The primary mission objective for TESS is to survey the brightest stars near the Earth for transiting exoplanets over a two-year period. The TESS project will use an array of wide-field cameras to perform an all-sky survey. It will scan nearby stars for exoplanets. With TESS, it will be possible to study the mass, size, density and orbit of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. TESS will provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future.
Previous sky surveys with ground-based telescopes have mainly picked out giant exoplanets. In contrast, TESS will examine a large number of small planets around the very brightest stars in the sky. TESS will record the nearest and brightest main sequence stars hosting transiting exoplanets, which will forever be the most favorable targets for detailed investigations.
TESS is designed to carry out the first space-borne all-skytransiting exoplanet survey. It is equipped with four wide-angle telescopes and associated charge-coupled device (CCD) detectors. Science data will be transmitted to Earth every two weeks. Full-frame images with an effective exposure time of two hours will be transmitted as well, enabling scientists to search for unexpected, transient phenomena, such as the optical counterparts to gamma-ray bursts.
In order to obtain unobstructed imagery of both the northern and southern hemispheres of the sky, TESS will utilize a 2:1 lunar resonant orbit called P/2, a never-before-used orbit. The spacecraft's 373,000 km (232,000 mi) apogee is timed to keep the craft away from the Moon, which acts as a destabilizing agent. This highly elliptical orbit should remain stable for decades, and will keep TESS's cameras in a stable temperature range. The majority of the orbit is spent outside the Van Allen belts to avoid radiation damage to TESS. Every 13.7 days at its perigee of 108,000 km (67,000 mi), TESS will downlink the data it has collected during the orbit to Earth over a period of approximately three hours.
TESS's survey will focus on G- and K-typestars with apparent magnitudes brighter than magnitude 12. Approximately 500,000 stars will be studied, including the 1,000 closest red dwarfs, across an area of sky 400 times larger than that covered by Kepler. TESS is expected to discover more than 3,000 transiting exoplanet candidates, including those which are Earth sized or larger.
The survey is broken up into 26 observation sectors, each sector being 24° x 96°, with an overlap of sectors at the ecliptic poles to allow for additional sensitivity toward smaller and longer-period exoplanets in that region of the celestial sphere. The spacecraft will spend two 13.7 day orbits observing each sector, mapping the northern hemisphere of sky in its first year of operation and the southern hemisphere in its second year. Each of TESS's cameras will take one-minute exposures as part of its transit search, and 30-minute full-frame exposures to search for other transient events.
The sole instrument on TESS is a package of four wide-field-of-view CCD cameras. Each camera features a low-noise, low-power 16.8 megapixel CCD detector created by the MIT Lincoln Laboratory. Each has a 24° × 24°field of view, a 100 mm (4 in) effective pupil diameter, a lens assembly with seven optical elements, and a bandpass range of 600 to 1000 nm.
^Ricker, George R. (June 26, 2014). Discovering New Earths and Super-Earths in the Solar Neighborhood. SPIE Astronomical Telescopes + Instrumentation. June 22–27, 2014. Montréal, Quebec, Canada. doi:10.1117/2.3201407.18.