@inproceedings{GrundmannLangeDachwaldetal.2015,
  author    = {Grundmann, Jan Thimo and Lange, Caroline and Dachwald, Bernd and Grimm, Christian and Koch, Aaron and Ulamec, Stephan},
  title     = {Small Spacecraft in Planetary Defence Related Applications-Capabilities, Constraints, Challenges},
  series = {IEEE Aerospace Conference},
  booktitle = {IEEE Aerospace Conference},
  pages     = {1 -- 18},
  year      = {2015},
  abstract  = {In this paper we present an overview of the characteristics and peculiarities of small spacecraft missions related to planetary defence applications. We provide a brief overview of small spacecraft missions to small solar system bodies. On this background we present recent missions and selected projects and related studies at the German Aerospace Center, DLR, that contribute to planetary defence related activities. These range from Earth orbit technology demonstrators to active science missions in interplanetary space. We provide a summary of experience from recently flown missions with DLR participation as well as a number of studies. These include PHILAE, the lander recently arrived on comet 67P/Churyumov-Gerasimenko aboard ESA's ROSETTA comet rendezvous mission, and the Mobile Asteroid Surface Scout, MASCOT, now underway to near-Earth asteroid (162173) 1999 JU3 aboard the Japanese sample-return probe HAYABUSA-2. We introduce the differences between the conventional methods employed in the design, integration and testing of large spacecraft and the new approaches developed by small spacecraft projects. We expect that the practical experience that can be gained from projects on extremely compressed timelines or with high-intensity operation phases on a newly explored small solar system body can contribute significantly to the study, preparation and realization of future planetary defence related missions. One is AIDA (Asteroid Impact \& Deflection Assessment), a joint effort of ESA,JHU/APL, NASA, OCA and DLR, combining JHU/APL's DART (Double Asteroid Redirection Test) and ESA's AIM (Asteroid Impact Monitor) spacecraft in a mission towards near-Eath binary asteroid (65803) Didymos.},
  language  = {en}
}
@incollection{BorggrafeOhndorfDachwaldetal.2012,
  author    = {Borggrafe, Andreas and Ohndorf, Andreas and Dachwald, Bernd and Seboldt, Wolfgang},
  title     = {Analysis of interplanetary solar sail trajectories with attitude dynamics},
  series = {Dynamics and Control of Space Systems 2012},
  booktitle = {Dynamics and Control of Space Systems 2012},
  publisher = {Univelt Inc},
  address   = {San Diego},
  isbn      = {978-0-87703-587-9},
  pages     = {1553 -- 1569},
  year      = {2012},
  abstract  = {We present a new approach to the problem of optimal control of solar sails for low-thrust trajectory optimization. The objective was to find the required control torque magnitudes in order to steer a solar sail in interplanetary space. A new steering strategy, controlling the solar sail with generic torques applied about the spacecraft body axes, is integrated into the existing low-thrust trajectory optimization software InTrance. This software combines artificial neural networks and evolutionary algorithms to find steering strategies close to the global optimum without an initial guess. Furthermore, we implement a three rotational degree-of-freedom rigid-body attitude dynamics model to represent the solar sail in space. Two interplanetary transfers to Mars and Neptune are chosen to represent typical future solar sail mission scenarios. The results found with the new steering strategy are compared to the existing reference trajectories without attitude dynamics. The resulting control torques required to accomplish the missions are investigated, as they pose the primary requirements to a real on-board attitude control system.},
  language  = {en}
}
@inproceedings{PirovanoSeefeldtDachwaldetal.2015,
  author    = {Pirovano, Laura and Seefeldt, Patric and Dachwald, Bernd and Noomen, Ron},
  title     = {Attitude and orbital modeling of an uncontrolled solar-sail experiment in low-Earth orbit},
  series = {25th International Symposium on Space Flight Dynamics ISSFD},
  booktitle = {25th International Symposium on Space Flight Dynamics ISSFD},
  pages     = {1 -- 15},
  year      = {2015},
  abstract  = {Gossamer-1 is the first project of the three-step Gossamer roadmap, the purpose of which is to develop, prove and demonstrate that solar-sail technology is a safe and reliable propulsion technique for long-lasting and high-energy missions. This paper firstly presents the structural analysis performed on the sail to understand its elastic behavior. The results are then used in attitude and orbital simulations. The model considers the main forces and torques that a satellite experiences in low-Earth orbit coupled with the sail deformation. Doing the simulations for varying initial conditions in attitude and rotation rate, the results show initial states to avoid and maximum rotation rates reached for correct and faulty deployment of the sail. Lastly comparisons with the classic flat sail model are carried out to test the hypothesis that the elastic behavior does play a role in the attitude and orbital behavior of the sail},
  language  = {en}
}
@inproceedings{DachwaldKahleWie2006,
  author    = {Dachwald, Bernd and Kahle, Ralph and Wie, Bong},
  title     = {Solar sail Kinetic Energy Impactor (KEI) mission design tradeoffs for impacting and deflecting asteroid 99942 Apophis},
  series = {AIAA/AAS Astrodynamics Specialist Conference and Exhibit},
  booktitle = {AIAA/AAS Astrodynamics Specialist Conference and Exhibit},
  doi       = {10.2514/6.2006-6178},
  pages     = {1 -- 20},
  year      = {2006},
  abstract  = {Near-Earth asteroid 99942 Apophis provides a typical example for the evolution of asteroid orbits that lead to Earth-impacts after a close Earth-encounter that results in a resonant return. Apophis will have a close Earth-encounter in 2029 with potential very close subsequent Earth-encounters (or even an impact) in 2036 or later, depending on whether it passes through one of several so-called gravitational keyholes during its 2029-encounter. Several pre-2029-deflection scenarios to prevent Apophis from doing this have been investigated so far. Because the keyholes are less than 1 km in size, a pre-2029 kinetic impact is clearly the best option because it requires only a small change in Apophis' orbit to nudge it out of a keyhole. A single solar sail Kinetic Energy Impactor (KEI) spacecraft that impacts Apophis from a retrograde trajectory with a very high relative velocity (75-80 km/s) during one of its perihelion passages at about 0.75 AU would be a feasible option to do this. The spacecraft consists of a 160 m x 160 m, 168 kg solar sail assembly and a 150 kg impactor. Although conventional spacecraft can also achieve the required minimum deflection of 1 km for this approx. 320 m-sized object from a prograde trajectory, our solar sail KEI concept also allows the deflection of larger objects. In this paper, we also show that, even after Apophis has flown through one of the gravitational keyholes in 2029, solar sail Kinetic Energy Impactor (KEI) spacecraft are still a feasible option to prevent Apophis from impacting the Earth, but many KEIs would be required for consecutive impacts to increase the total Earth-miss distance to a safe value. In this paper, we elaborate potential pre- and post-2029 KEI impact scenarios for a launch in 2020, and investigate tradeoffs between different mission parameters.},
  language  = {en}
}
@inproceedings{HallmannHeideckerSchlottereretal.2016,
  author    = {Hallmann, Marcus and Heidecker, Ansgar and Schlotterer, Markus and Dachwald, Bernd},
  title     = {GTOC8: results and methods of team 15 DLR},
  series = {26th AAS/AIAA Space Flight Mechanics Meeting, Napa, CA},
  booktitle = {26th AAS/AIAA Space Flight Mechanics Meeting, Napa, CA},
  year      = {2016},
  abstract  = {This paper describes the results and methods used during the 8th Global Trajectory Optimization Competition (GTOC) of the DLR team. Trajectory optimization is crucial for most of the space missions and usually can be formulated as a global optimization problem. A lot of research has been done to different type of mission problems. The most demanding ones are low thrust transfers with e.g. gravity assist sequences. In that case the optimal control problem is combined with an integer problem. In most of the GTOCs we apply a filtering of the problem based on domain knowledge.},
  language  = {en}
}
@inproceedings{DupratDachwaldHilchenbachetal.2013,
  author    = {Duprat, J. and Dachwald, Bernd and Hilchenbach, M. and Engrand, Cecile and Espe, C. and Feldmann, M. and Francke, G. and G{\"o}r{\"o}g, Mark and L{\"u}sing, N. and Langenhorst, Falko},
  title     = {The MARVIN project: a micrometeorite harvester in Antarctic snow},
  series = {44th Lunar and Planetary Science Conference},
  booktitle = {44th Lunar and Planetary Science Conference},
  year      = {2013},
  abstract  = {MARVIN is an automated drilling and melting probe dedicated to collect pristine interplanetary dust particles (micrometeorites) from central Antarctica snow.},
  language  = {en}
}
@inproceedings{DachwaldSeboldtLoebetal.2007,
  author    = {Dachwald, Bernd and Seboldt, Wolfgang and Loeb, Horst W. and Schartner, Karl-Heinz},
  title     = {A comparison of SEP and NEP for a main belt asteroid sample return mission},
  series = {7th International Symposium on Launcher Technologies, Barcelona, Spain, 02-05 April 2007},
  booktitle = {7th International Symposium on Launcher Technologies, Barcelona, Spain, 02-05 April 2007},
  pages     = {1 -- 10},
  year      = {2007},
  abstract  = {Innovative interplanetary deep space missions, like a main belt asteroid sample return mission, require ever larger velocity increments (∆V s) and thus ever more demanding propulsion capabilities. Providing much larger exhaust velocities than chemical high-thrust systems, electric low-thrust space-propulsion systems can significantly enhance or even enable such high-energy missions. In 1995, a European-Russian Joint Study Group (JSG) presented a study report on "Advanced Interplanetary Missions Using Nuclear-Electric Propulsion" (NEP). One of the investigated reference missions was a sample return (SR) from the main belt asteroid (19) Fortuna. The envisaged nuclear power plant, Topaz-25, however, could not be realized and also the worldwide developments in space reactor hardware stalled. In this paper, we investigate, whether such a mission is also feasible using a solar electric propulsion (SEP) system and compare our SEP results to corresponding NEP results.},
  language  = {en}
}
@inproceedings{Dachwald2005,
  author    = {Dachwald, Bernd},
  title     = {Global optimization of low-thrust space missions using evolutionary neurocontrol},
  series = {Proceedings of the international workshop on global optimization},
  booktitle = {Proceedings of the international workshop on global optimization},
  pages     = {85 -- 90},
  year      = {2005},
  abstract  = {Low-thrust space propulsion systems enable flexible high-energy deep space missions, but the design and optimization of the interplanetary transfer trajectory is usually difficult. It involves much experience and expert knowledge because the convergence behavior of traditional local trajectory optimization methods depends strongly on an adequate initial guess. Within this extended abstract, evolutionary neurocontrol, a method that fuses artificial neural networks and evolutionary algorithms, is proposed as a smart global method for low-thrust trajectory optimization. It does not require an initial guess. The implementation of evolutionary neurocontrol is detailed and its performance is shown for an exemplary mission.},
  language  = {en}
}
@inproceedings{DachwaldBaturkinCoverstoneetal.2005,
  author    = {Dachwald, Bernd and Baturkin, Volodymyr and Coverstone, Victoria and Diedrich, Ben and Garbe, Gregory and G{\"o}rlich, Marianne and Leipold, Manfred and Lura, Franz and Macdonald, Malcolm and McInnes, Colin and Mengali, Giovanni and Quarta, Alessandro and Rios-Reyes, Leonel and Scheeres, Daniel J. and Seboldt, Wolfgang and Wie, Bong},
  title     = {Potential effects of optical solar sail degredation on trajectory design},
  series = {AAS/AIAA Astrodynamics Specialist},
  booktitle = {AAS/AIAA Astrodynamics Specialist},
  pages     = {1 -- 23},
  year      = {2005},
  abstract  = {The optical properties of the thin metalized polymer films that are projected for solar sails are assumed to be affected by the erosive effects of the space environment. Their degradation behavior in the real space environment, however, is to a considerable degree indefinite, because initial ground test results are controversial and relevant inspace tests have not been made so far. The standard optical solar sail models that are currently used for trajectory design do not take optical degradation into account, hence its potential effects on trajectory design have not been investigated so far. Nevertheless, optical degradation is important for high-fidelity solar sail mission design, because it decreases both the magnitude of the solar radiation pressure force acting on the sail and also the sail control authority. Therefore, we propose a simple parametric optical solar sail degradation model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Using our model, the effects of different optical degradation behaviors on trajectory design are investigated for various exemplary missions.},
  language  = {en}
}
@inproceedings{GehlerOberBloebaumDachwald2009,
  author    = {Gehler, M. and Ober-Bl{\"o}baum, S. and Dachwald, Bernd},
  title     = {Application of discrete mechanics and optimal control to spacecraft in non-keplerian motion around small solar system bodies},
  series = {Procceedings of the 60th International Astronautical Congress},
  booktitle = {Procceedings of the 60th International Astronautical Congress},
  publisher = {Elsevier},
  address   = {Amsterdam},
  isbn      = {978-161567908-9},
  pages     = {1360 -- 1371},
  year      = {2009},
  abstract  = {Prolonged operations close to small solar system bodies require a sophisticated control logic to minimize propellant mass and maximize operational efficiency. A control logic based on Discrete Mechanics and Optimal Control (DMOC) is proposed and applied to both conventionally propelled and solar sail spacecraft operating at an arbitrarily shaped asteroid in the class of Itokawa. As an example, stand-off inertial hovering is considered, recently identified as a challenging part of the Marco Polo mission. The approach is easily extended to stand-off orbits. We show that DMOC is applicable to spacecraft control at small objects, in particular with regard to the fact that the changes in gravity are exploited by the algorithm to optimally control the spacecraft position. Furthermore, we provide some remarks on promising developments.},
  language  = {en}
}