Control of Lagrange point orbits using solar sail propulsion

Several missions have utilised halo orbits around the L1 and L2 previous termLagrangenext term points of the Earth-Sun system. Due to the instability of these orbits, station-keeping techniques are required to prevent escape after orbit insertion. This paper considers using solar sail propulsion to provide station-keeping at quasi-periodic orbits around L1 and L2. Stable manifolds will be identified which provide near-Earth insertion to a quasi-periodic trajectory around the libration point. The possible control techniques investigated include solar sail area variation and solar sail pitch and yaw angle variation. Hill's equations are used to model the dynamics of the problem and optimal control laws are developed to minimise the control requirements. The constant thrust available using solar sails can be used to generate artificial libration points Sunwards of L1 or Earthwards of L2. A possible mission to position a science payload Sunward of L1 will be investigated. After insertion to a halo orbit at L1, gradual solar sail deployment can be performed to spiral Sunwards along the Sun-Earth axis. Insertion -V requirements and area variation control requirements will be examined. This mission could provide advance warning of Earthbound coronal mass ejections (CMEs) responsible for magnetic storms

Dynamics, stability and control of displaced non-Keplerian orbits

Non-Keplerian trajectories around the Lagrange points of the three-body problem have been thoroughly investigated enabling many novel space science missions. Identification of heteroclinic manifolds linking halo orbits around the L1 and L2 Lagrange points has lead to the discovery of the so-called interplanetary superhighway. This thesis considers possible periodic and quasi-periodic non-Keplerian orbits around artificial libration points generated using solar sail propulsion. Dynamical models are developed to represent the motion of a solar sail in a two- and three- body context. Artificial libration points are identified using the solar sail to provide a constant axial force. The stability of these libration points is investigated using a linear approximation of the equations of motion and a non-linear analysis. Established techniques are applied to identify halo orbits and Lissajous trajectories around these libration points. Manifolds are identified to provide transfer trajectories to these orbits from near the Earth. Solar sail control techniques are developed to prevent escape from the nominal orbit after insertion

LDRD 2011 Annual Report: Laboratory Directed Research and Development Program Activities

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Synthesis of certain nitriles useful in the formation of pi complexes

Call number: LD2668 .T4 1962 B6

Why should wild nature be preserved? A dialogue between biblical theology and biodiversity conservation.

The past century has seen a rapid acceleration in global anthropogenic biodiversity loss, despite massively increased conservation effort and knowledge. Consequently, there are wide-ranging debates around whether economic and instrumental valuations of wild nature assist in its preservation, or whether they commodify entities that possess intrinsic or inherent value. This thesis seeks to bring insights from biblical theology into dialogue with conservation biology concerning the value of wild nature and the place of humanity in relation to it. Through a theological overview of four major biblical themes expressing God’s initiative towards all that exists (creation, covenant, reconciliation in Christ, and eschatological consummation), it is proposed that God’s relationship with nonhuman creation provides a useful conceptual structure in addressing contemporary conservation dilemmas. In particular, it is suggested that debates regarding anthropocentric or ecocentric, and instrumental (including economic) or intrinsic valuations of wild nature, and similarly between ‘conservation’ and ‘preservation’, may constructively be placed within a wider context regarding humanity’s place with regard to its fellow creatures. Within a Christian worldview it is proposed that this is ultimately a Theo-eco-centric context wherein all value, nonhuman and human, is contingent upon God’s purposes from creation to consummation. The conclusion of the thesis brings the theological insights of the four central chapters into dialogue again with contemporary conservation debates. Moving beyond ecocentric (nature for itself) and anthropocentric (nature for people) motivations for conserving wild nature, it proposes a concept of ‘people within nature’ that is theologically coherent but expressed in language that brings biblical theology into debate both with secular conservationists and those of other faith traditions. It recognises both humanity’s total dependence on thriving ecosystems and the particular role humans play in nature’s protection. The language of virtue ethics is posited as being particularly valuable in this regard. It is hoped that this thesis will be a useful contribution to current conservation debates surrounding how nature should be valued, and will also encourage deeper theological reflection on the place and value of nonhuman animals.No contractual arrangements, but received funding from the Faraday Institute for Science and Religio

Displaced geostationary orbits using hybrid low-thrust propulsion

In this paper, displaced geostationary orbits using hybrid low-thrust propulsion, a complementary combination of Solar Electric Propulsion (SEP) and solar sailing, are investigated to increase the capacity of the geostationary ring that is starting to become congested. The SEP propellant consumption is minimized in order to maximize the mission lifetime by deriving semi-analytical formulae for the optimal steering laws for the SEP and solar sail accelerations. By considering the spacecraft mass budget, the performance is also expressed in terms of payload mass capacity. The analyses are performed both for the use of pure SEP and hybrid low-thrust propulsion to allow for a comparison. It is found that hybrid low-thrust control outperforms the pure SEP case both in terms of payload mass capacity and mission lifetime for all displacements considered. Hybrid low-thrust propulsion enables payloads of 255 to 487 kg to be maintained in a 35 km displaced orbit for 10 to 15 years. Adding the influence of the J2 and J22 terms of the Earth’s gravity field has a small effect on this lifetime, which becomes almost negligible for small values of the sail lightness number. Finally, two SEP transfers that allow for an improvement in the performance of hybrid low-thrust control are optimized for the propellant consumption by solving the accompanying optimal control problem using a direct pseudospectral method. The first type of transfer enables a transit between orbits displaced above and below the equatorial plane, while the second type of transfer enables customized service for which a spacecraft is transferred to a Keplerian parking orbit when geostationary coverage is not needed. While the latter requires a modest propellant budget, the first type of transfer comes at the cost of an almost negligible SEP propellant consumption