International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / Over the last several years, the Data Systems Technology Division (DSTD) at Goddard Space Flight Center (GSFC) has developed software tools to generate simulated spacecraft data to support the development, test, and verification of prototype and production of its Very Large Scale Integration (VLSI) telemetry data systems. Recently, these data simulation tools have demonstrated their versatility and flexibility in the testing and deployment of several very high performance Level Zero Processing (LZP) systems. Because LZP involves the wide scale reordering of transmitted telemetry data, the data simulation tools were required to create a number of very large and complex simulated data sets to effectively test these high rate systems. These data sets simulated spacecraft with numerous instrument data sources downlinking out-of-sequence and errored data streams. Simulated data streams were encapsulated in Consultative Committee for Space Data Systems (CCSDS) packet and NASCOM data formats. The knowledge and expertise gained in the development of the current simulation tools has been used to develop a new generation data simulation tool, known as the Simulated Telemetry Generation (STGEN) package. STGEN is a menu driven software package running on UNIX platforms that can implement dynamic test scenarios with very fast turn around times from the data set design to the data set generation. The error options and locations in the telemetry data stream are fed via simple programs which are in turn script-driven. Scripts are used to manipulate packets, frames, and permit error insertion more easily and quickly. This paper first describes the STGEN software package and its test data design strategies. It then provides an example of STGEN 's first usage in the testing of systems to support EOS-AM spacecraft. Finally, a description of future planned improvements and uses of STGEN are provided.