Systems Tool Kit (formerly Satellite Tool Kit), often referred to by its initials STK, is a multi-physics software application from Analytical Graphics, Inc. (an Ansys company) that enables engineers and scientists to perform complex analyses of ground, sea, air, and space platforms, and to share results in one integrated environment.

Originally created[2] to solve problems involving Earth-orbiting satellites, it is now used in the aerospace and defense communities and for many other applications.

Clients of AGI are organizations such as NASA, ESA, CNES, DLR, Boeing, JAXA, ISRO, Lockheed Martin, Northrop Grumman, Airbus, The US DoD, and Civil Air Patrol.

[3] The original version of STK ran only on Sun Microsystems computers, but as PCs became more powerful, the code was converted to run on Windows.

The addition of 3D viewing capabilities led to the adoption of the STK by military users for real-time visualization of air, land and sea forces as well as the space domain.

[4] In 2019, Dutch amateur skywatcher Marco Langbroek used STK to analyze a high-resolution photograph of an Iranian launch site accident tweeted by former US President Donald Trump.

[6][5] The STK interface is a standard GUI display with customizable toolbars and dockable maps and 3D graphic windows.

STK is a modular product, in much the same way as MATLAB and Simulink, and allows users to add modules to the baseline package to enhance specific functions.