Mars Climate Orbiter

In September of 1999, after almost 10 months of travel to Mars, the Mars Climate Orbiter burned and broke into pieces. On a day when NASA engineers were expecting to celebrate, the ground reality turned out to be completely different, all because someone failed to use the right units, i.e., the metric units! The Scientific American Space Lab made a brief but interesting video on this very topic. The Mars Climate Orbiter, built at a cost of $125 million, was a 638-kilogram robotic space probe launched by NASA on December 11, 1998, to study the Martian climate, Martian atmosphere, and surface changes. In addition, its function was to act as the communications relay in the Mars Surveyor ’98 program for the Mars Polar Lander. The navigation team at the Jet Propulsion Laboratory (JPL) used the metric system of millimeters and meters in its calculations, while Lockheed Martin Astronautics in Denver, Colorado, which designed and built the spacecraft, provided crucial acceleration data in the English system of inches, feet, and pounds. JPL engineers did not take into consideration that the units had been converted, i.e., the acceleration readings measured in English units of pound-seconds^2 for a metric measure of force called newton-seconds^2. In a sense, the spacecraft was lost in translation. Figure 1: Artist’s conception of the Mars Climate Orbiter. Source: NASA/JPL/Corby Waste – Wikimedia Commons Before venturing further into what happened on that dreaded day, let’s try to understand the different units of measurement and how they came into use in various regions across the globe. In the past, various regions of the world followed the measurement systems and units that were most convenient for them. For example, in one part of the world, the cycle of the sun was assumed to be a measure of time, whereas elsewhere, it was the lunar cycles that were used to define time. Additionally, the lack of communication tools prevented scholars from communicating, discussing, and comparing ideas with scholars across the globe. Thus, over the course of centuries, different units and measuring standards have evolved independently. As the world has grown closer, the need for a single unified system of units has emerged. Credit to several developments in the metric system can be dated back to the French revolution when it was first envisioned. Subsequently, two platinum standards were created representing the meter and the kilogram in the Archives de la République in Paris. This can be considered the first step the development of the present International System of Units. Following the French revolution, Johann Carl Fredrich Gauss, a German mathematician, strongly promoted the use of this metric system. Alongside meters and kilograms, he added the “seconds” defined in astronomy, as a coherent system of units for the physical sciences. James Clerk Maxwell and Sir Joseph John Thomson, through the British Association for the Advancement of Science (BAAS), carried forward Gauss’ initiative to formulate the requirement for a coherent system of units with base units and derived units. The CGS system, a three-dimensional coherent unit system based on the three units—centimeter, gram and second—using prefixes ranging from micro to mega to express decimal sub-multiples and multiples, emerged because of their efforts. In 1889, the first General Conference on Weights and Measures (CGPM) sanctioned the international prototypes for the meter and the kilogram. Together with the astronomical second as the unit of time, these units constituted a three-dimensional mechanical unit system, just like the CGS system, but with the base units as meter, kilogram and second. It was Giovanni Giorgi, an Italian physicist and electrical engineer, who proved that it is possible to combine the mechanical units of this meter–kilogram–second system with the practical electric units to form a single coherent four-dimensional system by adding to the three base units, a fourt