The Centrifuge Rotor (CR) is a large life science experiment facility which will be installed in the International Space Station (ISS). It will provide artificial gravity of 2g or less by rotating up to 4 science habitats, and it will be the first such machinery to be used in space. To prevent vibration disturbance exchanges between the CR and the ISS, a soft 5 dof vibration isolation mechanism is used which cannot support the CR weight on the ground. Therefore, the CR on-orbit performance must be predicted by integrated analysis which must model all of the equipment including sensors, actuators, flexible structure, gyroscopic effects, and controllers. Here, we introduce the CR mechatronics, a verification procedure, and examples of the application of the integrated analysis which is based on the general-purpose mechanism analysis software ADAMS.
Two Rate Gyro Assemblies (RGAs) are used by the International Space Station (ISS) onboard Navigation function as a source of vehicle attitude rates. Prior to flight, it was necessary to make physical measurements of the actual achieved mounting orientation of these RGAs, relative to a fiducial reference frame embedded in the ISS truss structure. The resulting measurements were used to calculate initialization data for the flight software, and also provided a basis for a statistical statement relative to correct installation of the RGAs. The measurement process was accomplished using LASER ranging and angles data to establish inertial positions of several locations on the RGA optical cubes. A Least Squares Differential Correction (LSDC) process was used to yield an optimal estimate of the orientation of each RGA. Since the measurements set was not large, confidence intervals were used for statistical interpretation of the results.
The Department of Defense (DoD) has long depended on military support functions enabled by space reconnaissance, surveillance, and target acquisition (RSTA) assets. Future generation satellite capabilities will further push technologies in space - if the right technologies are deployed in the right numbers and with the right payloads. Modeling and simulation play major parts in developing and deploying such assets: 1) system and operational requirements determination, and 2) assessment of military utility of such assets. Each area is critical in a system’s life cycle. Requirements determination cuts across the issues of doctrine, organizations, training, materiel, leader development, personnel, and facilities (DOTMLPF). Military utility assessments are necessary to explore and quantify the military worth/benefit of space RSTA assets to operational commanders. Each of these areas requires relevant modeling/simulation tools which span the engineering to system to operational levels. Appropriate assessments of space with related air and ground RSTA assets. This paper will discuss some of the modeling and simulation requirements to address the above issues.
Space and orbiting systems impact multiple battlefield operating systems (BOS). Space support to current operations is a perfect example of how the United States fights. Satellite-aided munitions, communications, navigation and weather systems combine to achieve military objectives in a relatively short amount of time. Through representation of space capabilities within models and simulations, the military will have the ability to train and educate officers and soldiers to fight from the high ground of space or to conduct analysis and determine the requirements or utility of transformed forces empowered with advanced space-based capabilities. The Army Vice Chief of Staff acknowledged deficiencies in space modeling and simulation during the September 2001 Space Force Management Analsyis Review (FORMAL) and directed that a multi-disciplinary team be established to recommend a service-wide roadmap to address shortcomings. A Focus Area Collaborative Team (FACT), led by the U.S. Army Space & Missile Defense Command with participation across the Army, confirmed the weaknesses in scope, consistency, correctness, completeness, availability, and usability of space model and simulation (M&S) for Army applications. The FACT addressed the need to develop a roadmap to remedy Space M&S deficiencies using a highly parallelized process and schedule designed to support a recommendation during the Sep 02 meeting of the Army Model and Simulation Executive Council (AMSEC).
In this paper, Aximetric proposes a decentralized Command and Control (C2) architecture for a distributed control of a cluster of on-board health monitoring and software enabled control systems called SimBOX that will use some of the real-time infrastructure (RTI) functionality from the current military real-time simulation architecture. The uniqueness of the approach is to provide a “plug and play environment” for various system components that run at various data rates (Hz) and the ability to replicate or transfer C2 operations to various subsystems in a scalable manner. This is possible by providing a communication bus called “DistributedShared Data Bus” and a distributed computing environment used to scale the control needs by providing a self-contained computing, data logging and control function module that can be rapidly reconfigured to perform different functions. This kind of software-enabled control is very much needed to meet the needs of future aerospace command and control functions.
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into small spots at large distances from defining apertures. A classic example is the 1970s era “Star Wars” study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Based on estimates, the nonreversible terms should be small - of the order of 0.1 mm. If this is true, it is possible to design a practical electron beam directed weapon not limited by Coulomb repulsion.
Physical Sciences Inc. (PSI) is developing, with Navy SBIR Phase II funding, a hardware in the loop Global Positioning System (GPS) receiver Testbed. A computer simulation will "fly" a re-entry body (RB) along its trajectory and compute plasma properties that produce GPS signal attenuation and pseudo-range changes for each GPS satellite in view for the specified day and time. (The specified day and time determine the locations of the GPS satellites relative to the RB.) The simulation will compose digital instructions that specify GPS signal attenuation and pseudo-range change. The instructions will be sent to a GPS signal simulator via Ethernet using UDP. The GPS signal simulator generates analog RF electronic signals that are fed into a real, physical GPS receiver, thus emulating what would occur on an RB in flight. The GPS receiver navigational output will be compared to the input trajectory to determine the accuracy of the GPS receiver. Because attenuation of the GPS satellite signals will be, in general, different for each satellite, the effect of sequential loss of signal from various GPS satellites and the degradation on GPS trajectory determination will be part of the capability. In addition, when the RB goes into and returns from plasma blackout, the simulation can be continued to determine the time required for the GPS receiver to acquire and establish navigational capability.
Ball Aerospace & Technologies Corp. has an extensive history in modeling and simulation. Ball Aerospace has developed integrated system models for the Very Large Telescope (VLT) for European Southern Observatory (ESO), for the James Webb Space Telescope (JWST), for several NPOESS instruments including the Visible/Infrared/Radiometer Suite (VIIRS), the Conical Scanning Microwave Imager/Sounder (CMIS), and the Ozone Mapping Profiling Suite (OMPS), and many others. As a result, Ball Aerospace has developed a proprietary modeling and simulation tool, TRADES, that is used to analyze space-based systems. TRADES (Toolkit for Remote-Sensing Analysis, Design, Evaluation and Simulation) is a set of software tools in Matlab, designed and developed for simulating, analyzing, evaluating, and conducting design trade studies of remote sensing imagers. It supports simulations and analysis in any spectral regime, most scene sampling designs, and many sensor types. TRADES will provide a physically accurate simulation of a space-based system. This allows for trade studies to analyze the performance of different configurations, definition of subsystem specifications and error budgets for system performance, sensitivity analysis, and the optimization of instrument design to viewing. Explanations of TRADES’ major components will be presented along with examples of its use on several programs.
As the complexity of telescope systems have increased, system engineering trades related to cost and performance issues have become correspondingly more difficult. Many of the proposed space-based systems cannot be tested at the system level prior to launch and precursor technology missions are too expensive and do not fully duplicate the actual hardware. Therefore, industry is increasingly reliant upon modeling to predict end-to-end system performance from sub-system validation through laboratory testing. The increase of computational speed has enabled the development of integrated modeling tools which compliments the subsystem design process while facilitating system performance modeling. With integrated modeling, the optical design, structural dynamics, controls, disturbances, and sensor models are contained in a single environment. The challenge is to maintain computational speed and accurate computations while managing the complexity of multiple models, interfaces and hundreds of parameters. This paper discusses the issues involved with system modeling including architectural decisions, integration of subsystem models and disturbance modeling.
Dynamic ray tracing is a new tool that combines optical ray tracing and dynamic simulation codes. The implementation presented in this paper is a customization of the commercial code ADAMS. The tool features a special subroutine that was written and linked to the code, enabling it to compute and display the paths and intersection points of reflected and refracted optical rays as the optical surfaces move dynamically. Its first intended use would be for analysis and control of high-frequency jitter and lower-frequency drift. In addition to "undesired" motions or deformations, the method may also be used to simulate intentionally moving optical components such as scanners or zoom systems. The main difference in this capability and that of the existing optical design codes is that this method yields visual dynamic results. In quasi-real time, the user can watch the ray trace move and the resultant image quality metric change due to unwanted or intentional motion of the optical elements. This approach will enable the user to more quickly understand and visualize the situation and will reduce the chances of error that arise when two codes have to be used (static ray tracing and dynamic simulation) to analyze the system.
The Ozone and Mapping Profiler Suite (OMPS) is an instrument suite in the National Polar-orbiting Operation Environmental Satellite System (NPOESS). The OMPS instrument is designed to globally retrieve both total column ozone and ozone profiles. To do this, OMPS consists of three sensors, two Nadir Instruments and one Limb Instrument. Each OMPS sensor has an End-to-End Model (ETEM) developed using the Toolkit for Remote Sensing, Analysis, Design, Evaluation, and Simulation (TRADES), a Ball Aerospace proprietary set of software tools developed in Matlab. The end-to-end modeling activities, which includes a radiative transfer model, the ETEM, and retrieval algorithms, have three fundamental objectives: sensor performance validation, aid in algorithm development, and algorithm robustness validation. The end-to-end modeling activities are key to showing sensor performance meets the system level Environmental Data Record (EDR) requirements. To do this, the ETEM incorporates sensor data; including point spread functions, stray light, dispersion, bandpass, and focal plane array (FPA) noise parameters. The sensor model characteristics are first implemented with predictions and updated as component test data becomes available. To evaluate the system’s EDR performance, the input radiance derived from the radiative transfer model is entered into the ETEM, which outputs a simulated image. The retrieval algorithms process the simulated image to determine the ozone amount. The system level EDR performance is determined by comparing the retrieved ozone amount with the truth, which was entered into the forward model. Additionally, the ETEM aids the algorithm development by simulating the expected sensor and calibration data with the expected noise characteristics. Finally, the algorithm robustness can be validated against extreme conditions using the ETEM.
The United States does not have an Automated Rendezvous and Capture/Docking (AR&C) capability and is reliant on manned control for rendezvous and docking of orbiting spacecraft. This reliance on the labor intensive manned interface for control of rendezvous and docking vehicles has a significant impact on the cost of the operation of the International Space Station (ISS) and precludes the use of any U.S. expendable launch capabilities for Space Station resupply. The Marshall Space Flight Center (MSFC) has conducted pioneering research in the development of an automated rendezvous and capture (or docking) (AR&C) system for U.S. space vehicles. This AR&C system was tested extensively using hardware-in-the-loop simulations in the Flight Robotics Laboratory, and a rendezvous sensor, the Video Guidance Sensor was developed and successfully flown on the Space Shuttle on flights STS-87 and STS-95, proving the concept of a video- based sensor. Further developments in sensor technology and vehicle and target configuration have lead to continued improvements and changes in AR&C system development and simulation. A new Advanced Video Guidance Sensor (AVGS) with target will be utilized as the primary navigation sensor on the Demonstration of Autonomous Rendezvous Technologies (DART) flight experiment in 2004. Realtime closed-loop simulations will be performed to validate the improved AR&C systems prior to flight.
During the launch of a rocket under prevailing weather conditions,
commanders at Cape Canaveral Air Force station evaluate the
possibility of whether wind blown toxic emissions might reach
civilian and military personnel in the near by area. In our model,
we focused mainly on Hydrogen chloride (HCL), Nitrogen oxides
(NOx) and Nitric acid (HNO3), which are non-carcinogenic
chemicals as per United States Environmental Protection Agency
(USEPA) classification. We have used the hazard quotient model to
estimate the number of people at risk. It is based on the number
of people with exposure above a reference exposure level that is
unlikely to cause adverse health effects. The risk to the exposed
population is calculated by multiplying the individual risk and
the number in exposed population. The risk values are compared
against the acceptable risk values and GO or NO-go situation is
decided based on risk values for the Shuttle launch. The entire
model is simulated over the web and different scenarios can be
generated which allows management to choose an optimum decision.
During the launch of the Space Shuttle vehicle, the burning of
liquid hydrogen fuel with liquid oxygen at extreme high
temperatures inside the three space shuttle main engines, and the
burning of the solid propellant mixture of ammonium perchlorate
oxidizer, aluminum fuel, iron oxide catalyst, polymer binder, and
epoxy curing agent in the two solid rocket boosters result in the
formation of a large cloud of hot, buoyant toxic exhaust gases
near the ground level which subsequently rises and entrains into
ambient air until the temperature and density of the cloud reaches
an approximate equilibrium with ambient conditions. In this paper,
toxic gas dispersion for various gases are simulated over the web
for varying environmental conditions which is provided by
rawinsonde data. The model simulates chemical concentration at
ground level up to 10 miles (1 KM grids) in downrange up to an
hour after launch. The ambient concentration of the gas dispersion
and the deposition of toxic particles are used as inputs for a
human health risk assessment model. The advantage of the present
model is the accessibility and dissemination of model results to
other NASA centers over the web. The model can be remotely
operated and various scenarios can be analyzed.