Verification Testing of the Gossamer-1 Deployment Demonstrator

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 a qualification model for environmental testing currently being built

Development of New Solar Array Concepts for Space Applications

Solar arrays are the main power source in space. Conventionally they are composed of stiff backing structures and brittle PV cells. While the power demands of space missions are increasing, e.g. for electric propulsion, the increase of efficiency of the solar cells itself is limited. New developments make use of flexible and semi-flexible solar array designs in order to achieve higher power/mass and power/volume ratios. An example is a two-dimensional deployment of solar arrays in order to increase the deployed area as instigated in DLR’s GoSolAr project. Such deployment strategies can be combined either with conventional photovoltaics, also using thinned wafer technology, or with thin-film technologies that are truly flexible. Development of such technology involves also deployment testing and testing of materials under the specific radiation environment that is present in space. In this talk I would like to give an overview about the development aspects, showing how we try to go beyond conventional array designs but still using photovoltaic solar cells

Controlled Deployment of Gossamer Spacecraft

Deployable gossamer structures for solar sails need to be deployed in a controlled way. Several strategies present have the disadvantage that the sail membrane cannot always be tensioned during the deployment process. In combination with a slow deployment, this involves the risk of an entanglement of the sail. Slow deployments of at least several minutes are desirable in order to keep inertial loads low and to implement Fault-Detection, Fault-Isolation and Recovery Techniques (FDIR). This might further require completely stopping and resuming the deployment process. For gossamer spacecraft based on crossed boom configurations with triangular sail segments, a deployment strategy is described that is assumed to allow such a controlled deployment process. With a combination of folding and coiling, it is ensured that the deployed sail area can be held taut between the partly deployed booms. During deployment, four deployment units with two spools each on which the sail is mounted (a half segment stowed on each) moves away from the central bus unit, the center of the deployed sail. The development was made in the Gossamer-1 project of the German Aerospace Center (DLR). The folding and coiling of the membrane is mathematically modelled. This allows an investigation of the deployment geometry. It provides the mathematical relation between the deployed boom length and the deployed sail membrane geometry. By modelling the coiled zig-zag folding lines it is possible to calculate the deployment force vector as function of the deployment time. The stowing and deployment strategy was verified by tests with an engineering qualification model of the Gossamer-1 deployment unit. 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. A deeper understanding of the deployment process is gained by analyzing the deployment strategy mathematically

Soil to Sail - Asteroid Landers on Near-Term Sailcraft as an Evolution of the GOSSAMER Small Spacecraft Solar Sail Concept for In-Situ Characterization

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. 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. 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. 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. 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. 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. 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

Surface Modification of Space Materials Induced by Low Energetic Particle Irradiation

A set of six different materials frequently used in spacecraft engineering was irradiated with low energy (100 keV) proton irradiation to simulate the aging of their surfaces due to space radiation in Low Earth Orbit. A microscopic and spectroscopic analysis of the irradiated samples reveals that the tested materials containing organic polymers Polytetrafluoroethylene (PTFE) and carbon fiber reinforced plastic (CFRP) show significant changes in surface morphology. As opposed to this, samples with a metallic surface such as aluminum, titanium or multi-layer insulation (MLI) remain rather unaffected. This knowledge is highly relevant for the interpretation of optical data related to the observation of space debris (so-called light curves) as well as to studies about laser matter interaction for laser-based debris removal

Spacecraft Materials’ Reflectivity and Surface Morphology: Aging Caused by Proton Irradiation

The radiation environment in Low Earth Orbit (LEO) is dominated by protons captured by Earth’s magnetic field in the Inner Van-Allen belt. Defunct satellites and other space debris objects can be resident in this environment for several decades and even centuries. So far, there is little knowledge about the impact of long-duration proton exposure to the surface morphology and reflectivity in LEO environment. We report on a laboratory test campaign exposing typical spacecraft materials with protons of 100 keV and 2.5 keV kinetic energy and a fluence corresponding to an in-orbit duration of 100 years and 120 years, respectively, in an 800 km sun-synchronous orbit. Although we find microscopic changes in surface morphology, reflectivity changes of all tested materials were smaller than 15%. This result brings positive news for on-going efforts to use optical methods, e.g. lightcurve measurements or active polarimetry, for characterizing space objects, since it suggests that data can - to a good approximation - be analyzed without accounting for proton induced aging effects that might affect the materials’ optical properties over time

Soil to Sail - Asteroid Landers on Near-Term Sailcraft as an Evolution of the GOSSAMER Small Spacecraft Solar Sail Concept for In-Situ Characterization

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. 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. 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. 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. 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. 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. 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

Special Testing and Test Strategies for Unique Space Hardware Developments

Hardware developments for new and innovative space applications require extensive testing in order to demonstrate the functionality under the expected environmental conditions. Within several projects the German Aerospace Center (DLR), Institute of Space Systems used its test capabilities for unique tests campaigns that went beyond standard qualification testing

Membrane Deployment Technology Development at DLR for Solar Sails and Large-Scale Photovoltaics

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

Small Spacecraft in Small Solar System Body Applications

In the wake of the successful Philae landing on comet 67P/Churyumov-Gerasimenko and the launch of the first Mobile Asteroid Surface Scout, MASCOT, aboard the Hayabusa2 space probe to asteroid (162173) Ryugu, small spacecraft in applications related to small solar system bodies have become a topic of increasing interest. Their unique combination of efficient capabilities, resource-friendly design and inherent robustness makes them attractive as a mission element at the frontiers of exploration of the solar system by larger spacecraft as well as stand-alone low-cost approaches to open up the solar system for a broader range of interests. The operators' requirements for cutting-edge missions compatible with available launch capabilities impose significant constraints in resources, timelines, timeliness, mass and size. To create spacecraft feasible within these constraints, the mission design teams need to accept a broad range of equipment maturity levels from fresh concepts to off-the-shelf units. The resulting Constraints-Driven Engineering (CDE) environment has led to new methods which transcend traditional evenly-paced and sequential development. We evolved and extended Concurrent Design and Engineering (CD/CE) methods originally incepted for initial studies into Concurrent Assembly, Integration and Verification (CAIV). It is applied in all phases in most of our projects to achieve convergence of asynchronous subsystem maturity timelines and to match parallel tracks of integration and test campaigns. When facing such a challenge, Model-Based Systems Engineering (MBSE) supports design trades and constant configuration evolution due to unforeseen changes. Proactive change and schedule acceleration has resulted from system-level CD/CE optimization across interface boundaries by MBSE-aided CAIV