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

First, the Eastern Range typically allots 4-hour launch windows. Given the duration of Ares I-X (about seven minutes from liftoff until the final pieces splash down), more time is not required. As was demonstrated on the first launch attempt, the rocket can be reset quickly, so four hours was considered plenty of time to wait out weather and technical challenges.
 
Next, there are human limitations. Console operators in the Launch Control Center 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 on station for 11 hours before launch. There is also a lot of work to do after launch or after a scrub.

Additionally, anyone familiar with Florida weather understands that winds typically pick up later in the day as the atmosphere heats up and interacts with evaporation from the ocean. Central Florida’s “afternoon thunderstorms” produce a terrific number of lightning strikes. High winds are a problem for any launch. Because of its experimental nature, Ares I-X has very conservative wind constraints—20 knots (nautical miles per hour—about 23 statute miles per hour) 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 team the ability to complete all the preparation work, wait for the right combination of winds, weather and clouds and then go. Following the LCC guidelines gives Ares I-X the best chance to collect the important data that we need for next exploration steps we take.

Remember that probe on the top of the rocket? It’s still being watched carefully today, and not just because of its hard-to-remove cover.
 
As we noted yesterday, the five-hole probe is a very important set of sensors for collecting aerodynamic data during the flight. It remained covered while Ares I-X was rolled out to the launch pad and just prior to launch because the avionics team did not want water, bugs, bird messes, or other debris getting on or in the sensors. Inside the five holes is a diaphragm of flexible material against which air vibrates to produce data. If water or foreign object debris (FOD) gets onto the diaphragm, there is a risk that the data from the sensors could be harder to interpret after the flight. Once the Ground Operations team removed the cover, there is no way to put it back on short of rolling the rocket back into the Vehicle Assembly Building. The I-X team knew this might happen, but now that the cover is off, what next? Just to add to the challenge, Cape Canaveral expected (and got) an inch and a half of rain on Tuesday night.
 
What NASA did was take a spare five-hole probe out to the pad, put it on the fixed service structre and gave it a similar exposure to rain as the flight hardware. The spare unit was tested before and after the rain to determine its effects on the sensors’ behavior. In this way, NASA will be able to account for any changes in sensor measurements due to water on the sensor and use that information to interpret the data after the flight. This is just one of many lessons the Ares team is learning as it continues testing on the Ares I-X rocket.

Well, the weather didn’t cooperate with us today. Winds and clouds we’re outside of our allowable limits, so we’re packing it in and we’ll try again tomorrow. Launch window opens at 8:00 EDT on Oct. 28 and continues through until noon.

Launch coverage on NASA TV begins at 5 am EDT – www.nasa.gov/ntv