The upcoming launch of the first Orion spacecraft test flight Thursday (Dec. 4) is a major milestone for the NASA's plans for future space exploration, so it's no surprise that the agency tapped into social media to spark interest and excitement in the mission. But what may be surprising is who NASA turned to in order to spread the word: Hollywood.

As part of the "I'm On Board" Orion social media campaign (#imonboard), NASA recorded a series of public service announcements with actors familiar to even the most casual science fiction fan. Nichelle Nichols (Star Trek's Uhura), the Lou Ferrigno of the Incredible Hulk and even Elmo from Sesame Street added their support to NASA's Orion. And the campaign paid off in spades. More than 1 million people signed up to add their names to a small microchip riding on the Orion Exploration Test Flight 1, which launches early Thursday at 7:05 a.m. EST (1105 GMT). Scroll down to see more Orion videos by TV actors, starting with Nichelle Nichols:

As part of the "I'm On Board" campaign, NASA invited the public to sign up with a coloring sheet to pledge support. You can still show your support by getting the coloring sheet here: http://go.nasa.gov/1fAYxZS

Watch the 4.5-hour Orion test flight live on Space.com via NASA TV, beginning at 4 a.m. EST (0900 GMT) on Thursday.

Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik and Google+. Follow us @Spacedotcom, Facebook and Google+.