[13] The primary mission objective for TESS was to survey the brightest stars near the Earth for transiting exoplanets over a two-year period.

TESS records the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.

[15][16] Led by the Massachusetts Institute of Technology (MIT) with seed funding from Google,[17] on 5 April 2013, it was announced that TESS, along with the Neutron Star Interior Composition Explorer (NICER), had been selected by NASA for launch.

The concept of TESS was first discussed in 2005 by the Massachusetts Institute of Technology (MIT) and the Smithsonian Astrophysical Observatory (SAO).

[21] The genesis of TESS was begun during 2006, when a design was developed from private funding by individuals, Google, and The Kavli Foundation.

[22] In 2008, MIT proposed that TESS become a full NASA mission and submitted it for the Small Explorer program at Goddard Space Flight Center,[22] but it was not selected.

[26][27] The mission will find exoplanets that periodically block part of the light from their host stars, events called transits.

[28] and on 3 January 2020, the Transit Exoplanet Survey Satellite reported the discovery of TOI-700 d, its first potentially habitable Earth-sized planet.

Full-frame images with an effective exposure time of two hours are transmitted as well, enabling scientists to search for unexpected transient phenomena, such as the optical counterparts to gamma-ray bursts.

[30] TESS uses a novel highly elliptical orbit around the Earth with an apogee approximately at the distance of the Moon and a perigee of 108,000 km (67,000 mi).

Every 13.70 days at its perigee of 108,000 km (67,000 mi), TESS downlinks to Earth over a period of approximately 3 hours the data it has collected during the just finished orbit.

[33] Approximately 500,000 stars were to be studied, including the 1,000 closest red dwarfs across the whole sky,[34][35] an area 400 times larger than that covered by the Kepler mission.

The survey methodology was designed such that the area that will be surveyed, essentially continuously, over an entire year (351 observation days) and makes up about 5% of the entire sky, will encompass the regions of sky (near the ecliptic poles) which will be observable at any time of year with the James Webb Space Telescope (JWST).

[39] In October 2019, Breakthrough Listen started a collaboration with scientists from the TESS team to look for signs of advanced extraterrestrial life.

Thousands of new planets found by TESS will be scanned for "technosignatures" by Breakthrough Listen partner facilities across the globe.

[40] The TESS team also plans to use a 30-minute observation cadence for full-frame images, which has been noted for imposing a hard Nyquist limit that can be problematic for asteroseismology of stars.

After coasting for 35 minutes, the second stage performed a final 54-second burn that placed TESS into a supersynchronous transfer orbit of 200 × 270,000 km (120 × 167,770 mi) at an inclination of 28.50°.

[52] TESS uses an Orbital Sciences LEOStar-2 satellite bus, capable of three-axis stabilization using four hydrazine thrusters plus four reaction wheels providing better than three arcsecond fine spacecraft pointing control.

[54] On 17 May 2018, the spacecraft underwent a gravity assist by the Moon at 8,253.5 km (5,128.5 mi) above the surface,[55] and performed the final period adjustment burn on 30 May 2018.

If TESS receives an on-target or slightly above nominal orbit insertion by the Falcon 9, a theoretical mission duration in excess of 15 years would be possible from a consumables standpoint.

Each camera has a 24° × 24° field of view, a 100 mm (3.9 in) effective pupil diameter, a lens assembly with seven optical elements, and a bandpass range of 600 to 1000 nm.

The four telescopes in the assembly each have a 10.5-cm diameter lens entrance aperture, with a f/1.4 focal ratio, with a total of seven lenses in the optical train.

[61] Although both observatories plan to look at bright nearby stars using the transit method, CHEOPS is focused on collecting more data on known exoplanets, including those found by TESS and other survey missions.

[65] On 20 September 2018, the discovery of an ultra-short period planet was announced, slightly larger than Earth, orbiting the red dwarf LHS 3844.

A team of scientists got 23.4 orbits approved in the first Announcement of Opportunity (AO-1) for the CHEOPS Guest Observers (GO) Programme to characterize the planet.

[74] On 31 July 2019, the discovery of exoplanets around the M-type dwarf star Gliese 357 at a distance of 31 light years from Earth was announced.

[75] As of September 2019, over 1000 TESS Objects of Interest (ToI) have been listed in the public database,[76] at least 29 of which are confirmed planets, about 20 of which within the stated goal of the mission of Earth-sized (<4 Earth radii).

[81] On the same day, NASA announced that astronomers used TESS data to show that Alpha Draconis is an eclipsing binary star.

[83] On 25 January 2021, a team led by astrochemist Tansu Daylan, with the help of two high school interns as part of the Science Research Mentoring Program at Harvard & MIT, discovered and validated four extrasolar planets — composed of one super-Earth and three sub-Neptunes - hosted by the bright, nearby, Sun-like star HD 108236.

The two high schoolers, 18 year old Jasmine Wright of Bedford High School in Bedford, Massachusetts, and 16 year old Kartik Pinglé of Cambridge Ringe And Latin School, of Cambridge, Massachusetts, are reported to be the youngest individuals in history to discover a planet, let alone four.