Greger Thornell

Invited Article: Electric solar wind sail: Toward test missions

The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.

High Resolution 3D Microstructures Made by Localized Electrodeposition of Nickel

Techniques to create three-dimensional microstructures are still a matter of research, and localized electrodeposition is a promising path to inexpensive free-form microfabrication in metal. The principle is to put the tip of a needle very close to a cond

Microprocessing at the fingertips

Microprocessing, or micromachining, is here approached in a broad rather than profound way. Following a short description of its origin in microelectronics is a classification of more recent advances into three-dimensional processing, anisotropy inducing techniques, stencil processing and conventional machining adapted to micromachining. For each process the major advantages and drawbacks are accounted for. Also, a representative result accompanies every presentation. In all, more than 20 processes are dealt with: wet etching, dry etching, Lithographie-Galvanoformung-Abformung (LIGA), grey-tone lithography, spatial forming, stereolithography, laser chemical processing, local electrodeposition, two-photon-absorbed photopolymerization, focused ion beam (FIB), electrochemically and ion-induced anisotropy, nanoparticle lithography, fast atom beam (FAB), dicing, assembling, lathe machining, milling, die forging and electro-discharge machining (MEDM and WEDG).

Sodium hypochlorite as a developer for heavy ion tracks in polyimide

The developing and etching of heavy ion tracks in polyimide with sodium hypochlorite have been studied to gain control over the parameters that affect the etch result. The shape of the resulting pores is a function of both alkalinity and hypochlorite content of the solution. Sodium hypochlorite decomposes during etching, and the rate constant has been determined as a function of the alkalinity at 62 °C. Polished cross-sections have been examined to determine the pore shape, and this method has shown to be a straightforward way to characterise the pores. Decreasing the alkalinity gives more cylindrical pores, but increases the decomposition rate of the hypochlorite solution and decreases the etch rate.

Micromachining by ion track lithography

Abstract Micromachining by ion track etching (MITE) based on the lithographic projection of a mask onto an arbitrary ion track recording material using a parallel beam of highly energetic heavy ions, is described here. By this, deep microstructures have been produced in single crystalline quartz, phlogopite mica, polycarbonate, polyimide, and soda lime glass without any photolithographic masking. Moreover, with a semitransparent mask, depth modulation and negative resist characteristics can be produced. Edge definition and surface smoothness have been found to increase with increasing ion fluence.

Anisotropy-independent through micromachining of quartz resonators by ion track etching

A method to achieve deep and crystal cut-independent structuring of arbitrary lateral geometry in single crystalline quartz is demonstrated. It is based on local etching of the latent track-induced anisotropy resulting from heavy ion bombardment, and is close to independent of crystallographic orientation. Previous results are briefly reviewed and a more systematic and thorough study is presented. Miniature tuning fork structures of various sizes and directions have been realized, and the suitability for frequency control device production is discussed.

Quartz micromachining by lithographic control of ion track etching

A micromachining process, using ion track etching in combination with lithographic patterning, is presented. The technique employs a substrate pre‐irradiated with swift heavy ions and uses a conventional lithographic technique to control the access of a track‐selective etching medium to the ion tracks. Experimental results show the possibility of generating high aspect ratio structures in virtually any direction in single crystalline quartz, which otherwise exhibits a strong ‘‘natural’’ anisotropy to conventional wet etching. In this way complex, three‐dimensional quartz structures of 80 μm height with vertical or pre‐defined inclination angles of the walls were produced. The process can be applied to other, even highly radiation resistant, dielectric materials such as mica and organic polymers.

Design and fabrication of a gripping tool for micromanipulation

Abstract A tool for micromanipulation is presented in this paper. A titanium gripper is fabricated by a combination of electro-discharge machining and etching, the latter of which is to provide a material less prone to cracking by removing the heat-affected surface. Evaluation of the design has been carried out by finite-element analysis and the performance of the gripper has been qualitatively as well as quantitatively established. The manipulation system to which the tool belongs is also briefly described.

High-temperature zirconia microthruster with an integrated flow sensor

This paper describes the design, fabrication and characterization of a ceramic, heated cold-gas microthruster device made with silicon tools and high temperature co-fired ceramic processing. The de ...

A highly integratable silicon thermal gas flow sensor

Thermal flow sensors have been designed, fabricated, and characterized. All bulk material in these devices is silicon so that they are integratable in silicon-based microsystems. To mitigate heat losses and to allow for use of corrosive gases, the heating and sensing thin film titanium/platinum elements, injecting and extracting heat, respectively, from the flow, are placed outside the channel on top of a membrane consisting of alternating layers of stress-balancing silicon dioxide and silicon nitride. For the fabrication, an unconventional bond surface protection method using sputter-deposited aluminum instead of thermal silicon dioxide is used in the process steps prior to silicon fusion bonding. A method for performing lift-off on top of the transparent membrane was also developed. The sensors, measuring 9.5???9.5?mm2, are characterized in calorimetric and time-of-flight modes with nitrogen flow rates between 0 sccm and 300 sccm. The maximum calorimetric sensor flow signal and sensitivity are 0.95 mV and 29 ?V sccm?1, respectively, with power consumption less than 40?mW. The time-of-flight mode is found to have a wider detectable flow range compared with calorimetric mode, and the time of flight measured indicates a response time of the sensor in the millisecond range. The design and operation of a sensor with high sensitivity and large flow range are discussed. A key element of this discussion is the configuration of the array of heaters and gauges along the channel to obtain different sensitivities and extend the operational range. This means that the sensor can be tailored to different flow ranges.