> http://en.wikipedia.org/wiki/Mars_Climate_Orbiter Aye: The MCO MIB has determined that the root cause for the loss of the MCO spacecraft was the failure to use metric units in the coding of a ground software file, =93Small Forces,=94 used in trajectory models. Specifically, thruster performance data in English units instead of metric units was used in the software application code titled SM_FORCES (small forces). The output from the SM_FORCES application code as required by a MSOP Project Software Interface Specification (SIS) was to be in metric units of Newtonseconds (N-s). Instead, the data was reported in English units of pound-seconds (lbf-s). The Angular Momentum Desaturation (AMD) file contained the output data from the SM_FORCES software. The SIS, which was not followed, defines both the format and units of the AMD file generated by ground-based computers. Subsequent processing of the data from AMD file by the navigation software algorithm therefore, underestimated the effect on the spacecraft trajectory by a factor of 4.45, which is the required conversion factor from force in pounds to Newtons. An erroneous trajectory was computed using this incorrect data. Image of result on trajectory here http://upload.wikimedia.org/wikipedia/commons/thumb/8/83/Mars_Clim= ate_Orbiter_-_mishap_diagram.png/800px-Mars_Climate_Orbiter_-_mishap_diagra= m.png Intended altitude normal to planet for braking was 226 km. Orbiter was able to survive stresses down to 80 km but passed within 57 km of planet, or tried to. Litho-braking is more effective again. R > On Thu, Oct 20, 2011 at 7:03 AM, RussellMc wrote: > >> >>> think we had a NASA probe go astray years back over the use of >> >>> US Customary vs CGS units in a single calculation >> >> >> >> Surely one little miscalculation couldn't be *that* bad could it ? >> >> I assume that you know the answer to that. >> Apparently affected the braking burn after interplanetary coast, as I >> recall. >> I may recall wrong. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .