Original vintage Cold War-era 1963 Pratt & Whitney Aircraft  advertisement for fuel cells for the National Aeronautics and Space Administration's (NASA) Apollo spacecraft - "House power for our moon men will come from an efficient new fuel cell developed by Pratt & Whitney Aircraft for the National Aeronautics and Space Administration's Manned Spacecraft Center.  The fuel cell will generate life-sustaining electrical power during the Apollo spacecraft's round-trip voyage to the moon."
 
Dimensions: Roughly 7.50 inches wide by 11 inches high.
 
NASA's Apollo Space Program
The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which landed the first humans on the Moon in 1969.  Apollo was conceived in 1960 during the Dwight D. Eisenhower presidency in the form of Project Mercury and executed after Project Gemini.  Apollo was later dedicated to President John F. Kennedy's national goal, "before this decade is out, of landing a man on the Moon and returning him safely to the Earth" in his address to the U.S. Congress on May 25, 1961.
 
Kennedy's goal was accomplished on the Apollo 11 mission, when astronauts Neil Armstrong and Buzz Aldrin landed their Apollo Lunar Module (LM) on July 20, 1969, and walked on the lunar surface, while Michael Collins remained in lunar orbit in the command and service module (CSM), and all three landed safely on Earth in the Pacific Ocean on July 24.  Approximately 650 million people worldwide watched this first landing on television.  Five subsequent Apollo missions also landed astronauts on the Moon, the last, Apollo 17, in December 1972.  During these six spaceflights, twelve people walked on the Moon.
 
Apollo ran from 1961 to 1972, with the first crewed flight in 1968, but encountered a major setback in 1967 when the Apollo 1 cabin fire killed the entire crew during a prelaunch test.  After the first Moon landing, sufficient flight hardware remained for nine follow-on landings with a plan for extended lunar geological and astrophysical exploration.  
 
Budget cuts forced the cancellation of three of these. Five of the remaining six missions achieved landings; but the Apollo 13 landing had to be aborted after an oxygen tank exploded enroute to the Moon, crippling the CSM.  The crew barely managed a safe return to Earth by using the Lunar Module as a "lifeboat" on the return journey.  
 
Apollo used the Saturn family of rockets as launch vehicles, which were also used for an Apollo Applications Program, which consisted of Skylab, a space station that supported three crewed missions in 1973–1974, and the Apollo–Soyuz Test Project, a joint United States-Soviet Union low Earth orbit mission in 1975.
 
Apollo set several major human spaceflight milestones – Apollo 8 was the first crewed mission to leave low Earth orbit and to orbit another celestial body, and Apollo 11 was the first crewed mission to land humans on one.
 
Overall, the Apollo program returned 842 pounds (382 kg) of lunar rocks and soil to Earth, greatly contributing to the understanding of the Moon's composition and geological history.  The program laid the foundation for NASA's subsequent human spaceflight capability and funded construction of its Johnson Space Center and Kennedy Space Center.  Apollo also spurred advances in many areas of technology incidental to rocketry and human spaceflight, including avionics, telecommunications, and computers.
 
Following the end of the Apollo program, humans would not leave low Earth orbit until the Artemis II lunar flyby in 2026, as part of the Artemis program, established as a successor to Apollo in 2017. Artemis intends to return humans to the surface of the Moon no earlier than 2028.
 
The Apollo Spacecraft
The Apollo spacecraft was composed of several parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon – the expendable (single-use) spacecraft consisted of a combined command and service module (CSM) and an Apollo Lunar Module (LM).
 
Two additional components complemented the spacecraft stack for space vehicle assembly: a spacecraft–LM adapter (SLA) designed to shield the LM from the aerodynamic stress of launch and to connect the CSM to the Saturn launch vehicle and a launch escape system (LES) to carry the crew in the command module safely away from the launch vehicle in the event of a launch emergency.
 
The command module was the control center for the Apollo spacecraft and living quarters for the three crewmen.  It contained the pressurized main crew cabin, crew couches, control and instrument panel, Primary Guidance, Navigation and Control System, communications systems, environmental control system, batteries, heat shield, reaction control system to provide attitude control, forward docking hatch, side hatch, five windows, and a parachute recovery system.  It was the only part of the Apollo/Saturn space vehicle that returned to Earth intact.
 
The service module was unpressurized and contained a main service propulsion engine and hypergolic propellant to enter and leave lunar orbit, a reaction control system to provide attitude control and translational capability, fuel cells – like the one advertised in this advert – with hydrogen and oxygen reactants, radiators to dump waste heat into space, and a high gain antenna.  The oxygen was also used for breathing, and the fuel cells produced water for drinking and environmental control.  On Apollo 15, 16 and 17 it also carried a scientific instrument package, with a mapping camera and a small sub-satellite to study the Moon.
 
Pratt & Whitney
Pratt & Whitney is an American aerospace manufacturer with global service operations, and is a subsidiary of RTX Corporation (formerly Raytheon Technologies).  Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airliners) and military aviation.
 
The company is the world's second largest commercial aircraft engine manufacturer, with a 35% market share as of 2020. In addition to aircraft engines, Pratt & Whitney manufactures gas turbine engines for industrial use, marine propulsion, and power generation, and as of at least 2017, the company reported it supported more than 11,000 customers in 180 countries around the world.