# Time - has changed many times during history leading to...

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MAE 146: Astronautics TIME MODELING

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Time In Newtonian mechanics, time is independent of space Time is modeled as Euclidean 1-space. Def: Prop:  Def: A time reference frame is required to specify events and consists of: An origin (called epoch) A time unit (“unit vector”) The official SI time unit is the second as defined by the hyperfine radiation of cesium-133 atoms ( International Atomic Time or TAI ). Epochs are less standardized and chosen for the problems at end. One often used epoch in spaceflight is defined by the modified Julian calendar , which measures the the number of days passed since the beginning of Wednesday, November 17, 1858. MAE 146:  Astronautics Introduction BFV, 01/09/2009 1
Complications The actual definition of time has changed many times
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Unformatted text preview: has changed many times during history, leading to many conventions. Transformation from on set of time coordinates to another is often referred to as “calendrical computations”. Current civil time ( UTC; Coordinated Unversal Time ) differs from TAI by an integer number of leap seconds to follow the traditional astronomical time (based on the “mean Sun”): UTC = TAI on January 1, 1958. This year (2009) another leap second has been added to adjust the UTC time. GPS time is yet another time convention used by the Global Positioning System: GPS time = TAI – 19s GPS time = UTC on January 6, 1980. MAE 146: Astronautics Introduction 2 Def: Types of model Origin BFV, 01/09/2009...
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• Winter '08
• Villac
• Coordinated Universal Time, Universal Time, Leap second, Global Positioning System, atomic clock, International Atomic Time

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