Workshop on the Study of the Ice Giant Planets (2014) 2023.pdf

MUSE: EXPLORATION OF THE ICE-GIANT URANUS. S. J. Saikia1, I. J. Daubar2, E. Jens3, M. Bruck Syal4, M Bunte5, C. Cook6, E. Decrossas7, A. Dove8, D. Farnocchia7, J. Jonsson9, J. M. Mihaly10, A. Ollila11, M. C. Palucis12, M. J. Poston13, G. Vardaxis14, M. S. Veto5, C. J. Budney7, K. Mitchell7, G. S. Orton7, 1Purdue University, [email protected], 2University of Arizona, 3Stanford University, 4Brown University, 5Arizona State University, 6University of Idaho, 7JPL, 8University of Central Florida, 9NASA Ames Research Center, 10Caltech, 11, University of New Mexico,12The University of California, Berkeley, 13Georgia Institute of Technology,14Iowa State University.

Introduction: MUSE (Mission to Uranus for Sci- ated continuously during the 16-day orbit. The magne- ence and Exploration)—to explore the Uranian system tometer also takes measurements continuously. In addi- via an orbiter and a probe is presented. This mission tion, the mission could also take advantage of an op- concept accomplishes high-priority outer Solar System portunistic flyby of the satellite Umbriel from a dis- science goals as set forth by the 2013 Planetary Sci- tance of ~255,600 km at closest approach on one of its ence Decadal Survey [1]. Uranus belongs to a class of science orbits. The probe instruments take measure- planets called “ice giants:” The term “Ices” in this ments on noble-gas abundances, isotopic ratios, tem- context refers to volatile gases (e.g., H20, NH3, and perature, pressure, gravity, density, and cloud presence CH4) that are solid at low temperatures of the outer as a function of depth. Both orbiter and probe can use Solar System. Ice giants, including Neptune, are distin- radio tracking for gravity science. guished from gas giants Jupiter and Saturn by a lack of Table 1: Science instruments in MUSE large hydrogen and helium envelopes. Humankind’s Orbiter Measurement Objectives last close encounter with Uranus was Voyager 2 in Medium Angle Camera Global tracking of clouds, 1986, which greatly expanded our understanding of the Mid/Far Infrared Map- winds, chemical composition, planet [2]. Ice giants also have a growing relevance to ping Spectrometer and thermal emission of the (IRMS) atmosphere; ring and satellite exoplanet studies, as the majority of observed planets imaging are Uranus-sized [3]. The scientific objectives of Magnetometers (2) Magnetic field, interior struc- MUSE are adapted from those in Decadal Survey [1]. Doppler Imager (DI) ture Spacecraft and Mission Design: The MUSE Probe [4] Measurement Objectives spacecraft consists of an orbiter and a donated probe. Mass Spectrometer Atmospheric characteriza- The orbiter is a three-axis stabilized platform with a Atmospheric Structure tions: compositions, atmos- mass of 3192 kg). The 153-kg entry probe is a 45° Instrument Package pheric structure, cloud struc- sphere-cone and can operate between 100 mbar and 5 Nephelometer ture, particles bars. The orbiter is powered by four Advanced Stirling Ultra Stable Oscillator Atmospheric structure, gravity Radioisotope Generators combined with two ion batter- ies. Table 1 summarizes the science instruments on the Mission Cost: The quasi-grassrots models of the orbiter and the probe, together with the science objec- JPL Team-X generate the cost estimate; which is tives they address. Atlas 551 is the launch vehicle as- $1328.6M in Fiscal Year (FY) 2013 dollars not includ- sumed. An Earth-Mars-Jupiter gravity assist trajectory ing the launch-vehicle costs. The entry probe was con- with two deep-space maneuvers is used with a launch sidered to be provided as government furnished date of 03/02/2019, and time-of-flight of 14 years. The equipment, hence it did not contribute to the total cost. total ΔV for the mission is 1526 m/s. Acknowledgment: The work presented in this pa- th Science Operations: The nominal science orbit is per was completed during the 2013 NASA’s 25 An- 16 days and the nominal mission includes 17 such or- nual Planetary Science Summer School, at the NASA bits. The design of the science orbits (highly inclined, Jet Propulsion Laboratory. elliptical) is driven by the requirements of the onboard References: [1] Squyres, S. et al. (2011), Vision instruments. The periapse of the science orbit is be- and Voyages for Planetary Science in the Decade tween the inner rings and the planet, which represents 2013–2022, National Academies Press. [2] Bergstralh, some risks, but was necessary to close the design with- J. T., et al., (ed.) (1991) Uranus. University of Arizona in the requirements and ΔV budget. The Multi-spectral Press, Tucson, AZ. [3] Batalha, N. M., et al. (2013) Medium Angle Camera will take images on orbit days The A. J. Supplement Series, 204(2), 24. [4] Hubbard 2–16 in 300 to 900 nm range. The Doppler Imager (DI) W. B., (2010) Ice Giants Decadal Study, NASA. will be nominally active during days 6–11, when the orbiter is farthest from the planet, since it uses full-disk images that do not require high resolution.. The mid- and far Infrared Mapping Spectrometer IRMS is oper-