Did America Use the Metric System to Go to the Moon?

Many believe that the United States successfully landed humans on the moon using the familiar imperial units like inches, pounds, and gallons. However, the story behind the Apollo program’s measurement systems is more nuanced and complex than this popular misconception suggests.

The Role of the Metric System in Apollo

While it is often said that the imperial system was perfectly adequate for the Apollo missions, the truth is more layered. Wernher von Braun, the chief architect of the Saturn V rocket, envisioned extending the S-II stage into a space station, as depicted in the sketch shown in Wikimedia Commons. This sketch highlights the potential of the Apollo program, but it was ultimately executed using traditional imperial units.

The entire Apollo program, from its conception in the 1960s to its successful moon landings, was largely engineered using the United States Customary System (USCS). NASA, along with US industry, predominantly used these units for engineering and operations. The mission documentation, including radio transmissions, technical specifications, and launch details, consistently employed inches, pounds, and gallons. For example, the Apollo 11 mission radio transcripts discuss pressures in psi and altitudes in feet, while the rockets and spacecraft were designed to specifications of feet, inches, mils, and pounds. These American aerospace manufacturers used standard American parts, bolts, and wire, all of which were measured in USCS units.

It is essential to note that the USCS units used in America during the Apollo era were not the same as the later Imperial units developed in the United Kingdom. The Apollo Guidance Computer, for instance, had guidance calculations conducted by MIT in the metric system, which were then converted to imperial units for input, output, and display purposes.

The Shift to Metric in Modern NASA

Currently, NASA has a policy of using the metric system in its operations, but the legacy of the Apollo program remains deeply rooted in imperial units. Even today, different engineering disciplines within NASA tend to use imperial units. Propulsion, for example, is a prime example, dominated by discussions of “5-pound thrusters” and “350-psi tank pressure.” However, the transition to the metric system is gradually taking place, particularly in fields like mechanics and fluid dynamics, where terms like kpsi (ksi) are being replaced by pascals (Pa).

Electrical engineers, however, continue to primarily use the metric system, discussing factors like amps and volts. This has led to some interesting cultural differences among engineers, with the older mechanical engineers preferring ksi over pascals.

A Historical Perspective

A notable incident in 1999 highlighted the risks associated with unit systems in space exploration. NASA lost a Mars mission due to software expecting metric values, which were disrupted by receiving imperial units instead. This incident underscores the critical importance of standardization, especially when global communication and operations are involved.

While some individuals like the author prefer the metric system due to its simplicity and ease of use, the historical and practical realities of the Apollo program demonstrate the importance of using the imperial system in everyday operations. The transition to the metric system remains a gradual process, influenced by both technological advancements and historical precedents.

For more detailed information on the Apollo 11 mission, readers can explore the extensive online resources available, including the original radio transcripts and mission documentation.

Keywords: metric system, Apollo program, imperial units