SERVICING and DEPLOYMENT of NATIONAL RESOURCES in SUN-EARTH LIBRATION POINT ORBITS 53Th International Astronautical Congress

SERVICING AND DEPLOYMENT OF NATIONAL RESOURCES IN SUN-EARTH LIBRATION POINT ORBITS D. C. Folta, M. Beckman, S. J. Leete, G. C. Marr, M. Mesarch, and S. Cooley NASA Goddard Space Flight Center Greenbelt, MD, USA 53th International Astronautical Congress The World Space Congress - 2002 10-3 9 Oct 2002 I Houston, Texas For permission to copy or republish, contact the International Astronautical Federation, 3-5 Rue Mario-Nikis, 75015 Paris, France SERVICING AND DEPLOYMENT OF NATIONAL RESOURCES IN SUN-EARTH LIBRATION POINT ORBITS D. C. Folta, M. Beckman, G. C. Marr, M. Mesarch, S. Cooley Flight Dynamics Analysis Branch NASA Goddard Space Flight Center, Greenbelt, MD, USA dfolta@;gsfc.nasa.gov S. J. Leete Space Science Missions Branch, NASA Goddard Space Flight Center, Greenbelt, MD, USA Abstract Spacecraft travel between the Sun-Earth system, the Earth-Moon system, and beyond has received extensive attention recently. The existence of a connection between unstable regions enables mission designers to envision scenarios of multiple spacecraft traveling cheaply from system to system, rendezvousing, servicing, and refbeling along the way. This paper presents examples of transfers between the Sun-Earth and Earth-Moon systems using a true ephemeris and perturbation model. It shows the AV costs associated with these transfers, including the costs to reach the staging region from the Earth. It explores both impulsive and low thrust transfer trajectories. Additionally, analysis that looks specifically at the use of nuclear power in libration point orbits and the issues associated with them such as inadvertent Earth return is addressed. Statistical analysis of Earth returns and the design of biased orbits to prevent any possible return are discussed. Lastly, the idea of rendezvous between spacecraft in libration point orbits using impulsive maneuvers is addressed. Introduction Some obstacles to human servicing are the Satellite servicing has received a great deal orbital mechanics, the cost of lifting mass, and of study and significant execution. Several the problems associated with travel time and satellites were designed for servicing using thermal and instrument environmental the Multi-Mission Modular Spacecraft design, conditions. As more ambitious missions are including Solar Max Mission, Landsat IV & planned, such as the placement of the Next V, Upper Atmosphere Research Satellite, and Generation Space Telescope (NGST) and Extreme Ultra-Violet Explorer. Rescue several other missions into a Sun-Earth L2 missions have been performed on (SEL2) or SELl libration orbit, servicing by geostationary satellites trapped in low earth the Shuttle and the use of low-Earth orbits orbit, such as WESTAR-IV, PALAPA-B, (LEOS) will be limited. Development of Intelsat-VI, and LEASAT/SYNCOM-IV. robotic satellite servicing capabilities, such as More routine human servicing work DARPA’s Orbital Express, NASA’s occurs(ed) at various space stations Robonaut, and the University of Maryland’s (International Space Station, Skylab, Salyut, Ranger, may provide for the possibility of and Mir). The servicing of the Hubble Space robotic satellite servicing at various orbital Telescope (HST) has become a successful locations in the near- or mid-range time landmark, allowing HST to become one of frame. NASA’s most productive missions. 1,2,334 An enabling set of circumstances for an Copyright @ 2002 by the American Institute of Aeronautics and Astronautics, Inc. No Copyright is expansion of satellite servicing would be the asserted in the United States under Title 17, U.S. Code. placement of humans and valuable robotic The US. Government has a royalty-fiee license to assets in close proximity to one another, A exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner I space architecture that includes these The servicing of national resources in the conditions is a servicing facility in a lissajous Earth-Moon and the Sun-Earth regions is or halo orbit about one of the Earth-Moon LI made difficult by the unstable dynamics of (EMLI), Earth-Moon L2 (EML2), or Earth- these regions. Trip times associated with Moon L3 (EMLJ co-linear libration points6. achieving SELl and SEL2 orbits can vary From such an orbit, spacecraft have access to from weeks to months while achieving EML, a wide variety of interesting orbits at a and EML2 may vary from days to weeks, with relatively lower AV cost. Use of the Earth- both dependent upon many initial conditions Moon stable L4 and L5 Lagrange regions such as energy and departure locations. The provides additional scenarios. These servicing design of a trajectory used to achieve locations are also an excellent staging point servicing mission requirements is intricate but for lunar surface and Earth-Moon orbital can be facilitated by the use of unique orbits exploration.’ The orbits also have ready to achieve the proper flight time or to access to geostationary orbits and transfer minimize the necessary fuel mass. The use of back to LEO orbits. Table 1 provides a brief dynamical systems (such as invariant overview of Earth-Moon libration orbit manifolds) and optimization plays a key role staging node characteristics. in designing transfer trajectories, as these tools afford the luxury of using natural Table 1. Earth/Moon Libration Orbit dynamics where possible. Results Overviei demonstrate the viability of some unique Characteristics Potential Uses transfers that meet the NASA Exploration EMLl -Unstable orbit -Assembly & Team (NEXT) goals. These goals focus on between earth and maintenance of opening the human frontier beyond low-Earth moon SIC orbit by building infrastructure robotically and -Halo:continuous -Access to lunar with humans in-situ at strategic outposts - view of the earth, surface libration points, planetary moons, planets, etc. moon, and sun, -Low Av access - and include a wide range of exploration -Earth I moon to SEL, transfer always >150° manifolds tools (e.g., space planes, balloons, human- separation constructed and maintained observatories -Unstable orbit far -Assembly & located at libration point, etc.).8 side of moon maintenance of -Halo: continuous SIC A primary purpose of this paper is to detail view of earth, -Access to lunar mission planning scenarios for servicing of moon, sun, surface national resources and to contrast them to -At full moon, -Corn relay to other transfer options. It explores the transfer surdearthlmoord lunar far side, from the Earth-Moon region to Sun-Earth in alignment -Low Av access libration orbits. The AV and trip time to SEL, transfer manifolds associated with such a mission is compared to -Unstable orbit -Assembly & a more traditional direct injection and the opposite moon maintenance of relevant differences highlighted. Analysis -Halo: continuous slc that are recently completed for NGST orbit trades are view of earth, sun, thermally used where possible.’ The servicing options -At new moon, sensitive vary over a wide range, from low thrust direct surdearthlmoord -Low Av access transfers to transfers from elliptical orbits in alignment to SEL,, transfer achieved using bi-propellant systems. This manifolds paper covers only several of the many topics -Stable orbit, low -Minimum fuel analyzed, but it represents a general stationkeeping Av, loads investigation of possibilities. The results of -Moderate -Varying the analysis presented herein will be available sunlearthlmoon transfer to SEL, geometry to aid in the support of evaluating in-space 2 servicing options for mission studies in the scenario allows a fast transfer of human and GSFC Integrated Mission Design Center. expendable resources for deployment or servicing at the EML2 vicinity, with a round Software Applications and Assumptions trip servicing time of approximately a week. For this analysis, software applications that The transfers presented here demonstrate use high fidelity perturbation modeling and feasibility and are not fully optimized. full ephemeris data were utilized. The models utilized include as a minimum: End-To-End Transfer Scenarios The following scenarios demonstrate a cis- Earth potential, 4x4 or greater lunar transfer into an EMLl or EML2 orbit Point mass bodies based on full ephemeris where a human deployment or servicing of a (DE405) national resource can occur. A subsequent Solar radiation pressure transfer to and a return from the SELl via Jacchia-Roberts atmospheric drag EML2 is then designed that would provide for Spacecraft area and mass characteristics a second servicing opportunity. The initial cis- Spacecraft engine mass depletion and lunar trajectory is modeled as injection from a accelerations 28.5' inclined 186-km circular parking orbit Runge-Kutta 8/9 integrator based on expendable launch vehicle parameters. To obtain the trajectories in this Inertial and rotating coordinate systems scenario a combination of targeting goals Differential correctors and optimization were used including: lunar B-plane methods components, rotating coordinate system position and velocities, orbital energy, and The software used consists of GSFC's epochs and propagation duration. To achieve Swingby and Generator tools and MATLAB. targets, deterministic AVs were varied at the Swingby has been used operationally by parlung orbit injection, orbit insertion, and GSFC to support four libration and two lunar trajectory mid-poin ts . missions. In addition to using Swingby to model and target the solution set, software Figures 1 and 2 present a transfer

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