Has someone at NASA forgotten how to count? It would seem that way at first glance but the numbering system for all Shuttles (called Space Transportation System) actually makes a lot of sense.

Since the beginning of the shuttle program in 1981, shuttle missions have been ordered as they were formulated, up to five years before the launch date.

But when mission schedules are created, the launch dates almost inevitably lose their correspondence to the STS number. All sorts of factors are responsible for delays including late equipment, bad weather, etc.

So you end up with situations like these: STS-100 is actually the 103rd shuttle mission, while the hundredth shuttle mission, scheduled to be launched four months earlier, will be designated STS-97.

STS-93 is actually the 95th shuttle flight. While a year's worth of delays didn't help things, STS-93's designation was already out of order when it was scheduled.

NASA says it's not out of line to number the missions out of order. It would cost too much to go back and change the paperwork to ensure that each flight designation matches its launch order, said spokesman James Hartsfield.

And an attempt to change the STS system in the mid-1980s failed miserably, when a code that incorporated mission number, launch pad number, and the order of the launch during the fiscal year got just too confusing.

Looks like we're stuck to figuring out the order on our own. So if STS-92 comes after STS-101, then oh, you get the idea.