| 1. |
- Bazzocchi, Michael C. F., et al.
(författare)
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Study of Arjuna-Type Asteroids for Low-Thrust Orbital Transfer
- 2018
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics. - 0022-4650 .- 1533-6794. ; 55:1, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the accessible low-thrust transfer trajectories for a near-Earth asteroid transfer mission. The target asteroids considered are Arjuna-type asteroids, which are characterized by their Earth-like orbital paths including low eccentricity and low inclination. The asteroid range is characterized by a specific range of semimajor axes and transfer angles to provide an overall assessment of the potential Arjuna transfer domain. A single hovering ion beam spacecraft is employed for the task of asteroid redirection. The method uses a continuous thrust over the duration of the transfer maneuver to redirect the asteroid to an Earth-bound orbit. The transfer model employs a minimized form of Gauss's variational equations to determine the available trajectories for asteroid redirection. The transfer model employs, in addition to the aforementioned orbital equations, spacecraft thruster and sizing metrics as well as mission cost analysis formulae. The system parameters and orbital transfer paths are assessed with regard to key mission parameters, namely, time frame for redirection, number of orbital revolutions, system mass, propellant mass, thrust, power, system cost, and financial return rate
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| 2. |
- Bodin, Per, et al.
(författare)
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PRISMA : an in-orbit test bed for guidance, navigation, and control experiments
- 2009
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics (AIAA). - 0022-4650 .- 1533-6794. ; 46:3, s. 615-623
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents system-level hardware-in-the-loop real-time simulation results for three different guidance, navigation, and control experiments designed for in-flight demonstration on the PRISMA formation-flying satellite mission. The mission consists of two spacecraft: Main and Target The Main satellite has full orbit control capability, whereas Target is attitude-controlled only. Launch is planned for November 2009. The simulation results presented demonstrate the feasibility and readiness for flight as well as the expected in-flight performance. The three experiments include Global Positioning System and vision-based formation flying for two spacecraft in both passive and forced motion. In addition to these simulation results, the paper gives an overview of the PRISMA mission in general and the guidance, navigation, and control experiments in particular. The hardware-in-the-loop real-time test environment is also presented.
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| 3. |
- Browne Mwakyanjala, Moses, et al.
(författare)
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Functional Analysis of Software-Defined Radio Baseband for Satellite Ground Operations
- 2019
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics. - 0022-4650 .- 1533-6794. ; 56:2, s. 458-475
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents functional analysis and system specifications of a baseband system using software-defined radio (SDR) technology. The analysis is primarily based on the latest blue-book standards from the Consultative Committee for Space Data Systems (CCSDS). It covers telemetry, telecommand, and ranging, as well as some specifications of the associated physical layers. The SDR-based baseband system is envisioned to support ground operations in the form of a software-as-a-Service (SaaS) private cloud.
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| 4. |
- Kratz, Henrik, et al.
(författare)
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Design and Modeling of a thermally regulated communications module for nanospacecraft
- 2006
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics (AIAA). - 0022-4650 .- 1533-6794. ; 43:6, s. 1377-1386
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Tidskriftsartikel (refereegranskat)abstract
- A silicon-based integrated communications and thermal management microsystem qualifying for use on Nanospace-1, a modularized microsystem-based advanced integrated nanospacecraft, is presented. The transmitter and receiver share the same module framework with essential differences only in the electronics implementation. A data rate of 1 Mbps for the transmitter and 114 kbps for the receiver is accomplished with a transmitter power for the spacecraft and ground station of 2 and 10 W, respectively. Concurrent triple usage of paraffin as low loss antenna substrate, actuator material, and heat sink is designed and analyzed for the first time. On low-power or short-time high-power dissipation of heat from the electronics, energy is stored as latent heat in this phase-change material acting as a heat sink. Thermal transport through the module is initiated,by actuation of thermal switches when 75% of the paraffin's latent heat is consumed. A static thermal analysis reveals a thermal modulation factor of 5.6 between the on and off states of the thermal switches. The size of the module is 6.6 x 68 x 68 mm, and its weight is 43 g.
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| 5. |
- Mallol, Pau, et al.
(författare)
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Experiments and simulations of the deployment of a bistable composite boom
- 2018
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics Inc.. - 0022-4650 .- 1533-6794. ; 55:2, s. 292-302
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Tidskriftsartikel (refereegranskat)abstract
- The rapidly growing use of small satellites for space missions requires deployable systems to be highly storable yet large and with adequate mechanical properties when deployed. This paper focuses on the modeling and simulation of a meter-class passively deployable boom, based on the self-contained linear meter-class deployable boom, exploiting the bistable nature of composite shells. Experimental tests were performed on a boom prototype suspended in a gravity offloading system. The strain energy level, deployment time, and spacecraft displacements calculated from the finite element method agree well with analytical analyses, confirming the theoretical accuracy of the finite element method. Because friction and strain energy relaxation were not included in the model, the finite element simulations predicted deployment times up to five times shorter than those of the gravity offloaded boom experiments. The quick deployment and violent end-of-deployment shock created boom deployment dynamics that were not seen in the experiments. The observed differences between the finite element model and the tests were mainly due to inaccurate material and friction models.
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| 6. |
- Nguyen, Hugo, et al.
(författare)
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Structural Integrity of Flat Silicon Panels for Nanosatellites : Modeling and Testing
- 2006
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics (AIAA). - 0022-4650 .- 1533-6794. ; 43:6, s. 1319-1327
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Tidskriftsartikel (refereegranskat)abstract
- To utilize the high mass fraction of silicon material in a nanosatellite based on micro-electro-mechanical systems, part of the structural function has been assigned to the flat silicon stacks embracing these systems. Three modules for destructive testing in bending, warping and shearing cases were built with 68x68x1 mm silicon stacks bonded in aluminium frames by in-situ casting of silicone rubber. The rubber served as the deformation zone between the stiff and brittle silicon stacks and their weaker and ductile aluminium frames. A special test module of the same size was built with strain gauges of Nichrome (thin film deposited directly on the surface of the silicon stack). Elastic deformation tests on this as well as simulations using finite element analysis were performed for bending, warping and shearing loads of up to 80, 40 and 99 N, respectively. The test module was disassembled after the test series and examined. The actual thickness of the rubber was measured and entered into the model for simulation. The correlation between simulations and experimental measurements was good with deviation of about 30%. The results show that the rubber works well as a mechanical interface. Its thickness influences the stress in the silicon stack significantly. The silicon stack stiffens the module by a factor of 46 and lowers the stress in its frame 24 times in shearing mode, which is the most relevant loading case for the satellite framework. Thus, the concept of using flat silicon panels as structural elements is fully feasible.
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| 7. |
- Tibert, Gunnar, et al.
(författare)
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Deployable tensegrity reflectors for small satellites
- 2002
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics (AIAA). - 0022-4650 .- 1533-6794. ; 39:5, s. 701-709
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Tidskriftsartikel (refereegranskat)abstract
- Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which, although narrow, is too tall for many applications. An alternative approach is proposed, consisting of a deployable tensegrity prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design of a 3-m-diam, 10-GHz reflector with a focal-length-to-diameter ratio of 0.4 that can be packaged within an envelope of 0.1 x 0.2 x 0.8 m(3) is presented.
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| 8. |
- Neset, Tina-Simone, 1973-, et al.
(författare)
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Global phosphorus scarcity: identifying synergies for a sustainable future
- 2012
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Ingår i: Journal of the Science of Food and Agriculture. - : Wiley-Blackwell. - 0022-5142 .- 1097-0010. ; 92:1, s. 2-6
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Tidskriftsartikel (refereegranskat)abstract
- Global food production is dependent on constant inputs of phosphorus. In the current system this phosphorus is not predominantly derived from organic recycled waste, but to a large degree from phosphate-rock based mineral fertilisers. However, phosphate rock is a finite resource that cannot be manufactured. Our dependency therefore needs to be addressed from a sustainability perspective in order to ensure global food supplies for a growing global population. The situation is made more urgent by predictions that, for example, the consumption of resource intensive foods and the demand for biomass energy will increase. The scientific and societal debate has so far been focussed on the exact timing of peak phosphorus and on when the total depletion of the global reserves will occur. Even though the timing of these events is important, all dimensions of phosphorus scarcity need to be addressed in a manner which acknowledges linkages to other sustainable development challenges and which takes into consideration the synergies between different sustainability measures. Many sustainable phosphorus measures have positive impacts on other challenges; for example, shifting global diets to more plant-based foods would not only reduce global phosphorus consumption, but also reduce greenhouse gas emissions, reduce nitrogen fertiliser demand and reduce water consumption. Copyright © 2011 Society of Chemical Industry
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| 9. |
- Nordebo, Sven, et al.
(författare)
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Fisher information for inverse problems and trace class operators
- 2012
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Ingår i: Journal of Mathematical Physics. - : AIP Publishing. - 0022-2488 .- 1089-7658. ; 53:12
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a mathematical framework for Fisher information analysis forinverse problems based on Gaussian noise on infinite-dimensional Hilbert space. The covariance operator for the Gaussian noise is assumed to be trace class, andthe Jacobian of the forward operator Hilbert-Schmidt. We show that the appropriatespace for defining the Fisher information is given by the Cameron-Martin space. This is mainly because the range space of the covariance operator always is strictlysmaller than the Hilbert space. For the Fisher information to be well-defined, it is furthermore required that the range space of the Jacobian is contained in the Cameron-Martin space. In order for this condition to hold and for the Fisher information tobe trace class, a sufficient condition is formulated based on the singular values ofthe Jacobian as well as of the eigenvalues of the covariance operator, together withsome regularity assumptions regarding their relative rate of convergence. An explicit example is given regarding an electromagnetic inverse source problem with “external”spherically isotropic noise, as well as “internal” additive uncorrelated noise.
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