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Space Trajectory Optimization
Published in Ossama Abdelkhalik, Algorithms for Variable-Size Optimization, 2021
The optimization problem, in its general form, aims to minimize some cost function; usually the overall cost of the mission in terms of the fuel expenditure. Another possibility is to optimize mission trajectory to achieve minimum mission duration. Interplanetary missions usually benefit from the gravity assist maneuvers to reduce the overall cost of the mission. In some cases, applying a deep space impulsive maneuver reduces the overall mission cost. The launch and arrival dates also affect the mission cost. Hence, the space trajectory optimization process determines the optimal values for the following parameters: the number of swing-bys, the planets to swing-by, the number of deep space maneuvers and their amounts and locations, and the departure and arrival dates. This optimization problem, in its general form, is challenging. Several optimization algorithms were developed in the literature.
Maintaining Orbits
Published in Thomas Hockey, Jennifer Lynn Bartlett, Daniel C. Boice, Solar System, 2021
Thomas Hockey, Jennifer Lynn Bartlett, Daniel C. Boice
Space-mission planners use similar interactions, or gravity assists, to reduce the amount of fuel required to propel their spacecraft. NASA launched New Horizons to the Kuiper Belt in 2006 so that the spacecraft could get a boost from Jupiter in 2007, allowing it to reach Pluto in 2015. Although such maneuvers frequently speed up a spacecraft, they also can slow one. MErcury Surface, Space ENviroment, GEochemistry, and Ranging [MESSENGER] passed Earth and Venus, and then it flew-by Mercury three times to reduce its speed relative to Mercury so that it could start orbiting the planet in 2011.
Considerations for Implementing Presidential Memorandum-20 Guidelines for Nuclear Safety Launch Authorization for Future Civil Space Missions
Published in Nuclear Technology, 2021
The last NASA radioisotope power system (RPS) missions with EGA maneuvers were Galileo (1989 launch) and Cassini (1997 launch). Galileo successfully flew a Venus-Earth-Earth-Gravity-Assist (VEEGA) mission trajectory to Jupiter, and Cassini successfully flew a Venus-Venus-Earth-Jupiter-Gravity-Assist (VVEJGA) mission trajectory to Saturn. A nominal Earth (or other planet) gravity assist occurs when the spacecraft, during its mission trajectory, is maneuvered alongside and past the planet, thereby acquiring additional momentum and thus velocity. An EGA accidental reentry occurs when the spacecraft errantly enters the atmosphere, whether the result of natural (e.g., micrometeoroid strike) or artificial (e.g., software, hardware, or navigation error) causes. The reentry angle can vary from shallow (0 deg) to steep (−90 deg). Responses of radioisotope hardware to EGA reentry are generally predicted via analysis, with supporting test data as needed, and can result in 0% to 100% release of its internal fuel. The resulting risk estimate considers the probabilities of any accident scenarios, the predicted hardware responses, and any consequences such as human health effects or land contamination.