148 research outputs found
Sensitivity of Magnetospheric Multi-Scale (MMS) Mission Navigation Accuracy to Major Error Sources
The Magnetospheric Multiscale (MMS) mission consists of four satellites flying in formation in highly elliptical orbits about the Earth, with a primary objective of studying magnetic reconnection. The baseline navigation concept is independent estimation of each spacecraft state using GPS pseudorange measurements referenced to an Ultra Stable Oscillator (USO) with accelerometer measurements included during maneuvers. MMS state estimation is performed onboard each spacecraft using the Goddard Enhanced Onboard Navigation System (GEONS), which is embedded in the Navigator GPS receiver. This paper describes the sensitivity of MMS navigation performance to two major error sources: USO clock errors and thrust acceleration knowledge errors
Recommended from our members
Sequential estimation methods for small body optical navigation
As humans explore further into the solar system, small bodies such as asteroids and comets serve as critical stepping-stone destinations. Highly accurate navigation about these small bodies is critical for any future missions, and as a result is listed prominently among NASA's future goals in the NASA Office of Chief Technologist Roadmap. Due to the long communication light-time delays with the Earth, advances in small body navigation may enable missions currently not feasible, as well as significantly reduce dependence on ground resources. Increased operational agility will enable rapid decisions and opportunistic science measurements not possible in previous missions to small bodies. To assist NASA in accomplishing future small body navigation goals, several important advances are made. First, the effectiveness of modern orbit estimation techniques is investigated, with the higher order Additive Divided-Difference sigma point Filter (ADF) implemented and used along with the standard Extended Kalman Filter (EKF) to estimate the spacecraft state from optical small body surface landmark measurements. The ADF performs consistently better than the EKF in the simulations performed, with increasing improvement for higher levels of initial state error and longer intervals between photos of the surface. Second, a new method is created to improve onboard navigation filter performance in diverse and rapidly changing dynamical environments. The approach is to precompute a process noise profile along a reference trajectory using consider covariance analysis tools and filters. When used in an onboard navigation filter, the precomputed process noise allows the filter to account for time- and state-dependent perturbations in the dynamics. The new method also obviates the need for most or all traditional manual tuning of the filter, and provides significantly improved representation of the state uncertainty. Finally, a Simultaneous Localization And Mapping (SLAM) algorithm is employed to estimate the spin state of a tumbling small body (which are expected to be a significant percentage of the small bodies in the solar system), as well as the spacecraft state and surface landmark locations. For the small body characterization phase of the Rosetta mission, the state estimates converge successfully for large initial state errors. The SLAM algorithm remains effective for a range of small body spin states and masses that correspond to expected tumbling small bodies throughout the solar system. The SLAM algorithm is successfully applied to high fidelity independently simulated imagery of a tumbling small body generated by the European Space Agency, and a method for initializing the small body landmark locations is provided.Aerospace Engineerin
Sensitivity of Magnetospheric Multi-Scale (MMS) Mission Naviation Accuracy to Major Error Sources
The Magnetospheric Multiscale (MMS) mission consists of four satellites flying in formation in highly elliptical orbits about the Earth, with a primary objective of studying magnetic reconnection. The baseline navigation concept is independent estimation of each spacecraft state using GPS pseudorange measurements referenced to an Ultra Stable Oscillator (USO) with accelerometer measurements included during maneuvers. MMS state estimation is performed onboard each spacecraft using the Goddard Enhanced Onboard Navigation System (GEONS), which is embedded in the Navigator GPS receiver. This paper describes the sensitivity of MMS navigation performance to two major error sources: USO clock errors and thrust acceleration knowledge errors
Precomputing Process Noise Covariance for Onboard Sequential Filters
Process noise is often used in estimation filters to account for unmodeled and mismodeled accelerations in the dynamics. The process noise covariance acts to inflate the state covariance over propagation intervals, increasing the uncertainty in the state. In scenarios where the acceleration errors change significantly over time, the standard process noise covariance approach can fail to provide effective representation of the state and its uncertainty. Consider covariance analysis techniques provide a method to precompute a process noise covariance profile along a reference trajectory, using known model parameter uncertainties. The process noise covariance profile allows significantly improved state estimation and uncertainty representation over the traditional formulation. As a result, estimation performance on par with the consider filter is achieved for trajectories near the reference trajectory without the additional computational cost of the consider filter. The new formulation also has the potential to significantly reduce the trial-and-error tuning currently required of navigation analysts. A linear estimation problem as described in several previous consider covariance analysis publications is used to demonstrate the effectiveness of the precomputed process noise covariance, as well as a nonlinear descent scenario at the asteroid Bennu with optical navigation
Formative interventions and practice-development: A methodological perspective on teacher rounds
Highlights
• We examine Rounds in education from a methodological perspective.
• In doing so, we class Rounds as a formative intervention and compare it to another means of formative intervention—Developmental Work Research.
• We raise three methodological issues about both types of formative intervention: the role of theory; the relationship between the individual and the collective; and the meaning of collaboration
Entry Assessment in Community Colleges: Tracking or Facilitating?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66989/2/10.1177_009155219302100302.pd
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF
The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at
the Fermilab Long-Baseline Neutrino Facility (LBNF) is described
- …