CAPE CANAVERAL, Fla. — NASA's brand-new Ares 1-X rocket, the vehicle planned to launch astronauts spaceward after the space shuttles are retired, is poised to make its first-ever test flight Tuesday.

The experimental Ares I-X rocket is set to lift off at 8 a.m. EDT from Pad 39B here at Kennedy Space Center. NASA needs good weather in order to gather detailed data on how the $445 million booster performs during this maiden voyage. Unfortunately, weather officer Kathy Winters has predicted a grim 60 percent chance of clouds thwarting a launch attempt Tuesday.

"The weather is a little bit of a concern tomorrow," Winters said Monday.

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Ares I-X is a trial version of the Ares I rocket, planned under NASA's Constellation program to ferry astronauts to low-Earth orbit aboard an Orion spacecraft. The test rocket includes a real solid-rocket first stage, with a mock second stage and dummy Orion crew capsule on top to simulate the intended weight and size of Ares I. Ares I-X is the tallest booster in service or about to fly and stands about 327 feet high — 14 stories taller than NASA's space shuttles.

The test flight comes at an uncertain time for NASA. The agency's plans to use the Ares I rocket and Orion capsules to replace the shuttle fleet and return astronauts to the moon by 2020 are under review by President Barack Obama's administration. Last week, a report from an independent panel appointed by the White House suggested that NASA consider scrapping the Ares I rocket in lieu of commercial rockets that could be ready sooner.

Despite the uncertainty, NASA officials said they stand behind the flight test, which should be useful not just for designing Ares I but also for other future rockets.

"Much of that kind of learning will be applicable to any large-scale launch system," said Jeff Hanley, program manager for NASA's Constellation program, which encompasses Ares I and Orion.

NASA hopes to have the Ares I and Orion vehicles in service by 2015, but the White House panel said that date would likely slip to 2017.

Untried rocket

As an untried rocket, the flight does carry some risk, mission managers said.

"We're not going to guarantee this is going to work," said Steve Davis, Ares I-X deputy mission manager. "This is a flight test. We have very high confidence it's going to work but there's some areas we're testing for the first time, and that's why we're doing the test."

If the rocket were to fly sharply off-course and threatened to pose any danger to the public, an explosive mechanism onboard called the range safety system could be initiated to destroy the booster.

"[We'll] make sure that were providing safety to the public," said Ed Mango, Ares I-X launch director. "There's no chance that this vehicle is going to go anywhere where the range can't take care of anything it needs to."

Also adding to the potential hazard of the flight is the fact that the space shuttle Atlantis is currently poised atop its Launch Pad 39A, a mere 1.6 miles away. If Ares I-X were to explode, the nearby space shuttle could be in jeopardy. However, because of the trajectory planned for the rocket, as well as the high level of confidence that it will work generally as planned, NASA has estimated a slim 1-in-10,000 chance of catastrophic damage to Atlantis — a danger level the agency is willing to accept.

Gloomy skies

In fact, mission managers say their biggest fear now is the weather. When asked if any issues were keeping him up at night in advance of the flight, Ares I-X mission manager Bob Ess replied "mostly the weather."

Because this is the first launch of its kind, and a major goal is to photograph and videotape the rocket's performance, NASA requires pristine skies and clear visibility to loft the booster. Furthermore, the launch is constrained by the risk of a phenomenon called "triboelectrification," which could occur when the rocket passes through clouds and triggers static electricity that might interfere with the instruments onboard. This is not a concern with space shuttle launches, which have been proven immune to this occurrence.

Ares I-X has a four-hour launch window, from 8 a.m. to noon EDT, and it only needs about 10 minutes of clear skies within that time to launch. If the rocket cannot blast off on Tuesday, NASA can try again during the same window on Wednesday, when weather conditions are expected to improve.

NASA will begin counting down toward the planned liftoff at 1 a.m. EDT Tuesday, with a live television broadcast to begin at 5 a.m.

Ready to go

Despite the inherent uncertainty in Ares I-X's flight, mission managers said they are as confident as possible.

"We're in great shape, the vehicle's ready to go, and certainly all of us are really excited about Tuesday's launch," said NASA test director Jeff Spaulding during a Sunday briefing.

The rocket is slated to launch skyward, but stop short of reaching orbit, before falling back down to Earth. The entire mission is planned to last just over two minutes.

During that time over 700 sensors onboard will feed back meticulous measurements of the rocket's path and performance, while cameras on the ground and aboard airborne planes will take photographs to chart its trajectory.

"Our purpose is to validate the design and gain practical experience with the vehicle," Davis said. "The goal of the test is to get information, it's all about learning. The only failure on this flight is a failure to learn from it."