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TOPIC: Dawn spacecraft


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Let the countdown begin. NASA's Dawn spacecraft is less than one year away from giant asteroid Vesta.

Dawn is slated to enter orbit around Vesta in late July 2011. As the first breathtaking images are beamed back to Earth, researchers will quickly combine them into a movie, allowing us all to ride along.
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Title: The Dynamical Environment of Dawn at Vesta
Authors: Pasquale Tricarico, Mark V. Sykes
(Version v2)

Dawn is the first NASA mission to operate in the vicinity of the two most massive asteroids in the main belt, Ceres and Vesta. This double-rendezvous mission is enabled by the use of low-thrust solar electric propulsion. Dawn will arrive at Vesta in 2011 and will operate in its vicinity for approximately one year. Vesta's mass and non-spherical shape, coupled with its rotational period, presents very interesting challenges to a spacecraft that depends principally upon low-thrust propulsion for trajectory-changing manoeuvres. The details of Vesta's high-order gravitational terms will not be determined until after Dawn's arrival at Vesta, but it is clear that their effect on Dawn operations creates the most complex operational environment for a NASA mission to date. Gravitational perturbations give rise to oscillations in Dawn's orbital radius, and it is found that trapping of the spacecraft is possible near the 1:1 resonance between Dawn's orbital period and Vesta's rotational period, located approximately between 520 and 580 km orbital radius. This resonant trapping can be escaped by thrusting at the appropriate orbital phase. Having passed through the 1:1 resonance, gravitational perturbations ultimately limit the minimum radius for low-altitude operations to about 400 km, in order to safely prevent surface impact. The lowest practical orbit is desirable in order to maximize signal-to-noise and spatial resolution of the Gamma-Ray and Neutron Detector and to provide the highest spatial resolution observations by Dawn's Framing Camera and Visible InfraRed mapping spectrometer. Dawn dynamical behaviour is modelled in the context of a wide range of Vesta gravity models. Many of these models are distinguishable during Dawn's High Altitude Mapping Orbit and the remainder are resolved during Dawn's Low Altitude Mapping Orbit, providing insight into Vesta's interior structure.

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Engineers Assess Dawn's Reaction Wheel

Engineers are studying the reaction wheels on NASA's Dawn spacecraft after automatic sensors detected excess friction building up in one of them and powered it off early on the morning of June 17, 2010. Reaction wheels spin to help a spacecraft maintain attitude control, and Dawn, which is exploring the asteroid belt, uses three wheels in normal operations.
The three other reaction wheels are functioning normally. Mission managers said plans for Dawn to visit the asteroid Vesta in 2011 and 2012 and dwarf planet Ceres in 2015 will not be not affected.

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NASA's Dawn Spacecraft Fires Past Record for Speed Change

Deep in the heart of the asteroid belt, on its way to the first of the belt's two most massive inhabitants, NASA's ion-propelled Dawn spacecraft has eclipsed the record for velocity change produced by a spacecraft's engines.
The previous standard-bearer for velocity change, NASA's Deep Space 1, also impelled by ion propulsion, was the first interplanetary spacecraft to use this technology. The Deep Space 1 record fell on Saturday, June 5, when the Dawn spacecraft's accumulated acceleration over the mission exceeded 4.3 kilometres per second.

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Dawn remains on course and on schedule for its appointments with Vesta and Ceres, colossal protoplanets in the main asteroid belt. Under the gentle and continuous thrust of its ion propulsion system, its journey through the solar system brings it ever closer to its first target.
Last months log included an overview of many of the spacecrafts activities during the final 3 months before its August 2011 arrival in the first science orbit at Vesta.

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Dawn usually interrupts ion thrusting once a week for about 8 hours to point its main antenna to Earth. On November 30, however, instead of resuming thrusting, it dutifully followed different instructions that were stored onboard.
The spacecraft began the 5 days of special activities by activating the gamma ray and neutron detector (GRaND). Despite its name, GRaND is not at all pretentious, but its capabilities are quite impressive. It will reveal the atomic constituents of the surfaces of Vesta and Ceres. GRaNDs measurements of space radiation this month showed it to be in excellent health. After a week of smooth operation, it was deactivated on December 7.

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NASA's Dawn spacecraft re-entered our solar system's asteroid belt today, Nov. 13, and this time it will stay there.
Dawn first entered the belt (whose lower boundary may be defined as the greatest distance Mars gets from the sun (249,230,000 kilometres) in June 2008. It remained within the belt for 40 days before its carefully planned orbital path brought it below the asteroid belt's lower boundary.

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Dawn continues to make steady progress on its journey through the solar system. The spacecraft has devoted another month to thrusting with its ion propulsion system, ever with its sights set on its rendezvous with Vesta in July 2011. While it will have other assignments along the way, propelling itself to the giant protoplanet deep in the main asteroid belt remains its principal responsibility.

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Dawn is celebrating the second anniversary of leaving its home planet by engaging in the same function it has performed most of its time in space: with the utmost patience, it is using its ion propulsion system to gradually modify its orbit around the Sun.
In its interplanetary travels, the spacecraft has thrust for a total of about 389 days, or 53% of the time (and about 0.000000008% of the time since the Big Bang). While for most spacecraft, firing a thruster to change course is a special event, it is Dawn's wont. All this thrusting has cost the craft only 103 kilograms of its supply of xenon propellant, which was 425 kilograms on September 27, 2007.

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Update:
The DELTA 2 Rocket body re-entered the Earths atmosphere on the 18th September, 2009, @ 06:56 GMT 1 minute.

Inclination: 26.5
Revolution Number: 8159
Predicted Location: 22 S, 205 E

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