International Space Station (ISS) Engineering Decision Support

NASA Ames Research Center, May 01, 2004 -- A new tool under development at NASA Ames is a digital model of the International Space Station (ISS) designed to help engineers make better decisions about the station's construction and operation.

"The goal is to provide a system dynamics simulation of the major behaviors of the station," says project lead Mark Shirley.

The tool's name -- SimStation -- was inspired by the SimCity series of games that players use to design, build and run a dynamic virtual city.

In addition to simulation, SimStation provides engineers with a 3D model of the ISS for answering questions about relationships between the station's subsystems and modules. "Like SimCity, we want SimStation to help people develop an intuitive understanding of a very complex system. In this case it's an engineering tool rather than a game."

An increasingly complex machine

The ISS is the most complex vehicle ever flown, with thousands of engineers in 16 countries contributing to the design, maintenance and assembly of its systems.

The station is the first U.S. spacecraft to be built, tested and flown in stages, in orbit. As such, tracking the changes is a huge challenge. For example, adding a new part might only slightly affect the station's power distribution but effectively outdates all the documents and models describing the station's behavior.

Add to that the fact that as the ISS is assembled, the ISS program responds to unforeseen events such as budget cuts, technology and engineering innovations and insights into how the station's systems and components work together once they're online. Meanwhile, the volume of information associated with ISS grows, and the station becomes an even more complex machine.

Managing that machine

The ISS systems engineers perform about 50 trade studies a year to determine the consequences of some proposed change in a system, a vehicle configuration or mission design. These engineers need to know how the systems' parts work together to achieve the station's behavior. For example, what components are supplying power to a particular laboratory rack, or what else will fail if a particular component fails.

"These are questions for which answers are available, but it's often time-consuming to find the answer," says Shirley. "We're trying to make answering basic questions about the vehicle more efficient. What if we moved this part there, for example? Engineers ask these sorts of questions all the time."

SimStation is tailored to the needs of the systems engineers who perform the trade studies. The tool gives them a virtual vehicle for a comprehensive view of a wide range of options for understanding how to build and maintain a safe, efficient ISS.

"Determining the functional impact with design changes is extremely difficult and requires access to many nonintegrated sources. We're trying to build a framework to put those connections into place."

The SimStation project

Building SimStation requires integrating information from a wide variety of sources, many of which use different keys and naming conventions. To do this, a novel process of joining databases was developed by heuristically matching English language fields. This technique, called Database Reconciliation, is potentially useful for integrating other kinds of databases as well.

SimStation combines functionality from several other research efforts: the Synergistic Engineering Environment project at Langley Research Center, and the Bird's Eye View project at Johnson Space Center and the Intelligent Virtual Station and Diagnostic Data Server (a tool that serves both telemetry and simulation data) projects at Ames Research Center.

In a sense, SimStation is not new. Many projects modeling various aspects of the space station exist, but these projects have mostly been disconnected. The SimStation project has commissioned the creation of several reusable software components for vehicle modeling from these projects and added several more of its own. "We're trying to establish a culture of sharing vehicle modeling components within our part of NASA, a sort of internal Open Source community." SimStation is supported by NASA's Engineering for Complex Systems Program.