KEYWORDS: Planets, Stars, Signal to noise ratio, Planetary systems, Signal detection, Exoplanets, Space operations, Systems modeling, Charge-coupled devices, Observatories
The Kepler mission was a National Aeronautics and Space Agency (NASA) Discovery-class mission designed to continuously monitor the brightness of at least 100,000 stars to determine the frequency of Earth-size and larger planets orbiting other stars. Once the Kepler proposal was chosen for a flight opportunity, it was necessary to optimize the design to accomplish the ambitious goals specified in the proposal and still stay within the available resources. To maximize the science return from the mission, a merit function (MF) was constructed that relates the science value (as determined by the PI and the Science Team) to the chosen mission characteristics and to models of the planetary and stellar systems. This MF served several purposes; predicting possible science results of the proposed mission, evaluating the effects of varying the values of the mission parameters to increase the science return or to reduce the mission costs, and supporting quantitative risk assessments. The MF was also valuable for the purposes of advocating the mission by illustrating its expected capability. During later stages of implementation, it was used to keep management informed of the changing mission capability and support rapid design tradeoffs when mission down-sizing was necessary. The MF consisted of models of the stellar environment, assumed exoplanet characteristics and distributions, detection sensitivity to key design parameters, and equations that related the science value to the predicted number and distributions of detected exoplanet. A description of the MF model and representative results are presented. Examples of sensitivity analyses that supported design decisions and risk assessments are provided to illustrate the potential broader utility of this approach to other complex science-driven space missions.
A small fraction of Kepler telescope exposures are rejected because of transient, excess background in the field. The
patterns of illumination vary from broad streaks to diffuse patches, sometimes filling the focal plane. Examination of
such images and their temporal variation shows that they can be attributed to nearby particles crossing the field-of-view
of the telescope. Most of the particles appear to be receding. The visual appearance and frequency are consistent with the
"debris storms" reported by STEREO SECCHI observers and which they found to be coincident with meteoroid impacts.
In addition, a few events, lasting several hours each, appear to be caused by more distant extended sources, possibly the
remains of comet dust trails. The tracking cameras, located at the opposite end from the telescope's entrance, and pointed
at roughly right angles to its line-of-sight, also detected moving light sources. Their behavior was consistent with the
main telescope sightings. Future missions requiring precise, uninterrupted photometry and pointing may benefit from
understanding this phenomenon and mitigating it by design and data analysis.
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.
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, Planets, Point spread functions, Signal to noise ratio, Photometry, Charge-coupled devices, Computer simulations, Space operations, Data modeling, Quantum efficiency
The objective of the NASA Ames Kepler mission is the detection of extrasolar terrestrial-size planets through transit photometry. In an effort to optimize the Kepler system design, Ball Aerospace has developed a numerical photometer model to simulate the sensor as well as stars and hypothetical planetary transits. The model emulates the temporal behavior of the incident light from 100 stars (with various visual magnitudes) on one CCD of the Kepler focal plane array. Simulated transits are inserted into the light curves of the stars for transit detection signal-to-noise ratio analyses. The Kepler photometer model simulates all significant CCD characteristics such as dark current, shot noise, read out noise, residual non-uniformity, intrapixel gain variation, charge spill over, well capacity, spectral response, charge transfer efficiency, read out smearing, and others. The noise effects resulting from background stars are also considered. The optical system is also simulated to accurately estimate system optical point spread functions and optical attenuation. In addition, spacecraft pointing and jitter are incorporated. The model includes on-board processing effects such as analog-to-digital conversion, photometric aperture extraction, and 15-minute frame co-addition. Results from the model exhibit good agreement with NASA Ames lab data and are used in subsequent signal-to-noise ratio analyses to assess the transit detection capability. The reported simulations are run using system requirements rather than predicted performance to guarantee that mission science objectives can be attained. The Kepler Photometer Model has given substantial insight into the Kepler system design by offering a straightforward means of assessing system design impacts on the ability to detect planetary transits. It is used as one of the various tools for the establishment of system requirements to ensure mission success.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.