New Explorer mission to hover in `Goldilocks orbit`
Washington: The new Explorer mission will be placed in ` Goldilocks orbit` so that it is perfectly positioned to map the locations of more than 500 transiting exoplanets, extrasolar planets that eclipse their host star.
Previous sky surveys with ground-based telescopes have mainly detected giant planets, while NASA`s Kepler observatory has uncovered the existence of many smaller exoplanets, but their host stars are faint and difficult to study.
TESS, which NASA recently selected as a new Explorer mission, is going to use an array of wide-field cameras to perform the all-sky survey of a broad range of exoplanets, ranging from Earth-size to gas giants.
From this survey data, NASA`s James Webb Space Telescope as well as large ground-based observatories will be able to further characterize the targets, making it possible for the first time to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars.
TESS Principal Investigator George Ricker , a senior research scientist at the Massachusetts Institute of Technology`s (MIT) Kavli Institute for Astrophysics and Space Research, said that TESS will carry out the first spaceborne all-sky transit survey, covering 400 times as much sky as any previous mission.
He said that it is going to help identify thousands of new planets in the solar neighborhood, with a special focus on planets comparable in size to the Earth.
To carry out an exhaustive two-year survey of extrasolar planets in both celestial hemispheres, TESS needed to occupy a very particular position in space, a highly stable place that maximized sky coverage and gave the observatory a mostly unobstructed view of the cosmos, all from a low-radiation, thermally benign environment.
After exhaustive studies by Goddard engineers and The Aerospace Corporation, the TESS team chose a never-before-used lunar-resonant orbit known as P/2 in the parlance of scientists. This high-Earth, highly elliptical orbit has a period half that of the Moon`s orbital period, meaning that the satellite makes a complete orbital circuit every 13.7 days.
When the spacecraft is at the lowest point closest to Earth at 67,000 miles (17.0 earth radii), it remains well above geosynchronous orbit 22,236 miles above the equator where most communications satellites operate. At this lowest point, or perigee, TESS will orient its dish antenna to Earth and transmit data to ground stations below, a process that will take three hours. At its highest point, or apogee, some 232,000 miles above Earth (58.7 earth radii), it avoids the hazards posed by the Van Allen radiation belts, which extend from about 621 to 37,282 miles above the surface.
"This is the first time this orbit has been used," said Trevor Williams, a Goddard engineer who played a pivotal role in evaluating the trajectory`s appropriateness for the TESS mission. "It`s a stable orbit, stable in the sense that it isn`t plagued by attitude perturbations."
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