Engine Model: MB-45. Manufacturer Name: RS-73. Designer: Rocketdyne. Developed in: 1999. Propellants: Lox/LH2. Thrust(vac): 200.000 kN (44,960 lbf). Isp: 467 sec. Chambers: 1. Country: Japan. Status: Design 2004. MHI (Mitsubishi Japan)/Boeing joint project for an engine for Delta IV cryogenic upper stages. Expander bleed, pump-fed. Boeing’s Rocketdyne Division (USA) and Mitsubishi Heavy Industries (Japan) had announced on 14 February 2000 their agreement to jointly design and develop the MB-XX family of high-power cryogenic upper-stage engines for Boeing’s Delta-4 and Japan’s H-2A launch vehicles.