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

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

Capabilities of Gossamer-1 derived small spacecraft solar sails carrying MASCOT-derived nanolanders for in-situ surveying of NEAs

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. Parallel studies of Solar Polar Orbiter (SPO) and Displaced L1 (DL1) space weather early warning missions studies outlined very lightweight sailcraft and the use of separable payload modules for operations close to Earth as well as the ability to access any inclination and a wide range of heliocentric distances. 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. Development of closely related technologies is continued for very large deployable membrane-based photovoltaic arrays in the GoSolAr project. 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

Small Spacecraft Based Multiple Near-Earth Asteroid Rendezvous and Landing with Near-Term Solar Sails and ‘Now-Term‘ Technologies

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, theDisplaced-L1 (DL1) mission operates close to Earth, where objects of interest to PD and 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 thisand has already been adapted to the needs of the AIM spacecraft, former part of the NASA-ESA AIDA mission. Designing the combined spacecraft for piggy-back launch accommodation enables low-cost massively parallel access to the NEA population

Solar Sails for Planetary Defense and High-Energy Missions

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

Small Spacecraft Based Multiple Near-Earth Asteroid Rendezvous and Landing with Near-Term Solar Sails and ‘Now-Term‘ Technologies

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, theDisplaced-L1 (DL1) mission operates close to Earth, where objects of interest to PD and 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 thisand has already been adapted to the needs of the AIM spacecraft, former part of the NASA-ESA AIDA mission. Designing the combined spacecraft for piggy-back launch accommodation enables low-cost massively parallel access to the NEA population

Flights Are Ten a Sail – Re-use and Commonality in the Design and System Engineering of Small Spacecraft Solar Sail Missions with Modular Hardware for Responsive and Adaptive Exploration

The exploration of small solar system bodies started with fast fly-bys of opportunity on the sidelines of missions to the planets. The tiny new worlds seen turned out to be so intriguing and different from all else(and each other) that dedicated sample-return and in-situ analysis missions were developed and launched. Through these, highly efficient low-thrust propulsion expanded from commercial use into mainstream and flagship science missions, there in combination with gravity assists. In parallel, the growth of small spacecraft solutions accelerated in numbers as well as individual spacecraft capabilities. The on-going missions OSIRIS-REx (NASA) or Hayabusa2 (JAXA) with its landers MINERVA-II and MASCOT, and the upcoming NEA scout mission are examples of this synergy of trends. The continuation of these and other related developments towards a propellant-less and highly efficient class of spacecraft for solar system exploration emerges in the form of small spacecraft solar sails designed for carefree handling and equipped with carried landers and application modules. These address the needs of all asteroid user communities– planetary science, planetary defence, and in-situ resource utilization – as well as other fields of solar system science and applications such as space weather warning and solar observations. Already the DLR-ESTEC GOSSAMER Roadmap for Solar Sailing initiated studies of missions uniquely feasible with solar sails such as Displaced L1 (DL1) space weather advance warning and monitoring and Solar Polar Orbiter(SPO) delivery, which demonstrate the capabilities of near-term solar sails to reach any kind of orbit in the inner solar system. This enables Multiple Near-Earth Asteroid (NEA) rendezvous missions (MNR),from Earth-coorbital to extremely inclined and even retrograde target orbits. For these mission types using separable payloads, design concepts can be derived from the separable Boom Sail Deployment Units characteristic of DLR GOSSAMER solar sail technology, nanolanders like MASCOT, or microlanders like the JAXA-DLR Jupiter Trojan Asteroid Lander for the OKEANOS mission which can shuttle from the sail to the targets visited and enable multiple NEA sample-return missions. These nanospacecraft scale components are an ideal match creating solar sails in micro-spacecraft format whose launch configurations are compatible with secondary payload platforms such as ESPA and ASAP. The DLR GOSSAMER solar sail technology builds on the experience gained in the development of deployable membrane structures leading up to the successful ground deployment test of a (20 m) solar sail at DLR Cologne in 1999 and in the 20 years since

Regulative Characteristic of Methanol–Copper Heat Pipes for Asteroid Lander “MASCOT”

Variable conductance heat pipes (VCHPs) are the main part of the MASCOT (mobile asteroid surface SCOuT) lander thermal control system (TCS). They provide variable conductivity by utilizing the heat transfer limitations. This allows the heat pipes to act as thermal switches without additional constructive elements, thus leveraging the simple and compact design of conventional heat pipes. Two cylindrical methanol–copper heat pipes with shell length of 0.482 m and 0.438 m and external diameter of 0.006 m, having copper discrete metal fiber wick and copper shell were constructed and verified in the temperature range between -75 and +60 C. The purpose is to apply this design into the MASCOT TCS and to investigate the heat pipes’ regulative characteristics and heat transfer limitations. VCHPs show a change of thermal resistivity from 70 K/W at a heat sink temperature of -60 C, to 0.8 K/W at a heat sink temperature of +60 C; with an obtained maximal heat transfer rate of 5 W and 16 W, respectively. It is found that the switching effect of the heat pipes is governed by the sonic velocity limitation, the saturation vapor pressure of the working fluid, and the maximal capillary pressure of the wick. The operation of the heat pipes as the part of the TCS has confirmed their variable thermal propertie