The Orion spacecraft may have had its maiden flight, but it's still waiting for the Space Launch System (SLS) booster that will send it beyond the Moon. That wait got a bit shorter on Friday as NASA test fired the RS-25 engine that will power the SLS. The first of eight hot tests, it took place at NASA's Stennis Space Center near Bay St. Louis, Mississippi.

The RS-25 engine is best known for being the main engine for the now retired US Space Shuttle fleet. Derived from an engine originally created for the Saturn V rocket during the Apollo-era, the cryogenic RS-225 engine was notable for its robustness and recycling the design for the SLS fit in with NASA's waste-not-want-not philosophy when it came to Shuttle technology.

In this case, the RS-25 engine in the test firing is a development model of the new expendable versions of the main engines that propelled the Space Shuttle into orbit. Though the design is very similar to the Shuttle engines, the latest RS-25s are made to be cheaper one-use power plants. When completed, the SLS will use four of the new engines.

According to NASA, the January 9 firing lasted 500 seconds and was intended to provide data for inlet pressure conditions and the performance of the new version of the engine's controller unit. The latter is the computer that controls the engine through a system of valves. Its job is to carry out flight commands while returning telemetry about engine performance. In addition, it monitors and regulates the engine. For the latest version of the RS-25, the engine controller unit contains updated software and hardware to match the SLS's new avionics.

"We’ve made modifications to the RS-25 to meet SLS specifications and will analyze and test a variety of conditions during the hot fire series," says Steve Wofford, manager of the SLS Liquid Engines Office at NASA's Marshall Space Flight Center. "The engines for SLS will encounter colder liquid oxygen temperatures than Shuttle; greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration; and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles."

NASA says that further engine tests are on hold while the high pressure industrial water system on the test stand is being upgraded. When the firings resume in April, the space agency will complete eight tests with the current development engine for a total run time of 3,500 seconds. A second engine will then undergo another ten test firings for a total of 4,500 seconds.

The SLS is scheduled to fly in 2018.

The video below shows Friday's test.

Source: NASA

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