SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way Galaxy (MW), trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the interstellar gas in the Galaxy and the Local Group that is 1,000 times larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies.The scope and flexibility of SDSS-V will be unique among both extant and anticipated spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-infrared and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultrawide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be perfectly timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, Spektr-RG-eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration spirit and infrastructure, and product deliverables in astronomy. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments. SDSS-V is actively seeking to build its consortium of institutional and individual members for a worldwide, partner-driven collaboration.

We present the first study of high-precision internal proper motions (PMs) in a large sample of globular clusters, based on Hubble Space Telescope (HST) data obtained over the past decade with the ACS/WFC, ACS/HRC, and WFC3/UVIS instruments. We determine PMs for over 1.3 million stars in the central regions of 22 clusters, with a median number of ∼60,000 stars per cluster. These PMs have the potential to significantly advance our understanding of the internal kinematics of globular clusters by extending past line-of-sight (LOS) velocity measurements to two-or three-dimensional velocities, lower stellar masses, and larger sample sizes. We describe the reduction pipeline that we developed to derive homogeneous PMs from the very heterogeneous archival data. We demonstrate the quality of the measurements through extensive Monte-Carlo simulations. We also discuss the PM errors introduced by various systematic effects, and the techniques that we have developed to correct or remove them to the extent possible. We provide in electronic form the catalog for NGC 7078 (M 15), which consists of 77,837 stars in the central 2. ′ 4. We validate the catalog by comparison with existing PM measurements and LOS velocities, and use it to study the dependence of the velocity dispersion on radius, stellar magnitude (or mass) along the main sequence, and direction in the plane of the sky (radial/tangential). Subsequent papers in this series will explore a range of applications in globular-cluster science, and will also present the PM catalogs for the other sample clusters.

We simulate the evolution of halo wide binaries in the presence of the massive compact halo objects (MACHOs) and compare our results to the sample of wide binaries in a companion paper. The observed distribution is well fitted by a single power law for angular separations, 3B5 < Á < 900 00 , whereas the simulated distributions show a break in the power law whose location depends on the MACHO mass and density. This allows us to place upper limits on the density of MACHOs as a function of their assumed mass. At the 95% confidence level, we exclude MACHOs with masses M > 43 M at the standard local halo density H . This all but removes the last permitted window for a full MACHO halo for masses M > 10 À7:5 M .

We mine the Tycho-Gaia astrometric solution (TGAS) catalog for wide stellar binaries by matching positions, proper motions, and astrometric parallaxes. We separate genuine binaries from unassociated stellar pairs through a Bayesian formulation that includes correlated uncertainties in the proper motions and parallaxes. Rather than relying on assumptions about the structure of the Galaxy, we calculate Bayesian priors and likelihoods based on the nature of Keplerian orbits and the TGAS catalog itself. We calibrate our method using radial velocity measurements and obtain 6196 highconfidence candidate wide binaries with projected separations s 1 pc. The normalization of this distribution suggests that at least 0.6% of TGAS stars have an associated, distant TGAS companion in a wide binary. We demonstrate that Gaia's astrometry is precise enough that it can detect projected orbital velocities in wide binaries with orbital periods as large as 10 6 yr. For pairs with s < ∼ 4 × 10 4 AU, characterization of random alignments indicate our contamination to be ≈5%. For s 5 × 10 3 AU, our distribution is consistent withÖpik's Law. At larger separations, the distribution is steeper and consistent with a power-law P(s) ∝ s −1.6 ; there is no evidence in our data of any bimodality in this distribution for s 1 pc. Using radial velocities, we demonstrate that at large separations, i.e., of order s ∼ 1 pc and beyond, any potential sample of genuine wide binaries in TGAS cannot be easily distinguished from ionized former wide binaries, moving groups, or contamination from randomly aligned stars.