughout the mission, interrupted only by manoeuvres. The last of these had to be done with the attitude thrusters after exhausting the ion thruster's xenon fuel. The impact was observed from Earth by radio and infrared telescopes worldwide in an international campaign.
SMART-1 is the first of a series of ESA Small Missions for Advance Research and Technology where ... more SMART-1 is the first of a series of ESA Small Missions for Advance Research and Technology where elements of the platform and the payload technology have been conceived as a demonstration for future cornerstone missions and an early opportunity for science. SMART-1 has also been an opportunity to experiment with new ways of conducting ground operations taking advantage of both increased satellite autonomy and ground automation tools. The paper will focus on three areas:The accumulated performance of the technology demonstration components since launch as the electrical propulsion engine, the triple-junction solar cells, the lithium-ion batteries, the 32 bit CPU ERC32 Single Chip, the CAN bus, the DTU Star Trackers and the complex on-board autonomy.The changes implemented on-board and on the ground during the lunar phase to increase the data return.The pros and contras in some of the choices made for SMART-1, the developments and solutions implemented to mitigate the problems, the tools developed to automate the operations and the distribution of data.
Uploads
Papers