Gravitationally bound geoengineering dust shade at the inner Lagrange point

This paper presents a novel method of space-based geoengineering which uses the mass of a captured near Earth asteroid to gravitationally anchor a cloud of unprocessed dust in the vicinity of the _L1${\mathrm{L}}_1$ position to reduce the level of solar insolation at Earth. It has subsequently been shown that a cloud contained within the zero-velocity curve of the largest near Earth asteroid, Ganymed, can lead to an insolation reduction of 6.58% on Earth, which is significantly larger than the 1.7% required to offset a 2 °C increase in mean global temperature. The masses of the next largest near Earth asteroids are found to be too small to achieve the required level of insolation reduction, however, they are significant enough to be used as part of a portfolio of geoengineering schemes.     

Mission analysis and systems design of a near-term and far-term pole-sitter mission

This paper provides a detailed mission analysis and systems design of a near-term and far-term pole-sitter mission. The pole-sitter concept was previously introduced as a solution to the poor temporal resolution of polar observations from highly inclined, low Earth orbits and the poor high-latitude coverage from geostationary orbit. It considers a spacecraft that is continuously above either the north or south pole and, as such, can provide real-time, continuous and hemispherical coverage of the polar regions. Being on a non-Keplerian orbit, a continuous thrust is required to maintain the pole-sitter position. For this, two different propulsion strategies are proposed, which result in a near-term pole-sitter mission using solar electric propulsion (SEP) and a far-term pole-sitter mission where the SEP thruster is hybridized with a solar sail. For both propulsion strategies, minimum propellant pole-sitter orbits are designed. In order to maximize the spacecraft mass at the start of the operations phase of the mission, the transfer from Earth to the pole-sitter orbit is designed and optimized assuming either a Soyuz or an Ariane 5 launch. The maximized mass upon injection into the pole-sitter orbit is subsequently used in a detailed mass budget analysis that will allow for a trade-off between mission lifetime and payload mass capacity. Also, candidate payloads for a range of applications are investigated. Finally, transfers between north and south pole-sitter orbits are considered to overcome the limitations in observations due to the tilt of the Earth's rotational axis that causes the poles to be alternately situated in darkness. It will be shown that in some cases these transfers allow for propellant savings, enabling a further extension of the pole-sitter mission.     

Atmospheric science on the Galileo mission

Observations from the ground and four fly-by spacecraft have provided initial reconnaissance of Jupiter's atmosphere. The Pioneer and Voyager data have raised new questions and underlined old ones about the basic state of the atmosphere and the processes determining the atmosphere's behavior. This paper discusses the main atmospheric science objectives which will be addressed by the Galileo (Orbiter and Probe) mission, organizing the discussion according to the required measurements of chemical composition, thermal structure, clouds, radiation budget, dynamics, upper atmosphere, and satellite atmospheres. Progress on the key questions will contribute not only to our knowledge of Jupiter's atmosphere but to a general understanding of atmospheric processes which will be valuable for helping us to understand the atmosphere and climate of the Earth.Realization of the atmospheric science objectives of the Galileo mission depends upon: (a) coordinated measurements from the entry probe and the orbiter; (b) global observations; and (c) observations over the range of time-scales needed to characterize the basic dynamical processes.The Atmospheres Working Group also includes: M. D. Allison, M. J. S. Belton, R. W. Boese, R. W. Carlson, C. R. Chapman, T. Encrenaz, V. R. Eshleman, P. J. Gierasch, C. W. Hord, H. T. Howard, L. J. Lanzerotti, H. B. Niemann, G. S. Orton, T. Owen, C. B. Pilcher, J. B. Pollack, B. Ragent, W. B. Rossow, A. Seiff, A. I. Stewart, P. H. Stone, F. W. Taylor, G. L. Tyler, U. von Zahn, and R. A. West.