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Using Gravity Assists in the Earth-moon System as a Gateway to the Solar SystemFor spacecraft departing the Earth - Moon system, lunar flybys can significantly increase the hyperbolic escape energy (C3, in km (exp 2) /sec (exp 2) ) for a modest increase in flight time. Within approx 2 months, lunar flybys can produce a C3 of approx 2. Over 4 - 6 months, lunar flybys alone can increase the C3 to approx 4.5, or they can provide for additional periapsis burns to increase the C3 from approx 2 -3 to 10 or more, suitable for planetary missions. A lunar flyby departure can be followed by additional delta -V (such as that efficiently provided by a low thrust system, eg. Solar Electric Propulsion (SEP)) to raise the Earth - relative velocity (at a ratio of more than 2:1) before a subsequent Earth flyby, which redirects that velocity to a more distant target, all within not more than a year. This paper describes the applicability of lunar flybys for different flight times and propulsion systems, and illustrates this with instances of past usage and future possibilities. Examples discussed include ISEE-3, Nozomi, STEREO, 2018 Mars studies (which showed an 8% payload increase), and missions to Near Earth Objects (NEOs). In addition, the options for the achieving the initial lunar flyby are systematically discussed, with a view towards their practical use within a compact launch period. In particular, we show that launches to geosynchronous transfer orbit (GTO) as a secondary payload provide a feasible means of obtaining a lunar flyby for an acceptable cost, even for SEP systems that cannot easily deliver large delta-Vs at periapsis. Taken together, these results comprise a myriad of options for increasing the mission performance, by the efficient use of lunar flybys within an acceptable extension of the flight time.
Document ID
20140002056
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
External Source(s)
Authors
McElrath, Timothy P.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lantoine, Gregory
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Landau, Damon
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Grebow, Dan
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Strange, Nathan
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Wilson, Roby
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Sims, Jon
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
March 19, 2014
Publication Date
May 22, 2012
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: Global Space Exploration Conference
Location: Washington, DC
Country: United States
Start Date: May 22, 2012
End Date: May 24, 2012
Sponsors: American Inst. of Aeronautics and Astronautics, International Astronautical Federation
Distribution Limits
Public
Copyright
Other
Keywords
Solar Electric Propulsion (SEP)
lunar flybys
Near Earth Objects (NEOs)

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