Photo courtesy of NASA

The space shuttle Atlantis is on Launch Pad 39A being readied for liftoff. Oxidizers are being loaded in to the orbital maneuvering system (OMS) and reaction control system (RCS) tanks. Both the OMS and RCS are thruster systems used largely to maneuver the shuttle. The OMS engines slow the shuttle down before it enters the atmosphere for landing. Both systems use hypergolic propellants, chemicals that burn on their own when they come in contact with one another.