This paper describes the architecture of ORK, an open source real-time kernel that implements the Ravenscar profile for the
GNAT compilation system on a bare ERC32 computer. The kernel has a reduced size and complexity, and has been carefully designed
in order to make it possible to build reliable software for on-board space applications. The kernel is closely integrated
with the GNAT runtime library, and supports Ada tasking in an efficient and compact way.
This work has been funded by ESA/ESTEC contract no. No.13863/99/NL/MV.