On July 22, 1962, an Atlas-Agena rocket launched from Cape Canaveral carrying the first American probe destined for Venus. The mission, known as Mariner 1, was intended to gather data about the planet. However, less than five minutes after launch, the rocket was destroyed above the Atlantic Ocean. The cause was a missing horizontal bar in a guidance equation used by the onboard computer. This small oversight, which occurred during manual transcription of data onto a punched card, led to incorrect trajectory calculations. The missing bar, which indicated a smoothed average in the data, caused the computer to interpret normal speed fluctuations as actual deviations from the planned path. As a result, the rocket made abrupt corrections and veered off course. NASA estimates that the cost of the failure was approximately 18.5 million dollars in 1962, which would be around 200 million dollars in today’s terms. The rocket, an Atlas LV-3 Agena-B, launched at 9:21 GMT from Launch Complex 12. The probe, designed by the Jet Propulsion Laboratory, weighed about 203 kilograms. During the ascent, ground radar tracked the rocket and sent radio corrections through a transponder on board. However, the transponder lost contact with the ground, forcing the onboard computer to switch to a backup equation. This equation was incorrect and lacked the smoothing bar, leading to the erroneous trajectory adjustments. The incident became a cautionary tale in engineering and mathematics. Arthur C. Clarke, a science fiction writer and futurist, famously referred to the missing bar as "the most expensive dash in history," though NASA later clarified that the error was not a dash but a mathematical overbar. The confusion between a dash and an overbar highlights the importance of precise notation in scientific calculations. Despite the failure of Mariner 1, NASA quickly learned from the mistake. Just 36 days later, on August 27, 1962, a nearly identical probe, Mariner 2, was launched on another Atlas-Agena rocket. This time, the mission succeeded. Mariner 2 reached Venus on December 14, 1962, and returned valuable data about the planet’s atmosphere and magnetic field. It transmitted information until January 3, 1963, marking the first successful flyby of another planet by a human-made probe. While Mariner 2 succeeded, the Soviet Union had previously attempted a Venus mission with Venera 1 in May 1961. However, Venera 1 failed to return any data due to a communications issue, narrowly missing the planet. The success of Mariner 2 was a significant achievement for NASA, helping to establish the United States as a leader in planetary exploration.