2008 AGI Users' Conference

AGI and CSSI subject matter experts discuss highly technical aspects of astrodynamics and AGI software technology during "Under the Hood" technical seminars. During “Solution Sessions,” the AGI product management and business development team, will detail how the technology can be employed for specialized application areas.

Astrodynamics

Access Fundamentals
Dr. Vince Coppola, AGI senior astrodynamics specialist
Visibility (access) computations are a core functional component of STK. The results of these computations are most commonly used to determine time periods for satellite contacts and remote sensing opportunities, but are also used as the building blocks for more complicated analyses. This presentation will cover the major algorithmic components of the access engine including sampling strategies, constraint evaluation, and event detection.

A Critical Assessment of Satellite Drag and Atmospheric Density Modeling
David Vallado, CSSI senior research astrodynamicist and Dr. David Finkleman, CSSI senior scientist
This paper examines diverse approaches to representing gas dynamic drag effects on Low Earth Orbit (LEO) satellites. Although the total drag force on a satellite can be measured, the physics of gas dynamic 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. Our goal is to consolidate the existing information, establish a framework for future research, and expose practical issues.

Automating Real-Time Maneuver Processing Using Multiple Models
Richard S. Hujsak, AGI ODTK lead software engineer
Maneuvering satellites pose a significant challenge for space surveillance, space safety analyses, and space situational awareness. The usual approach in the space surveillance community is a two-step process, first detecting that the maneuver has occurred and then determining the new post-maneuver orbit parameters. This implies a delay in finding the new orbit and therefore a risk in performing various missions. This presentation uses a real-time method that has been used in tracking maneuvering aircraft for many years, called Multiple Models. Multiple ODTK filters are used to process the same tracking data under different maneuver hypotheses and thus automatically adapt to unknown maneuvers. The theoretical discussion is short and the presentation focuses on results, with an emphasis on geosynchronous satellite maneuvers.

Extending Radar System Analysis Capability with User-defined Parameters
Dr. Haroon Rashid, AGI satellite communications specialist
The STK/Radar software module carries out radar system performance analysis in a dynamic environment. Extensive data is computed regarding the geometric relationships between the radar object and its targets, radar system performance analysis, and signal characteristics. Many of these data items can be selected by a user for reporting and graphing. Sometimes it is necessary to extend the analysis capability by defining new parameters and using those in the subsequent analysis. Two user plugin interfaces have been added to STK/Radar, which allow a user to receive most of the previously computed data and use it as a basis to derive new data items. The newly defined data can be reported, post-processed, constrained, or used as a figure of merit. For example, data from two orthogonal polarized channels can be combined to compute the enhanced signal to noise ratio (SNR) values. Interface details for Search/Track and SAR modes are described and examples of user plugin scripts are discussed.

The Impact of Radar RCS Polarization on Radar System Performance Analysis
Dr. Haroon Rashid, AGI satellite communications specialist
A radar system's performance is directly related to the target’s radar cross section (RCS). As a target's RCS is a characteristic function of the signal frequency and polarization, reflections from a target can be enhanced by illuminating it with dual signals with orthogonal polarizations. Modeling polarized radar signals, however, requires complex RCS data. The complex RCS pattern, where each data point is a complex scattering matrix, completely relates the interaction of the incident and the scattered polarized fields. Formats for complex scattering RCS are discussed. The analysis can be extended to radar performance under jamming. Each orthogonal channel, as impacted by polarized or unpolarized jammers, can be evaluated independently. The analysis can be carried out for monostatic or bistatic radars operating in Search/Track or SAR modes. Several of the computed parameters can be constrained and used as a figure of merit value with wide area Coverage or radar Attitude Coverage analysis.

Improved Conjunction Monitoring via Collaboration
Dr. T.S. Kelso, CSSI senior research astrodynamicist
The US Space Surveillance Network (SSN) is responsible for tracking more than 13,000 objects in Earth orbit, each of which represents a potential threat to the 900 operational satellites currently in orbit. The SSN tracks these objects using a collection of radar and optical sensors, but the sparse observation opportunities and uncooperative tracking result in large uncertainties in these satellite positions. As a result, satellite owner/operators must examine large volumes around their satellites to ensure they don't miss any potential threats. Unfortunately, that also means handling a large number of false alarms. But for each of these conjunctions, satellite owner/operators have much improved orbital information for their own satellite. Using this information can significantly reduce the number of false alarms, particularly with conjunctions between two operational satellites.

CSSI has now implemented a new SOCRATES service on CelesTrak—known as SOCRATES-GEO—that uses a variety of improved orbital data sources to provide improved conjunction monitoring for participating satellite owner/operators. Beginning with ephemerides (including planned maneuvers) provided directly by satellite owner/operators and incorporating data sources used in generating CelesTrak's supplemental TLEs, SOCRATES-GEO is able to provide this service via user-defined notification directly to affected parties. This presentation will not only outline and demonstrate the SOCRATES-GEO service, but will show the dramatic accuracy improvements possible using satellite owner/operator data.

Interplanetary Travel with STK
Dr. Matt Berry, AGI astrodynamics engineer
STK has been used to plan a variety of interplanetary missions, from the Messenger mission to Mercury to the New Horizons mission to Pluto. Interplanetary missions require precise integration of high-fidelity force models, well-defined coordinate frames, and accurate planetary ephemeris. In addition, planning the mission requires a robust trajectory design method. This presentation discusses how STK performs these functions, including the use of search algorithms in STK/Astrogator to design the trajectory.

Lunar Mission Modeling Considerations
Dr. James Woodburn, AGI technical director/chief orbital scientist
The design and operation of lunar missions requires additional modeling decisions beyond those normally involved in the Earth-based missions. The decision-making process is further complicated by the fact that the limited number of lunar missions to date have not resulted in well known data standards and data products often have significant uncertainty. In this presentation we will discuss some of the available data sets, the modeling decisions behind the data and the uncertainties associated with use of the data. We will describe some of the commonly used reference frames for lunar analyses and the transformations between those frames. Finally, we will cover details on the use of the JPL DE planetary and lunar ephemerides.

Sensor Swath Algorithms
Dr. Sergei Tanygin, AGI senior astrodynamics specialist
Sensor swath generates contours on the ground over a specified period of time. Within these contours lie areas that become visible to the sensor at some point within the specified period of time. Areas outside of these contours remain hidden from the sensor during the specified period of time. This information is crucial to the design and operation of remote sensing missions. If posed as a coverage problem, sensor swath computation can require a lot of computer memory and CPU time. In this presentation we will discuss new sensor swath algorithms aimed at reducing both memory and CPU requirements. One algorithm generates a fast analytical approximation of the extents of the sensor footprint. The other creates an accurate enveloping contour using local differential geometry of the sensor footprint. Both algorithms can be applied to a variety of sensor types and pointing geometries.

The New Attitude of the Earth: ICRF vs. J2000
Dr. Vince Coppola, AGI senior astrodynamics specialist
The IAU 2000 resolutions define a new inertial frame, ICRF, which is more consistent with improved stellar observations and general relativity than the J2000 frame that is based upon the older FK5 IAU76 theory. In fact, the orientation of J2000 changes over time with respect to ICRF. The two frames may be related to each other by comparing their orientations to the Earth Fixed frame. Along with the new inertial frame, the IAU resolutions define a new computation for the orientation of the Earth Fixed frame, one that is no longer defined using concepts like 'mean equator' and 'mean equinox'. This new algorithm is simpler to understand and can be computed much faster than the old algorithm. We will discuss the ICRF frame, the new Fixed-to-Inertial computations, and make comparisons with the J2000 frame and the FK5 IAU76 theory.

Trajectory Optimization in STK/Astrogator: Interface and Applications
Jonathan Lowe, AGI applications engineer
STK 9 features usability and functionality enhancements to the search algorithm plugin point available in STK/Astrogator. This plugin point allows the default differential corrector to be replaced with an alternative search algorithm. Integration of a constrained optimization algorithm through the plugin point allows for the solution of new types of problems, such as minimizing fuel or transfer time, while meeting various equality or inequality constraints and maintaining the existing trajectory design workflow within the STK/Astrogator mission control sequence. In this presentation, we will examine multiple plugin implementations using different search algorithms and discuss the application of these algorithms to particular types of problems. Select use cases will compare the results of optimization algorithms to the differential corrector.

Variable-Lag Smoother
James Wright, AGI spacecraft orbit determination specialist/ODTK architect
In this presentation, Jim will share a new algorithm for a forward-running sequential smoother with variable time lag—a near-real-time nonlinear multidimensional variable-lag smoother (VLS). The VLS is derived as a synthesis of the linear Kalman filter, the linear fixed-epoch Carlton and Rauch smoother in Frazer form, and extension to nonlinear algorithm. The VLS is free of the matrix inverse required for other smoothers. Initialization of the VLS has symmetry with its sequential operation in that the filter time-update is employed for VLS time-update and the fixed-epoch smoother measurement update is employed for VLS measurement update. The VLS will enable solutions of unsolved estimation problems for near-real-time (NRT) application. Examples include NRT orbit determination with global atmospheric density estimation; and NRT orbit determination of GPS NAVSTAR orbits and estimation of GPS clock parameters using GPS pseudo-range and GPS carrier-phase-as-range measurements simultaneously.

Technology

Scalable Servers and Applications using AGI Components
Kevin Ring, AGI senior software engineer
AGI's component technology has been architected with scalability in mind—which is extremely important considering the landscape of current hardware. Most desktops and laptops are multi-core and applications running on them are expected to take advantage of these resources. AGI components' code base is fundamentally thread-safe. The access engine and propagators are multi-threaded. This presentation provides an insight into the architecture and the kinds of applications that can benefit from this scalability.

User Interface (UI) and Engine Plug-ins
Sylvain Dupont, AGI lead software architect
AGI provides a variety of different ways to extend our products, often in the form of plug-ins. These extensibility mechanisms fall in different slices of the spectrum, depending on the area of the product that it provides extensibility to (e.g. user interface, engine, etc). This presentation attempts to clarify these different extensibility mechanisms by discussing their architecture and looking at examples of each.

Addressing Architectural Issues with AGI Components
Kevin Ring, AGI senior software engineer
The architecture for AGI's component technology has been influenced by a slew of requirements such as scalability, 64-bit, and support for world-readiness. AGI wants its customers to be able to build Web applications, thin clients, and service-oriented architectures using our component technology. We also have internal goals that drive us such as automated documentation generation, automated unit testing, and continuous integration. This presentation gives you a sneak peek into the architecture that enabled us to accomplish all of this.

AGI Data Model and SensorML
Frank Stoner, AGI aerospace software engineer
AGI products often perform analysis by ingesting external data and information. These analysis results are then often fed into other applications for additional analysis. Defining a data model for the kinds of data that we consume and generate helps ease integration with other applications and helps facilitate information exchange in large scale software architectures. This presentation provides insight into the work that has been done in this area and will specifically focus on SensorML—an OGC standard—and its applicability to our analysis.

Space Superiority
Travis Langster, AGI business development director, intelligence community
Discover how to use AGI software to: assess new foreign launches; detect laser illumination; improve geo-location; perform rendezvous and proximity operations; track RSOs, and assess space order of battle.

C4ISR/Battlespace Management
Victor Alvarez, AGI product manager
Discover how to use AGI software to: attain visibility into all battlespace assets via integrated displays, real-time data feeds, terrain analysis, and GIS data support.

Space Exploration
Bob Hall, AGI product manager
Discover how to use AGI software to: evaluate spacecraft characteristics; analyze and visualize sensors; design communications systems, rendezvous, or proximity operations; study launch opportunities; model flight characteristics; and calculate interplanetary trajectories.

Missile Defense
Victor Alvarez, AGI product manager
Discover how to use AGI software to: model ballistic missiles, kinetic interceptors, sensor systems, and integrated missile defense architectures and perform radar, communications, and interference analyses.

Geospatial Intelligence
Todd Smith, AGI business development, new markets
Discover how to add the component of time to geospatial information, create map objects/layers, retrieve and write GIS data to geodatabases, and predict sensor analysis from aircraft or satellites.