Mission Elapsed Time

Mission Elapsed Time (MET) is set to zero at the moment of liftoff and counts forward in normal days, hours, minutes, and seconds. For example, 2/03:45:18 MET means it has been 2 days, 3 hours, 45 minutes, and 18 seconds since liftoff.

One of the reasons we use MET is to make our premission planning more independent of launch time. As an example, imagine you are taking a trip in your car. You can plan an itinerary as follows:

• 8:00am - leave home
• 8:15am - stop for gas at your favorite station
• 10:00am - stop to walk the dog
• 11:45am - arrive at your destination

But, suppose you have a window during which you will leave, for example, between 7:30am and 8:30am. You can then build an itinerary based on Elapsed Time:

• 0:00 - leave home
• 0:15 - stop for gas at your favorite station
• 2:00 - stop to walk the dog
• 3:45 - arrive at your destination

Now, if you set the clock in your car to show Elapsed Time, you will know when to stop to walk the dog without having to recalculate your schedule.

Similarly, we plan onboard events in Mission Elapsed Time to minimize the effects of the launch window, which could be several hours in length.

There are MET clocks on board; the other on-board clock is the GMT clock.

Other "clocks"

| MET | UTC | Countdown & Liftoff | Flight day | Apollo era |