STEP-TAS technical details

Reliable and easy-to-use exchange of electronic data is essential for efficient and cost-effective industrial product development processes. This is true for all disciplines involved in space product development and certainly also for (space) thermal control engineering, which comprises design, analysis and verification activities.
The exchange of space thermal analysis models within a space thermal analysis project where the partners use different analysis tools has been a long-standing problem. Many tool-to-tool converters have been created which provide a short-term advantage to the particular projects, but which also raise other issues for long-term maintenance (see also the 'Conductor options' link).
After taking all arguments into account, data exchange via open standards is the only viable approach that is reliable and affordable in the long term.

In fact, the same argument is valid for all application domains in all industrial sectors. Several industrial and academic groups involved in various European and US research projects came to the same conclusion in 1984 and started the development of the ISO "STEP" standard.
"The objective of ISO 10303 [STEP] is to provide a means of describing product data throughout the life cycle of a product that is independent from any particular computer system."

ISO 10303, informally known as "STEP", is a multi-part international standard for the computer-interpretable representation and exchange of product data. Among other things, the different parts describe how the standards (and standards layered on top of them) should be defined, as well as how building blocks for common product data items such as geometrical representations, material properties, etc. should be handled. A complete STEP Overview can be found under Setting the Standards for Industrial Data on the official ISO TC184/SC4 web site.

At a higher level there are different STEP protocols for different application domains, and although they might share some of the lower-level building blocks, they are separate protocols. Today in the aerospace industry, STEP standards are used primarily for the exchange of 3D CAD models and associated Product Data Management (PDM) information:

  • ISO 10303-203 STEP Application Protocol - Configuration Controlled 3D Designs of mechanical parts and assemblies (also known as STEP AP203)
  • ISO 10303-214 STEP Application Protocol - Core data for automotive mechanical design processes (also known as STEP AP214)

Unfortunately, none of the STEP protocols under the official ISO umbrella address the needs of the space thermal analysis community, but they do provide the foundations for a new application protocol specifically designed to meet these needs.
The objective of STEP-TAS (Thermal Analysis for Space) is to provide an open, neutral, efficient standard for the exchange, processing and long term archiving of (space) thermal analysis models and results.

The STEP-TAS standard actually consists of a protocol (a formal data model) containing four main modules:

  • NRF: Network model and Results Format
  • MGM: Meshed Geometric Model
  • SKM: Space Kinematic Model
  • SMA: Space Mission Aspects
and a runtime loadable dictionary of predefined terms (or instances in object-oriented software engineering terminology).

These four modules mean that STEP-TAS contains the building blocks for storing network model results, meshed geometrical models, orbits and mission parameters, and kinematics and pointing. STEP-TAS provides a tool-neutral format for storing data related to:

  • a spacecraft geometry represented by a bounded face model with minimum topology and material properties
  • the exchange of thermal network models
  • the capture of results data from analysis, test or operation
These three areas, and sub-divisions within them, are reflected by different levels of conformance classes.

The runtime loadable dictionary allows possible future extension of the terms needed for the standard, but in a backwards-compatible way. Loading the dictionary is fast, and so does not impede the overall model conversion time. The dictionary can also be published on the Internet so that real-time updates to the latest version are possible.
STEP-TAS converter tool architecture
STEP-TAS converter tool architecture
STEP-TAS converter tool architecture
The diagram shows also areas of responsibility for ESA and tool developers. ESA coordinates the protocol and dictionary definition, and provides the software libraries that are needed for efficient implementation of the standard. The tool developers are responsible for the implementation of reader/writer (export/import) interfaces that map tool native data structures onto STEP-TAS structures and vice-versa.

The diagram also show two neutral exchange file formats that are provided by the runtime library:

  • the ISO 10303-21 or the .stp "stepfile", an ASCII text encoding of a STEP protocol compliant dataset
  • the HDF5 file, an efficient binary portable file, in the HDF version 5 public domain format specified by the US National Center for Supercomputing Applications
The .stp file format is fully implemented and used in all TASverter releases. The HDF5 interface is experimental and still under development. The HDF5 format is very promising for very large datasets containing hundreds of MB or several GB of analysis results data.
TASverter is an in-house ESA implementation of a STEP-TAS model converter. It can read spacecraft geometrical models in various tool specific formats, convert them to internal data structures based directly on STEP-TAS entities, and can write to various other tool specific formats. TASverter has been essential for the validation of the concepts and entities described by the STEP-TAS protocol.
The development model
Incremental development scheme
Incremental development scheme
ESA has been following an incremental development scheme. STEP-TAS has now been under development since 1994, and has been revised several times to reflect the experience gained in implementing new areas of functionality for new tools.
Last update: 5 March 2007

Direct links

 •  Converter options (
 •  ISO 10303 examples (
 •  STEP-TAS NRF module (
 •  STEP-TAS MGM module (
 •  STEP-TAS SKM module (
 •  STEP-TAS SMA module (
 •  STEP-TAS Conformance Classes (
 •  TASverter (

Related links

 •  ISO TC184/SC4 (
 •  ISO (