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Operating Systems
The operating systems for space flight software were originally designed by industry for 16-bit computers – for example, Astres and Moses for the MA31750. Thirty-two-bit computers are now running proprietary or open source existing operating systems, such as VxWorks (used, for example, in the Standard Payload Computer (SPLC)) or RTEMS on the ERC32 and Leon. Linux also enters into the picture with its real-time versions.
RTEMS validation and tools
Saab Space AB performed a validation of the real-time operating system RTEMS. Since it is available for many different targets and includes a multitude of functionality, ranging from I/O drivers to file-systems and beyond, it was agreed to only focus on the parts that were applicable for European space community applications. This implied that only the ERC32 target and a limited sub-set of the configurable RTEMS managers had to be considered.

Subsequently, Edisoft has reached an agreement with OAR to implement an RTEMS maintenance centre (see related link) in Europe. Edisoft has complemented the validation and the toolset associated with RTEMS for the specific needs of the European space industry. Gaisler Research also provides services based around RTEMS on ERC32 and Leon.

RTEMS has already been used in several space applications, in particular FedSat (a scientific Research and Development microsatellite), the Surrey's Solid State Data Recorder (a component used in the Disaster Monitoring Constellation), ChipSat (a System-on-Chip architecture), the Electra UHF antenna of the Mars Reconnaissance Orbiter and in the Galileo GIOVE-A and Herschel-Planck satellites.
RTAI Linux in ExOS for Mars robots and in PISA for instruments
A version of RTAI Linux for Pentium 3, ExOS has been developed for a robotic application, the ExoMaDeR planetary rover prototype. As a consequence, particular attention was given to the capability of RTAI to supply a reliable hard real-time execution environment for the ExoMaDeR operations scenario. One of the focal points is the control of the motors of the rover, as they are controlled by FPGAs and need timely actuation. The work demonstrated that the prototype behaved properly and allowed a nominal robot trajectory, which was not the case with a normal Linux in overload situations.

PISA is a software framework for integrated satellite payload controllers, based on Linux. It allows the separate development of several Principal Investigator applications on Linux systems. The applications are then integrated on the flight instrument.
XLuna, a Leon-based Linux on top of RTEMS
Critical Software is developing XLuna, a real time version of Linux. It has adopted RTEMS as the underlying real-time scheduler, and runs on the Leon processor.
Last update: 23 July 2008


More information
SPLC (pdf)ExOS (pdf)Linux based sw architecture (PISA) (pdf)
Related links
RTEMS (OAR)RTEMS Maintenance Center (Edisoft)Gaisler ResearchCritical Software
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