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The sign near the J-2 engine.

It reads

J-2 Engine

One engine of this type powered the second stage of the Saturn IB during the manned Apollo Lunar Module and Command and Service Module Earth-orbit testing of orbital/docking/reentry maneuvers, and the three Skylab crew launches into Earth orbit.

One restartable engine powered the third stage and a cluster of five engines powered the second stage of the Saturn V launch vehicle during all Apollo manned flights to the Moon. The cluster of five engines on the second stage also helped propel the Skylab orbiting laboratory into Earth orbit.

The engines on the second stage burned for about 6½ minutes, lifting the spacecraft to a height of about 108 miles and a speed of about 17,400 miles-per-hour. The third stage restartable engine burned for about 2 minutes and placed the spacecraft into Earth orbit, and later burned for about 6 minutes, placing it on its course to the Moon at a speed of about 24,000 miles-per-hour.

The J-2 burns a high-energy combination of liquid hydrogen and liquid oxygen to attain a thrust of 200,000 pounds. The engine weights 2,729 pounds.