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 CEAS Space JournalJournal Prestige (SJR): 0.278 Citation Impact (citeScore): 1Number of Followers: 2      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502 Published by Springer-Verlag  [2351 journals]
• A crushable shell for small body landers
• Abstract: Last year, the DLR built Mobil Asteroid Surface Scout (MASCOT) decoupled from the Hayabusa-2 spacecraft and performed surface science at the asteroid (162173) Ryugu. The MASCOT lander itself didn’t need a dedicated damping system for its touchdown since the impact velocity was very low in the range of a few cm/s. This was due to the relatively small size (D = 900m) and hence low gravitational pull of the target asteroid. In a next step, DLR is developing further nano lander technologies for larger celestial bodies with respectively higher surface gravity and therefore higher impact velocities. Previous investigations have shown that for larger bodies, the landing velocity is in the range of 4 m/s which produces high shock loads. A possible low complex and lightweight solution of damping the shocks is the use of a crushable shell around the lander. This crushable shell could be made out of aluminum honeycomb core with a high-performance polyethylene cover sheet. The idea is to convert the kinetic energy into deformation work of the shell and reduce the shock load to the instrument platform. The design is particularly advantageous since no moving parts or other mechanisms are required, thus making the system very robust and fail safe. This paper concentrates on a hardware test campaign recently done at DLR’s landing and mobility test facility (LAMA). It will show the design of the shell, the test setup and the results of the campaign.
PubDate: 2019-06-07

• Thin glass shells for active optics for future space telescopes
• Abstract: We present a method for the manufacturing of thin shells of glass, which appears promising for the development of active optics for future space telescopes. The method exploits the synergy of different mature technologies, and leverages the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via direct hot slumping technology. The replication concept is advantageous for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporarily stiffened by a removable holder. In this paper, we report on the results so far achieved on a 130 mm glass shell case study.
PubDate: 2019-06-06

• Influence of energy accommodation on a robust spacecraft rendezvous
maneuver using differential aerodynamic forces
• Abstract: Differential aerodynamic forces are a promising propellant-less option to control satellite formation flight. To this day, satellite lift is the most frequently neglected and, as a consequence, the methodology of differential lift only poorly studied. This is because the adsorption of atomic oxygen on the satellite’s surfaces in Very Low Earth Orbit induces diffuse reflection and high levels of energy accommodation, both of which results in the low lift coefficients experienced in-orbit so far. Analysis has shown that surface materials which promote specular or quasi-specular reflections are able to strongly increase the magnitude of the available differential lift forces. An influence of advanced surface materials on respective maneuver sequences, however, has not yet been analyzed at all. In addition, the robustness of the differential lift-based controller proposed up to now is questionable and not able to cope with the occurring uncertainties and dynamic variations. This paper aims to address these two research gaps. To do so, a robust control approach based on Lyapunov principles developed by Pérez and Bevilacqua for the differential drag-based control of the in-plane relative motion is used in a subsequent second control phase to control the out-of-plane relative motion via differential lift. In a successive second step, the influence of different levels of energy accommodation on the full rendezvous maneuver sequence is analyzed. The results show that even a modest reduction in energy accommodation strongly reduces the maneuver times as well as the resulting orbital decay. In all analyzed cases, the proposed control approach led to a successful rendezvous.
PubDate: 2019-06-05

• Evaluation and optimization of heat transfer at the interfaces of
spacecraft assemblies
• Abstract: This paper presents the experimental and numerical work achieved in the aim of evaluating the heat transfer at the interfaces of threaded spacecraft assemblies, where Thermal Interface Materials (TIMs) are placed between two surfaces to improve the thermal performance. Developing a model to predict thermal resistance for such an assembly is a serious challenge, which has to take various influencing parameters into account. First, mechanical and thermal experiments used to characterise TIMs are summarised. Second, a numerical model capable of representing the behaviour of these materials is built. To verify the mechanical model, the preload of a single fastener assembly is measured and compared with a simulation. The thermo-mechanical model is verified by an assembly heated by a power resistor to evaluate the thermal aspects. The proposed material model is able to predict the loss of preload caused by creep/relaxation of the TIM and the temperature distribution of the assembly. This work is part of a broader study that seeks to develop a multi-physics approach to evaluate the heat transfer at interfaces of space application assemblies.
PubDate: 2019-06-01

• On the accuracy of the SGP4 to predict stellar occultation events using
ENVISAT/GOMOS data and recommendations for the ALTIUS mission
• Abstract: In preparation for the operations of the ALTIUS mission, research is carried out to assess the accuracy of the SGP4 orbital propagator in predicting stellar occultation events. The quantification of the accuracy and its consequent improvement will enable reliable measurement planning and, therefore, maximize the number of measurements. To this end, predictions are made for the timing of occultations for the GOMOS instrument on-board the ENVISAT, which are then compared to actual occultation occurrences. It is found that the error is substantial but follows a trend that can be interpolated. This enables devising a method for highly accurate predictions given a sufficient number of data points. Statistically significant results for the accuracy of the propagator and a calibration method are presented. Recommendations for a measurement planning procedure of ALTIUS are formulated.
PubDate: 2019-06-01

• Abstract: The new ACLAD philosophy for launcher/spacecraft mechanical-coupled load analysis (CLA) is presented. ACLAD stands for “A CLA a Day”. We encourage the development of a work method that would allow spacecraft manufacturers to perform a very high number of CLA, instead of once or twice per each program as done today. Such analyses provide the best possible estimation of the spacecraft loads during flight and often underline that the mechanical requirements are much higher than the actual need. If performed many times during a project, CLA could help prevent overdesign and overtesting by inducing lower specifications. Lower costs and mass of the structures could be attained. Some possible implementations of ACLAD are presented in this paper.
PubDate: 2019-06-01

• Robustness of Astrix Fiber Optic Gyros in space radiative environment
• Abstract: When developing the Fiber Optics Gyro Astrix™ family, Airbus and Ixblue faced the problematics of the possible radiation effects on optical and opto-electronics parts. After bibliographic research on the subject, selection of parts was made according to existing knowledge, and batch qualification tests performed to quantify the radiation effects. On-ground test results were introduced in worst case optical budget for the optical loop dimensioning. Several years later, following consequent in-orbit data gathering, we can assess that radiation effect are barely noticeable and that inertial performances remain tremendously stable. The careful design of the Astrix optical loop and the proper selection of opto parts were mastered key factor for such an in-flight success.
PubDate: 2019-06-01

• Finite element modelling and performance optimization of an ion thruster
depending on the nature of the propellant
• Abstract: The electrostatic propulsion is a class of space propulsion which makes use of electrical power and this kind of systems are characterized by high exhaust velocities and specific impulse, enhancing the propulsive performances of thrusters compared to conventional chemical thrusters. Since the ionized particle exhaust velocity is a function of the ratio between the electrical charge and their molecular mass, the obvious solution is to use ions with low electrical charge–molecular mass ratio. Currently, the most used propellant for the space propulsion is the Xenon gas, as it has a series of important advantages, but is quite expensive when compared to other propellants. This paper aims to make an optimization of the ideal ion propulsion systems depending on the nature of the propellant, like common used substances in the space propulsion, but also other substances which are potential candidates for this application. A variety of ion thruster performances will be analyzed, such as force, specific impulse, efficiency for the same power available onboard, the same accelerating voltage, and the same ion current. Also, for the Xenon case a numerical simulation was performed to highlight the behavior and trajectory of the ionized particles and their velocity. The conclusion obtained following the study is that a reasonable ion thruster regarding the dimensions should use an accelerating potential of at least 4000 V and 2 A of ion current.
PubDate: 2019-06-01

• Accurate numerical simulation on the structural response of the VEGA
payload fairing using modal coupling approach
PubDate: 2019-06-01

• An academic approach to the multidisciplinary development of liquid-oxygen
turbopumps for space applications
• Abstract: Since 2015, the Technical University of Munich and the German Aerospace Center have intensified their research on liquid-oxygen turbopumps for space propulsion applications in a joined project. Together, they concentrate on the special challenges concerning the design, construction and operation of parts of turbopumps, as well as the development and validation of tools to interpret and predict the aforementioned. This is accompanied by experimental works on the level of components of the pump, the bearing unit and seals. Alongside this, numerical tools are used which have been developed both commercially and at the Technical University of Munich. The research combines the expertise of several institutes in the fields of space propulsion, applied mechanics, rotordynamics and numerical mechanics in a multidisciplinary approach. The incorporation of student and doctoral theses allows for the investigation of the components of liquid-oxygen turbopumps in a very wide variety. High emphasis is put on the interaction between the turbopump subsystems. The present paper presents the work on each subsystem and the links between them.
PubDate: 2019-06-01

• Effects of the rotational vehicle dynamics on the ascent flight trajectory
of the SpaceLiner concept
• Abstract: During the preliminary design of space transportation systems, the vehicle dynamics are commonly reduced to a point-mass model for definition of the flight trajectory. While this approach effectively reduces the number of model parameters in the design process, it neglects the rotational dynamics of the vessel completely. Since the rotational degrees of freedom (DOF) have a significant influence on the vehicle’s controllability, a sole analysis of the translational dynamics is insufficient to assess the general feasibility of the concept. This study investigates the ascent flight trajectory of the SpaceLiner vehicle, a concept for a hypersonic suborbital space plane, based on a newly developed 6-DOF flight dynamics simulation to determine the influence of the rotational dynamics on the vehicle’s controllability and performance. The first part of this paper will focus on the developed vehicle model which features a transient inertia model, as well as an algorithmic-designed flight control system. The second part will present several simulations of nominal and off-nominal ascent trajectories. Based on the results it will be shown that SpaceLiner’s thrust vector control system is sufficiently dimensioned for the investigated mission scenarios, while the vehicle performance is only slightly influenced by the rotational dynamics.
PubDate: 2019-06-01

• Dynamic guidance of orbiter gliders: alignment, final approach, and
landing
• Abstract: A new algorithm capable of guiding an orbiter glider to a target point with a prescribed alignment and descent path angle is presented. This algorithm can initiate Terminal Area Energy Management (TAEM) before reaching steady state and perform the Final Approach and Landing (FA&L). During TAEM, runway alignment is done through a moving virtual target derived from steady state, while during FA&L, a transient (or flare) is used to reach the extremely shallow descent path angles. All decisions are made dynamically relying solely on local information (position, speed, attitude, and atmospheric parameters), and all structural limits of the glider are respected at all times. As a proof of concept, a Space Shuttle return flight is simulated. For a large multitude of initial conditions and targets, the algorithm is able to consistently deliver distance errors below 19 m (transverse errors below 4 m), alignment errors below $$1^{\circ }$$ , descent path angles at the intended $$-\,2^{\circ }$$ , and vertical descent speeds below 8.5 m/s with control time intervals of 0.1 s.
PubDate: 2019-06-01

• Integration of thermo-elastic characteristics in finite element method
reduced models
• Abstract: A simple method for integrating thermo-elastic characteristics in finite element method (FEM) reduced models is presented. Methods like Guyan or Craig-Bampton reductions are widely used in the space industry, as they drastically decrease the size of models and also allow safe model exchanges between companies without disclosing sensitive technologies. On the other hand, reduced models cannot be implemented in thermo-elastic analyses, which are of paramount importance for spacecrafts mainly for on-orbit sizing and pointing analyses. The new presented method is simple to implement and consists of replacing the dropped thermo-elastic characteristics of the reduced models by a set of interface forces and moments. These are computed by clamping the physical FEM model at its interfaces and applying unit thermal loads on the different internal zones. An analytical and a numerical example are presented. The implementation in FEM shows high accuracy.
PubDate: 2019-06-01

• Design and testing of inflatable gravity-gradient booms in space
• Abstract: Inflatable space structures have many advantages such as small size, high reliability, and low cost. Aiming at a gravity-gradient boom for an XY-1 satellite, New Technology Verifying Satellite-1, a slender inflatable boom with low magnetic is presented. First of all, an inflatable boom with six self-supporting thin shells made of carbon and Vectran fiber composite materials on the inner wall was designed for eliminating a magnetic dipole moment and increasing structural stiffness. A precise stowage was designed for a tip mass surrounded by a pair of lightweight honeycomb blocks added on the top of the boom. The stowed boom was tested by sine sweep vibrations with three directions on the ground to verify the reasonable design. The XY-1 satellite which carried the inflatable boom was launched into low orbit. After being stowed state in space for at least 6 months, the inflatable boom orderly unfolded a 2.0 kg tip mass to 3.0 m away in May, 2013. The inflatable boom was successfully deployed from a series of photographs received on the satellite. The results show that this kind of lightweight inflatable boom with self-supporting thin shells can orderly unfold and fulfil the function of gravity-gradient in space for a long time.
PubDate: 2019-05-31

• Protected silver coatings for reflectors
• Abstract: For ground- and spaced-based applications, Ag-coated reflectors are indispensable because of their high reflectivity. The transport, assembly, and storage of these reflectors take places over a long period before they are finally commissioned for application. To endure this period without a decrease of reflectivity, protective coatings with a final layer, which offers a high resistance to aqueous solutions, and a low mechanical stress should be used. These criteria were taken into account for the selection of a final layer for a protected Ag coating, which was applied for reflectors utilized in the CRIRES+-instrument (an IR spectrograph used at the VLT). Reactively sputtered Al2O3, SiO2 and Si3N4 layers were investigated with regard to these criteria. In aqueous (alkaline) solutions, the investigated Si3N4 layers are more stable than the SiO2 layers and the SiO2 layers more stable than the Al2O3 layers. This shows the influence of the intrinsic material properties. The mechanical stress of the sputtered layers depends on the deposition conditions and thus on the selected parameters. A Si3N4 layer with a high resistance to aqueous (alkaline) solutions also offers low and stable mechanical stress. Therefore, the deposition parameters used for this layer were applied for sputtering the final layer of the protected Ag coating for the reflectors.
PubDate: 2019-05-28

• On the exploitation of differential aerodynamic lift and drag as a means
to control satellite formation flight
• Abstract: For a satellite formation to maintain its intended design despite present perturbations (formation keeping), to change the formation design (reconfiguration) or to perform a rendezvous maneuver, control forces need to be generated. To do so, chemical and/or electric thrusters are currently the methods of choice. However, their utilization has detrimental effects on small satellites’ limited mass, volume and power budgets. Since the mid-80s, the potential of using differential drag as a means of propellant-less source of control for satellite formation flight is actively researched. This method consists of varying the aerodynamic drag experienced by different spacecraft, thus generating differential accelerations between them. Its main disadvantage, that its controllability is mainly limited to the in-plain relative motion, can be overcome using differential lift as a means to control the out-of-plane motion. Due to its promising benefits, a variety of studies from researchers around the world have enhanced the state-of-the-art over the past decades which results in a multitude of available literature. In this paper, an extensive literature review of the efforts which led to the current state-of-the-art of different lift and drag-based satellite formation control is presented. Based on the insights gained during the review process, key knowledge gaps that need to be addressed in the field of differential lift to enhance the current state-of-the-art are revealed and discussed. In closer detail, the interdependence between the feasibility domain/the maneuver time and increased differential lift forces achieved using advanced satellite surface materials promoting quasi-specular or specular reflection, as currently being developed in the course of the DISCOVERER project, is discussed.
PubDate: 2019-05-27

• Diode-pumped Alexandrite laser for next generation satellite-based earth
observation lidar
• Abstract: In this work, the design of a diode-pumped Alexandrite ring laser in Q-switched single-longitudinal-mode (SLM) operation for a spaceborne lidar mission is presented. The laser is pumped by a self-developed fiber-coupled laser diode pump device and yields a pulse energy of 1.7 mJ at a repetition rate of 500 Hz with an excellent beam quality of M2 < 1.1. By seeding the resonator with a narrow band diode laser, SLM operation with a linewidth of approximately 10 MHz is achieved. The electro-optical efficiency of 2% is the highest achieved for all Alexandrite lasers in SLM operation and reasonable for space operation. The performance analysis as well as benchmarking with the space-qualified mounting technology points out the TRL and the remaining effort for the development of the technology. An estimation of the requirements for a spaceborne resonance lidar mission underlines the suitability of such a lidar system with a diode-pumped Alexandrite laser as the beam source.
PubDate: 2019-05-25

• Integrated atomic quantum technologies in demanding environments:
development and qualification of miniaturized optical setups and
integration technologies for UHV and space operation
• Abstract: Employing quantum sensors in field or in space implies demanding requirements on the used components and integration technologies. Within our work on compact atomic sensors, we develop miniaturized, ultra-stable optical setups for optical cooling and trapping of cold atomic gases on atom chips. Besides challenging demands on alignment precision and thermo-mechanical durability, we specifically address ultra-high vacuum (UHV) compatibility of our adhesive integration technology and the assembled optical components. A prototype of an UHV-compatible, crossed beam optical dipole trap at 1064 nm for application within a cold rubidium atomic quantum sensor currently in development at the Joint Lab Integrated Quantum Sensors at Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik is described. We describe the design and first qualification efforts on adhesive micro-integration technologies. These tests are conducted in application-relevant geometries and material combinations common for micro-integrated optical setups. Adhesive aging will be investigated by thermal cycling and radiation exposure. For vacuum compatibility testing, a versatile UHV testing system for samples up to $$65\times 65\,\text{mm}^2$$ footprint is currently being set up, enabling residual gas analysis, temperature cycling up to $$200\,^{\circ }\text{C}$$ and measurement of total gas rates down to expected $$5\times 10^{-10}\,\text{mbar}\,\text{l/s}$$ at a base pressure of $$10^{-11}\,\text{mbar}$$ , exceeding the common ASTM E595 test.
PubDate: 2019-05-25

• Magnetic Mars dust-removal technology
• Authors: Francisco J. Arias; Salvador De Las Heras
Abstract: Environmental data recorded by the Mars exploration rovers show that the martian dust is magnetic containing mostly the strong magnetic mineral magnetite ( $${\text {Fe}}_3{\text {O}}_4$$ ). On the other hand, it is known that dust settling onto the surface of solar arrays can affect the utility on solar power on any Mars mission, and particulary for long-term operation. Dust obscuration of solar arrays can be a special issue for the case of a future 6-month sample fetching rover (SFR) mission, where the current baseline architecture contemplates the use of solar array and where dust storms can jeopardize the entire mission, not only affecting the supply of energy for locomotion but for the communication with the Mars ascent vehicle (MAV). Today, available dust-removal techniques have been classified into four categories: natural, mechanical, electromechanical, and electrostatic. However, by aforementioned, an additional category may be included in this portfolio based in the magnetic properties of the martian dust. Here a first scoping study for a magnetic Mars dust technology is outlined. Finally, a specific ad hoc magnetic technology is proposed an analyzed.
PubDate: 2019-02-04
DOI: 10.1007/s12567-019-0235-y

• Structural development of ultra-lean-burn preburners for small liquid
engines
• Authors: Jaehan Yoo; Seong-up Ha; Soo Yong Lee
Abstract: An ultra-lean-burn preburner has been developed by KARI. This paper describes the general structural design, the results of the finite element analyses (FEA) and the experimental results related to structural issues during the development. Before the fabrication, two burst experiments with the specimens simulating the brazing joints were performed and compared with the FEA results, which increases the reliability of the analyses and the design. Also, 2D FEA of the combustion chamber cooling channel were performed for the first combustion region upstream of the liquid oxygen (LOX) hole and the second region downstream of the hole, where the hottest spot locates downstream of the region between the adjacent LOX holes. Various structural modifications were analyzed by 3D FEA and a screen structure was introduced to reduce the stress over highly stressed regions. During the development, some proof and leakage tests were performed for the head, the chamber with and without flange, and the preburner assembly, of which the burst test was performed. Several firing tests of the assembly were performed to show the operation without any structural failure.
PubDate: 2019-02-01
DOI: 10.1007/s12567-019-0238-8

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