Fall 2011 ASN Seminar

The fall semester Astrodynamics and Satellite Navigation Seminar will provide speakers (local and visitors) on topics of interest in GNSS and astrodynamics. Anyone is welcome to attend the seminars.

Logistics

Coordinators:
- Scott Palo
Office: ECOT 617
Phone: (303) 492-4289
scott.palo@colorado.edu

- Erin Griggs
erin.griggs@colorado.edu

- Marcin Pilinski
marcin.pilinski@colorado.edu

Wednesdays 3-3:50 PM, normally in ECCR 110

Schedule

August 24, 2011 : No seminar
August 26, 2011 (Friday): Dr. Grace Xingxin Gao, Stanford, Towards Navigation Based on 120 Satellites
August 31, 2011 : Marcin Pilinski, CU, Dynamic Gas-Surface Interaction Modeling for Satellite Aerodynamic Computations
September 7, 2011 : Laura Stiles, CU, Electrostatic Inflation of Membrane Space Structures
September 14, 2011: Christine Hartzell, Electrostatic Dust Motion on Airless Bodies
September 23, 2011(NO SEMINAR THIS WEEK):
September 28, 2011 : Logan Scott, Making the GNSS Environment Hostile to Jammers and Spoofers
October 5, 2011: Dr. Shyam Bhaskaran (JPL), Navigation of the EPOXI Spacecraft to Comet Hartley 2
October 12, 2011 : Kyle Kemble, CU,The Drag and Atmospheric Neutral Density Explorer (DANDE)
October 19, 2011 : Dr. Delores Knipp, Satellites in Low Earth Orbit: What a Drag
October 26, 2011 : TBD, TBD
November 2, 2011 : TBD, TBD
November 11, 2011 (NOTE FRIDAY SEMINAR) : Ashley Moore, Discrete Mechanics and Optimal Control for Space Trajectory Design
November 16, 2011 (NOTE LOCATION: DLC COLLABORATORY) : David Vallado, CSSI/AGI A Critical Assesment of Satellite Drag and Atmospheric Density Modeling
November 23, 2011: THANKSGIVING BREAK, NO SEMINAR
November 30, 2011 : Dr. Demoz Gebre, Integration of Low Cost Inertial Sensors and Vision-Based Navigation Systems
December 7, 2011 : Fabien Gachet, CU, Orbit Estimation for GNSS Space-Based Augmentation Satellites
December 14, 2011 : Dr. Zoltan Sternovsky, CU, Lunar Dust EXperiment (LDEX)

Click on the dates or scroll down for Abstracts and Bios



August 26, 2011 : Dr. Grace Xingxin Gao

  • Title: Towards Navigation Based on 120 Satellites
  • Abstract: Global Navigation Satellite Systems (GNSS) are entering a new era. The US GPS and Russian Glonass constellations are being joined by the European Galileo and Chinese Compass systems. If all of these new systems are implemented, we will have 120 satellites and over 300 signals in space for global navigation by 2030. Thus far, two test satellites of the Galileo system and one medium-earth-orbit satellite from the Compass system have been launched. Unfortunately, when the new satellites were put into orbit, their signal specifications were unpublished. In this talk, I will present my approach of decoding the spread spectrum codes and deriving the underlying code generators for the open civil signals based on observations alone. My decoding work has built a foundation for research on multi-constellation interoperability and redundancy. I will then answer the question, how many satellites are too many. If time allows, I will also present my recent work on mitigating positioning errors, such as pulsed interference from existing radio systems. I will show with our flight test data that my time-frequency hybrid blanking algorithm outperforms existing methods.
  • Bio: Grace Xingxin Gao is a research associate in the Department of Aeronautics and Astronautics at Stanford University. She received her B.S. degree in Mechanical Engineering in 2001 and her M.S. degree in Electrical Engineering in 2003, both at Tsinghua University, China. She obtained her Ph.D. degree in Electrical Engineering at Stanford University in 2008. She currently leads 3 projects, Arctic Navigation, Multi-constellation Global Navigation Satellite System (GNSS), and GNSS monitoring, all sponsored by Federal Aviation Administration. She has won a number of awards, including RTCA William E. Jackson Award, Institute of Navigation Early Achievement Award, and 50 GNSS Leaders to Watch by GPS World Magazine.




August 31, 2011 : Marcin Pilinski

  • Title: Dynamic Gas-Surface Interaction Modeling for Satellite Aerodynamic Computations
  • Abstract: Drag coefficients are a large source of uncertainty when predicting the aerodynamic forces on orbiting satellites. Errors in aerodynamic coefficients can reach 5-30% depending on the altitude of the satellite. The focus of the presented research is to improve the fidelity of drag coefficient modeling through the investigation of gas-surface interactions (GSI) in low earth orbit. The resulting drag coefficient model is based on oxygen adsorption because it has been shown that atomic oxygen adsorbs to satellite surface and that such contamination can drastically change the nature of GSI. Fitted drag coefficients for 68 objects were provided by Air Force Space Command Drag Analysis Office and analyzed using analytical and numerical aerodynamic models. Gas-surface parameters are estimated by comparing the model results to the observed coefficients. The results indicate that a predictive relationship between aerodynamic coefficients and atomic oxygen partial-pressure can be obtained with gas-surface models incorporating Langmuir adsorption. The implications of dynamic changes in aerodynamics on the determination of Geophysical parameters such as Thermospheric density and winds will also be discussed.
  • Bio: Marcin Pilinski's research focus is aerodynamic drag and gas-surface interactions (GSI) in the free-stream and transition regimes. This work includes the computation of specific drag coefficient values for aeronomic spacecraft such as CHAMP as well as the evaluation and development of general GSI models appropriate for flight through the earth's thermosphere. Prior to this work, Marcin spent two years working at the Colorado Space Grant Consortium as a program manager for the development and testing of a 50 kg space-weather research satellite (winner of the NanoSat 5 competition). He also helped design and build an in-situ sensor for determining Thermospheric winds during this time. Marcin received his bachelor degrees in Engineering and Physics from The University of Texas in Austin as well as a Master of Science in Aerospace Engineering Sciences from the University of Colorado.




September 7, 2011 : Laura Stiles

  • Title: Electrostatic Inflation of Member Space Structures
  • Abstract: Lightweight, gossamer spacecraft provide an alternative to the traditional mechanical systems which are typically more expensive, massive, and complex. In this talk, a novel concept for deployment of these membrane structures using electrostatic charge is explored. A structure is given an absolute electrostatic charge through active charge emission, leading to repulsive electrostatic forces which inflate the loose membranes into a semi-rigid structure. Challenges to the implementation of this concept include the plasma Debye shielding, orbital perturbations, complex structural dynamics, and the time varying space plasma environment. Past work in addressing these challenges is discussed and future experiments and simulations are described. Successful terrestrial laboratory experiments of electrostatically inflating simple prototype gossamer structures will be described through video.
  • Bio: Laura Stiles is a 4th year graduate student in Dr. Hanspeter Schaub's research group. Her research has focused on exploring the use of electrostatic charge for deploying membrane space structures. The research addresses a broad range of topics, such as orbital mechanics, structural dynamics, electrostatics and plasma physics. Laura received her B.S. in Engineering Physics at the University of Kansas.




September 14, 2011 : Christine Hartzell

  • Title: Electrostatic Dust Motion on Airless Bodies
  • Abstract: In addition to aiding our understanding of the evolution of airless bodies, understanding electrostatically-dominated dust particle motion on the Moon and asteroids has implications for future exploration missions. The electrostatically-dominated motion of small dust particles on airless bodies has been hypothesized since the Surveyor observations of Lunar Horizon Glow. Additional evidence came from the Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment and NEAR\u2019s observations of dust ponds on the asteroid Eros. Whether or not electrostatic forces are strong enough to launch dust particles off the surface of the Moon and asteroids continues to be debated. We will present analysis showing the magnitude of the electric field that is required to launch dust particles when the cohesion of the particles is considered. It can be seen that, unless large charge inhomogeneities exist, the electric field required for launching is much larger than expected to be present in situ. Additionally, it is unknown if dust levitation, which has been observed in numerical simulations, can occur in situ. We have studied dust particle levitation for three models of the plasma sheath. By analyzing the linearized system, we gain insight into the behavior of levitating particles and constrain the initial conditions that lead to dust particle levitation. By studying dust motion, we can understand the evolution of these bodies and aid in the design of future sample collection devices, dust mitigation techniques and surface operations.
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    September 23, 2011 NO SEMINAR

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    September 28, 2011 : Logan Scott

    • Title: Making the GNSS Environment Hostile to Jammers & Spoofers
    • Abstract: Growing dependence on GPS and the widespread availability of inexpensive jammers has prompted concern that jamming and spoofing could become a serious threat to civil GPS uses. Most civil GPS receivers do not maintain even the most basic situational awareness regarding interference. Deeply embedded GPS receivers present a particular problem since they may report incorrect position and time to dependent systems when interference is present. This seminar focuses on simple steps that receivers can take to become situationally aware and a proposed receiver certification program.
    • Bio: Logan Scott is a consultant specializing in radio frequency signal processing and waveform design for communications, navigation, radar, and emitter location. He has more than 30 years of GPS systems engineering experience. He has developed gain and frequency plans, non-uniform analog/digital conversion techniques, fast acquisition architectures, baseband signal processing algorithms and adaptive array approaches. He is currently active in location based encryption and authentication, high performance / low bias adaptive array developments, and RFID systems for medical applications. He holds 31 US patents.




    October 5, 2011: Dr. Shyam Bhaskaran

    • Title: Navigation of the EPOXI Spacecraft to Comet Hartley 2
    • Abstract: On November 4, 2010, the EPOXI spacecraft flew by the comet Hartley 2, marking the fourth time that a NASA spacecraft successfully captured high resolution cometary nucleus. This is the extended-mission of the Deep Impact mission, which delivered an impactor on comet Tempel-1 on July 4, 2005. This talk presents an overview of the design of the trajectory which accomplished the science objectives, the challenges of determining the spacecraft and comet orbit, and the maneuver strategy to achieve the desired targeting conditions.
    • Bio: Dr. Shyam Bhaskaran has been at JPL since 1992. During this time, he has worked on numerous missions in various roles, including radiometric and optical navigation specialist, and as the Navigation Team Lead. He is one of the principal architects of the Deep Space 1 Autonomous Navigation System; this system was also used successfully on the Stardust and Deep Impact missions and their follow-ons, NExT and EPOXI. Currently, he serves as the Supervisor for the Outer Planet Navigation Group, overseeing a team of specialists navigating missions such as Cassini, Juno, and Dawn. Dr. Bhaskaran has a B.S. (in 1985) and M.S. (in 1987) from the University of Texas at Austin, and a Ph.D. from the University of Colorado in 1991. He is the recipient of several NASA Group Achievement awards, and two NASA Exceptional Achievement Medals.




    October 12, 2011 : Kyle Kemble

    • Title: Drag & Atmospheric Neutral Density Explorer (DANDE)
    • Abstract: The DANDE spacecraft is a student built spacecraft, winner of the 5th Iteration of the Air Force Research Laboratories University NanoSatellite Competition. Beginning in January 2007 the first two years of competition were with 10 other universities from around the country participating in government and industry level reviews, culminating in a final down select of one spacecraft to move on in January 2009. With this win AFRL advocates for a launch of DANDE through the Scientific Experiments Review Board (SERB) process on the premise of utility to the military for protection of their space born assets. DANDE is unique in the fact that it is a purpose built space weather satellite measuring sub-\u03bcg accelerations as well as numerical density of the thermosphere. These two measurements coupled with its near spherical structure allow for either a priori knowledge on the ground or direct in-situ measurements of the full drag equation. This scientific data will ultimately be used for validating existing density models at higher inclinations and drive the overall error associated with predicting density variations down. DANDE is currently manifested for CRS-1 on a SpaceX Falcon 9 with an official launch date of February 2012.
    • Bio: Kyle Kemble is a first year graduate student in the Aerospace Engineering Sciences department, he received a B.S. in Aerospace Engineering Sciences from CU-Boulder. His work on DANDE began in 2008 working on the fabrication methodology for the solar panels of the spacecraft. After the competition win he became the integration and testing lead overseeing major system level tests of the mass properties and thermal vacuum of the separation system. Now as the program manager the satellite is in the final stages of test and integration for delivery to AFRL for environmental testing and launch.




    October 19, 2011 : Dr. Delores Knipp

    • Title: Satellites in Low Earth Orbit: What a Drag
    • Abstract: There are two fundamental aspects of satellite drag: the determination of atmospheric density, and the interaction of the satellite surface with the atmosphere. A previous seminar by Marcin Pilinski addressed the latter. In this presentation I will review some general aspects of the atmospheric density problem identified in the 2008 AIAA study entitled "A Critical Assessment of Satellite Drag and Atmospheric Density Modeling" and in CU "Neutral Atmospheric Density Interdisciplinary Research" effort supporting the US Air Force. During the latter part of the presentation I will focus on very recent results derived from neutral density and energy deposition measurements made by the CHAMP and DMSP satellites, respectively. These data, along with advanced models, provide new insight into regions of strong local heating and localized density anomalies.
    • Bio: Dr. Knipp earned a Ph D. in Atmospheric Science from the University of California, Los Angeles in 1989. Since then she has been on faculty at the US Air Force Academy (Physics Department) and at the University of Colorado (CU), Boulder (Aerospace Engineering Sciences Department). Her research focuses on space weather and its effects on technologies in space and on the ground. She is currently working on a project to improve the understanding of the satellite drag environment. From 2005-2006, she served on the national panel performing a decadal assessment of the National Space Weather Program run by the Office of the Federal Coordinator for Meteorology. In 2009, she was selected as a National Research Council Senior Associate and assigned to the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center. During that six-month tenure, she worked with numerous researchers to characterize space weather effects on satellite orbits. In addition to her faculty position at CU, she a senior research associate with the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, CO. Dr Knipp teaches ASEN 5335, Aerospace Environments. She is developing a space weather short course for the American Meteorological Society.




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    November 2, 2011 : TBD

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    November 9, 2011 : Ashley Moore

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    November 16, 2011: David Vallado (NOTE LOCATION CHANGE: DLC COLLABORATORY)

    • Title: A Critical Assesment of Satellite Drag and Atmospheric Density Modeling
    • Abstract: This talk examines diverse approaches to representing gasdynamic drag effects on Low Earth Orbit (LEO) satellites. Although the total drag force on a satellite can be measured, the physics of gasdynamic resistance, dynamics of the orbiting body, and characteristics of the atmosphere are inextricably combined. Investigators must hypothesize physical relationships among the drag force, body shape, size, and orientation, the distribution of density, and the predictive assessment of density. Drag coefficients determined under one set of hypotheses are often employed improperly in orbital assessments that use a different set of hypotheses. The goal is to consolidate the existing information, establish a framework for future research, and expose practical issues.
    • Bio: Lt Col (Ret) David A. Vallado is currently working as a Senior Research Astrodynamicist with Analytical Graphics Inc. in the Center for Space Standards and Innovation. He is also the author of the advanced astrodynamics textbook, Fundamentals of Astrodynamics and Applications (3rd edition, Microcosm, 2007). He is a Fellow in the American Astronautical Society (2006), and recognized in Who's Who (several) and as a 1998 Outstanding Young Men of America.




    November 30, 2011 : Dr. Demoz Gebre

    • Title: Integration of Low Cost Inertial Sensors and Vision-Based Navigation Systems
    • Abstract: In this presentation we examine the performance of algorithms for integrating low cost Inertial Navigation Systems (INS) with Vision-based Navigation (VISNAV) systems. Two Extended Kalman Filtering (EKF) approaches called loose and tight integration are compared. The tight INS-VISNAV integration approach fuses INS information with camera generated pixel measurements and uses non-linear time and measurement update equations. The loose integration approach fuses INS information with the position and attitude solution generated using the camera pixel measurements. The loose integration uses a non-linear time update equation but linear measurement equation. The results show that although tight integration yields a more accurate navigation solution, it has a tendency to diverge under certain conditions. It shown that the conditions which lead to divergence are related to: (1) Unfavorable relative geometry between the camera and feature points used to construct the VISANV solution and (2) Large errors in the position and attitude solution about which the tight integration measurement equations are linearized. This latter condition can occur when VISNAV updates are infrequent or spaced far apart in time. On the other hand, loose integration shows better stability and robustness in the unfavorable geometry conditions which lead to tight integration divergence. Furthermore, since the loose measurement update equations are linear, it is insensitive to the infrequent or widely spaced measurement updates.
    • Bio: Demoz Gebre-Egziabher is an associate professor of Aerospace Engineering and Mechanics at the University of Minnesota, Twin Cities Campus. His research focuses on the design of algorithms and hardware for the navigation and guidance of aircraft, small satellites and ground vehicles. He was the secretary of the Satellite Division of the Institute of Navigation (ION) from 2008 - 2010 and an associate editor (navigation) for the IEEE Transactions on Aerospace and Electronic Systems. Prior to joining the faculty at the University of Minnesota he was a commissioned naval officer and served as a System Engineer at the Naval Sea Systems Command (NAVSEA) Division of Naval Reactors in Washington D.C from 1990 - 1996. He holds a Bachelor of Science degree in Aerospace Engineering from the University of Arizona, a Master of Science degree in Mechanical Engineering from George Washington University and a Ph.D. in Aeronautics and Astronautics from Stanford University.




    December 7, 2011 : Fabien Gachet

    • Title: Orbit Estimation for GNSS Space-Based Augmentation Satellites
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    December 14, 2011 : Dr. Zoltan Sternovsky

    • Title: Lunar Dust EXperiment (LDEX)
    • Abstract: The Lunar Dust EXperiment (LDEX) is a dust detector instrument designed and built for the LADEE (Lunar Atmosphere and Dust Environment Explorer) mission. The goal of LDEX is to map the dust environment of the Moon from a ~ 50 km altitude orbit. There are two basic mechanisms that can elevate dust particles to high altitudes. The first is due to the continual micrometeoroid bombardment of the lunar surface that is generating a permanently present dust cloud around the Moon. Similar dust clouds have been detected near the Galilean moons of Jupiter, but not yet around the Moon, likely because of the insufficient sensitivity of previously flown instruments. The second possible mechanism is due to the electrostatic charging of the lunar surface that has been theorized being capable of lofting small dust particles to high altitudes. LDEX is a dust impact detector, which will measure the density and mass of dust particles. LDEX is sensitive to individual impacts by particles > 0.25 micron in radius. Smaller particles can be detected in a cumulative mode, if present in sufficient quantities. LDEX is the first dust detector instrument optimized for operation while exposed to the UV environment above the sunlit lunar surface. The engineering model (EM) has been constructed and calibrated. The flight unit is currently under construction and will be tested and calibrated at two dust accelerator facilities: one at the Max-Planck Institute in Heidelberg and one at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), University of Colorado.
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