Subjects -> MATHEMATICS (Total: 1074 journals)     - APPLIED MATHEMATICS (86 journals)    - GEOMETRY AND TOPOLOGY (23 journals)    - MATHEMATICS (793 journals)    - MATHEMATICS (GENERAL) (43 journals)    - NUMERICAL ANALYSIS (23 journals)    - PROBABILITIES AND MATH STATISTICS (106 journals) MATHEMATICS (793 journals)                  1 2 3 4 | Last

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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  [2570 journals]
• Design of a direct-detection wind and aerosol lidar for mars orbit
• Abstract: Abstract The present knowledge of the Mars atmosphere is greatly limited by a lack of global measurements of winds and aerosols. Hence, measurements of height-resolved wind and aerosol profiles are a priority for new Mars orbiting missions. We have designed a direct-detection lidar (MARLI) to provide global measurements of dust, winds and water ice profiles from Mars orbit. From a 400-km polar orbit, the instrument is designed to provide wind and backscatter measurements with a vertical resolution of 2 km and with resolution of 2° in latitude along track. The instrument uses a single-frequency, seeded Nd:YAG laser that emits 4 mJ pulses at 1064 nm at a 250 Hz pulse rate. The receiver utilizes a 50-cm diameter telescope and a double-edge Fabry-Pérot etalon as a frequency discriminator to measure the Doppler shift of the aerosol-backscatter profiles. The receiver also includes a polarization-sensitive channel to detect the cross-polarized backscatter profiles from water ice. The receiver uses a sensitive 4 × 4 pixel HgCdTe avalanche photodiode array as a detector for all signals. Here we describe the measurement concept, instrument design, and calculate its performance for several cases of Mars atmospheric conditions. The calculations show that under a range of atmospheric conditions MARLI is capable of measuring wind speed profiles with random error of 2–4 m/s within the first three scale heights, enabling vertically resolved mapping of transport processes in this important region of the atmosphere.
PubDate: 2020-02-17

• Aerodynamic database of the HEXAFLY-INT hypersonic glider
• Abstract: Abstract The present paper is devoted to the aerodynamic characterization and analysis of the HEXAFLY-INT hypersonic glider, developed in the frame of an international project co-funded by the European Community and the European Space Agency. This project aims to design, manufacture and flight test an innovative gliding hypersonic vehicle, which is based on the configuration developed in the previous projects LAPCAT I, II (Steelant et al. in 1st International conference on high-speed vehicle science and technology (HiSST), HiSST-2018-3101064, 26–29/11/2018, Moscow, Russia; Steelant in 15th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2008-2578, 28 April–01 May 2008, Dayton, Ohio, USA) and HEXAFLY (Steelant et al. in 21st AIAA international space planes and hypersonic systems and technology conference, AIAA-2017-2393, 6–9 March 2017, Xiamen, China) and other technologies elaborated in ATLLAS I and II (Steelant et al. in 20th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2015-3677, 5–8 July 2015, Glasgow, Scotland, UK; Steelant in 15th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2008-2582, 28 April–01 May 2008, Dayton, Ohio, USA). The flight experiment consists of a self-controlled glider configuration featuring a high aerodynamic efficiency. This flight demonstrator is equipped with an on-board breakthrough sensing and data acquisition system that will provide valuable aero-thermodynamic and thermo-mechanical data. The measured data will serve to validate the design methodologies and demonstrate the technologies that enable hypersonic transportation. The aerodynamic database comprises an extensive set of CFD simulations of increasing level of accuracy, and an experimental test campaign carried out in the TsAGI T-116 wind tunnel.
PubDate: 2020-02-05

• Utility and constraints of PocketQubes
• Abstract: Abstract PocketQubes are a form factor of highly miniaturized satellites with a body of one or more cubic units of 5 cm. In this paper, the characteristics of PocketQubes in terms of their constraints and their (potential) utility are treated. To avoid space debris and limit collision risk, the orbits of PocketQubes need to be constraint. An analysis of orbital decay characteristics has been carried out which, considering existing space regulations and a pro-active attitude, PocketQubes should preferably be launched in low Earth orbits below 400 km altitude. Due to technical constraints, such as form factor, power and attitude control, the domain of applications for single PocketQube missions is limited. Still, they can act as low-cost training and technology demonstration platforms. To make PocketQubes an attractive platform for other types of missions, not only the launch cost, but also the development, production and operations cost should be significantly lower than CubeSats. When the PocketQube platform matures and produced in high numbers, networks of PocketQubes can enable new applications. Applications considered feasible are in the field of (but not limited to) continuous surveillance using optical instruments, gravity field monitoring using precise orbit determination, in-situ measurements of the space environment, low data rate or bandwidth communication services and inexpensive probes around other celestial bodies.
PubDate: 2020-02-05

• Polygon stacks and time reference conversions
• Abstract: Abstract This paper describes how a time-based planning system, which supports resource constraints, may be extended such that a resource constraint interval does not have to refer to the start- or end-time of the underlying activity but to any linear combination thereof, such as the middle. This way, an activity with multiple resource constraints referring to different time intervals no longer has to be split into sub-activities, which may simplify the planning model and the algorithm. To be able to describe the necessary transformations, we introduce the concept of PolygonStacks and describe the operations which a typical planning engine requires to intersect the sets of consistent timeline entries of all constraints defined on an activity. We then introduce Sliders and Offsets, which allow specifying the constraint intervals in a more generic way as supported in current planning models. Based on this preparation, we can derive two lemmas, which provide the conversions required by Sliders and Offsets. We continue with several conversion examples and point out how to solve the issues which will occur during implementation. A short sketch of the complexity of our current implementation demonstrates that further work on performance should be considered, even though in practice we observe that the bottleneck of calculation remains within profile calculation rather than PolygonStack operations.
PubDate: 2020-01-27

• Exploring our solar system with CubeSats and SmallSats: the dawn of a new
era
• Abstract: Abstract We are on the threshold of a new era in robotic exploration of our solar system, one in which CubeSats and SmallSats will play an important role. As the National Aeronautics and Space Administration (NASA)’s lead center for robotic solar system exploration, JPL has a strategic interest in these new capabilities that enable planetary scientists to expand our knowledge of how our solar system formed, how it works, and even how life originated. In November 2018, JPL’s two Mars Cube One (MarCO) spacecraft, launched with the InSight Discovery mission, made history as they flew past Mars. This first pair of interplanetary CubeSats navigated their way independently to Mars to provide a relay capability for the InSight lander back to Earth. Lunar Flashlight and Near-Earth Asteroid Scout, two CubeSats that are currently under development, will form part of the ‘swarm’ of CubeSats escorted onto a lunar trajectory by NASA’s Artemis-1 mission—the first launch of its new Space Launch System (SLS) rocket. This paper provides an overview of these and other CubeSat and SmallSat mission developments at JPL from the author’s perspective. It is intended to inspire others to follow the trail blazed by these pioneering missions.
PubDate: 2020-01-22

• Thank you to our CEAS Space Journal Reviewers
• PubDate: 2020-01-13

• Injector-coupled thermoacoustic instabilities in an experimental
LOX-methane rocket combustor during start-up
• Abstract: Abstract This paper reports the investigation of acoustic combustion instability experienced during repetitive ignition testing of a sub-scale LOX-methane rocket thrust chamber. The occurrence of resonant coupling between the LOX injectors and the combustion chamber acoustic modes was assessed from the experimental data recorded during the highly transient phase of operation from ignition up to around 2 s. A method was developed to model the evolution of acoustic properties in both the combustion chamber and the injectors during the transient period. For the LOX injectors, the Woods equation was used to estimate the speed of sound in the two-phase flow. The models were used to identify the corresponding mode frequencies in the unsteady pressure measurements, and show that the high-amplitude instability occurred when they intersected. Very close coupling of less than 3% frequency difference is required for high amplitudes to be observed. However, the condition was necessary but not sufficient for high amplitudes to be reached.
PubDate: 2020-01-08

• From TechnoSat to TUBIN: performance upgrade for the TUBiX20
microsatellite platform based on flight experience
• Abstract: Abstract On July 14th, 2017, the 20 kg satellite TechnoSat was carried into orbit from Baikonur Cosmodrome as the first satellite based on Technische Universität Berlin’s novel modular TUBiX20 microsatellite platform. Its mission is the in-orbit demonstration of the platform and seven additional payloads. The second mission based on TUBiX20 is TUBIN, which is scheduled for launch in 2020. The satellite carries two infrared imagers accompanied by a camera for the visible light spectrum and shall demonstrate wildfire detection from orbit. While the platform concept already proved itself successful during TechnoSat operations, its performance needs to be further enhanced for TUBIN to meet the requirements of its Earth observation payload. This paper describes the upgrade of the TUBiX20 platform according to the requirements of the TUBIN mission. Here, the focus is set on illustrating how the modular platform design allows scaling the performance while at the same time keeping the modifications to the flight-proven system at a minimum. Second, the paper gives insights into the results of the TechnoSat mission and outlines how the experience gained in orbit benefits the platform upgrade for TUBIN.
PubDate: 2020-01-08

• Correction to: The TRIPLE/nanoAUV initiative a technology development
initiative to support astrobiological exploration of ocean worlds
• Abstract: The article “The TRIPLE/nanoAUV initiative a technology development initiative to support astrobiological exploration of ocean worlds”, written by Christoph Waldmann and Oliver Funke, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 10 September 2019 with open access.
PubDate: 2020-01-01

• Influence of energy accommodation on a robust spacecraft rendezvous
maneuver using differential aerodynamic forces
• Abstract: 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: 2020-01-01

• Design and testing of inflatable gravity-gradient booms in space
• Abstract: 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: 2020-01-01

• Manufacture and test of C/C–SiC sandwich structures
• Abstract: Abstract Sandwich structures based on C/C–SiC composites (carbon fibre-reinforced carbon with silicon carbide matrix), manufactured using the liquid silicon infiltration (LSI) process and an in situ joining method, offer high specific stiffness and strength, low thermal expansion, high environmental stability, and temperature resistance. Potential application areas are thermal protection systems (TPS) for spacecraft, optical benches in satellites, and hot structures in aerospace. In this work, C/C–SiC sandwich parts of two different geometries, small sandwich samples and large sandwich structures, were manufactured and tested. Carbon fibre-reinforced polymer (CFRP) plates for the skin panels as well as for the cores were made via warm pressing of prepregs based on a 2D carbon (C) fibre fabric, preimpregnated with phenolic resin. After pyrolysis, carbon fibre-reinforced carbon (C/C) core structures were built up and joined to C/C skin panels. Finally, the resulting C/C sandwich preforms were infiltrated with molten silicon (Si), building up a silicon carbide (SiC) matrix. The resulting C/C–SiC sandwich parts were tested in four-point and three-point bending. The applied forces and the correspondent displacements and strain of the skin panels were determined. The bending and shear stiffness as well as bending moment were evaluated through analytical and finite-element (FE) simulation approaches. Furthermore, failure modes of the sandwich samples were analysed. Sandwich stiffness and ultimate bending moment obtained in the bending tests were close to the expected theoretical values, calculated on the basis of the material properties and the sandwich geometry.
PubDate: 2020-01-01

• Novel gratings for astronomical observation
• Abstract: Abstract The choice of transmission grating can facilitate downsizing of a spectrograph and make it possible to achieve a perfect Littrow configuration. We are developing transmission gratings for next-generation instruments for the 8.2 m Subaru Telescope, the Thirty Meter Telescope (TMT), and other ground-based and space-borne telescopes. These include, a volume binary grating developed for an echelle grism (direct vision grating) for the Subaru Multi-Object InfraRed Camera and Spectrograph (MOIRCS); a reflector facet transmission (RFT) grating, a surface relief grating with sawtooth-shaped ridges of an acute vertex angle, expected to be deployed for the TMT Wide Field Optical Spectrograph (WFOS), and a hybrid grism for use as a medium-dispersion grism in MOIRCS, developed as a prototype of RFT grating. We describe the simulation results, fabrication methods, and experimental results of these prototype transmission gratings in this article.
PubDate: 2020-01-01

• The TRIPLE/nanoAUV initiative a technology development initiative to
support astrobiological exploration of ocean worlds
• Abstract: Abstract From a scientific point of view, the exploration of oceans on other planets and moons in our solar system is extremely enticing, however, from a technical point of view, it is an almost insurmountable challenge. It is this particular combination of space and ocean-going equipment that makes developing a coherent system such a demanding task. The TRIPLE/nanoAUV Initiative, where the acronym TRIPLE stands for “Technologies for Rapid Ice Penetration and subglacial Lake Exploration”, is intended to specifically address the design and realization of an autonomous underwater vehicle, the nanoAUV, for future space missions that can be operated in conjunction with melting probes for reaching subglacial lakes or ocean waters. Any conceivable technical concept has to first undergo extensive testing in appropriate Earth-analogue environments which at least come close to the actual conditions that are expected on the envisaged space mission in order to provide an indication of the technical feasibility. For the time being Antarctica appears to be the most favorable region for the anticipated test missions including reaching subglacial lakes like the one in the Dome C region although other regions like Devon Ice Cap in Canada will be considered as well. It is not just the basic physical conditions such as a thick ice cover above liquid water/seawater but also the sparsity of microbial life forms that makes it a good Earth-analogue environment [1] as it poses similar challenges to the deployed systems as found on space missions. Just recently, it was discerned that the basic requirements of a planetary mission, melting through the ice and deploying robotic systems into the water body below, are perfectly matching the interest of terrestrial scientific missions. The recent larger breaks off of the Antarctic ice shelf have exposed pristine ocean regions that due to their difficult accessibility necessitate the use of robotic exploration tools. This momentum shall be used to get one step closer to a future planetary mission by evaluating related scientific and technical concepts in Earth-analogue environments.
PubDate: 2020-01-01

• On the exploitation of differential aerodynamic lift and drag as a means
to control satellite formation flight
• Abstract: 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: 2020-01-01

• A crushable shell for small body landers
• Abstract: 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: 2020-01-01

• The aerodynamics of real space vehicles in the light of supersonic and
hypersonic approximate theories
• Abstract: Abstract In the frame of the hypersonic flow theory, the small perturbation approach was applied to simplify the governing equations. The goal was to determine flows past blunt and slender bodies (or flows with low angles of attack). The outcome of these investigations was the Mach number independence principle of hypersonic flows by K. Oswatitsch, some similarity rules for the transformation between hypersonic flows past affine configurations with different thicknesses, the classification of hypersonic flows by the Tsien parameter and a non-linear equation describing the aerodynamic coefficients (lift and drag) past an inclined thin flat plate. In the light of this hypersonic flow theory, the aerodynamic data of the winged re-entry vehicles: the Shuttle Orbiter, the Hermes re-entry vehicle, the X-33 demonstrator and the X-38 crew rescue vehicle as well as the hypersonic cruise vehicle Sänger are investigated. Remarkable similarities regarding the lift and drag coefficients between all these real configurations for hypersonic and supersonic Mach numbers are found.
PubDate: 2020-01-01

• Design, development, and flight testing of the vertical take-off and
landing GNC testbed EAGLE
• Abstract: Abstract Precise landing on planets, moons, and other larger celestial bodies requires powered descent, hovering, and vertical landing. Similarly, recent and future concepts for re-usable launch vehicle (RLVs) also involve a vertical take-off and landing. The development of guidance, navigation, and control (GNC) for this type of vehicles is a challenging task. To support this, a vertical take-off and landing vehicle has been developed for demonstrating the capability of conducting soft landings, smooth ascent, and hovering. The focus was put on a platform for testing new and advanced guidance, navigation, and control (GNC) algorithms that employ a base set of sensors and actuators typically present on such vehicles. It should represent a dynamics similar to a thrust vector controlled planetary lander or RLV, and should allow fast turn-around times as well as rapid prototyping capabilities for testing. In addition, the platform should provide the option for an additional small payload, e.g., enhancing the on-board avionics with different or more precise sensors. The result of this platform development is EAGLE (environment for autonomous GNC landing experiments). Its lift-off mass is about $$30\, \text{kg}$$ and it is powered by a jet engine with a maximum thrust of $$400\, \text{N}$$.
PubDate: 2020-01-01

• Concept for a Gossamer solar power array using thin-film photovoltaics
• Abstract: Abstract In recent years, the German Aerospace Center (DLR) developed Gossamer deployment systems in different projects. As power requirements of spacecraft are getting more and more demanding, DLR recently focused on the development of new deployable photovoltaic (PV) technologies that are suitable for generating 10’s of kW per array. Possible space applications that may also require high power supply are missions using electric propulsion such as interplanetary missions, placing of geostationary (GEO) satellites in their orbit or even more future oriented as space tugs or lightweight power generation on extra-terrestrial infrastructures. The paper gives an overview about a feasibility study for flexible solar arrays based on new thin-film photovoltaics. It is expected that the combination of new thin-film PV technologies, e.g., copper indium gallium selenide (CIGS) cells or gallium–arsenide (GaAs) cells, together with Gossamer deployment technologies, could significantly increase the power availability for spacecraft. Based on a requirement, analysis system concepts were evaluated. A focus is on the potential of CIGS PV combined with a two-dimensional deployment of the array and DLR’s coilable carbon fibre-reinforced plastic (CFRP) booms. Therefore, a concept based on crossed booms with a foldable PV membrane is considered as baseline for further developments. The array consists of rectangular PV generators that are interconnected by flexible printed circuit board (PCB) harness. By a double-folding technique, these generators are laid on top of each other in such that the membrane can be extracted from its stowing box during the deployment in a controlled manner. Considering constantly increasing efficiencies of the CIGS PV combined with Gossamer structures, there is clear potential of reaching a very high specific power value exceeding that of conventional PV systems. Furthermore, the CIGS PV appears to be more radiation resistant and has already reached more than 21% efficiency in laboratories. Such efficiencies are expected to be achieved in the near future in a standard manufacturing process. However, flexible, thin-film GaAs cells are also subject of consideration within GoSolAr. With this prospect, DLR’s research has the goal to develop a Gossamer Solar Array (GoSolAr) to exploit the described potential.
PubDate: 2020-01-01

• Simulation of the electrostatic charging of the MetOp-SG satellites in the
polar auroral zone
• Abstract: Abstract The ability to withstand the harsh space environment is one of the key challenges in the design and construction of satellites. One of these special characteristics of space is the plasma environment encountered in orbit. In this paper, the system-level charging analysis and simulations for the METOP-SG satellites are presented. The METOP-SG satellites will be launched into a sun-synchronous low Earth orbit (LEO) with an altitude of 835 km. In this orbit, the local plasma parameters in the so-called auroral zone close to the poles can lead to critical charging of the satellites [1]. The simulations are performed using a three-dimensional satellite model, where the main elements and surfaces are included. The tool for the simulations is the spacecraft plasma interaction software (SPIS) which has been developed under ESA contract [2]. The calculated surface potentials on the satellite are critically reviewed, the possibility for electrostatic discharges (ESD) is analysed, and protective measures for the minimization of the risks to the satellite mission are discussed.
PubDate: 2020-01-01

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