The Aestus storable propellant engine currently powers the second stage of the Ariane 5 (pictured at right - DASA photo).  As part of the Ariane 5 performance improvement program, DaimlerChrysler, who manufactures the Aestus engine, has teamed with Boeing Rocketdyne to develop the Aestus II.  The Aestus II engine will be a part of the Perfo 2000 program which will feature a redesigned and upgraded Ariane 5 second stage.  The prime modification to the Aestus engine will be the elimination of the pressure feed propulsion system in favor of an integrated turbopump (gas generator) powerpack derived from the Rocketdyne XLR-132 engine.  The Aestus II engine will also feature a larger area ratio nozzle.  The combined modifications significantly increase the thrust and Isp of the Ariane 5 second stage.

Boeing Rocketdyne is offering their own version of the Aestus II engine, the RS-72.  The RS-72 will use an upgraded powerpack (870 psia versus 725 psia) and a larger area ratio nozzle to further increase thrust and Isp over the Aestus II.  Boeing is marketing the engine commercially but has no customers as of May 1999.