Japan plans in 2010 to drop-test a subscale engine that will accelerate to Mach 2 over Sweden's Esrange test area.

The Japan Aerospace Exploration Agency is developing the pre-cooled-cycle turbojet, the Small (S)-Engine, as a subscale testbed for air-breathing propulsion systems.

The S-Engine is 2.2m (7.2ft) long, 230mm (9in) wide, burns 0.06kg (0.13lb) of hydrogen per second and is ex­pected to generate 269lb of thrust (1.2kN) with an initial specific impulse of 2,100s. A full-scale production engine would be used in the first stage of a two-stage to orbit launcher.

Originally planned for 2008, the engine is designed to ignite 30s after being released. For the drop test, the S-Engine is fitted to JAXA's balloon-operated vehicle, which looks like a missile, and raised to 131,000ft.

If it is successful, JAXA says that "a subscale engine could be ground-tested in 2011 and by 2018 another subscale engine could be flight-tested, but it will require an improved combustor and [related] materials".

In October 2009 the S-Engine to be air dropped was ground-tested using liquid hydrogen as the fuel. The 2010 drop test is the fourth for the balloon-operated vehicle, although it is to be called BOV three. Vehicles one, two and four were used for microgravity experiments.

Source: Flight International