On April 2004, the United States National Aeronautics and Space Administration (NASA) called for scientific experiments and instruments proposals for a planned Mars Science Laboratory rover mission. Launch was proposed for September 2009. Eight proposals were selected, including instruments from Russia and Spain. Testing of components also began in late 2004, including Aerojet's monopropellant engine with the ability to throttle from 15–100 percent thrust with a fixed propellant inlet pressure.






