The next Space Shuttle crew can expect an even safer ride into orbit, thanks
to the completion of a new Space Shuttle Main Engine. Workers installed one
of the new engines, called the Block II configuration, on Space Shuttle
Atlantis, April 24, at NASA’s Kennedy Space Center, Fla.

Atlantis’ first flight using the new engine is targeted for no earlier than
June 14 on mission STS-104 to the International Space Station. Atlantis will
use one Block II Main Engine and two Block IIA Main Engines to complete its
full complement of three engines.

Improvements to the main engines, managed by NASA’s Marshall Space Flight
Center in Huntsville, Ala., continue to evolve to produce the safest, most
reliable and reusable space transportation system in the world.

The Block II Main Engine configuration includes a new Pratt & Whitney
high-pressure fuel turbopump.

The primary modification to the engine is elimination of welds by using a
casting process for the housing, and an integral shaft/disk with thin-wall
blades and ceramic bearings. This makes the pump stronger and should
increase the number of flights between major overhauls. Although the new
pump adds 300 pounds (135 kilograms) of weight to the Shuttle, the results
are a more reliable and safer engine because of increased pump robustness.

“With this design change, we believe we have more than doubled the
reliability of the engine,” said George Hopson, manager of the Space Shuttle
Main Engine Project at Marshall.

Previous improvements to the Space Shuttle Main Engine include the Block I
configuration, which featured an improved high-pressure liquid oxygen
turbopump, two-duct engine power head and single-coil heat exchanger. The
turbopump incorporated ball bearings of silicon nitride — a ceramic
material 30 percent harder and 40 percent lighter than steel. The Block I
engine first flew in 1995.

The Block IIA engine added a larger-throat main-combustion chamber to Block
I improvements. The new chamber lowered the engine’s operating pressures and
temperatures while increasing the engine’s operational safety margin. This
engine first flew in 1998.

Developed in the 1970s by Marshall, the Space Shuttle Main Engine is the
world’s most sophisticated reusable rocket engine. Each powerful Main Engine
is 14 feet long (4.3 meters), weighs about 7,000 pounds (3,175 kilograms)
and is 7.5 feet (2.3 meters) in diameter at the end of the nozzle.

The engines operate for about eight-and-one-half minutes during liftoff and
ascent and shut down just before the Shuttle reaches low-Earth orbit.

The engines perform at greater temperature extremes than any mechanical
system in common use today. At minus 423 degrees Fahrenheit (minus 217
degrees Celsius), the liquid hydrogen fuel is the second coldest liquid on
Earth. When it and the liquid oxygen are combusted, the temperature in the
main combustion chamber of the engine is 6,000 degrees Fahrenheit (3,316
degrees Celsius), hotter than the boiling point of iron.

Boeing Rocketdyne in Canoga Park, Calif., manufactures the Space Shuttle
Main Engine.