Presently many types of spacecraft use a Spacecraft Attitude Control System (ACS) with momentum w... more Presently many types of spacecraft use a Spacecraft Attitude Control System (ACS) with momentum wheels for steering and electrochemical batteries to provide electrical power for the eclipse period of the spacecraft orbit. Future spacecraft will use Flywheels for combined use in ACS and Energy Storage. This can be done by using multiple wheels and varying the differential speed for ACS and varying the average speed for energy storage and recovery. Technology in these areas has improved since the 1990s so it is now feasible for flywheel systems to emerge from the laboratory for spacecraft use. This paper describes a new flywheel system that can be used for both ACS and energy storage. Some of the possible advantages of a flywheel system are: lower total mass and volume, higher efficiency, less thermal impact, improved satellite integration schedule and complexity, simplified satellite orbital operations, longer life with lower risk, less pointing jitter, and greater capability for hig...
AIAA Guidance, Navigation, and Control Conference, 2010
This paper revisits the Bode integral theorem, first described in 1945 for feedback amplifier des... more This paper revisits the Bode integral theorem, first described in 1945 for feedback amplifier design, in the context of modern satellite Attitude Control System (ACS) design tasks. Use of Bode's Integral clarifies in an elegant way the connection between open-loop stability margins and closed-loop bandwidth. More importantly it shows that there is a very strong tradeoff between disturbance rejection below the satellite controller design bandwidth, and disturbance amplification in the 'penalty region' just above the design bandwidth. This information has been successfully used to re-tune the control designs for several NASA science-mission satellites. The Appendix of this paper contains a complete summary of the relevant integral conservation theorems for stable, unstable, and nonminimum-phase plants.
Constellation Pathfinder will demonstrate the feasibility of fabricating and launching three 1-kg... more Constellation Pathfinder will demonstrate the feasibility of fabricating and launching three 1-kg satellites (nanosatellites) that are capable of collecting and returning quality scientific and engineering data for several months. The nanosatellite to be launched is based on one that has been under development for the past two years through the Magnetospheric Mapping Mission (MMM), a NASA New Mission Concept study. The study objective of MMM is to assess the feasibility of placing hundreds of nanosatellites equipped with magnetometers into orbits extending into the tail of the magnetosphere, thereby obtaining a much more detailed three-dimensional picture of dynamic phenomena in geospace than has been possible previously. The Constellation Pathfinder Mission (CPM) will take the first step toward such an ultimate implementation by launching similar satellites from the Shuttle. The hardware demonstration of building and flying such a satellite, or small suite of satellites, will provide a proof of principle of the satellite design that will be helpful in many scientific and strategic applications where a fleet of small satellites is required.
MEMS and Microstructures in Aerospace Applications, 2005
Greenbelt, Maryland. In this capacity, he plans and directs a varied portfolio of advanced space ... more Greenbelt, Maryland. In this capacity, he plans and directs a varied portfolio of advanced space system technology developments ranging from affordable, modular and reconfigurable space platform architectures to miniaturized sensor/actuator avionics for Microsat mission applications to precision Guidance, Navigation, and Control (GN&C) systems for multi-spacecraft formation flight. Mr. Dennehy's professional interests include the infusion of Micro Electro Mechanical Systems (MEMS) technology into NASA's future Science and Exploration missions, especially in the area of Guidance, Navigation and Control.
In addition to traditional fault detection and recovery, the algorithms must be robust to fleet-l... more In addition to traditional fault detection and recovery, the algorithms must be robust to fleet-level faults, loss of shared information, communication latency, relative control and estimation, and collisions. • The computation, information management and communication must be well distributed. • Robust distributed autonomous GN&C algorithms are required. The flight software must be flexible and easy to adapt, such as allowing the software blocks to be dynamically loaded.
A retrospective consideration of two 15-year old Guidance, Navigation and Control (GN&C) technolo... more A retrospective consideration of two 15-year old Guidance, Navigation and Control (GN&C) technology 'vision' predictions will be the focus of this paper. A look back analysis and critique of these late 1990s technology roadmaps outlining the future vision, for two then nascent, but rapidly emerging, GN&C technologies will be performed. Specifically, these two GN&C technologies were: 1) multi-spacecraft formation flying and 2) the spaceborne use and exploitation of global positioning system (GPS) signals to enable formation flying. This paper reprises the promise of formation flying and spaceborne GPS as depicted in the cited 1999 1 and 1998 2 papers. It will discuss what happened to cause that promise to be mostly unfulfilled and the reasons why the envisioned formation flying dream has yet to become a reality. The recent technology trends over the past few years will then be identified and a renewed government interest in spacecraft formation flying/cluster flight will be highlighted. The authors will conclude with a reality-tempered perspective, 15 years after the initial technology roadmaps were published, predicting a promising future of spacecraft formation flying technology development over the next decade.
Over the past several years the Guidance, Navigation and Control Center (GNCC) at NASA's Goddard ... more Over the past several years the Guidance, Navigation and Control Center (GNCC) at NASA's Goddard Space Flight Center (GSFC) has actively engaged in the development of advanced GN&C technology to enable future Earth and Space science missions. The Multi-Function GN&C System (MFGS) design presented in this paper represents the successful coalescence of several discrete GNCC hardware and software technology innovations into one single highly integrated, compact, low power and low cost unit that simultaneously provides autonomous real time on-board attitude determination solutions and navigation solutions with accuracies that satisfy many future GSFC mission requirements. The MFGS is intended to operate as a single self-contained multi function unit combining the functions now typically performed by a number of hardware units on a spacecraft. However, recognizing the need to satisfy a variety of future mission requirements, design provisions have been included to permit the unit to interface with a number of external remotely mounted sensors and actuators such as magnetometers, sun sensors, star cameras, reaction wheels and thrusters. The result is a highly versatile MFGS that can be configured in multiple ways to suit a realm of mission-specific GN&C requirements. It is envisioned that the MFGS will perform a mission enabling role by filling the microsat GN&C technology gap. In addition, GSFC believes that the MFGS could be employed to significantly reduce volume, power and mass requirements on conventional satellites.
Over the past several years the Guidance, Navigation and Control Center (GNCC) at NASA's Godd... more Over the past several years the Guidance, Navigation and Control Center (GNCC) at NASA's Goddard Space Flight Center (GSFC) has actively engaged in the development of advanced GN&C technology to enable future Earth and Space science missions. The Multi-Function GN&C System (MFGS) design presented in this paper represents the successful coalescence of several discrete GNCC hardware and software technology innovations into one single highly integrated, compact, low power and low cost unit that simultaneously provides autonomous real time on-board attitude determination solutions and navigation solutions with accuracies that satisfy many future GSFC mission requirements. The MFGS is intended to operate as a single self-contained multifunction unit combining the functions now typically performed by a number of hardware units on a spacecraft. However, recognizing the need to satisfy a variety of future mission requirements, design provisions have been included to permit the unit to i...
The Inertial Stellar Compass (ISC) is a miniature, low power, stellar inertial attitude determina... more The Inertial Stellar Compass (ISC) is a miniature, low power, stellar inertial attitude determination system with an accuracy of better than 0.1 degree (1 sigma) in three axes. The ISC consumes only 3.5 Watts of power and is contained in a 2.5 kg package. With its embedded on-board processor, the ISC provides attitude quaternion information and has Lost-in-Space (LIS) initialization capability. The attitude accuracy and LIS capability are provided by combining a wide field of view Active Pixel Sensor (APS) star camera and Micro- ElectroMechanical System (MEMS) inertial sensor information in an integrated sensor system. The performance and small form factor make the ISC a useful sensor for a wide range of missions. In particular, the ISC represents an enabling, fully integrated, micro-satellite attitude determination system. Other applications include using the ISC as a single sensor solution for attitude determination on medium performance spacecraft and as a bolt on independent saf...
A retrospective consideration of two 15-year old Guidance, Navigation and Control (GN&C) technolo... more A retrospective consideration of two 15-year old Guidance, Navigation and Control (GN&C) technology 'vision' predictions will be the focus of this paper. A look back analysis and critique of these late 1990s technology roadmaps out-lining the future vision, for two then nascent, but rapidly emerging, GN&C technologies will be performed. Specifically, these two GN&C technologies were: 1) multi-spacecraft formation flying and 2) the spaceborne use and exploitation of global positioning system (GPS) signals to enable formation flying. This paper reprises the promise of formation flying and spaceborne GPS as depicted in the cited 1999 and 1998 papers. It will discuss what happened to cause that promise to be mostly unfulfilled and the reasons why the envisioned formation flying dream has yet to become a reality. The recent technology trends over the past few years will then be identified and a renewed government interest in spacecraft formation flying/cluster flight will be high...
Greenbelt, Maryland. In this capacity, he plans and directs a varied portfolio of advanced space ... more Greenbelt, Maryland. In this capacity, he plans and directs a varied portfolio of advanced space system technology developments ranging from affordable, modular and reconfigurable space platform architectures to miniaturized sensor/actuator avionics for Microsat mission applications to precision Guidance, Navigation, and Control (GN&C) systems for multi-spacecraft formation flight. Mr. Dennehy's professional interests include the infusion of Micro Electro Mechanical Systems (MEMS) technology into NASA's future Science and Exploration missions, especially in the area of Guidance, Navigation and Control.
Spacecraft Hybrid Control At NASA: A Look Back, Current Initiatives, and Some Future Considerations
There is a heightened interest within NASA for the design, development, and flight implementation... more There is a heightened interest within NASA for the design, development, and flight implementation of mixed actuator hybrid attitude control systems for science spacecraft that have less than three functional reaction wheel actuators. This interest is driven by a number of recent reaction wheels failures on aging, but still scientifically productive, NASA spacecraft. This paper describes the highlights of the first NASA Cross-Center Hybrid Control Workshop that was held in Greenbelt, Maryland in April of 2013 under the sponsorship of the NASA Engineering and Safety Center (NESC). A brief historical summary of NASA's past experiences with spacecraft mixed actuator hybrid attitude control approaches, some of which were implemented on-orbit, will be provided. This paper will also convey some of the lessons learned and best practices captured at that workshop. Some relevant recent and current hybrid control activities will be described with an emphasis on work in support of a repurposed Kepler spacecraft. Specific technical areas for future considerations regarding spacecraft hybrid control will also be identified.
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Papers by Neil Dennehy