In 1993-94 a feasibility study for AUSTRON, a neutron spallation source, was made. At that time the machine was a synchrotron cycling at 50 Hz and delivering an average beam power of 410 kW at 1.6 GeV. In 1998, the Austrian Government decided to contribute one third of the total cost of the facility and invited international partners to participate. In 1999, a more ambitious upgrading of the original concept was proposed aiming at 0.5 MW, pulsed at either 50 Hz or 10 Hz. The slower repetition rate is achieved by the addition of a storage ring holding four consecutive (single bunch) pulses from the 50 Hz synchrotron until a fifth pulse is accelerated and transferred to the target with the four stored ones, hereby increasing the intensity per pulse by a factor 5. The resulting 5-bunch pulse duration is 1 µs. The choice of the geometry is discussed, and the lattice design for the storage ring and the transfer line from the synchrotron presented. Also addressed are the critical longitudinal aspects resulting from the mandatory use of harmonic number one
