Question

What does "t-minus" mean when counting down to rocket liftoff?

Answer 1

When time is represented on a graph or timeline or drawing, convention shows time increasing positive in the right direction and increasing negative (minus) to the left direction.

Explanation:

Suppose you had to make a chart or timeline to describe all the requirements to make that rocket liftoff at the exact time `T` it had to leave. The liftoff timing has to do with obtaining the correct trajectory, best weather conditions and many other concerns. There may be vey few times in a year that the timing will be opportune.

It means you are starting with an exact time the rocket has to liftoff, and you are planning all the events backwards to the present time. That is, you are timing negatively with numbers of increasing value from a future fixed time.

T-minus can be counted in seconds, minutes, hours, days, weeks, months and years ahead of a fixed liftoff time.