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  • richardmitnick 8:31 pm on December 3, 2013 Permalink | Reply
    Tags: , , , , NASA Dawn   

    From NASA/JPL at Caltech: “NASA’s Dawn Fills out its Ceres Dance Card” 

    December 03, 2013
    Jia-Rui Cook 818-354-0850
    Jet Propulsion Laboratory, Pasadena, Calif.
    jccook@jpl.nasa.gov

    It’s going to be a ball when NASA’s Dawn spacecraft finally arrives at the dwarf planet Ceres, and mission managers have now inked in the schedule on Dawn’s dance card.

    dawn
    DAWN

    ceres
    Ceres

    Dawn has been cruising toward Ceres, the largest object in the main asteroid belt between Mars and Jupiter, since September 2012. That’s when it departed from its first dance partner, Vesta.

    vesta
    Vesta

    Ceres presents an icy — possibly watery — counterpoint to the dry Vesta, where Dawn spent almost 14 months. Vesta and Ceres are two of the largest surviving protoplanets — bodies that almost became planets — and will give scientists clues about the planet-forming conditions at the dawn of our solar system.

    When Dawn enters orbit around Ceres, it will be the first spacecraft to see a dwarf planet up-close and the first spacecraft to orbit two solar system destinations beyond Earth.

    “Our flight plan around Ceres will be choreographed to be very similar to the strategy that we successfully used around Vesta,” said Bob Mase, Dawn’s project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “This approach will build on that and enable scientists to make direct comparisons between these two giants of the asteroid belt.”

    As a prelude, the team will begin approach operations in late January 2015. The next month, Ceres will be big enough in Dawn’s view to be imaged and used for navigation purposes. Dawn will arrive at Ceres — or, more accurately, it will be captured by Ceres’ gravity — in late March or the beginning of April 2015.

    Dawn will make its first full characterization of Ceres later in April, at an altitude of about 8,400 miles (13,500 kilometers) above the icy surface. Then, it will spiral down to an altitude of about 2,750 miles (4,430 kilometers), and obtain more science data in its survey science orbit. This phase will last for 22 days, and is designed to obtain a global view of Ceres with Dawn’s framing camera, and global maps with the visible and infrared mapping spectrometer (VIR).

    Dawn will then continue to spiral its way down to an altitude of about 920 miles (1,480 kilometers), and in August 2015 will begin a two-month phase known as the high-altitude mapping orbit. During this phase, the spacecraft will continue to acquire near-global maps with the VIR and framing camera at higher resolution than in the survey phase. The spacecraft will also image in “stereo” to resolve the surface in 3-D.

    Then, after spiraling down for two months, Dawn will begin its closest orbit around Ceres in late November, at a distance of about 233 miles (375 kilometers). The dance at low-altitude mapping orbit will be a long waltz — three months — and is specifically designed to acquire data with Dawn’s gamma ray and neutron detector (GRaND) and gravity investigation. GRaND will reveal the signatures of the elements on and near the surface. The gravity experiment will measure the tug of the dwarf planet, as monitored by changes in the high-precision radio link to NASA’s Deep Space Network on Earth.

    At this low-altitude mapping orbit, Dawn will begin using a method of pointing control that engineers have dubbed “hybrid” mode because it utilizes a combination of reaction wheels and thrusters to point the spacecraft. Up until this final mission phase, Dawn will have used just the small thruster jets, which use a fuel called hydrazine, to control its orientation and pointing. While it is possible to explore Ceres completely using only these jets, mission managers want to conserve precious fuel. At this lowest orbit, using two of the reaction wheels to help with pointing will provide the biggest hydrazine savings. So Dawn will be spinning up two of the gyroscope-like devices to aid the thrusters.

    In 2011, the Dawn team prepared the capability to operate in a hybrid mode, but it wasn’t needed during the Vesta mission. It was only when a second (of four) reaction wheels developed excessive friction while Dawn was leaving Vesta in 2012 that mission managers decided to use the hybrid mode at Ceres. To prove the technique works, Dawn engineers completed a 27-hour in-flight test of the hybrid mode, ending on Nov. 13. It operated just as expected.

    “The successful test of this new way to control our orientation gives us great confidence that we’ll have a steady hand at Ceres, which will enable us to get really close to a world that we only know now as a fuzzy dot amidst the stars,” said Marc Rayman, Dawn’s chief engineer and mission director, based at JPL.

    Of course, mission planners have built some extra days into the schedule to account for the small uncertainty in the efficiency of the solar arrays at such a large distance from the sun, where sunlight will be very faint. The solar arrays provide power to the ion propulsion system, in addition to operating power for the spacecraft and instruments. Mission planners also account for potential variations in the gravity field of Ceres, which will not be known precisely until Dawn measures them.

    “We are expecting changes when we get to Ceres and, fortunately, we built a very capable spacecraft and developed flexible plans to accommodate the unknowns,” said Rayman. “There’s great excitement in the unexpected — that’s part of the thrill of exploration.”

    See the full article here.

    Dawn is a space probe launched by NASA on September 27, 2007, to study the two most massive objects of the asteroid belt – the protoplanet Vesta and the dwarf planet Ceres. Currently en route to Ceres and scheduled and expected to arrive in February 2015,[2][5] Dawn was the first spacecraft to visit Vesta, entering orbit on July 16, 2011.[6][7] Should its mission succeed, it will also be the first spacecraft to visit Ceres and to orbit two separate extraterrestrial bodies.[8]

    Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. The California Institute of Technology in Pasadena manages JPL for NASA.

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 6:27 pm on April 1, 2013 Permalink | Reply
    Tags: , , , , NASA Dawn,   

    From JPL at Caltech: “A Hard Day’s Flight: Dawn Achieves Orbital Velocity” 

    NASA Dawn Banner

    “As NASA’s Dawn spacecraft makes its journey to its second target, the dwarf planet Ceres, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

    NASA Dawn Spacescraft

    April 1, 2013
    Marc Rayman

    The indefatigable Dawn spacecraft is continuing to forge through the main asteroid belt, gently thrusting with its ion propulsion system. As it gradually changes its orbit around the sun, the distance to dwarf planet Ceres slowly shrinks. The pertinacious probe will arrive there in 2015 to explore the largest body between the sun and Neptune that has not yet been glimpsed by a visitor from Earth. Meanwhile, Vesta, the fascinating alien world Dawn revealed in 2011 and 2012, grows ever more distant. The mini-planet it orbited and studied in such detail now appears only as a pinpoint of light 15 times farther from Dawn than the moon is from Earth.

    Climbing through the solar system atop a column of blue-green xenon ions, Dawn has a great deal of powered flight ahead in order to match orbits with faraway Ceres. Nevertheless, it has shown quite admirably that it is up to the task. The craft has spent more time thrusting and has changed its orbit under its own power more than any other ship from Earth. While most of the next two years will be devoted to still more thrusting, the ambitious adventurer has already accomplished much more than it has left to do. And now it is passing an interesting milestone on its interplanetary trek.”

    See the full post here.

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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