POST2 increases the trajectory simulation capability of the original POST computer code and provides a state-of-the-art software tool. POST2 contains many basic models (such as atmosphere, gravity, propulsion and navigation system models) that are used to simulate a wide variety of launch, orbital, and entry missions. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.