Large apertures in space have applications for telecommunications, Earth observation and scientific missions. This paper reviews advances in mechanical architectures and technologies for large deployable apertures for space antennas and telescopes. Two complementary approaches are described to address this challenge: the deployment of structures based on quasi-rigid members and highly flexible structures. Regarding the first approach, deployable articulated structures are classified in terms of their kinematics as 3D or planar linkages in multiple variants, resulting in different architectures of radial, peripheral or modular constructions. A dedicated discussion on the number of degrees of freedom and constraints addresses the deployment reliability and thermo-elastic stability of large elastic structures in the presence of thermal gradients. This aspect has been identified as a design driver for new developments of peripheral ring and modular structures. Meanwhile, other design drivers are maintained, such as the optimization of mass and stiffness, overall accuracy and stability, and pragmatic aspects including controlled industrial development and a commitment to operators’ needs. Furthermore, reflecting surface technologies and concepts are addressed with a view to the future, presenting advances in technical solutions for increasing apertures and reducing areal mass densities to affordable levels for future missions. Highly flexible materials capable of producing ultra-stable shells are described with reference to the state of the art and new developments. These concepts may enable large deployable surfaces for antennas and telescopes, as well as innovative optical concepts such as photon sieves. Shape adjustment and shape control of these surfaces are described in terms of available technologies and future needs, particularly for the reconfiguration of telecommunications antennas. In summary, the two complementary approaches described and reviewed cover the domain of present and foreseeable space applications. Recent European developments are discussed within a global context and a critical review of the state of the art and recent advances taking into account the reliability and structural stability as design drivers.
Design information of a spacecraft is collected over all phases in the lifecycle of a project. A lot of this information is exchanged between different engineering tasks and business processes. In some lifecycle phases, model-based system engineering (MBSE) has introduced system models and databases that help to organize such information and to keep it consistent for everyone. Nevertheless, none of the existing databases approached the whole lifecycle yet. Virtual Satellite is the MBSE database developed at DLR. It has been used for quite some time in Phase A studies and is currently extended for implementing it in the whole lifecycle of spacecraft projects. Since it is unforeseeable which future use cases such a database needs to support in all these different projects, the underlying data model has to provide tailoring and extension mechanisms to its conceptual data model (CDM). This paper explains the mechanisms as they are implemented in Virtual Satellite, which enables extending the CDM along the project without corrupting already stored information. As an upcoming major use case, Virtual Satellite will be implemented as MBSE tool in the S2TEP project. This project provides a new satellite bus for internal research and several different payload missions in the future. This paper explains how Virtual Satellite will be used to manage configuration control problems associated with such a multi-mission platform. It discusses how the S2TEP project starts using the software for collecting the first design information from concurrent engineering studies, then making use of the extension mechanisms of the CDM to introduce further information artefacts such as functional electrical architecture, thus linking more and more processes into an integrated MBSE approach.
The Sentinel-1A SAR mission was launched in April 2014, followed by the Sentinel-1B Spacecraft in April 2016. Since then, several sets of in-orbit data have been evaluated to correlate the thermal model for being able to provide more detailed in-flight predictions. The need for detailed in-flight predictions is justified by the fact that the imaging performance of a SAR instrument depends mainly on the thermal performance of its high dissipative units. Components reaching their temperature limits during operational time define the end of the imaging phase, and thus the timespan during which and how often imaging operations can take place. An STM (Structural/Thermal Model) test correlation is standard throughout all missions, which usually delivers a very reliable model for further in-flight predictions. Nevertheless, this correlation does not give information about thermo-optical property degradation or environmental influences, because the effects in space on the thermally active surfaces are very hard to predict. For this reason, thermal engineers use relatively conservative values for in-flight predictions and End-of-Life thermal performance assessments. This might lead to mission performance limitations which predict a too short feasible imaging time of the Radar instrument. For this reason, the first approach was to evaluate the early acquired in-orbit data and to correlate the thermal model with the thermal configuration at Begin-of-Life to assess the maximum possible high dissipative imaging time possible for the Begin-of-Life situation. Then the flight data over a longer timespan were evaluated to determine potential temperature trends which could be caused by thermo-optical property degradation as well as seasonal-related influences. These two assessments combined, allow a thermal performance prediction for Mission End-of-Life, and thus a reliable determination of potential SAR imaging performance over the full mission time. The paper will present the correlation results of the initially measured in-flight data, the determined long-term in-orbit data over 3 years, and the combination of both assessments including its impact on SAR imaging performance over the full mission.
In a hybrid rocket, paraffin-based fuels are characterised by high regression rates and zero chemical explosion potential. However, paraffin wax is a brittle material and exhibits poor mechanical strength. The production of large-scale paraffin motors is a challenging task because of the poor structural performance of such motors. The addition of polymers and metallic additives to paraffin wax can considerably enhance mechanical performance. In this study, three different paraffin-based fuels, namely paraffin–aluminium (P–Al), paraffin–boron (P–B), and paraffin–carbon black (P–CB), were prepared using polyethylene (PE) polymer additive. The effects of these additives on the thermal, mechanical, and ballistic performance of the paraffin-based fuels were examined. The mechanical strength of these fuels was evaluated using compressive tests. Differential scanning calorimetry (DSC) experiments were performed to study the thermal decomposition of these paraffin-based fuels. A lab-scale ballistic evaluation motor was used to study the regression rates in a gaseous oxygen environment. The results revealed that the addition of the polymer and metallic additives improved the mechanical strength of fuels. The DSC results demonstrated that the addition of the additives accelerated oxidation and improved the heat release rate during combustion. The oxidation enthalpies for the P–Al, P–B, and P–CB samples were 291, 274, and 268 J/g, respectively. Finally, the ballistic results indicated that the regression rate decreased when 10 wt% PE was added to the paraffin wax, and such depreciation of regression rate due to polymer addition was compensated by the addition of the Al, B, and CB additives.
An approach is developed to compute quasi-impulsive maneuvers to steer the orbital elements of a spacecraft to a desired value. Using Gauss variational equations it is possible to define the location along the orbit as well as the magnitude of the maneuver(s) so that specific orbital elements can be changed with little influence on the others. The possibility to include the effect of the perturbations allows an accurate evaluation of the time required to reach the maneuvering location. Including a model of the propulsion system makes the simulation more realistic, if compared with an impulsive maneuver implementation, since a burning arc can replace the instantaneous change of the orbital elements, which is instead associated with the impulsive approach. Simulations have been performed to compare perturbed and unperturbed cases and the results from the comparisons are presented.
This study researches a novel advanced joining technique, utilizing metal additive manufacturing, named μPinning. μPins are small pin-like structures manufactured on a metal substrate and used to penetrate and be consolidated inside a fibre-reinforced polymer (FRP) laminate as through-the-thickness reinforcement during curing (Ucsnik et al. in Composite to composite joint with lightweight metal reinforcement for enhanced damage tolerance. ECCM16—16th European Conference on Composite Materials, Seville, Spain, 2014, Parkes et al. in Compos Struct 118:250–256, 2014). Prior studies have shown a significant increase in the load bearing capabilities of the joint [1, 2], as well as greater performance in dynamic and fatigue loads (Graham et al. in Compos Part A 64:11–24, 2014, Chang et al. in Compos Sci Technol 66(13):2163–2176, 2006, Ko et al. in Compos Struct 119:59–66, 2015]. The main objective of this research is to use numerical optimization tool to optimize the shape of a μPin, as studies have shown that the shape of the μPin exhibits a significant role in the mechanical response [1, 2, 5, 7]. After the numerical optimization, experimental testing was performed to validate the assumption of the importance of the μPin shape in the joint loading response. Finally, this study aims to lead to future research on the design of metal inserts in sandwich structures and struts for use in space applications.
Mechanical properties of two high-strength metallic alloys, fabricated using additive manufacturing (AM) technology, were characterised down to − 269 °C. A test setup has been developed to accommodate the specific sample geometry and manufacturing conditions for these tests. Tensile, compression, pin-bearing, and shear tests were performed at room temperature, − 73 °C, − 196 °C, and − 269 °C. Test equipment and fixtures were designed and optimized to survive the test loads up to 100 kN at low temperatures. Instrumentation for strain, temperature, and displacement was also carefully chosen to record the specimen behaviour and apply the test requirements. The KRP cryo apparatus provided fast cooling and temperature stability during the entire duration of testing. In this paper, we describe the design of the test apparatus, the challenges in development and some results of test runs.
In the present study, the influence of active cooling on hypersonic boundary-layer transition at different Mach numbers, from 7 up to 10, is investigated. The analyses are carried out on a $$7^\circ$$ 7 ∘ half-angle, blunted cone with different nose radii and various gas injection mass flow rates. In all cases, low mass fluxes, which do not inducing visible shocks in the schlieren images, are applied. As injection gas nitrogen is used. At the considered free stream conditions, second modes are the dominant boundary-layer instabilities, which are consequently the focus of this study. The stability analyses are performed by means of the stability code NOLOT, NOnLOcal Transition analysis, of the German Aerospace Center (DLR). The influence of different mass injections on the frequencies and growth rates of the second modes is analyzed in detail. The effect on the transition onset locations is discussed. The numerical predictions are compared with experimental results. The experimental data referred to in the present study were obtained in the DLR High Enthalpy Shock Tunnel Göttingen.
Norway currently operates four satellites with Automatic Identification System (AIS) receivers. The first-generation satellites, AISSat-1 and AISSat-2, are equipped with a two-channel, single-antenna AIS receiver, while NorSat-1 and NorSat-2 are equipped with an improved AIS receiver capable of decoding on all four AIS channels and using the two antennas installed on the NorSat satellites. This paper aims to investigate the ship tracking performance enhancement realised by the technology improvements of antenna diversification, frequency diversification, and advanced algorithms. The ship tracking capability of the NorSat satellites is presented and shown to yield a significant improvement, up to a 20% point increase, over the first AISSat generation ship tracking capability. A further 20% point increase is achieved in select areas using frequency diversity introduced in the AIS system since the development of the AISSat satellites. In addition, NorSat-1 detected 34% more vessels than AISSat-2 over the same timeframe. The contribution to the performance improvement from the incremental improvements in decoding algorithms, antenna diversity, and frequency diversity is indicated in the results. The results indicate that, in the short term, upgrading to the latest algorithms, low noise electronics, and taking advantage of antenna diversity is the greatest performance enhancer. In the medium and long term, the frequency diversity likely yields the greatest performance enhancement.