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The Dawn science operations team has designed the Vesta mission within the constraints of a low-cost Discovery mission, and will apply the same methodology to the Ceres mission. The design employs proactive mapping mission strategies and tactics such as functional redundancy, adaptability to trajectory uncertainties, and easy sequence updates to deliver reliable and robust sequences. Planning tools include the Science Opportunity Analyzer and other multi-mission tools, and the Science time-ordered listings. Science operations are conducted jointly by the Science Operations Support Team at the Jet Propulsion Laboratory (JPL) and the Dawn Science Center at the University of California, Los Angeles (UCLA). The UCLA Dawn Science Center has primary responsibility for data archiving while the JPL team has primary responsibility for spacecraft and instrument operations. Constraints and uncertainties in the planning and sequencing environment are described, and then details of the science plan are presented for each mission sub-phase. The plans indicate that Dawn has a high probability of meeting its science objectives and requirements within the imposed constraints.

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The Dawn spacecraft orbited Asteroid (4) Vesta for a year, and returned diskresolved images and spectra covering visible and near-infrared wavelengths at scales as high as 20 m/pix. The visible geometric albedo of Vesta is ∼ 0.36. The disk-integrated phase function of Vesta in the visible wavelengths derived from Dawn approach data, previous ground-based observations, and Rosetta OSIRIS observations is consistent with an IAU H-G phase law with H=3.2 mag and G=0.28. Hapke's modeling yields a disk-averaged single-scattering albedo of 0.50, an asymmetry factor of -0.25, and a roughness parameter of ∼20 deg at 700 nm wavelength. Vesta's surface displays the largest albedo variations observed so far on asteroids, ranging from ∼0.10 to ∼0.76 in geometric albedo in the visible wavelengths. The phase function of Vesta displays obvious systematic variations with respect to wavelength, with steeper slopes within the 1-and 2-micron pyroxene bands, consistent with previous ground-based observations and laboratory measurement of HED meteorites showing deeper bands at higher phase angles. The relatively high albedo of Vesta suggests significant contribution of multiple scattering. The non-linear effect of multiple scattering and the possible systematic variations of phase function with albedo across the surface of Vesta may invalidate the traditional algorithm of applying photometric correction on airless planetary surfaces.179

Dawn is the first mission to attempt to orbit two distant planetary bodies. The objects chosen, 4 Vesta followed by 1 Ceres, are the two most massive members of the asteroid belt that appear to have been formed on either side of the dew line in the early solar nebula. This paper describes the present status of the mission development and the plans for operation at Vesta and Ceres.