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Mission update.


One of two new Discovery-class missions selected by NASA managers last year, Kepler is to search for Earth-like extrasolar planets using transit photometry. Kepler's 0.95-meter-aperture Schmidt telescope will stare for four years at a single 12[degrees]-wide field in Cygnus, monitoring 100,000 stars brighter than 14th magnitude and measuring their brightness every 15 minutes to an accuracy of 0.0001 magnitude. This should reveal the faint dimming caused by any planet whose orbital plane happens to carry it in front of a star as seen from Earth. Kepler will be launched into solar orbit by a Delta rocket in 2006. The telescope's single instrument uses an array of 42 CCD cameras with a total of 100 million pixels. These detectors will be deliberately placed out of focus to improve the accuracy of the brightness measurements: spreading the light over 10 arcseconds averages out instrumental variations and improves statistics, and the image quality won't suffer as long as the star images don't overlap.


The second Discovery winner, Dawn, is a nine-year mission to orbit the two largest asteroids in the main belt, 1 Ceres and 4 Vesta. With launch scheduled for May 2006, this will be the first interplanetary spacecraft to take advantage of the type of ion-drive engine used by Deep Space 1 (S&T: December 2001, page 18). Using three of these engines, Dawn should take four years to reach Vesta. Then, in July 2010, a conventional hydrazine-fueled braking engine will place the spacecraft in a 700-kilometer-high orbit. Over the next year the spacecraft will close in to a height of only 120 km, studying the surface of the asteroid all the while. In July 2011, Dawn sets itself free of Vesta, using the ion engines again for a three-year trip to Ceres. After a year of studies there, the primary mission ends in July 2015.


The Applied Physics Laboratory in Maryland is fine-tuning the Contour comet probe for its upcoming mission. Engineers conducted vibration and spin-balance tests in January and February, followed by thermal-vacuum tests in March. Launch should occur this July, when a Delta 7425 rocket will place the spacecraft into an elliptical 200-by-109,000-km orbit around Earth. Contour (a contraction for Comet Nucleus Tour) will spend up to 112 months in this parking orbit, a clever hedge against liftoff delays. Whatever the launch day, the orbit will be adjusted so that on August 15th it will be in exactly the right place for a solid-fuel rocket to put Contour in its intended solar orbit. This will range between the orbits of Venus and Mars, with a perihelion of 0.80 astronomical unit and an aphelion of 1.35 a.u. After a swingby of Earth in August 2003, Contour will zip past Comet 2P/Encke three months later. Another Earth flyby the following August will send Contour on an 18-month "backflip" across the inner solar system at an inclination of 12[degrees] (see page 14). A second series of Earth flybys concluding in February 2006, sets up an encounter with Comet 73P/Schwassmann-Wachmann 3 in June 2006 and probably with a third comet --possibly 6P/d'Arrest--in 2008. NASA planners note that the mission design is so flexible that, given enough lead time, the spacecraft can be redirected to intercept an unexpected cometary visitor passing through the inner solar system.

JONATHAN MCDOWELL, an astronomer at the Harvard-Smithsonian Center for Astrophysics, writes a weekly electronic newsletter on the space program (http://hea-www
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Title Annotation:the latest space missions
Author:McDowell, Jonathan
Publication:Sky & Telescope
Geographic Code:1USA
Date:Jun 1, 2002
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