It's lift-off for Nasa's new era in planet-hunting.
The mission will look at a huge area of stars, hoping to catch the dips in brightness that happen when orbiting planets travel over their faces.
Tess's goal is to put together a list that other telescopes can then focus in on for more detailed investigation.
"Tess is equipped with four very sensitive cameras that will enable it to monitor nearly the entire sky," said George Ricker, the mission's principal investigator from the Massachusetts Institute of Technology, which leads the project.
"The types of planets that Tess will detect are revealed by a process called a transit. We can see the shadow, effectively, of the planet as it passes in front of its host star."
Nasa's latest space telescope went up on a SpaceX Falcon 9 rocket on Wednesday evening.