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Abstract: In the early to mid-2000s, NASA made substantial progress in the development of solar sail propulsion systems. Solar sail propulsion uses the solar radiation pressure exerted by the momentum transfer of reflected photons to generate a net force on a spacecraft. To date, solar sail propulsion systems were designed for large robotic spacecraft. Recently, however, NASA has been investigating the application of solar sails for small satellite propulsion. The NanoSail-D is a subscale solar sail system designed for possible small spacecraft applications. The NanoSail-D mission flew on board the ill-fated Falcon Rocket launched August 2, 2008, and due to the failure of that rocket, never achieved orbit. The NanoSail-D flight spare is ready for flight and a suitable launch arrangement is being actively pursued. This paper will present an introduction solar sail propulsion systems and an overview of the NanoSail-D spacecraft. [ABSTRACT FROM AUTHOR]

Abstract: Orbital debris poses a significant threat to spacecraft health and safety. Recent events such as China''s anti-satellite test and the Breeze-M rocket explosion have led to an even greater awareness and concern in the satellite community. Therefore, the National Aeronautics and Space Administration (NASA) has established requirements that routine conjunction assessment screening shall be performed for all maneuverable spacecraft having perigees <2000km or within 200km of geosynchronous altitude. NASA''s Goddard Space Flight Center (GSFC) has developed an operational collision risk assessment process to protect NASA''s high-value unmanned (robotic) assets that has been in use since January 2005. This paper provides an overview of the NASA robotic conjunction assessment process, including descriptions of the new tools developed to analyze close approach data and of the risk mitigation strategies employed. In addition, statistical data describing the number of conjunctions experienced are presented. A debris avoidance maneuver performed by Aura in June of 2008 is described in detail to illustrate the process. [Copyright &y& Elsevier]

Abstract: As the NASA Vision for Space Exploration takes shape, one of the key issues that will affect the lunar exploration is the ability to provide electric power to various surface locations. This power should be available through daylight times as well as night times. While nuclear reactors and radioisotope power sources are a choice for continuous power, it is the purpose of this paper to explore the advantages of an electric propulsion spacecraft plus laser power beaming to provide power to any location on the lunar surface. The starting point for the electric propulsion mission is a 500km altitude. Thrusting only occurs when the satellite is in sunlight. Radiation damage that occurs during transit of the Earth''s radiation belts is taken into account. The satellite is placed in a 30,000 by 500km orbit around the moon where it beams power to locations within 45° north or south of the equator. Laser power beaming only occurs when the satellite views the sun and the surface location is in the dark. Power delivered to the surface over a two year mission is presented along with the results of adding a second satellite. With two satellites, the maximum time when the site won’t receive power at night is about three days. This significantly reduces the need for a lunar storage system. [Copyright &y& Elsevier]

Abstract: First in NASA''s New Frontiers series of missions, the New Horizons spacecraft was successfully launched on January 19, 2006. New Horizons is scheduled to perform a gravity assist at Jupiter on February 28, 2007, arrive at Pluto on July 14, 2015; completing an extended mission to at least one Kuiper Belt Object in subsequent years. The concept of operations requires a star tracker that operates autonomously both in a standard three-axis “staring” mode during operations involving instrument observations and in a spin stabilized mode during cruise operations with nominal rotational rates up to 5rpm. With the support of the Johns Hopkins University Applied Physics Laboratory, Galileo Avionica redesigned their Autonomous Star Trackers (ASTR) to use time-delayed integration techniques to provide autonomous spacecraft attitude estimates at 10Hz at spin rates up to 10rpm. This paper will present the performance of the upgraded ASTR in both inertial stare and spin stabilized modes for the first six months of the mission. In addition, effects of the vehicle motion on performance, effects of stray light and direct Sun blinding on tracking and performance, and unanticipated “features” or characteristics of the ASTRs will be discussed. [Copyright &y& Elsevier]

Abstract: Upcoming National Aeronautics and Space Administration (NASA) mission concepts include satellite arrays to facilitate imaging and identification of distant planets. These mission scenarios are diverse, including designs such as the terrestrial planet finder-occulter (TPF-O), where a monolithic telescope is aided by a single occulter spacecraft, and the micro-arcsecond X-ray imaging mission (MAXIM), where as many as 16 spacecraft move together to form a space interferometer. Each design, however, requires precise reconfiguration and star tracking in potentially complex dynamic regimes. This paper explores control methods for satellite imaging array reconfiguration in multi-body systems. Specifically, optimal nonlinear control and geometric control methods are derived and compared to the more traditional linear quadratic regulators, as well as input state feedback linearization. These control strategies are implemented and evaluated for the TPF-O mission concept. [Copyright &y& Elsevier]

Abstract: The intentional break-up of the Fengyun-1C spacecraft on 11 January 2007 via a hypervelocity collision with a ballistic object created the most severe artificial debris cloud in Earth orbit since the beginning of space exploration. More than 2000 debris of the order of 10cm or greater in size have been identified by the US Space Surveillance Network. The majority of these debris reside in long-lived orbits. The NASA Orbital Debris Program Office has conducted a thorough examination of the nature of the Fengyun-1C debris cloud, using Space Surveillance Network (SSN) data for larger debris and special Haystack radar observations for smaller debris. These data have been compared with the NASA standard satellite break-up model for collisions, and the results are presented in this paper. The orbital longevity of the debris have also been evaluated for both small and large debris. The consequent long-term spatial density effects on the low Earth orbit regime and the potential effect of the debris cloud on the growth of the near-Earth satellite population have been addressed. [Copyright &y& Elsevier]

Abstract: The Cassini Mission to Saturn, a joint undertaking by NASA, the European Space Agency, and the Italian Space Agency, is now at about the mid-point of its planned four-year tour of the Saturnian system. Close encounters with Titan and the smaller icy satellites are occurring on schedule, and observations of these bodies along with Saturn''s atmosphere, its rings, and magnetosphere are being made and scientific data returned on a daily basis. The icy satellites are turning out to be more distinct and unique than had been anticipated, the dynamics of the ring particles have been shown to be even more extensive than expected, and Titan''s atmosphere had surprises for both the scientists as well as the engineers. A denser than expected upper atmosphere of Titan has led to the requirement to modify the planned orbital tour about Saturn to increase the flyby altitudes for about 20 of the Titan flybys to values above the originally planned 950km level in order to avoid the risk of atmospherically induced torques causing the spacecraft to be unable to maintain its commanded attitude. Navigation of the spacecraft on the tour continues to go exceptionally well, with optical navigation enabling delivery accuracies to some of the satellites down to the 1 or 2km level, and propellant consumption is running slightly below budget. Science observation sequence development and execution have been highly successful in acquiring virtually all of the originally designed observations. This paper summarizes the supporting engineering activities over the past year in support of operating the mission, as well as provides a high-level summary of the scientific results of the Cassini mission to date. [Copyright &y& Elsevier]

Abstract: Students from the University of Michigan have developed a small satellite—dubbed Icarus—to serve as an active endmass for NASA''s ProSEDS (Propulsive Small Expendable Deployer System) electrodynamic-tether propulsion mission. The ProSEDS experiment will be launched in early 2004 as a secondary payload attached to the second stage of a Delta-II rocket. Following the completion of the Delta-II primary mission, the Icarus endmass satellite will be cast off from the Delta-II second stage, deploying a 12 km space tether. Throughout tether deployment, and for the duration of the ProSEDS mission, Icarus will collect and transmit data on tether deployment and dynamics. The endmass is responsible for providing tether–endbody location information (using a GPS receiver) and endbody attitude dynamics (using an aspect magnetometer). The data from these instruments will be stored and transmitted to ground telemetry stations. This paper details the Icarus satellite system and lessons learned from the project. [Copyright &y& Elsevier]

Delta IV is one of two competing Evolved Expendable Launch Vehicle (EELV) systems being developed in an industry/United States Government partnership to meet the needs of the new era of space launch for the early decades of the 21st Century. The Rocketdyne Division of The Boeing Company and the United States Air Force have developed a 650 Klbf sea-level (2.9 MN) class liquid hydrogen/liquid oxygen main engine for the Delta IV family of EELV. The purpose of this paper is to present the innovative approach to the design, development, testing and certification of the RS-68 engine. [Copyright &y& Elsevier]