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The sign accompanying the RL-10. It reads

Pratt & Whitney RL-10 Rocket Engine

Develops 15,000 lbs. of thrust.

Two RL-10 engines power the Centaur upper stage vehicle. Centaur was the first operational rocket to use high energy cryogenic propellant:

• Liquid oxygen: -297°F (-183°C)
• Liquid hydrogen: -423°F (-253°C)

Glenn pioneered in the research of these propellants in the 1950s.

Liquid hydrogen and liquid oxygen are used on the Space Shuttle, Atlas-Centaur, and Titan-Centaur.