POST2 was developed from the original POST software starting in 1995 and was the 2006 NASA Software of the Year Runner-Up. POST development began in the early 1970’s in partnership with the Martin Marietta Co. as a space shuttle simulation program. Throughout the years, many models and capabilities have been added to POST; the program has been significantly improved with additional capabilities added in the area of vehicle modeling, trajectory simulation, and targeting and optimization. Three and Six degree-of-freedom (3- and 6-DOF) versions of POST that can optimize and target ascent, entry, and orbital trajectories have been available since the early 1980’s. POST has become an industry standard trajectory simulation and optimization tool that has been transferred to hundreds of organizations in government, industry, and academia.

The ability to analyze only one vehicle within a single simulation is insufficient to properly study advanced launch vehicle concepts such as a multi-stage to orbit vehicle with flyback boosters. Traditionally POST users had to do several trajectory simulations and optimize the problem external to POST; however, POST II allows this problem to be solved within a single trajectory simulation. The problem of determining where expended stages of a launch vehicle or jettisoned portions of entry and orbital vehicles impact the attracting body while including the primary vehicle in the simulation permits faster evaluations such as is necessary to support spacecraft and launch vehicle operations.

The analysis, design, and testing of missile interceptors is more complete using POST2. Not only can the interceptor have a complex guidance and control system model, but the target can also have its own detailed model of these systems in the same simulation. The complexity of the target vehicle allows detailed testing of interceptor concepts for robustness and performance. The POST2 capability to start multiple vehicles from a single “parent” also enhances the modeling of difficult intercept problems in a single simulation; that is, multiple interceptors can track multiple targets in the same simulation.

The ability to take advantage of the best traits of both C and FORTRAN programming languages for data input, storage, access, and calculation is highly desirable. An enhanced input processor in POST2 increases code portability to other computer platforms, operating systems (e.g. Linux, OSX, and Windows), and compilers. The ability to handle N-dimensional tables also enables detailed modeling of various systems; that is, an unlimited number of independent variables in POST2 tables enables greater detail in simulation models such as atmosphere and vehicle aerodynamics (within the physical memory limitations of the platform being used).

Further capabilities were added with subsequent versions. In general, some code modification for stability and optimization (decrease runtime) was done. Also, several enhancements were made including: SNAPSHOT variables for capturing variable values at events (plus and/or minus side), useful for Monte Carlo type analyses; increased pending events to 30 from 10; increased number of engines to 30; increased to 10 reference timers; increased special variables (SPCV, SPCI, NSPC) to 300; increased gravity field support to 360×360; and Program scope (independent of vehicle data) general tables (GNV).