Artist rendition of Dawn on approach to Ceres with the spacecraft's xenon ion engine glowing brightly. Image credit: NASA/JPL-Caltech

Mar 9, 2015 Dawn at Ceres: the next phase of the mission

Sen—Since departing asteroid Vesta back in September of 2012, NASA's Dawn spacecraft has been slowly traveling towards its final destination dwarf planet Ceres, the largest body in the asteroid belt, at 2.87 AU from the Sun. On Friday came the news that Dawn is officially in orbit around Ceres ending its 4.9 billion km trek that started from Earth in 2007.

This achievement has garnered Dawn the honor of being the first spacecraft to orbit a dwarf planet. Although not the only mission to visit a dwarf planet this year, Dawn will be the only spacecraft to orbit. The New Horizons mission will only be able to whiz by the Pluto-Charon system in July before heading out in to the depths of the Kuiper belt.

Right now the spacecraft is on the dark side of Ceres, where it only sees the dwarf planet as a thin illuminated sliver of a crescent at its current distance away of 60,800 kilometers. Over the next 16 months Dawn will perform science campaigns at 4 different distances above Ceres. Now that it has been gently grabbed by the gravitational pull of Ceres, Dawn will spiral in closer towards the asteroid for its first mapping orbit.

The next phase of science operations begins if all goes well on about Apr. 23rd where Dawn will begin to take new science images of Ceres to beam back to Earth. The wait will be worth it. Sitting at 13,500 km above Ceres, the frame camera will have a spatial resolution nearly 20 times better than what was achievable with the Hubble Space Telescope!

Animation of Dawn's manuevering to the first science orbit. Animation credit: NASA/JPL-Caltech

Dawn will be in a polar orbit revolving about the asteroid on a 15 day orbit. As Dawn flys from north to south above Ceres, the same patch of surface below will rotate in and out of view every 9 hours. All of Dawn's science payload will take observations in this first campaign. Dawn is equipped with four main instruments: its German built framing camera, a visible and infrared spectrometer (VIR) , and a Gamma Ray and Neutron Detector. (GRaND). The framing camera is equipped with a clear filter and 7 filters to help identify minerals. VIR will help probe the mineralogy and chemistry on Ceres. GRaND will tell us about the atomic makeup of materials on Ceres' to a depth of 1-meter.  The entire instrument suite will take data in April during this first campaign. During this twenty-day span, over 1,000 images by the framing camera and several million spectra from the VIR are planned in this first sequence of science observations. GRaND will still be sampling the cosmic gamma ray flux. It will take closer orbits for GRaND for to be sensitive to surface composition on Ceres.

Once the first set of science observations are completed at the beginning of May, Dawn will descend even lower for the next science orbit. For most of June, Dawn will enter its survey phase spending its time located at an altitude of 4,400 km. This next stage will last 22 days and will provide improved views for the framing camera and spectrometer. Then Dawn will spend July maneuvering even closer to a distance of 1,480 km above Ceres' surface during its high-altitude mapping orbit (HAMO) phase. During this part of the mission from August to mid October, Dawn will be acquiring stereo pairs with its framing camera to enable 3-D imaging of the surface. The HAMO is planned to last 56 days. The last and final orbit planed for the primary science mission is at a mere 375 km. It is expected to take 2 months just to maneuver down to such a short distance above the asteroid. At this close range, designed for GRaND to. This is also when the gravity experiment will use The gravity experiment will use change in the radio link to the NASA’s Deep Space Network to measure the subtle differences in the gravitational pull of Ceres and the spacecraft orbits. This will reveal clues about the interior of Ceres and how mass is structured below the surface.

Dawn will be in a polar orbit revolving about the asteroid on a 15 day orbit. As Dawn flys from north to south above Ceres, the same patch of surface below will rotate in and out of view every 9 hours. Dawn's science payload is equipped with a German built framing camera, a visible and infrared spectrometer (VIR) and a Gamma Ray and Neutron Detector (GRaND). The framing camera is equipped with a clear filter and 7 filters to help identify minerals. VIR will help probe the mineralogy and chemistry on Ceres, whilst GRaND will tell us about the atomic makeup of materials on Ceres to a depth of 1-meter.

The entire instrument suite will take data in April during this first campaign. Over this twenty-day span, more than 1,000 images by the framing camera and several million spectra from VIR are planned in this first sequence of science observations. Unlike VIR and the framing camera, GRaND won't be inspecting Ceres yet at these distances. It will still be sampling the cosmic gamma ray flux. It will take closer orbits later on in the mission for GRaND to be sensitive to the surface composition on Ceres.

Once the first set of science observations are completed at the beginning of May, Dawn will descend even lower for the next science orbit. For most of June, Dawn will enter its survey phase spending its time located at an altitude of 4,400 km. This next stage will last 22 days and will provide improved views for the framing camera and VIR. Then Dawn will spend July maneuvering even closer to a distance of 1,480 km above Ceres' surface during its high-altitude mapping orbit (HAMO) phase. During this part of the mission from August to mid October, Dawn will be acquiring stereo pairs with its framing camera to enable 3-D imaging of the surface. The HAMO is planned to last 56 days. The last and final orbit planed for the primary science mission is at a mere 375 km. It is expected to take 2 months just to maneuver down to such a short distance above the asteroid. This close range is specifcially for GRaND to perform its elemental anlysis. Also during this orbit using the spacecraft itself and its radio attenna will be used to measure the changes in gravity around Ceres. The gravity experiment will use the change in the radio link to the Deep Space Network attenae to measure the subtle differences in the gravitational field as Dawn orbits. This will reveal clues about the interior of Ceres and how mass is structured below the surface.

The end of Dawn's primary mission is slated for the end of June in 2016. Based on the health of the spacecraft and the amount of hydrazine thruster fuel remaining will likely determine if NASA approves an extended mission for the pioneering spacecraft. Dawn uses thrusters to point the spacecraft including the its ion engine, so once the hydrazine is exhausted, the spacecraft will not be able to point its solar panels to recharge its batteries and turn off. It will be left silently orbiting around Ceres. In the meantime, there's plenty of science to do and new mysteries to find and unravel.

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Ceres captured by Dawn's framing camera in February during approach. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Before June 2016, we'll hopefully know what are the two bright white dots spotted on Ceres' surface during Dawn's approach. Interestingly these features are in the same rough location as where previous Herschel observations detected water vapor. Perhaps these are signs of salts or water ice left over from a recent release of water from the deep interior or from a subsurface ocean. We'll know more once the framing camera, VIR, and GRaND have gotten a closer look with lots more science yet to come.

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