Wednesday, 09 December 2009 19:18
| SOHO, the SOlar Heliospheric Observatory, is a joint effort between NASA and ESA to perform helioseismology and monitor the solar atmosphere, corona and wind.
SOHO was launched on December 2, 1995, was declared fully operational in April of 1996, and completed a successful two-year primary mission in May of 1998. It then entered into its extended mission phase. After roughly two months of nominal activity; contact with SOHO was lost on June 25, 1998.
Among other causes of the accident as reported by the Complex Research Laboratory of the Massachusetts Institute of Technology in 2002: - There was an error in the spacecraft’s navigation measurements of nearly 100 km, which resulted in a much lower altitude than expected and led to the vehicle’s break-up in the atmosphere.
- The conversion factor from English to Metric units was erroneously left out of the AMD files.
- Interface Specification required that the impulse-bit calculations should be done using Metric Units.
- The software supplied by a vendor used English units.
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Wednesday, 09 December 2009 19:16
| NASA successfully launched the Mars Climate Orbiter December 11, 1998, from a Delta II 7425 launch vehicle. As the orbitor began its nine-month Jaunt to Mars, controllers at NASA’s Jet Propulsion Laboratory noticed small discrepancies between computer predictions and antenna signals indicating the spacecraft’s actual location. On September 23, 1999, the craft ended its 286-day journey to Mars and began its Mars Orbit Insertion maneuver just as the craft passed behind the planet as predicted. Flight controllers eagerly waited the estimated 21 minutes for the return signal, but it never came.
Upon further review it was noted that the spacecraft had entered the Martian atmosphere 90 km (56 miles) lower than intended. The orbitor’s actual altitude was below the survivable altitude for such a spacecraft. Consequently atmospheric stresses and friction likely destroyed the $125 million Mars Climate Orbiter.
What was the cause of this $125 million mistake? The Mars Climate Orbiter Investigation Panel found the root cause to be “failure to use metric units in the coding of a ground software file used in trajectory models.” Lockheed Martin, the prime contractor for the mission, had measured the thrust firings in pounds of force as opposed to metric force units of Newtons as NASA had requested. |
Wednesday, 09 December 2009 19:15
| One significant metric mishap happened as a result of simply not having a feel for metric units. In 1983, Air Canada flight 143 ran out of fuel in mid-flight and began dropping at more than 600 meters per minute (1,970 feet per minute) with no hope of reaching its destination in Winnipeg. An incorrect conversion factor was used in the refueling of the Boeing 767, causing the flight crew to believe the aircraft had twice as much fuel as it actually did. Amazingly no one was hurt during the emergency landing at an abandoned Air Force base. Mix-ups like that can be avoided with proper training and education. |
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