NASA's Ares 1-X set for another launch attempt today

NASA's Ares 1-X rocket set for launch around 9 a.m.

NASA's Ares 1-X is slated for launch between 8:45 and 9:00 this morning, following a scrub yesterday for bad weather.

Ares 1-X is a test version of a rocket NASA is building to replace the space shuttle. It is designed as the US space program's next taxi for astronauts headed into to low-Earth orbit.

Weather remains a concern today. Yesterday's forecast called for a 40 percent chance that weather would scrub today's launch attempt. But that changed overnight, and for now, launch officials are looking at the same problem with high-altitude clouds they faced yesterday.

Overnight, thunderstorms rolled across the area, according to Jon Cowart, the mission's deputy manager.  Several bolts of lightning dropped within .6 miles of the launch pad, although nothing hit the rocket or the lightning protection system set up around the pad.

Still, the lightning strikes hit close enough to trigger procedures for checking the rocket's electronics to make sure critical systems received no damage.

The overnight rain also is likely to have affected sensors near the tip of the rocket's nose cone.  Yesterday, technicians removed the sensors' protective cover at the proper stage in the countdown. But once ground crews remove the cover (old fashioned tug-of-war style, by hauling on a parachute cord tied to the cover as the tugger stands on the rocket's service structure), there's no way to replace it if a launch is scubbed.

Essentially, engineers don't want water to collect inside the sensors. So they took a spare sensor, mounted it on the service structure to capture rain as well. Now it's in the lab, where engineers will see what affect the rain has on the sensors' performance. They can used that information to help compensate for any degradation of data the nose-cone sensors experience.

These sensors area among 700 throughout the test rocket.

A successful launch would represent an important milestone in NASA's Constellation program. Constellation is NASA's approach to replacing the space shuttles, which are set for retirement at the end of 2010.

The  plan involves building Ares 1, which would be used to launch crews into low-Earth orbit. Crews would  ride atop Ares 1 in the Orion crew capsule. NASA also would build Ares 5, aimed at launching heavy payloads into orbit or to destinations such as the moon or Mars.  And the plan also includes Altair,  a lunar lander.

The program currently is under review by the Obama administration.