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Leah and Marcus were preparing a new museum panel about the Mars Climate Orbiter . At first glance , their draft looked finished . It had a launch picture , a map of Mars and a short explanation of the mission . Yet one sentence said only that “ the spacecraft confused two systems of measurement ” . Leah opened NASA's investigation report . The orbiter had launched on 11 December 1998 to study the climate of Mars and act as a communications relay . Contact ended on 23 September 1999 , when the spacecraft reached Mars but failed to enter its planned orbit . “ If we had trusted the old draft , visitors would be reading an oversimplified explanation now , ” Leah said . The spacecraft itself had not made a simple choice between two rulers . The investigation located the root cause in a file produced by ground software . The file contained thruster data in pound - force seconds , while the software interface required newton - seconds . The navigation team assumed that the data followed that requirement . Because the units did not match , small errors entered the estimated trajectory . Marcus studied the technical pages under pressure . “ If the report were easier to read , we might have checked it sooner , ” he admitted . Leah replied that difficulty was not an excuse for changing a precise finding into a catchy but inaccurate sentence . The report said that the spacecraft approached Mars on a path about 170 kilometres lower than planned . After it passed behind the planet , controllers did not receive its signal again . Investigators concluded that it was either destroyed in the atmosphere or returned to space in an orbit around the Sun . If Leah had not opened the original report , the inaccurate caption would still be on the panel . She replaced “ the spacecraft confused the units ” with a more exact description : ground software supplied data in one unit system when the navigation interface required another . The team also changed the final section . NASA's board did not treat the unit mismatch as the only lesson . It noted that project processes had failed to recognise and correct the error before it became critical . “ If our deadline were less tight , we would have compared the sources before designing the layout , ” Marcus said . This contrast mattered to them : a present working condition had affected an earlier decision . They could not change that decision , but they could change their method . They added a source box and asked another editor to check every number . If Marcus were less willing to revise , they would have printed the first version yesterday . Instead , the corrected panel was ready by the end of the afternoon . The small wording change made its way across the whole display . A diagram now separated the spacecraft from the ground software , and the timeline distinguished the planned orbit from the path described in the investigation . Leah looked at the finished panel . If they had not changed the diagram , the display would still be giving visitors the wrong impression . Accuracy had required more than fixing a number ; it had required showing where the mismatch occurred and where the checks failed .
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