Steel is rising for two towers that will compose a 215-foot-tall structural test stand for NASA's Space Launch System at NASA's Marshall Space Flight Center in Huntsville, Alabama.

The first tiers were welded into place on Aug. 31, 2015, and the towers are already visible above the tree line.

When construction is completed, hydraulic cylinders at Test Stand 4693 will push, pull and bend the liquid hydrogen tank of the SLS's massive core stage to subject the tank and hardware to the same loads and stresses they will endure during launch.

SLS, the most powerful rocket ever built, will carry astronauts in NASA's Orion spacecraft on deep space missions, including to an asteroid placed in lunar orbit and on the journey to Mars.

The new test stand is designed to accommodate future tests of different tank sizes and other equipment, in addition to the SLS core stage liquid hydrogen tank.

It is being built in Marshall's West Test Area on the foundation of the stand where the Apollo Saturn V F-1 engine was tested during the 1960s.