The orbital flight's five-hour launch window opens at 8:02 p.m. ET, with a backup window for 8:05 p.m. ET on Thursday, Sept. 16.
The mission aboard the Falcon 9 rocket and Dragon Resilience spacecraft is crewed by mission commander and billionaire Jared Isaacman, mission pilot Sian Proctor, medical officer Hayley Arceneaux and mission specialist Chris Sembroski.
The flight will last for approximately three days and is targeting an orbit of around 575 kilometers – or nearly 358 miles. It is the highest that any humans have gone into orbit since the Hubble Space Telescope service technicians.
The four crew members will conduct experiments designed to expand our knowledge of the universe and of human health during spaceflight.
When the mission is over, the crew will splash down off the coast of Florida.
The U.S Space Force's 45th Weather Squadron has forecast an 80% chance of favorable conditions on Wednesday.
A webstream of the event on SpaceX's YouTube is slated for 3:45 p.m. ET.
"Watch Countdown on Netflix about Inspiration4 mission launching today," SpaceX founder Elon Musk tweeted early Wednesday morning.