Andrew H. Weisberg

Reversible (unitised) PEM fuel cell devices

Regenerative fuel cells (RFCs) are enabling for many weight-critical portable applications, since the packaged specific energy (>400 Wh/kg) of properly designed lightweight RFC systems is several-fold higher than that of the lightest-weight rechargeable batteries. RFC systems can be rapidly refueled (like primary fuel cells), or can be electrically recharged (like secondary batteries) if a refueling infrastructure is not conveniently available. Higher energy capacity systems with higher performance, reduced weight and freedom from fueling infrastructure are the features that RFCs promise for portable applications. Reversible proton exchange membrane (PEM) fuel cells, also known as unitised regenerative fuel cells (URFCs), or reversible regenerative fuel cells, are RFC systems which use reversible PEM cells, where each cell is capable of operating both as a fuel cell and as an electrolyser. URFCs further economise portable device weight, volume and complexity by combining the functions of fuel cells and electrolysers in the same hardware, generally without any system performance or efficiency reduction. URFCs are being made in many forms, some of which are already small enough to be portable. Lawrence Livermore National Laboratory (LLNL) has worked with industrial partners to design, develop and demonstrate high-performance and high-cycle-life URFC systems. LLNL is also working with industrial partners to develop breakthroughs in lightweight pressure vessels that are necessary for URFC systems to achieve the specific energy advantages over rechargeable batteries. Proton Energy Systems Inc is concurrently developing and commercialising URFC systems (its Unigen ; product lproduct line), in addition to PEM electrolyser systems (the Hogen ; product lproduct line), and primary PEM fuel cell systems. LLNL is constructing demonstration URFC units in order to persuade potential sponsors, often in their own conference rooms, that advanced applications based on URFCs are feasible. Safety and logistics force these URFC demonstration units to be small, transportable and easily set up, hence they already prove the viability of URFC systems for portable applications.

Wafer-Scale Laser Lithography: I. Pyrolytic Deposition Of Metal Microstructures

Mechanisms for laser-driven pyrolytic deposition of micron-scale metal structures on crystalline silicon have been studied. Models have been developed to predict temporal and spatial properties of laser-induced pyrolytic deposition processes. An argon ion laser-based apparatus has been used to deposit metal by pyrolytic decomposition of metal alkyl and carbonyl compounds, in order to evaluate the models. These results of these studies are discussed, along with their implications for the high-speed creation of micron-scale metal structures in ULSI systems.

Eyeglass: a very large aperture diffractive space telescope

Eyeglass is a very large aperture (25 - 100 meter) space telescope consisting of two distinct spacecraft, separated in space by several kilometers. A diffractive lens provides the telescopes large aperture, and a separate, much smaller, space telescope serves as its mobile eyepiece. Use of a transmissive diffractive lens solves two basic problems associated with very large aperture space telescopes; it is inherently fieldable (lightweight and flat, hence packagable and deployable) and virtually eliminates the traditional, very tight, surface shape tolerances faced by reflecting apertures. The potential drawback to use of a diffractive primary (very narrow spectral bandwidth) is eliminated by corrective optics in the telescopes eyepiece. The Eyeglass can provide diffraction-limited imaging with either single-band, multiband, or continuous spectral coverage. Broadband diffractive telescopes have been built at LLNL and have demonstrated diffraction-limited performance over a 40% spectral bandwidth (0.48 - 0.72 μm). As one approach to package a large aperture for launch, a foldable lens has been built and demonstrated. A 75 cm aperture diffractive lens was constructed from 6 panels of 1 mm thick silica; it achieved diffraction-limited performance both before and after folding. This multiple panel, folding lens, approach is currently being scaled-up at LLNL. We are building a 5 meter aperture foldable lens, involving 72 panels of 700 μm thick glass sheets, diffractively patterned to operate as coherent f/50 lens.

Electrolysis Propulsion for Spacecraft Applications

Electrolysis propulsion has been recognized over the last several decades as a viable option to meet many satellite and spacecraft propulsion requirements. This technology, however, was never used for in-space missions. In the same time frame, water based fuel cells have flown in a number of missions. These systems have many components similar to electrolysis propulsion systems. Recent advances in component technology include: lightweight tankage, water vapor feed electrolysis, fuel cell technology, and thrust chamber materials for propulsion. Taken together, these developments make propulsion and/or power using electrolysis/fuel cell technology very attractive as separate or integrated systems. A water electrolysis propulsion testbed was constructed and tested in a joint NASA/Hamilton Standard/Lawrence Livermore National Laboratories program to demonstrate these technology developments for propulsion. The results from these testbed experiments using a 1-N thruster are presented. A concept to integrate a propulsion system and a

Design trade space for a Mars ascent vehicle for a Mars sample return mission

Abstract The design of an ascent vehicle for Mars sample return is one of the most challenging problems to be addressed for this type of mission. This paper identifies the spectrum of performance requirements that could be required of a Mars ascent vehicle for a sample return mission. With this understanding of performance requirements, an investigation of technology requirements is presented. These technology requirements are compared to past and existing technology in order to identify which are the lagging technologies and where development investment should be made. Mars ascent approaches which include storable propellants and in-situ production of propellants are considered. Several technology comparisons are performed to illustrate performance regions that are appropriate for different technologies. Several promising propulsion technologies are identified: miniature constant displacement pumps, bladder lined composite tankage, thin wall metal tankage and advanced propellants. Technologies that have been designed, built, tested and flown are emphasized.

Preliminary demonstration of power beaming with non-coherent laser diode arrays

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a ∼15×25 cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The source radiance is approximately 5×109 W/m2-steradian. With the existing 20 cm aperture, useful power transmission over ranges to ∼100 meters should be achievable with a DC to DC efficiency of greater than 10%. Non-coherent sources of this type are readily scalable to powers of tens of kilowatts, and with larger apertures can be used directly for power transmission up to several kilometers. Future non-coherent diode laser sources may be suitable for power transmission over hundreds of kilometers. Also, the experience gained with non-coherent arrays will be directly applicable to power beaming systems using coherent diode arrays or other array-type laser sources.A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a ∼15×25 cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The s...

Process Margins for Laser Planarization of 1 to 5 µm Gold Films

A pulsed excimer laser or flashlamp-pumped dye laser is used to melt 1 to 5 µm Au layers. The size of feature which can be filled by laser planarization is limited because of the finite melt duration, but the basic goal of levelling local surface topography is accomplished. Laser reflow of thicker films reveals fundamental differences between the excimer laser and the flashlamp-pumped dye laser, resulting from the order-of-magnitude difference in pulse duration. The excimer pulse is short compared to the thermal diffusion time of the metal layer and this can create voids and craters in the metal above discontinuities in the underlying structure. For Au thicknesses greater than about 3 µm, void formation occurs at fluences at or below that necessary to planarize the film. The dye laser has a planarization threshold similar to that of the excimer but it takes over 60% greater energy to create voids than to planarize a 5 µm film. A second damage mode, common to both laser sources, occurs where adjacent planarization zones overlap in a patterned area: thin spots can be created by the first planarization pulse which are vaporized by the second pulse.

Development of Large-Aperture, Light-Weight Fresnel Lenses for Gossamer Space Telescopes

In order to examine more distant astronomical objects, with higher resolution, future space telescopes require objectives with significantly larger aperture than presently available. NASA has identified a progression in size from the 2.4m aperture objective currently used in the HUBBLE space telescope[1,2], to 25m and greater in order to observe, e.g., extra-solar planets. Since weight is a crucial factor for any object sent into space, the relative weight of large optics over a given area must be reduced[3]. The areal mass density of the primary mirror for the Hubble space telescope is ~200 kg/m. This is expected to be reduced to around 15 kg/m for the successor to Hubble – the next generation space telescope (NGST)[4]. For future very large aperture telescopes needed for extra-solar planet detection, the areal mass density must be reduced even further. For example, the areal mass density goal for the Gossamer space telescopes is 10m size is also an enabling technology for many other applications such as Earth observation, power beaming, and optical communications.