NASA will take a huge step this week in its efforts to build the technology, rockets and spacecraft needed to send astronauts to Mars.

Orion, the first spacecraft NASA has built to carry astronauts into deep space since the Apollo missions of the 1960s and 1970s, is set to lift off on its first test flight Thursday morning from Cape Canaveral Air Force Station. Riding on top of a United Launch Alliance Delta IV heavy rocket, the spacecraft is scheduled to launch at 7:05 a.m., though that window could extend to 9:44 a.m. if needed.

As of Wednesday morning, meteorologists have given the launch a 70% chance of "go" because of a weather pattern that could bring low clouds, showers and winds too high for a safe liftoff. The weather has been improving, however, and NASA is moving ahead with its launch plans.

The launch can be viewed at NASA's web site.

"Orion's flight test is designed to test many of the riskiest elements of leaving Earth and returning home in the spacecraft," NASA stated. "Testing these capabilities now will help ensure that Orion will be the next-generation spacecraft for missions in the 2020s that will put Mars within the reach of astronauts in the 2030s."

Orion's first test flight will have no crew, but the next-generation spacecraft will carry 1,200 sensors to measure conditions throughout the craft for the entire length of the mission. With no astronauts onboard, the sensors will provide NASA engineers with information on conditions inside the crew's cabin as the spacecraft travels 3,600 miles above Earth -- 15 times farther than the International Space Station. On its return, the spacecraft will pass through high radiation and reach temperatures of 4,000 degrees Fahrenheit as it enters the Earth's atmosphere at a speed of 20,000 mph.

The sensors also will measure the stress on the spacecraft as it ultimately splashes down, using three parachutes, in the Pacific Ocean about 4.5 hours after launch.

"We are ready," said Mike Sarafin, lead flight director for the test flight mission. "It's just a great time to be here. We haven't had this feeling in a while – not since retiring the space shuttles – of launching a spacecraft from American soil."

Sarafin, speaking during a press conference Wednesday, said Orion should reach its first orbit 17 minutes after liftoff. During that first trip around the Earth, the spacecraft will be flying at about the same orbital level as the International Space Station.

Two hours into the mission, the rocket's second stage engine will ignite, pushing Orion into a higher orbit, where it will twice pass through the Van Allen Belts, an area of dangerous radiation. Orion's sensors will measure the effects of radiation on the spacecraft's computers and navigation systems, as well as the environment in the crew compartment.

The sensors also will monitor stress on Orion's heat shield, which is the world's largest, measuring at 16.5 feet in diameter. The heat shield will bear the brunt of the scorching temperatures on reentry, as the spacecraft shifts from 20,000 mph to 0 mph in 11 minutes.

Thursday's launch will also be the first test of Orion's Launch Abort system, which is designed to pull the spacecraft and its crew out of harm's way if there is trouble with the rocket during launch. Engineers will only activate the jettison motor during this first test flight. The entire system will not be activated.

"We are beginning a new mission," said Mark Geyer, Orion's program manager. "It's the beginning of exploring beyond Earth orbit, and Orion is a key part of that… This is in the same category as starting the space shuttle missions and starting Apollo."

While this launch will test many systems that will be needed for a deep space flight, it won't test the heavy-lift rocket known as the Space Launch System. The rocket, designed to be the most powerful ever built, isn't expected to be used until Orion's second uncrewed test flight, scheduled for 2017 or 2018.

Orion will carry what NASA called major advances in computers, electronics, life support and propulsion. Each of those systems will be monitored and evaluated during Thursday's flight.

"Before we can send astronauts into space on Orion, we have to test all of its systems," NASA said on its website. "There's only one way to know if we got it right: Fly it in space."

Orion, eventually is expected to travel farther from Earth than any other human-carrying spacecraft. Scientists believe the spacecraft is their best bet for taking astronauts into deep space.

"The first future human mission to Mars and those that follow will require the ingenuity and dedication of an entire generation," NASA noted. "It's a journey worth the risks. We take the next step on that journey this Thursday… Orion will open the space between Earth and Mars for exploration by astronauts. This proving ground will be invaluable for testing capabilities future human Mars missions will need."

Orion's first crewed flight is not expected until 2021.