Colorado Center for Astrodynamics Research

Engineering, United States

Colorado Center for Astrodynamics Research

Engineering, United States
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Argrow B.M.,Research and Engineering Center for Unmanned Vehicles | Palo S.E.,Colorado Center for Astrodynamics Research
Journal of Spacecraft and Rockets | Year: 2010

The energy-accommodation coefficient is an important parameter affecting satellite drag and orbit predictions. Previous estimates of this coefficient have been based on interpolation from values tabulated at several altitudes and solar conditions. In an effort to improve drag coefficient accuracy and to compute values of the accommodation coefficient that respond to the real variability of the atmosphere, a first-principles approach is desired. The present work combines the theory that gas-surface interactions in low Earth orbit are driven by adsorption of atomic oxygen, with observations of satellite accommodation collected during solar cycle 22. The result is a semiempirical model based on Langmuir's adsorption isotherm, which agrees with the data to within 3%. This model can be used to improve drag predictions during a wide range of space weather conditions, as well as to improve the accuracy for atmospheric densities derived from satellite drag. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.


News Article | December 15, 2016
Site: www.rdmag.com

A team led by the University of Colorado Boulder has found the mechanism behind the sudden onset of a "natural thermostat" in Earth's upper atmosphere that dramatically cools the air after it has been heated by violent solar activity. Scientists have known that solar flares and coronal mass ejections (CMEs) -- which release electrically charged plasma from the sun -- can damage satellites, cause power outages on Earth and disrupt GPS service. CMEs are powerful enough to send billions of tons of solar particles screaming toward Earth at more than 1 million miles per hour, said CU Boulder Professor Delores Knipp of the Department of Aerospace Engineering Sciences. Now, Knipp and her team have determined that when such powerful CMEs come off the sun and speed toward Earth, they create shock waves much like supersonic aircraft create sonic booms. While the shock waves from CMEs pour energy into Earth's upper atmosphere, puffing it up and heating it, they also cause the formation of the trace chemical nitric oxide, which then rapidly cools and shrinks it, she said. "What's new is that we have determined the circumstances under which the upper atmosphere goes into this almost overcooling mode following significant heating," said Knipp, also a member of CU Boulder's Colorado Center for Astrodynamics Research. "It's a bit like having a stuck thermostat -- it's really a case of nature reining itself in." Knipp gave a presentation at the 2016 fall meeting of the American Geophysical Union being held in San Francisco Dec. 12 through Dec. 16. The presentation was tied to an upcoming paper that is slated to be published in the journal Space Weather. Solar storms can cause dramatic change in the temperatures of the upper atmosphere, including the ionosphere, which ranges from about 30 miles in altitude to about 600 miles high -- the edge of space. While CME material slamming into Earth's atmosphere can cause temperature spikes of up to 750 degrees Fahrenheit, the nitric oxide created by the energy infusion can subsequently cool it by about 930 F, said Knipp. The key to solving the mystery came when Knipp was reviewing satellite data from a severe solar storm that pounded Earth in 1967. "I found a graphic buried deep in a long forgotten manuscript," she said. "It finally suggested to me what was really happening." Because the upper atmosphere expands during CMEs, satellites in low-Earth orbit are forced to move through additional gaseous particles, causing them to experience more drag. Satellite drag -- a huge concern of government and aerospace companies -- causes decays in the orbits of spacecraft, which subsequently burn up in the atmosphere. As part of the new study, Knipp and her colleagues compared two 15-year-long satellite datasets. One was from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument riding on NASA's TIMED satellite. The other was from data collected by U.S. Department of Defense satellites. "We found that the fastest material streaming off the sun was triggering these shockwaves, causing the atmosphere to heave up and heat up," she said. "But it became very clear that these shock waves were at the root of creating the nitric oxide, which caused the atmosphere to shed energy and cool." SABER has been collecting data on nitric oxide in the atmosphere since its launch in 2001, following on the heels of another nitric oxide-measuring satellite known as the Student Nitric Oxide Explorer (SNOE). Launched in 1998, SNOE involved more than 100 CU Boulder students, primarily undergraduates, in its design and construction. Once in orbit, SNOE was controlled by students on campus 24 hours a day for nearly six years. Geomagnetic storms have had severe impacts on Earth. A 1989 storm caused by a CME resulted in the collapse of the Hydro-Quebec's electricity transmission system, causing six million Canadians to lose power. In 1859 a solar storm called the Carrington Event produced auroras from the North Pole to Central America and disrupted telegraph communications, even sparking fires at telegraph offices that caused several deaths.


News Article | December 14, 2016
Site: www.eurekalert.org

A team led by the University of Colorado Boulder has found the mechanism behind the sudden onset of a "natural thermostat" in Earth's upper atmosphere that dramatically cools the air after it has been heated by violent solar activity. Scientists have known that solar flares and coronal mass ejections (CMEs) -- which release electrically charged plasma from the sun -- can damage satellites, cause power outages on Earth and disrupt GPS service. CMEs are powerful enough to send billions of tons of solar particles screaming toward Earth at more than 1 million miles per hour, said CU Boulder Professor Delores Knipp of the Department of Aerospace Engineering Sciences. Now, Knipp and her team have determined that when such powerful CMEs come off the sun and speed toward Earth, they create shock waves much like supersonic aircraft create sonic booms. While the shock waves from CMEs pour energy into Earth's upper atmosphere, puffing it up and heating it, they also cause the formation of the trace chemical nitric oxide, which then rapidly cools and shrinks it, she said. "What's new is that we have determined the circumstances under which the upper atmosphere goes into this almost overcooling mode following significant heating," said Knipp, also a member of CU Boulder's Colorado Center for Astrodynamics Research. "It's a bit like having a stuck thermostat -- it's really a case of nature reining itself in." Knipp gave a presentation at the 2016 fall meeting of the American Geophysical Union being held in San Francisco Dec. 12 through Dec. 16. The presentation was tied to an upcoming paper that is slated to be published in the journal Space Weather. Solar storms can cause dramatic change in the temperatures of the upper atmosphere, including the ionosphere, which ranges from about 30 miles in altitude to about 600 miles high -- the edge of space. While CME material slamming into Earth's atmosphere can cause temperature spikes of up to 750 degrees Fahrenheit, the nitric oxide created by the energy infusion can subsequently cool it by about 930 F, said Knipp. The key to solving the mystery came when Knipp was reviewing satellite data from a severe solar storm that pounded Earth in 1967. "I found a graphic buried deep in a long forgotten manuscript," she said. "It finally suggested to me what was really happening." Because the upper atmosphere expands during CMEs, satellites in low-Earth orbit are forced to move through additional gaseous particles, causing them to experience more drag. Satellite drag -- a huge concern of government and aerospace companies -- causes decays in the orbits of spacecraft, which subsequently burn up in the atmosphere. As part of the new study, Knipp and her colleagues compared two 15-year-long satellite datasets. One was from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument riding on NASA's TIMED satellite. The other was from data collected by U.S. Department of Defense satellites. "We found that the fastest material streaming off the sun was triggering these shockwaves, causing the atmosphere to heave up and heat up," she said. "But it became very clear that these shock waves were at the root of creating the nitric oxide, which caused the atmosphere to shed energy and cool." SABER has been collecting data on nitric oxide in the atmosphere since its launch in 2001, following on the heels of another nitric oxide-measuring satellite known as the Student Nitric Oxide Explorer (SNOE). Launched in 1998, SNOE involved more than 100 CU Boulder students, primarily undergraduates, in its design and construction. Once in orbit, SNOE was controlled by students on campus 24 hours a day for nearly six years. Geomagnetic storms have had severe impacts on Earth. A 1989 storm caused by a CME resulted in the collapse of the Hydro-Quebec's electricity transmission system, causing six million Canadians to lose power. In 1859 a solar storm called the Carrington Event produced auroras from the North Pole to Central America and disrupted telegraph communications, even sparking fires at telegraph offices that caused several deaths. In addition to Knipp, CU Boulder graduate students Dan Pette and Alfredo Cruz participated in the research, as did undergraduate Tristan Isaacs through CU Boulder's Research Experience for Undergraduates (REU) program.


Anderson R.L.,University of Colorado at Boulder | Anderson R.L.,Colorado Center for Astrodynamics Research | Lo M.W.,Jet Propulsion Laboratory | Lo M.W.,High Capability Computing and Modeling Group
Journal of Guidance, Control, and Dynamics | Year: 2010

In this analysis the relationship between a planar Europa Orbiter trajectory and the invariant manifolds of resonant periodic orbits is studied. An understanding of this trajectory with its large impulsive maneuvers should provide basic tools that can be extended to cases that approximate low thrust with many small maneuvers. This study therefore represents a step in understanding low-thrust trajectories. Unstable resonant orbits are computed along with their invariant manifolds in order to examine the resonance transitions that the planar Europa Orbiter trajectory travels through. The stable manifold of a Lyapunov orbit at the L2 libration point is used to show why a 5:6 resonance is necessary at this energy for capture around Europa. 2009. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.


Hudson J.S.,University of Michigan | Scheeres D.J.,University of Colorado at Boulder | Scheeres D.J.,Colorado Center for Astrodynamics Research
Journal of Guidance, Control, and Dynamics | Year: 2011

A method to evaluate the trajectory dynamics of low-thrust spacecraft is applied to targeting and optimal control problems. Averaged variational equations for the osculating orbital elements are used to estimate a spacecraft trajectory over many spiral orbits. Fourteen Fourier coefficients of the thrust acceleration vector represent the fundamental trajectory dynamics. Spacecraft targeting problems are solved using the averaged variational equations and a general cost function represented as a Fourier series. The resulting fuel costs and dynamic fidelity of the targeting solutions are evaluated. The goal of the method is not precise targeting, but easy reconstruction of the basic elements of the thrusting trajectory and control law. Copyright © 2011 by Jennifer Hudson.


Mullen J.,University of Colorado at Boulder | Schaub H.,University of Colorado at Boulder | Schaub H.,Colorado Center for Astrodynamics Research
Journal of Guidance, Control, and Dynamics | Year: 2010

A subfamily of attitude coordinates called the hypersphere stereographic orientation parameters (SOPs) (HSOPs), which contain both the previous MRPs (particular set of symmetric SOPs) and the asymmetric stereographic attitude parameters (ASOP), allowing for all this work to be combined into a single, minimal attitude parameter description, is reported. HSOPs are different than MRPs because of the different singular behaviors of each attitude coordinate set. This offers great flexibility, as the singular orientation can be placed at a full revolution or at particular rotations about particular body axes. In all cases, the kinematic differential equation only has quadratic nonlinear terms equivalent to those of the MRPs.


Hogan E.A.,Colorado Center for Astrodynamics Research | Schaub H.,Colorado Center for Astrodynamics Research
Journal of Guidance, Control, and Dynamics | Year: 2013

The charged relative-motion dynamics and control of a two-craft system is investigated if one vehicle is performing a low-thrust orbit correction using inertial thrusters. The nominal motion is an along-track configuration where active electrostatic charge control is maintaining an attractive force between the two vehicles. In this study the charging is held fixed and the inertial thruster of the tugging vehicle is controlled to stabilize the relative motion to a nominal fixed separation distance. Using a candidate Lyapunov function, the relative orbit control law is shown to be asymptotically stable. Analysis of the control system gains is performed in order to achieve a desired settling time and damping ratio. The effects of uncertainties in the vehicle charges are also examined. Using numerical simulation, the performance of the proposed control system is investigated for a formation in geosynchronous earth orbit. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


Jones B.A.,University of Colorado at Boulder | Jones B.A.,Colorado Center for Astrodynamics Research | Doostan A.,University of Colorado at Boulder | Born G.H.,University of Colorado at Boulder | Born G.H.,Colorado Center for Astrodynamics Research
Journal of Guidance, Control, and Dynamics | Year: 2013

This paper demonstrates the use of polynomial chaos expansions for the nonlinear, non-Gaussian propagation of orbit state uncertainty. Using linear expansions in tensor products of univariate orthogonal polynomial bases, polynomial chaos expansions approximate the stochastic solution of the ordinary differential equation describing the propagated orbit, and include information on covariance, higher moments, and the spatial density of possible solutions. Results presented in this paper use non-intrusive, i.e., sampling-based, methods in combination with either least-squares regression or pseudospectral collocation to estimate the polynomial chaos expansion coefficients at any future point in time. Such methods allow for the usage of existing orbit propagators. Samples based on sunsynchronous and Molniya orbit scenarios are propagated for up to ten days using two-body and higher-fidelity force models. Tests demonstrate that the presented methods require the propagation of orders of magnitude fewer samples than Monte Carlo techniques, and provide an approximation of the a posteriori probability density function that achieves the desired accuracy. Results also show that Poincaré-based polynomial chaos expansions require fewer samples to achieve a given accuracy than Cartesian-based solutions. In terms of probability density function accuracy, the polynomial chaos expansion-based solutions represent an improvement over the linear propagation and unscented transformation techniques. Copyright © 2012 by Brandon A. Jones, Alireza Doostan, and George H. Born. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.


Scheeres D.J.,University of Colorado at Boulder | Scheeres D.J.,Colorado Center for Astrodynamics Research
Journal of Guidance, Control, and Dynamics | Year: 2012

Space missions to small solar system bodies such as asteroids and comets must deal with multiple perturbations acting on the spacecraft. These include strong perturbations from the gravity field and solar tide, but for small bodies, the most important perturbations may arise from solar radiation pressure acting on the spacecraft. Previous research has generally investigated the effect of the gravity field, solar tide, and solar radiation pressure acting on a spacecraft trajectory about an asteroid in isolation and has not considered their joint effect. In this paper, a more general theoretical discussion of the joint effects of these forces will be given. Specific criteria are found for when it is possible for a spacecraft to orbit about a small body in a bound orbit. In the case where such bound motion is possible, a general solution for the averaged motion of a spacecraft subject to solar radiation pressure perturbations is given. Finally, interactions between solar radiation pressure and gravity field perturbations are investigated. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


News Article | December 14, 2016
Site: phys.org

Scientists have known that solar flares and coronal mass ejections (CMEs)—which release electrically charged plasma from the sun—can damage satellites, cause power outages on Earth and disrupt GPS service. CMEs are powerful enough to send billions of tons of solar particles screaming toward Earth at more than 1 million miles per hour, said CU Boulder Professor Delores Knipp of the Department of Aerospace Engineering Sciences. Now, Knipp and her team have determined that when such powerful CMEs come off the sun and speed toward Earth, they create shock waves much like supersonic aircraft create sonic booms. While the shock waves from CMEs pour energy into Earth's upper atmosphere, puffing it up and heating it, they also cause the formation of the trace chemical nitric oxide, which then rapidly cools and shrinks it, she said. "What's new is that we have determined the circumstances under which the upper atmosphere goes into this almost overcooling mode following significant heating," said Knipp, also a member of CU Boulder's Colorado Center for Astrodynamics Research. "It's a bit like having a stuck thermostat—it's really a case of nature reining itself in." Knipp gave a presentation at the 2016 fall meeting of the American Geophysical Union being held in San Francisco Dec. 12 through Dec. 16. The presentation was tied to an upcoming paper that is slated to be published in the journal Space Weather. Solar storms can cause dramatic change in the temperatures of the upper atmosphere, including the ionosphere, which ranges from about 30 miles in altitude to about 600 miles high—the edge of space. While CME material slamming into Earth's atmosphere can cause temperature spikes of up to 750 degrees Fahrenheit, the nitric oxide created by the energy infusion can subsequently cool it by about 930 F, said Knipp. The key to solving the mystery came when Knipp was reviewing satellite data from a severe solar storm that pounded Earth in 1967. "I found a graphic buried deep in a long forgotten manuscript," she said. "It finally suggested to me what was really happening." Because the upper atmosphere expands during CMEs, satellites in low-Earth orbit are forced to move through additional gaseous particles, causing them to experience more drag. Satellite drag—a huge concern of government and aerospace companies—causes decays in the orbits of spacecraft, which subsequently burn up in the atmosphere. As part of the new study, Knipp and her colleagues compared two 15-year-long satellite datasets. One was from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument riding on NASA's TIMED satellite. The other was from data collected by U.S. Department of Defense satellites. "We found that the fastest material streaming off the sun was triggering these shockwaves, causing the atmosphere to heave up and heat up," she said. "But it became very clear that these shock waves were at the root of creating the nitric oxide, which caused the atmosphere to shed energy and cool." SABER has been collecting data on nitric oxide in the atmosphere since its launch in 2001, following on the heels of another nitric oxide-measuring satellite known as the Student Nitric Oxide Explorer (SNOE). Launched in 1998, SNOE involved more than 100 CU Boulder students, primarily undergraduates, in its design and construction. Once in orbit, SNOE was controlled by students on campus 24 hours a day for nearly six years. Geomagnetic storms have had severe impacts on Earth. A 1989 storm caused by a CME resulted in the collapse of the Hydro-Quebec's electricity transmission system, causing six million Canadians to lose power. In 1859 a solar storm called the Carrington Event produced auroras from the North Pole to Central America and disrupted telegraph communications, even sparking fires at telegraph offices that caused several deaths.

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