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Kepler Mission
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The Kepler Mission is a NASA space telescope designed to search for Earth-like planets orbiting other stars. Using a space photometer developed by NASA, it will observe the brightness of over 100,000 stars over 3.5 years to detect periodic transits of a star by its planets (the transit method of detecting planets). The mission is named in honor of German astronomer Johannes Kepler.
Kepler is a mission under NASA's Discovery Program of low-cost, focused science missions.
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The Kepler Mission is a NASA space telescope designed to search for Earth-like planets orbiting other stars. Using a space photometer developed by NASA, it will observe the brightness of over 100,000 stars over 3.5 years to detect periodic transits of a star by its planets (the transit method of detecting planets). The mission is named in honor of German astronomer Johannes Kepler.
Kepler is a mission under NASA's Discovery Program of low-cost, focused science missions. NASA's Ames Research Center is the home organization of the science principal investigator and is responsible for the ground system development, mission operations and science data analysis. Kepler mission development is managed by NASA's Jet Propulsion Laboratory. Ball Aerospace & Technologies Corp. is responsible for developing the Kepler flight system.
The Kepler Spacecraft lifted off on March 6, 2009, at 22:49 Eastern Time Zone. (March 7, 03:49 UTC)
Objectives and methods
The scientific objective of the Kepler Mission is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to achieve several goals:
- Determine how many terrestrial and larger planets there are in or near the habitable zone of a wide variety of spectral types of stars
- Determine the range of sizes and shapes of the orbits of these planets
- Estimate how many planets there are in multiple-star systems
- Determine the range of orbit size, brightness, size, mass and density of short-period giant planets
- Identify additional members of each discovered planetary system using other techniques
- Determine the properties of those stars that harbor planetary systems.
Most of the extrasolar planets detected so far by other projects are giant planets, mostly the size of Jupiter and bigger. Kepler is designed to look for planets 30 to 600 times less massive, closer to the order of Earth's mass. The method used, the transit method, involves observing repeated transit of planets in front of their stars, which causes a slight reduction in the star's apparent magnitude, on the order of 0.01% for an Earth-sized planet. The degree of this reduction in brightness can be used to deduce the mass of the planet, and the interval between transits can be used to deduce the size of the planet's orbit and estimate its temperature.
The random probability of a planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit. For an Earth-like planet at 1 AU transiting a solar-like star the probability is 0.465%, or about 1 in 215. At 0.72 AU (the orbital distance of Venus) the probability is slightly larger, at 0.65%; such planets would be Earth-like if the host star is a late G-type star such as Tau Ceti. In addition, because planets in a given system tend to orbit in similar planes, the possibility of multiple detections around a single star is actually rather high. For instance, if an alien Kepler-like mission observed Earth transiting the Sun, there is a 12% chance of also seeing Venus transit.
The Kepler Mission has a much higher probability of detecting Earth-like planets than the Hubble Space Telescope, since it has a much larger field of view (approximately 10 degrees square), and will be dedicated for detecting planetary transits. The Hubble Space Telescope is, in contrast, used to address a wide range of questions and rarely looks continuously at just one starfield. The Kepler Mission is designed to observe 100,000 stars simultaneously, measuring variations in their brightness every 30 minutes. This provides a much better chance for seeing a transit. In addition, the 1 in 215 probability means that if 100% of stars observed had the exact same diameter as the Sun, and each had one Earth-like terrestrial planet in an orbit identical to that of the Earth, Kepler would find about 465 of them. The mission is therefore ideally suited to determine the frequency of Earth-like planets around other stars.
Since Kepler must see at least three transits to be sure the dimming was caused by a planet, and since larger planets give a signal that is easier to check, scientists expect the first reported results will be larger Jupiter sized planets in tight orbits. These could be reported after only a few months of operation. Smaller planets, and planets further from their sun will take longer, and discovering planets comparable to Earth is expected to take three years or longer.
Data from the mission will also be used for studying variable stars of various types and performing asteroseismology, particularly on stars showing solar-like oscillations.
Status
The observatory was launched on March 7, 2009 at 03:49:57 UTC (10:49:57 pm EST time on March 6) aboard a Delta II rocket from Cape Canaveral Air Force Station, Florida. The launch was a complete success and all 3 stages were successfully completed by 04:55 UTC. The spacecraft will be in a commissioning phase for approximately 60 days undergoing calibration and testing before beginning science observation.
In January 2006, it was delayed eight months because of budget cuts and consolidation at NASA. It was delayed again by 4 months in March 2006 due to fiscal problems. At this time the high-gain antenna was changed from a gimballed design to one fixed to the frame of the spacecraft to reduce cost and complexity, at the cost of one observation day per month.
Mission details
Kepler is not in an Earth orbit but in an Earth-trailing solar orbit so that Earth will not occlude the stars which are to be observed continuously and the photometer will not be influenced by stray light from Earth. This orbit also avoids gravitational perturbations and torques inherent in an Earth orbit, allowing for a more stable viewing platform. The photometer will point to a field in the constellations of Cygnus and Lyra, which is well out of the ecliptic plane, so that sunlight never enters the photometer as the spacecraft orbits the Sun. Cygnus is also a good choice to observe because it will never be obscured by Kuiper belt objects or the asteroid belt.
An additional benefit of that choice is that Kepler will be pointing in the direction of the Solar System's motion around the center of the galaxy. Thus, the stars which are observed by Kepler will be roughly the same distance from the galaxy center as the Solar System, and will also be close to the galactic plane. This fact is important if position in the galaxy is related to habitability, as suggested by the Rare Earth hypothesis.
The spacecraft is estimated to have a mass of , have a aperture, a primary mirror (the largest on any telescope outside of Earth orbit), have a 105 deg˛ (about 12 degree diameter) field of view (FOV), equivalent to roughly two hands held at arm's length. The photometer will have a soft focus to provide excellent photometry, rather than sharp images. The combined differential photometric precision (CDPP) for a m(V)=12 solar-like star for a 6.5 hour integration will be 20 ppm, including an expected stellar variability of 10 ppm. An earth-like transit produces a brightness change of 84 ppm and lasts for 13 hours when it crosses the center of the star. The focal plane is made up of 42 1024 × 2200 CCDs with 27 micrometer pixels, making it the largest camera launched into space. The array will be cooled by heat pipes connected to an external radiator. The CCDs are read out every 3 seconds and co-added on board for 15 minutes. Only the pixels of interest from each of the target stars are stored and telemetered to the ground. The mission's life-cycle cost is estimated at US$600 million, including funding for 3.5 years of operation.
Mission operations
The Kepler mission will be operated out of Boulder, Colorado, by the Laboratory for Atmospheric and Space Physics (LASP). The solar array will be rotated to face the Sun at the solstices and equinoxes. These rotations will be used to optimize the amount of sunlight falling on the solar array and to keep the heat radiator pointing towards deep space. Together, LASP and Ball Aerospace & Technologies Corp. (who are responsible for building the spacecraft and instrument) will control the spacecraft from the mission operations center located on the research campus of the University of Colorado. LASP will also perform essential mission planning and the initial collection and distribution of the science data.
NASA will contact the spacecraft using the X band communication link twice a week for command and status updates. Scientific data will be downloaded once a month using the Ka band link at a maximum data transfer rate of 4.33 Mb/s. The Kepler spacecraft will conduct its own partial analysis on board and only transmit scientific data deemed necessary to the mission in order to conserve bandwidth.
See also
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