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Greenwich Mean Time
One of the things you will notice is that ISS EarthKAM now tells time in GMT (Greenwich Mean Time) rather than MET (Mission Elapsed Time). Read on to learn about why we chose this time format, how to compute GMT, and how to execute an ISS mission using GMT.
On past shuttle missions, ISS EarthKAM tracked time by MET. In this time
scheme, the MET is set to zero at the time of the vehicle's launch. From
the time this clock is set, time is counted forward in days, hours, minutes, and
seconds. MET is a useful method of measuring time for a vehicle, such as
the Space Shuttle, which is only in orbit for a period of days. However, MET is
an inappropriate time scheme for the ISS. The first parts of the Station
were launched several years ago, but there is no specific launch time
associated with the Station. Furthermore, the Station will remain in orbit
for many years; keeping time for many years based off a launch time is
impractical.
Greenwich Mean Time (GMT), also called Coordinated Universal Time (UTC),
provides an alternative time reference. GMT became a time standard in the
19th century for British maritime navigation. Currently, GMT is used
worldwide for navigation and scientific purposes. GMT is the time
determined at the Prime Meridian (0 longitude), which passes through the
Royal Observatory in Greenwich, England. From the Prime Meridian, the
world is divided into 24 time zones at increments of 15 degrees longitude, though
the lines often zigzag due to political boundaries. Each time zone differs
from adjacent time zones by one hour.
During a mission, we reccomend that you keep a clock set to GMT posted prominently in your SMOC. If possible, a clock which includes the numbers 13-24 (corresponding to the standard times 1pm-12midnight) should be used. Refer to the following chart to determine how your local time zone relates to GMT. Don't forget to add an hour during Daylight Savings Time!
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