The MCO was lost because of a mix-up in the units used to calculate the force needed to correct its trajectory. Ground-based computers generated the force correction file. On September 29, 1999, it was discovered that the forces reported by the ground-based computer for use in MCO navigation software were low by a factor of 4.45. The erroneous trajectory brought the MCO 56 km above the surface of Mars; the correct trajectory would have brought the MCO approximately 250 km above the surface. At 250 km, the MCO would have successfully entered the desired elliptic orbit. The data contained in the force correction file were delivered in lb-sec instead of the required SI units of newton-sec for the MCO navigation software. The newton is the SI unit of force and is described in Appendix B. The British Engineering (gravitational) system uses a pound (lb) as a unit of force and ft/s² as a unit of acceleration. In turn, the pound is defined as the pull of Earth on a unit of mass at a location where the acceleration caused by gravity is 32.174 ft/s². The unit of mass in this case is the slug, which is 14.59 kg. Thus,

 

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BE unit of force = 1 pound = (slug)(ft/s²) Use this information to confirm that BE unit of force = 4.45X SI unit of force 1 pound 4.45 newton =