Optimal Trajectories for Secondary Payloads from Geosynchronous Transfer Orbits to the Moon
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Optimal Trajectories for Secondary Payloads from Geosynchronous Transfer Orbits to the Moon Scott R. Dahlke! and Brian E. McKay2 Abstract Trajectories that provide fuel-efficient transfers from Geosynchronous Transfer Orbits (GTO) to the Moon are examined in this paper. These trajectories are becoming more important as relatively inexpensive launch options to GTO are now available by launching as a secondary payload. The main focus of this research is to explore possibilities for reaching lunar orbit via methods other than launching directly into the lunar orbit plane or waiting in a parking orbit for orbit perturbations to create favorable transfer conditions. Through the use of carefully chosen bi-elliptic type transfers or transfer orbits with optimally placed plane changes, this research shows that relatively efficient transfers to the Moon can be obtained from GTO.
Introduction This paper focuses on finding low LlV trajectories from Geosynchronous Transfer Orbits (GTO) to the Moon. The driving factor behind this research is that, recently, options have been increasing for launching spacecraft as secondary payloads on many different launch vehicles. By designing spacecraft to launch as a secondary payload, launch costs can be realized at a much lower level than launching as a primary payload. More than a dozen different launch vehicles are available that can provide a secondary payload capability. [1] Trajectories that provide fuel-efficient transfers from these Geosynchronous Transfer Orbits to the Moon may then be implemented for low cost lunar missions. Although being launched as a secondary payload has its monetary advantages, the disadvantages that exist can be quite difficult to overcome. For secondary payloads wishing to go into lunar orbit, it has been found that an efficient lunar transfer can be accomplished from GTO if: 1) the spacecraft can be launched at a specific time 'Associate Professor, Department of Astronautics, United States Air Force Academy, CO 80840. E-mail: [email protected]. 2Cadet, Department of Astronautics, United States Air Force Academy, CO 80840. E-mail: [email protected].
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of the day allowing for a lunar transfer window or 2) enough radiation protection can be applied to the spacecraft to allow it to remain in GTO until the apogee direction precesses into the lunar orbit plane. The main aspect of this paper is to explore possibilities for reaching lunar orbit via methods other than those discussed above. Since most secondary payloads cannot choose their launch time, and the satellites are generally without heavy radiation protection, these alternative methods of transferring to the Moon may be desirable. One possibility is to go directly from the GTO to lunar orbit with two impulsive bums involving plane changes. This method works regardless of the relative position of both the Moon and the spacecraft, and regardless of the difference in inclination between the GTO and Moon's orbit. However, in general, this method requires a large amount
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