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In a similarly brief event some 10½ years before Apophis' fly-by on Friday, April 13th, 2029, the Mobile Asteroid Surface Scout, MASCOT, successfully completed its 17-hours mission on the ~km-sized C-type potentially hazardous asteroid (162173) Ryugu. Investigating the surface and its thermal properties, looking for a magnetic field, and imaging the stark landscapes of this dark rubble pile, it contributed valuable close-up information before the surface sampling by its mothership, HAYABUSA2. We outline the capabilities of the asteroid nanolanders MASCOT, MASCOT2, and the options for optimized MASCOT@Apophis designs in particular for small spacecraft rendezvous missions to Apophis.

By the time of Apophis' fly-by on Friday, April 13th, 2029, more satellites than have ever been launched since the beginning of the space age to this day will reach low Earth orbit (LEO). Almost all of them will be microsatellites of less than ~250 kg equipped with solar-electric propulsion (SEP). We propose the use of already created low-thrust trajectories to Apophis to help advance design trades in the early study phases of missions to Apophis. It appears that small spacecraft missions could benefit from solar-electric or sail propulsion.

Gossamer structures for innovative space applications, such as solar sails, require technology that allows their controlled and thereby safe deployment. Before employing such technology for a dedicated science mission, it is desirable, if not necessary, to demonstrate its reliability with a Technology Readiness Level (TRL) of six or higher. The aim of the work presented here is to provide reliable technology that enables the controlled deployment and verification of its functionality with various laboratory tests, thereby qualifying the hardware for a first demonstration in low Earth orbit (LEO). The development was made in the Gossamer-1 project of the German Aerospace Center (DLR). This paper provides an overview of the Gossamer-1 mission and hardware development. The system is designed based on the requirements of a technology demonstration mission. The design rests on a crossed boom configuration with triangular sail segments. Employing engineering models, all aspects of the deployment were tested under ambient environment. Several components were also subjected to environmental qualification testing. An innovative stowing and deployment strategy for a controlled deployment, as well as the designs of the bus system, mechanisms and electronics are described. The tests conducted provide insights into the deployment process and allow a mechanical characterization of that deployment process, in particular the measurement of the deployment forces. Deployment on system level could be successfully demonstrated to be robust and controllable. The deployment technology is on TRL four approaching level five, with a qualification model for environmental testing currently being built.

20 years after the successful ground deployment test of a (20 m)2 solar sail at DLR Cologne, and in the light of the upcoming U.S. NEAscout mission, we provide an overview of the progress made since in our mission and hardware design studies as well as the hardware built in the course of our solar sail technology development. We outline the most likely and most efficient routes to develop solar sails for useful missions in science and applications, based on our developed ‘now-term’ and near-term hardware as well as the many practical and managerial lessons learned from the DLR-ESTEC Gossamer Roadmap. Mission types directly applicable to planetary defense include single and Multiple NEA Rendezvous ((M)NR) for precursor, monitoring and follow-up scenarios as well as sail-propelled head-on retrograde kinetic impactors (RKI) for mitigation. Other mission types such as the Displaced L1 (DL1) space weather advance warning and monitoring or Solar Polar Orbiter (SPO) types demonstrate the capability of near-term solar sails to achieve asteroid rendezvous in any kind of orbit, from Earth-coorbital to extremely inclined and even retrograde orbits. Some of these mission types such as SPO, (M)NR and RKI include separable payloads. For one-way access to the asteroid surface, nanolanders like MASCOT are an ideal match for solar sails in micro-spacecraft format, i.e. in launch configurations compatible with ESPA and ASAP secondary payload platforms. Larger landers similar to the JAXA-DLR study of a Jupiter Trojan asteroid lander for the OKEANOS mission can shuttle from the sail to the asteroids visited and enable multiple NEA sample-return missions. The high impact velocities and re-try capability achieved by the RKI mission type on a final orbit identical to the target asteroid's but retrograde to its motion enables small spacecraft size impactors to carry sufficient kinetic energy for deflection.

Following the highly successful flight of the first interplanetary solar sail, JAXA's IKAROS, with missions in the pipeline such as NASA's NEASCOUT nanospacecraft solar sail and JAXA's Solar Power Sail solar-electric propelled mission to a Jupiter Trojan asteroid, and on the back-ground of the ever increasing power demand of GEO satellites now including all-electric spacecraft, there is renewed interest in large lightweight structures in space. Among these, deployable membrane or 'gossamer' structures can provide very large functional area units for innovative space applications which can be stowed into the limited volumes of launch vehicle fairings as well as secondary payload launch slots, depending on the scale of the mission. Large area structures such as solar sails or high-power photovoltaic generators require a technology that allows their controlled and thereby safe deployment. Before employing such technology for a dedicated science or commercial mission, it is necessary, to demonstrate its reliability, i.e., TRL 6 or higher. A reliable technology that enables controlled deployment was developed in the GOSSAMER-1 solar sail deployment demonstrator project of the German Aerospace Center, DLR, including verification of its functionality with various laboratory tests to qualify the hardware for a first demonstration in low Earth orbit. We provide an overview of the GOSSAMER-1 hardware development and qualification campaign. The design is based on a crossed boom configuration with triangular sail segments. Employing engineering models, all aspects of the deployment were tested under ambient environment. Several components were also subjected to environmental qualification testing. An innovative stowing and deployment strategy for a controlled deployment and the required mechanisms are described. The tests conducted provide insight into the deployment process and allow a mechanical characterization of this process, in particular the measurement of the deployment forces. The stowing and deployment strategy was verified by tests with an engineering qualification model of one out of four GOSSAMER-1 deployment units. According to a test-as-you-fly approach the tests included vibration tests, venting, thermal-vacuum tests and ambient deployment. In these tests the deployment strategy proved to be suitable for a controlled deployment of gossamer spacecraft, and deployment on system level was demonstrated to be robust and controllable. The GOSSAMER-1 solar sail membranes were also equipped with small thin-film photovoltaic arrays intended to supply the core spacecraft. In our follow-on project GOSOLAR, the focus is now entirely on deployment systems for huge thin-film photovoltaic arrays. Based on the GOSSAMER-1 experience, deployment technology and qualification strategies, new technologies for the integration of thin-film photovoltaics are being developed and qualified for a first in-orbit technology demonstration within five years. Main objective is the further development of deployment technology for a 25 m² gossamer solar power generator and a flexible photovoltaic membrane. GOSOLAR enables a wider range of deployment concepts beyond solar sail optimized methods. It uses the S²TEP bus system developed at the Institute of Space Systems as part of the DLR satellite roadmap.

Solar sail technology has been developed by the German Aerospace Center (DLR) since the 1990s, culminating in a successful (20 m)² sail ground demonstrator deployment test in 1999 at DLR Cologne. In the last years a further development of the technology for controlled deployment of gossamer spacecraft was made in the DLR GOSSAMER-1 Project. The DLR-ESTEC GOSSAMER roadmap originally envisaged the extremely fast-paced development of solar sailing technology by a series of successively leapfrogging low-cost demonstrator flights leading towards the technological basis for first science missions. In this framework, the GOSSAMER-1 deployment demonstrator for a (5 m)² sail structure in low Earth orbit dominated by drag was to be followed by the (20 m)² sail effect and attitude control demonstrator GOSSAMER-2 for higher Earth orbits dominated by solar radiation pressure, and the (50 m)² GOSSAMER-3 sailcraft proving the principle within the Earth-Moon system. It was to demonstrate sufficient trajectory and attitude control for science missions using a simple lightweight camera for timed pointing and localization reference imaging and a magnetometer to study the space environment around a sail. Since the first Roadmap studies, the expected payload capability increased from a few to several kg. Three scientific mission types which are exclusively feasible with the unique capabilities of solar sail propulsion were identified and studied in detail by science working groups as candidates for a first science mission. These studies were based on the expected performance of solar sail technology developed in the Roadmap. Each mission was to be completed within 10 years: • Multiple Near-Earth Asteroids (NEA) Rendezvous (MNR) & station-keeping, with optional Near-Earth Object (NEO) fly-bys of opportunity, • Displaced Lagrange point 1 (DL1) solar storm early warning at twice L1 distance from Earth, • Solar Polar Orbiters (SPO) for solar wind and coronal research and/or spectroscopic imaging of the Sun. For MNR, trajectories for several triple-rendezvous missions were calculated assuming near-term 1st-generation sailcraft performance. Notably, a solar sail based mission can change target NEAs in flight whenever new knowledge triggers a change of interest. The science payload of 12 kg included a multispectral imager, a vis-NIR point spectrometer, an IR radiometer, and three 1U-CubeSat-sized drop probes. The spacecraft was expected to fit a standard ESPA or ASAP ‘micro’ piggy-back payload launch envelope. The ‘mini’-class ENEAS missions with launch masses from 150 to 750 kg studied a decade earlier based on similar sail performance estimates include single- and triple-sample-return mission profiles. Sailcraft with a performance between MNR and ENEAS could carry a single MASCOT-type or several CubeSat-like landers to each rendezvous target. Sharing of the science payload between lander and sailcraft may be feasible for missions focusing more on a single target. With the technology available already now, it would be possible to develop a lightweight solar sail that fulfills the mission requirements of a 10-year multiple NEO rendezvous mission, thereby providing the means to study, prospect, or even deflect such potentially mineable or dangerous objects. In recent years, DLR has gained significant experience in realizing small spacecraft based projects on very short timelines with a high degree of strategic re-use of proven components between projects such as MASCOT and its successors, GOSSAMER-1, ROBEX, the ADEO dragsail, the GOSSAMER successor project GOSOLAR for very large scale photovoltaics, and others. Also, the infrastructure has been expanded to include facilities for functional and qualification testing, and the study and testing of critical effects of the space environment on new types of structures such as sail foils and thin-film photovoltaics.

Gossamer space structures like solar sails, drag sails or solar arrays expand to very large dimensions while at the same time aiming for low masses, leading to a low areal density. In many cases these applications are designed using long lightweight booms, spanning out sails or other membranes. For launch and transfer however the booms need to be stowable and compact, while they are demanded to withstand the sail loads during deployment and in operation phase. In DLR´s Solar Sail demonstrator Gossamer-1, a 5 m x 5 m squared solar sail, four sail quadrants are spanned out by four thin shell CFRP booms. Facilitating a tip deployment, the booms are flattened and coiled each on a cylinder of a deployment unit for stowage, while the boom roots are fixed in an interface to the spacecraft bus in a cross like arrangement. Having its purpose in transferring occurring boom loads into the main structure, the interface needs to be flexible at the same time, mimicking the changing cross section of the boom, once it deploys and transforms from flat to its full cross sectional dimensions. Another interface connects the sails to the booms, while holding the boom´s cross section in a semi-deployed state. These found conditions are imperfect compared to using the full cross sectional shape of the boom with its full second moment of area and an ideally clamped root fixation. Simulating the boom and its interfaces of the Gossamer-1 demonstrator, several booms are tested in an advanced vertical boom test stand at the DLR Space Structures Lab @ Uni of DLR Braunschweig. Mechanical characteristics and properties of full scale booms with ideal boundary conditions and realistic interfaces are being investigated, enabling a direct comparison. Applying certain realistic load cases, like lateral bending, axial compression and combinations of both, thresholds and robustness as well as load carrying capabilities after buckling several times are quantified in practical tests. Thus characterizing the Gossamer-1 boom under ideal and realistic boundary conditions is realized, specifying the boom performance in reality and providing the base for a robust Gossamer Spacecraft design that facilitates thin shell CFRP booms. This paper gives a detailed insight on the test stand and setup, used interfaces and boundary conditions, testing procedures, and discusses the test results of both configurations on characteristic load-displacement curves and acquired values for buckling failure design.

Vortragsfolien zum Thema "Asteroidenalarm" - eine Übersicht über die realen Möglichkeiten der Asteroidenabwehr mit den neuesten Entwicklungen von der Planetary Defense Conference 2015 und der dortigen Experten-Übung. (mit Reserve-Folien für evtl. Fragen)

Gossamer structures for innovative space applications, such as solar sails, require a technology that allows their controlled and thereby safe deployment. Before employing such technology for a dedicated science mission, it is necessary, to demonstrate its reliability with a Technology Readiness Level of six or higher. The aim of the presented work is to provide a reliable technology that enables the controlled deployment and verification of its functionality with various laboratory tests to qualify the hardware for a first demonstration in low Earth orbit. The development was made in the Gossamer-1 project of the German Aerospace Center. This presentation provides an overview of the Gossamer-1 hardware development. The design is based on a crossed boom configuration with triangular sail segments. Employing engineering models, all aspects of the deployment were tested under ambient environment. Several components were also subjected to environmental qualification testing. An innovative stowing and deployment strategy for a controlled deployment and the required mechanisms are described. The tests conducted provide insight into the deployment process and allow a mechanical characterization of this process, in particular the measurement of the deployment forces. Deployment on system level could partially be demonstrated to be robust and controllable. The deployment technology is on Technology Readiness Level four approaching level five, with an engineering qualification model (EQM) for environmental testing currently being tested.

Space Debris and Drag Augmentation Introduction - What can we learn from precursor projects? Applications for Deployable Membranes Membrane Stowing Membrane Design Aspects Materials and Space Environment Deployable Booms - Gossamer Structures Verification Strategies

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

Poster of DLR's Gossamer-1 technology.

The aim of the GOSSAMER-1 mission is an in-orbit deployment of versatile ultra-lightweight deployable sail hardware as a feasibility demonstration. The presented work focuses on the design and manufacturing of the sail membrane for GOSSAMER-1. The work has reached a preliminary design status which shall be presented in this paper. It includes mechanical analysis as well as a description of manufacturing strategies at the department of System Conditioning at the DLR Institute of Space Systems in Bremen.

Physical interaction with small solar system bodies (SSSB) is key for in-situ resource utilization (ISRU). The design of mining missions requires good understanding of SSSB properties, including composition, surface and interior structure, and thermal environment. But as the saying goes "If you've seen one asteroid, you've seen one Asteroid": Although some patterns may begin to appear, a stable and reliable scheme of SSSB classification still has to be evolved. Identified commonalities would enable generic ISRU technology and spacecraft design approaches with a high degree of re-use. Strategic approaches require much broader in-depth characterization of the SSSB populations of interest to the ISRU community. The DLR-ESTEC GOSSAMER Roadmap Science Working Groups identified target-flexible Multiple Near-Earth asteroid (NEA) Rendezvous (MNR) as one of the missions only feasible with solar sail propulsion, showed the ability to access any inclination and a wide range of heliocentric distances as well as continuous operation close to Earth's orbit where low delta-v objects reside.

In recent years the German Aerospace Center (DLR) developed gossamer deployment systems in the GOSSAMER- 1 project with a focus on solar sails also equipped with small thin-film photovoltaic arrays. With our new project GOSOLAR ahead, the focus is now entirely on gossamer deployment systems for huge thin-film photovoltaic arrays. Based on the previous achievements in the field of deployment technology and qualification strategies, new technology for the integration of thin-film photovoltaics will be developed and qualified with the goal of a first inorbit technology demonstration. The time frame for this development is about five years. The two major objectives of the project are the further development of deployment technology for a 25 m² gossamer solar power generator and the development of a flexible photovoltaic membrane. In contrast to the GOSSAMER-1 deployment approach, GOSOLAR enables a wider range of deployment concepts. The technology demonstration is supposed to employ the S²TEP bus system which is developed on-site in parallel. While the development of a bus system is in consequence not part of the GOSOLAR project, there are special challenges when it comes to the development of huge solar arrays. The level of power required in the solar array application is about two orders of magnitude higher than for a sailcraft of the same size. The currents required to carry power off the thin-film structure at commonly used bus voltages result in a substantial harness cross-section. At the same time, there is a desire for higher voltages, e.g. to power electrical propulsion directly. In consequence the first system GOSOLAR will be a low voltage system employing offthe- shelf small spacecraft power system technology. The development of high power systems will be studied in parallel and its implementation is left to future projects. Using an established test strategy, a characterization of the deployment performance and deployment forces will be made based on a test-as-you-fly approach. It includes vibration testing, fast decompression, partial deployment under thermal-vacuum and full-scale ambient deployment on a test rig previously developed for GOSSAMER-1. The data gained can be used for further development and as input for mechanism and structure sizing. Examples for the application of those testing strategies are the previous DLR GOSSAMER-1 project, the ESA drag sail projects ‘Deployable Membrane’ and ‘Architectural Design and Testing of a De-Orbiting Subsystem’ (ADEO) as well as the tether deployment of the HP³ experiment on the NASA/JPL Mars mission INSIGHT.

Any effort which intends to physically interact with specific asteroids requires understanding at least of the composition and multi-scale structure of the surface layers, sometimes also of the interior. Therefore, it is necessary first to characterize each target object sufficiently by a precursor mission to design the mission which then interacts with the object. In small solar system body (SSSB) science missions, this trend towards landing and sample-return missions is most apparent. It also has led to much interest in MASCOT-like landing modules and instrument carriers. They integrate at the instrument level to their mothership and by their size are compatible even with small interplanetary missions.\ud \ud The DLR-ESTEC GOSSAMER Roadmap NEA Science Working Groups‘ studies identified Multiple NEA Rendezvous (MNR) as one of the space science missions only feasible with solar sail propulsion. The parallel Solar Polar Orbiter (SPO) study showed the ability to access any inclination and a wide range of heliocentric distances. It used a separable payload module conducting the SPO mission after delivery by sail to the proper orbit. The Displaced L1 (DL1), spaceweather early warning mission study, outlined a very lightweight sailcraft operating close to Earth, where all objects of interest to planetary defence must pass.\ud \ud These and many other studies outline the unique capability of solar sails to provide access to all SSSB, at least within the orbit of Jupiter. Since the original MNR study, significant progress has been made to explore the performance envelope of near-term solar sails for multiple NEA rendezvous.\ud \ud However, although it is comparatively easy for solar sails to reach and rendezvous with objects in any inclination and in the complete range of semi-major axis and eccentricity relevant to NEOs and PHOs, it remains notoriously difficult for sailcraft to interact physically with a SSSB target object as e.g. the HAYABUSA missions do.\ud \ud The German Aerospace Center, DLR, recently brought the GOSSAMER solar sail deployment technology to qualification status in the GOSSAMER-1 project and continues the development of closely related technologies for very large deployable membrane-based photovoltaic arrays in the GOSOLAR project, on which we report separately.\ud \ud We expand the philosophy of the GOSSAMER solar sail concept of efficient multiple sub-spacecraft integration to also include landers for one-way in-situ investigations and sample-return missions. These are equally useful for planetary defence scenarios, SSSB science and NEO utilization. We outline the technological concept used to complete such missions and the synergetic integration and operation of sail and lander.\ud \ud We similarly extend the philosophy of MASCOT and use its characteristic features as well as the concept of Constraints-Driven Engineering for a wider range of operations. For example, the MASCOT Mobility hopping mechanism has already been adapted to the specific needs of MASCOT2. Utilizing sensors as well as predictions, those actuators could in a further development be used to implement anti-bouncing control schemes, by counteracting with the lander‘s rotation. Furthermore by introducing sudden jerk into the lander by utilization of the mobility, layers of loose regolith can be swirled up for sampling.

Following the recent successful landings and occasional re-awakenings of PHILAE, the lander carried aboard ROSETTA to comet 67P/Churyumov-Gerasimenko, and the launch of the Mobile Asteroid Surface Scout, MASCOT, aboard the HAYABUSA2 space probe to asteroid (162173) Ryugu we present an overview of the characteristics and peculiarities of small spacecraft missions to small solar system bodies (SSSB). Their main purpose is planetary science which is transitioning from a ‘pure’ science of observation of the distant to one also supporting in-situ applications relevant for life on Earth. Here we focus on missions at the interface of SSSB science and planetary defence applications. We provide a brief overview of small spacecraft SSSB missions and on this background present recent missions, projects and related studies at the German Aerospace Center, DLR, that contribute to the worldwide planetary defence community. 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 of ESA’s ROSETTA comet rendezvous mission now on the surface of comet 67P/Churyumov-Gerasimenko, and the Mobile Asteroid Surface Scout, MASCOT, now in cruise to the ~1 km diameter C-type near-Earth asteroid (162173) Ryugu aboard the Japanese sample-return probe HAYABUSA2. 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-Earth binary asteroid system (65803) Didymos. DLR is currently applying MASCOT heritage and lessons learned to the design of MASCOT2, a lander for the AIM mission to support a bistatic low frequency radar experiment with PHILAE/ROSETTA CONSERT heritage to explore the inner structure of Didymoon which is the designated impact target for DART.

Physical interaction with small solar system bodies (SSSB) is the next step in planetary science, planetary in-situ resource utilization (ISRU), and planetary defense (PD). It requires a broader understanding of the surface properties of the target objects, with particular interest focused on those near Earth. Knowledge of composition, multi-scale surface structure, thermal response, and interior structure is required to design, validate and operate missions addressing these three fields. The current level of understanding is occasionally simplified into the phrase, "If you've seen one asteroid, you've seen one Asteroid", meaning that the in-situ characterization of SSSBs has yet to cross the threshold towards a robust and stable scheme of classification. This would enable generic features in spacecraft design, particularly for ISRU and science missions. Currently, it is necessary to characterize any potential target object sufficiently by a dedicated pre-cursor mission to design the mission which then interacts with the object in a complex fashion. To open up strategic approaches, much broader in-depth characterization of potential target objects would be highly desirable. In SSSB science missions, MASCOT-like nano-landers and instrument carriers which integrate at the instrument level to their mothership have met interest. By its size, MASCOT is compatible with small interplanetary missions. The DLR-ESTEC Gossamer Roadmap Science Working Groups' studies identified Multiple Near-Earth asteroid (NEA) Rendezvous (MNR) as one of the space science missions only feasible with solar sail propulsion. The Solar Polar Orbiter (SPO) study showed the ability to access any inclination and a wide range of heliocentric distances, with a separable payload module delivered by sail to the proper orbit. The Displaced-L1 (DL1) spaceweather early warning mission study sailcraft operates close to Earth, where all objects of interest to PD must pass and low delta-v objects for ISRU reside. Other studies outline the unique capability of solar sails to provide access to all SSSB, at least within the orbit of Jupiter, and significant progress has been made to explore the performance envelope of near-term solar sails for MNR. However, it is difficult for sailcraft to interact physically with a SSSB. We expand and extend the philosophy of the recently qualified DLR Gossamer solar sail deployment technology using efficient multiple sub-spacecraft integration to also include landers for one-way in-situ investigations and sample-return missions by synergetic integration and operation of sail and lander. The MASCOT design concept and its characteristic features have created an ideal counterpart for this. For example, the MASCOT Mobility hopping mechanism and its power supply concept have already been adapted to the specific needs of MASCOT2 which was to be carried on the AIM spacecraft of ESA as part of the NASA-ESA AIDA mission to binary NEA Didymos. The methods used or developed in the realization of MASCOT such as Concurrent Engineering, Constraints-Driven Engineering and Concurrent Assembly Integration and Verification enable responsive missions based on now available as well as near-term technologies. Designing the combined spacecraft for piggy-back launch accommodation enables low-cost massively parallel access to the NEA population.