 放大圖片
在上一期，我們閱讀過有關修正太空望遠鏡的光學誤差，不過，並非所有錯誤都可在事後改正的。「火星氣候探測者」是美國太空總署火星探測98計劃的一部分，計劃的目標是探測火星氣候的長期及周期性變化。價值3億美元的「火星氣候探測者」於1999年初發射，於同年9月中旬到達火星附近，並向地球拍回一幅遠距離火星照片(見圖)，想不到這也是探測器拍回的唯一照片。探測器上的推進器原定把探測器導入距火星地面140至150公里的軌道，可是一個地面控制軟件出錯，指令探測器上的推進器發出超量4.5倍的推動力，把探測器送入距火星表面只有57公里的高度，導致探測器在大氣中燒毀。其後經美國太空總署調查，發現出錯軟件的部分指令使用了英制而非公制單位，錯誤的存在亦顯示太空署的檢測過程出現漏洞。
An unrecoverable error
The Mars Climate Orbiter belonged to the NASA Mars Surveyor '98 program. The mission was to study the Martian climate and to search for evidence of long-term and episodic climate changes. When the spacecraft arrived at the vicinity of Mars, it was intended to enter orbit at an altitude of 140-150km above Mars. However, a navigation error caused the spacecraft to dive as low as 57km. The spacecraft was destroyed by atmospheric stresses and friction at this low altitude. The error arose because a software that was used to control the thrusters on the spacecraft was not properly tested and crossed-checked. It was using English units instead of the metric system. Only one photograph of Mars was sent back by this ill-fated spacecraft. ■甄枝強 資深天文愛好者
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放大圖片
