Kepler in orbit
Artist's impression of the Kepler telescope
Mission typeSpace telescope
OperatorNASA / LASP
COSPAR ID2009-011A
SATCAT no.34380
Mission durationPlanned: 3.5 years
Final: 9 years, 7 months, 23 days
Spacecraft properties
ManufacturerBall Aerospace & Technologies
Launch mass1,052.4 kg (2,320 lb)[1]
Dry mass1,040.7 kg (2,294 lb)[1]
Payload mass478 kg (1,054 lb)[1]
Dimensions4.7 m × 2.7 m (15.4 ft × 8.9 ft)[1]
Power1100 watts[1]
Start of mission
Launch dateMarch 7, 2009, 03:49:57 (2009-03-07UTC03:49:57) UTC[2]
RocketDelta II (7925-10L)
Launch siteCape Canaveral SLC-17B
ContractorUnited Launch Alliance
Entered serviceMay 12, 2009, 09:01 UTC
End of mission
DeactivatedNovember 15, 2018 (2018-11-15)
Orbital parameters
Reference systemHeliocentric
Semi-major axis1.0133 AU
Perihelion altitude0.97671 AU
Aphelion altitude1.0499 AU
Inclination0.44747 degrees
Period372.57 days
Argument of perihelion294.04 degrees
Mean anomaly311.67 degrees
Mean motion0.96626 deg/day
EpochJanuary 1, 2018 (J2000: 2458119.5)[3]
Main telescope
Diameter0.95 m (3.1 ft)
Collecting area0.708 m2 (7.62 sq ft)[A]
Wavelengths430–890 nm[3]
BandwidthX band up: 7.8 bit/s – 2 bit/s[3]
X band down: 10 bit/s – 16 kbit/s[3]
Ka band down: Up to 4.3 Mbit/s[3]
Kepler Logo.png
← Dawn

The Kepler space telescope is a retired space telescope launched by NASA to discover Earth-size planets orbiting other stars.[5][6] Named after astronomer Johannes Kepler,[7] the spacecraft was launched on March 7, 2009,[8] into an Earth-trailing heliocentric orbit. The principal investigator was William J. Borucki. After nine years of operation, the telescope's reaction control system fuel was depleted, and NASA announced its retirement on October 30, 2018.[9][10]

Designed to survey a portion of Earth's region of the Milky Way to discover Earth-size exoplanets in or near habitable zones and estimate how many of the billions of stars in the Milky Way have such planets,[5][11][12] Kepler's sole scientific instrument is a photometer that continually monitored the brightness of approximately 150,000 main sequence stars in a fixed field of view.[13] These data are transmitted to Earth, then analyzed to detect periodic dimming caused by exoplanets that cross in front of their host star. Only planets whose orbits are seen edge-on from Earth can be detected. During its over nine and a half years of service, Kepler observed 530,506 stars and detected 2,662 planets.[14]


The Kepler space telescope was part of NASA's Discovery Program of relatively low-cost science missions. The telescope's construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system. The Ames Research Center is responsible for the ground system development, mission operations since December 2009, and scientific data analysis. The initial planned lifetime was 3.5 years,[15] but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to be extended until 2016,[16] but on July 14, 2012, one of the spacecraft's four reaction wheels used for pointing the spacecraft stopped turning, and completing the mission would only be possible if all other reaction wheels remained reliable.[17] Then, on May 11, 2013, a second reaction wheel failed, disabling the collection of science data[18] and threatening the continuation of the mission.[19]

On August 15