Tim Furniss/LONDON

NASA HAS RECEIVED the first of Rockwell's next-generation Space Shuttle main engines (SSME). The programme is aimed at improving safety and reliability on future Shuttle missions.

The SSME will now undergo testing, including a single 520s static firing at the space agency's Stennis Space Center, Mississippi. After testing, the first of seven planned Block 1 engines (being developed under a NASA-funded engine upgrade programme) will be flown alongside two standard Rockwell SSMEs on the Space Shuttle Atlantis STS71 in June.

A plan to fly the first three Block 1 engines on one launch was vetoed by the Astronaut and Space Shuttle Operations offices. Flying one Block 1 engine minimises the risk should there be a failure, leaving two standard engines with which to carry out an abort.

Should the STS71 evaluation of the first Block 1 engine be a success, three upgrade engines, which incorporate a new high-pressure oxygen-oxidiser alternate turbo-pump made by Pratt & Whitney is likely to be used to launch the STS73/Columbia in September.

The P&W turbo-pump, is designed to be flown on ten missions, before it needs to be removed or replaced, compared with the single-launch capability of the original Rockwell turbo-pump.

The SSME upgrade programme is aimed at improving safety and reliability, increasing hardware life and reducing inspections between Shuttle missions. Despite that, Royce Mitchell, Rockwell's SSME deputy manager, says that the standard engine "is the most reliable and most tested rocket engine built".

With the exception of the Challenger flight in 1986 and one engine shutdown during the launch of the STS51F in August 1985, the power plant has been successful in 65 launches.

The Block 1 upgrade also includes an improved power-head and a new heat-exchanger coil, which converts liquid oxygen (Lox) to gas, to pressurise the Lox portion of the external tank. New technologies and advanced materials not available when the engine was first built are also included in the new design.

By the time the final Block 1 engine is delivered in May 1996, work will be nearing completion of the first of a fleet of Block 2 engines on which testing will start at Stennis in January 1997.

These will include the Block 1 improvements, plus a large-throat main combustion chamber and P&W's high-pressure hydrogen-fuel alternate turbo-pump.

The new combustion chamber "...will be the most important feature of all the engine upgrades", says Mitchell. "It will provide lower operating pressures and temperatures, reducing stress on the entire operating system," possibly doubling the reliability of the SSME.

Source: Flight International