KEYWORDS: Stars, Planets, Space operations, Photometry, Charge-coupled devices, Data centers, System on a chip, Aerospace engineering, Space telescopes, Signal to noise ratio
The Kepler Mission is a search for terrestrial planets specifically designed to detect Earth-size planets in the habitable zones of solar-like stars. In addition, the mission has a broad detection capability for a wide range of planetary sizes, planetary orbits and spectral types of stars. The mission is in the midst of the developmental phase with good progress leading to the preliminary design review later this year. Long lead procurements are well under way. An overview in all areas is presented including both the flight system (photometer and spacecraft) and the ground system. Launch is on target for 2007 on a Delta II.
KEYWORDS: Systems engineering, Stars, Performance modeling, Space operations, Photometry, Signal to noise ratio, Data modeling, Data acquisition, Planets, Error analysis
The Kepler mission will launch in 2007 and determine the distribution of earth-size planets (0.5 to 10 earth masses) in the habitable zones (HZs) of solar-like stars. The mission will monitor > 100,000 dwarf stars simultaneously for at least 4 years. Precision differential photometry will be used to detect the periodic signals of transiting planets. Kepler will also support asteroseismology by measuring the pressure-mode (p-mode) oscillations of selected stars. Key mission elements include a spacecraft bus and 0.95meter, wide-field, CCD-based photometer injected into an earth-trailing heliocentric orbit by a 3-stage Delta II launch vehicle as well as a distributed Ground Segment and Follow-up Observing Program. The project is currently preparing for Preliminary Design Review (October 2004) and is proceeding with detailed design and procurement of long-lead components. In order to meet the unprecedented photometric precision requirement and to ensure a statistically significant result, the Kepler mission involves technical challenges in the areas of photometric noise and systematic error reduction, stability, and false-positive rejection. Programmatic and logistical challenges include the collaborative design, modeling, integration, test, and operation of a geographically and functionally distributed project. A very rigorous systems engineering program has evolved to address these challenge. This paper provides an overview of the Kepler systems engineering program, including some examples of our processes and techniques in areas such as requirements synthesis, validation & verification, system robustness design, and end-to-end performance modeling.
The primary goal of Kepler, a recently selected Discovery mission, is to search for terrestrial size planets orbiting other stars using the transit method. To accomplish this goal, a space-based photometer is being developed that employs a 0.95-meter Schmidt camera incorporating a large focal plane array (FPA). The FPA is populated with 42 large format custom CCD detectors with integral field flattening optics covering a 100 square degree field of view. The FPA will measure the precise relative intensity of approximately 100,000 main sequence stars nearly continuously over the mission's 4-year lifetime to search for the small changes caused by planetary transits. All critical electronics are housed immediately behind the FPA, which yields a low noise compact design that is both robust and fault tolerant. The design and development of the FPA, its detectors, its main systems issues, and their relationship to photometric precision will be discussed along with results from detailed performance models.
KEYWORDS: Planets, Stars, Photometry, Signal to noise ratio, Point spread functions, Planetary systems, Space operations, Data archive systems, Space telescopes, Sun
NASA's Kepler Mission is designed to determine the frequency of Earth-size and larger planets in the habitable zone of solar-like stars. It uses transit photometry from space to determine planet size relative to its star and orbital period. From these measurements, and those of complementary ground-based observations of planet-hosting stars, and from Kepler's third law, the actual size of the planet, its position relative to the habitable zone, and the presence of other planets can be deduced. The Kepler photometer is designed around a 0.95 m aperture wide field-of-view (FOV) Schmidt type telescope with a large array of CCD detectors to continuously monitor 100,000 stars in a single FOV for four years. To detect terrestrial planets, the photometer uses differential relative photometry to obtain a precision of 20 ppm for 12th magnitude stars. The combination of the number of stars that must be monitored to get a statistically significant estimate of the frequency of Earth-size planets, the size of Earth with respect to the Sun, the minimum number of photoelectrons required to recognize the transit signal while maintaining a low false-alarm rate, and the areal density of target stars of differing brightness are all critical to the photometer design.
KEYWORDS: Stars, Charge-coupled devices, Planets, Photometry, Point spread functions, Space operations, Signal to noise ratio, Interference (communication), Cameras, Received signal strength
The thirty or so extrasolar planets that have been discovered to date are all about as large as Jupiter or larger. Finding Earth-size planets is a substantially more difficult task. We propose the use of spacebased differential photometry to detect the periodic changes in brightness of several hours duration caused by planets transiting their parent stars. The change in brightness for a Sun-Earth analog transit is 8 X 10-5. We describe the instrument and mission concepts that will monitor 100,000 main-sequence stars and detect on the order of 500 Earth-size planets, if terrestrial planets are common in the extended solar neighborhood.
KEYWORDS: Stars, Photometry, Signal to noise ratio, Space operations, Charge-coupled devices, Point spread functions, Numerical simulations, Planets, Image processing, Control systems
We have performed end-to-end laboratory and numerical simulations to demonstrate the capability of differential photometry under realistic operating conditions to detect transits of Earth-sized planets orbiting solar-like stars. Data acquisition and processing were conducted using the same methods planned for the proposed Kepler Mission. These included performing aperture photometry on large-format CCD images of an artificial star fields obtained without a shutter at a readout rate of 1 megapixel/sec, detecting and removing cosmic rays from individual exposures and making the necessary corrections for nonlinearity and shutterless operation in the absence of darks. We will discuss the image processing tasks performed `on-board' the simulated spacecraft, which yielded raw photometry and ancillary data used to monitor and correct for systematic effects, and the data processing and analysis tasks conducted to obtain lightcurves from the raw data and characterize the detectability of transits. The laboratory results are discussed along with the results of a numerical simulation carried out in parallel with the laboratory simulation. These two simulations demonstrate that a system-level differential photometric precision of 10-5 on five- hour intervals can be achieved under realistic conditions.
KEYWORDS: Planets, Stars, Photometry, Space operations, Charge-coupled devices, Exoplanets, Analog electronics, Sun, Signal to noise ratio, Planetary systems
With the detection of giant extrasolar planets and the quest for life on Mars, there is heightened interset in finding earth-class planets, those that are less than ten earth masses and might be life supporting. A space-based photometer has the ability to detect the periodic transits of earth-class planets for a wide variety of spectral types of stars. From the data and known type of host star, the orbital semi-major axis, size and characteristic temperature of each planet can be calculated. The frequency of planet formation with respect to spectral type and occurrence for both singular and multiple-stellar systems can be determined. A description is presented of a one-meter aperture photometer with a twelve-degree field of view and a focal plane of 21 CCDs. The photometer woudl continuously and simultaneously monitor 160,000 stars of visual magnitude <EQ 14. Its one-sigma system sensitivity for a transit of a 12th magnitude solar-like star by a planet of one-earth radius would be one part in 50,000. It is anticipated that about 480 earth-class planets would be detected along with 140 giant planets in transit and 1400 giant planets by reflected light. Densities could be derived for about seven case where the planet is seen in transit and radial velocities are measurable.
The Submillimeter Wave Astronomy Satellite (SWAS) mission will study galactic star formation and interstellar chemistry. To carry out this mission, SWAS will survey dense (nH2 > 103 cm-3) molecular clouds within our galaxy in either the ground-state or a low- lying transition of five astrophysically important species: H2O, H218O, O2, CI, and 13CO. By observing these lines SWAS will: (1) test long-standing theories that predict that these species are the dominate coolants of molecular clouds during the early stages of their collapse to form stars and planets and (2) supply heretofore missing information about the abundance of key species central to the chemical models of dense interstellar gas. During its two-year mission, SWAS will observe giant and dark cloud cores with the goal of detecting to setting an upper limit on the water abundance of 3 X 10-6 (relative to H2) and on the molecular oxygen abundance of 2 X 10-6 (relative to H2). SWAS is designed to carry all elements of a ground based radiotelescope. The telescope is a highly efficient 54 X 68-cm off-axis Cassegrain antenna with an aggregate surface error less than or equal to 11 micrometers rms. The receiver system consists of two independent heterodyne receivers with second harmonic Schottky diode mixers, passively cooled to approximately equals 150 K. The spectrometer is a single acousto-optical spectrometer (AOS) with 1400 1-MHz channels enabling simultaneous observations of the H2O, O2, CI, and 13CO lines.
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