Original Date: 04/20/1998
Revision Date: 01/18/2007
Best Practice : National Polar-orbiting Operational Environmental Satellite System Data to Product Simulation
In the past, ITT Aerospace/Communications Division (A/CD) built weather satellite sensors to hardware specifications, while the government designed the software algorithms. Modeling was specifically tailored for various hardware requirements (e.g., radiometry, optics, structural). However, radical change in customer requirements for the National Polar-orbiting Operational Environmental Satellite System (NPOESS) required ITT Aerospace/ Communications Division to develop new design analysis techniques. For this next-generation satellite, only the results expected from the system via 28 environmental data records (EDRs) were specified. EDRs are the useable products (e.g., images, temperature, cloud cover, moisture profiles) which are translated from raw sensor data by satellite hardware and software algorithms. ITT A/CD had to devise a new system design simulator which was capable of simulating many iterations of a complex hardware/software system.
Although the requirements of the NPOESS sensor are derived via physics to compute the EDRs parameter of interest, the system (consisting of the algorithmic software and the sensor) must meet the system EDRs requirements. Performance against each EDR parameter must be evaluated for all EDRs. To verify the NPOESS performance against the 28 EDRs product specifications, a very flexible simulation tool was needed to simulate the input data, the sensors, and each of the EDR algorithmic software elements. Extensive analysis of the simulation results to derive the performance levels was also required. ITT A/CD, along with Nichols Research Corporation, developed the FlexSim simulator for this purpose.
FlexSim is based on object oriented programming principles using C++, and provides a very flexible, modular framework for simulation. Other contractors on the NPOESS program contribute system components and provide subsystem simulation models to ITT A/CD which must be integrated into the system simulation. FlexSim provides this flexibility, allowing models built from many software languages to be integrated and various computer hosts including PCs to be used. Another challenging aspect of the NPOESS development is the input data for simulation. Since the NPOESS has no existing source from which to receive actual input data, ITT A/CD must either derive data from sources with similar information or create data from scratch. Extreme care must be taken to account for errors which may be introduced in the data due to the derivations. In addition, the huge size (gigabyte range) of the input databases is a complicating factor.
By using FlexSim and its modular simulation approach, ITT A/CD can accommodate the developmental nature of the NPOESS design, allowing the rapid assembly of a simulation from modules. The NPOESS level performance can also be verified by this approach. Cost and performance tradeoff studies will enable ITT A/CD to choose the optimum conceptual approach. This tool is being applied to new and old programs, giving customers new information about their designs.
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