Why a Four-Hour Launch Window?

One question thatcomes up a lot is why Ares I-X has a four-hour launch window. After all, unlikethe Space Shuttle, it doesn’t have to rendezvous with the Space Station, sowhat’s the challenge? Actually, there are several.

First, the Eastern Range typically allots 4-hour launch windows. Given theduration of Ares I-X (about seven minutes from liftoff until the final piecessplash down), more time is not required. As was demonstrated on the firstlaunch attempt, the rocket can be reset quickly, so four hours was consideredplenty of time to wait out weather and technical challenges.
 
Next, there are human limitations. Console operators in the Launch ControlCenter must be at their consoles at least 7 hours before the planned launch.When you add the 4-hour window this means that operators may have to be onstation for 11 hours before launch. There is also a lot of work to do afterlaunch or after a scrub.

Additionally, anyone familiar with Florida weather understands that windstypically pick up later in the day as the atmosphere heats up and interactswith evaporation from the ocean. Central Florida’s “afternoon thunderstorms”produce a terrific number of lightning strikes. High winds are a problem forany launch. Because of its experimental nature, Ares I-X has very conservativewind constraints—20 knots (nautical miles per hour—about 23 statute miles perhour) as opposed to the Space Shuttle, which can fly in winds up to 30 knots(34.5 miles per hour).

A 4-hour window, gives the teamthe ability to complete all the preparation work, wait for the rightcombination of winds, weather and clouds and then go. Following the LCCguidelines gives Ares I-X the best chance to collect the important data that weneed for next exploration steps we take.