The On-board Command Language (OCL) was developed to allow more flexible on-board sequencing of space borne applications. While software in traditional on-board applications is static during the mission, OCL provides support for safe and secure updating and upgrading functions even at runtime.

The ground segment of OCL compiles the source code of so called On-Board Control Procedures (OBCPs) from a programming language similar to C into simple binary token code. This token code can be uploaded to the OCL space segment at the satellite platform or instrument where it is managed automatically by the OBCP Manager. Multiple virtual machines are used to execute different OBCPs in parallel and strictly separated from other parts of the on-board software.
There are only two methods for OBCPs to operate the actual hardware: Via a secure set of runtime library functions (RTL) or via telecommands generated from data structures automatically imported from the satellite's reference data base.

The following missions make use of OCL on instrument or platform level:

• Rosetta/OSIRIS (instrument)
• Dawn/FC (instrument)
• Venus Express/VMC (instrument)
• GOCE (platform)
• Herschel-Planck (platform)