Michael F. Piszczor

Development of the ultra-light stretched lens array

At the last IEEE-PVSC, the new stretched lens array (SLA) concept was introduced. Since that conference, the SLA team has made significant advances in the SLA technology, including component-level improvements, array-level optimization, space environment exposure testing, and prototype hardware fabrication and evaluation. This paper will describe the evolved version of the SLA, highlighting the improvements in the lens, solar cell, rigid panel structure, and complete solar array wing. The near-term SLA will provide outstanding wing-level performance: >180 W/kg specific power, >300 W/sq.m. power density, >300 V operational voltage, and excellent durability in the space environment.

Benefits of Power and Propulsion Technology for a Piloted Electric Vehicle to an Asteroid

Abstract NASA’s goal for human spaceflight is to expand permanent human presence beyond low Earth orbit (LEO). NASA is identifying potential missions and technologies needed to achieve this goal. Mission options include crewed destinations to LEO and the International Space Station; high Earth orbit and geosynchronous orbit; cis-lunar space, lunar orbit, and the surface of the Moon; near-Earth objects; and the moons of Mars, Mars orbit, and the surface of Mars. NASA generated a series of design reference missions to drive out required functions and capabilities for these destinations, focusing first on a piloted mission to a near-Earth asteroid. One conclusion from this exercise was that a solar electric propulsion stage could reduce mission cost by reducing the required number of heavy lift launches and could increase mission reliability by providing a robust architecture for the long-duration crewed mission. Similarly, solar electric vehicles were identified as critical for missions to Mars, including orbiting Mars, landing on its surface, and visiting its moons. This paper describes the parameterized assessment of power and propulsion technologies for a piloted solar electric vehicle to a near-Earth asteroid. The objective of the assessment was to determine technology drivers to advance the stateof the art of electric propulsion systems for human exploration. Sensitivity analyses on the performance characteristics of the propulsion and power systems were done to determine potential system-level impacts of improved technology. Starting with a “reasonable vehicle configuration” bounded by an assumed launch date, we introduced technology improvements to determine the system-level benefits (if any) that those technologies might provide. The results of this assessment are discussed and recommendations for future work are described.

The stretched lens ultralight concentrator array

This paper describes a new type of space photovoltaic array, including test results for the first fully functional prototype panel. The stretched lens array (SLA) is a high-efficiency, ultralight, stowable, folding-blanket concentrator array. A prototype SLA panel has been performance tested at NASA GRC, with results confirming 27.4% net efficiency (375 W/sq.m areal power) under AM0 sunlight at room temperature. Furthermore, the total prototype panel areal mass, including stretched membrane Fresnel lens concentrators, fully assembled triple-junction cell receivers, and graphite cloth composite radiators, was 0.99 kg/sq.m, resulting in a specific power of 378 W/kg at the fully functional panel level. This is the first space solar array panel of any kind to simultaneously achieve over 300 W/sq.m and over 300 W/kg. In addition, the new SLA has been integrated into a relatively mature flexible blanket platform (ABLEs Aurora(R) array), with near-term array-level performance of 300 W/sq.m and 170 W/kg.

Ultralight stretched Fresnel lens solar concentrator for space power applications

A unique ultra-light solar concentrator has recently been developed for space power applications. The concentrator comprises a flexible, 140-micron-thick, line-focus Fresnel lens, made in a continuous process from space-qualified transparent silicone rubber material. For deployment and support in space, end arches are used to tension the lens material in a lengthwise fashion, forming a cylindrical stressed membrane structure. The resultant lens provides high optical efficiency, outstanding tolerance for real-world errors and aberrations, and excellent focusing performance. The stretched lens is used to collect and focus sunlight at 8X concentration onto high-efficiency multi-junction photovoltaic cells, which directly convert the incident solar energy to electricity. The Stretched Lens Array (SLA) has been measured at over 27% net solar-to-electric conversion efficiency for space sunlight, and over 30% net solar-to-electric conversion efficiency for terrestrial sunlight. More importantly, the SLA provides over 180 W/kg specific power at a greatly reduced cost compared to conventional planar photovoltaic arrays in space. The cost savings are due to the use of 85% less of the expensive solar cell material per unit of power produced. SLA is a direct descendent of the award-winning SCARLET array which performed flawlessly on the NASA/JPL Deep Space 1 spacecraft from 1998-2001.

RECENT ADVANCES IN SOLAR CELL TECHNOLOGY

The advances in solar cell efficiency, radiation tolerance, and cost over the last decade are reviewed. Potential performance of thin-film solar cells in space are discussed, and the cost and the historical trends in production capability of the photovoltaics industry are considered with respect to the requirements of space power systems. Concentrator cells with conversion efficiency over 30%, and nonconcentrating solar cells with efficiency over 25 % are now available, and advanced radiation-tolerant cells and lightweight, thin-film arrays are both being developed. Nonsolar applications of solar cells, including thermophotovoltaics, alpha- and betavoltaics, and laser power receivers, are also discussed.

The stretched lens array (SLA) [spacecraft solar power]

At IECEC 2001, this team presented a paper on the new stretched lens array (SLA), including its evolution from the successful SCARLET array on the NASA/JPL Deep Space 1 spacecraft. Since that conference, the SLA team has made significant advances in SLA technology, including component-level improvements, array-level optimization, space environment exposure testing, and prototype hardware fabrication and evaluation. This paper describes the evolved version of the SLA, highlighting recent improvements in the lens, solar cell, photovoltaic receiver, rigid panel structure, and complete solar array wing. In addition to excellent durability in the space environment, the near-term SLA will provide outstanding wing-level performance parameters: 180 W/kg specific power; 300 W/m/sup 2/ power density; 300 V operational voltage; 85% savings in cell area (cm/sup 2//W) and cell-related cost (

Advanced solar cell and array technology for NASA deep space missions

/W) compared to planar arrays; 9 kW/m/sup 3/ stowed power at launch.

The stretched lens array (SLA): a low-risk cost-effective concentrator array offering wing-level performance of 180 W/kg and 300 W/m/sup 2/ at 300 VDC

A recent study by the NASA Glenn Research Center assessed the feasibility of using photovoltaics (PV) to power spacecraft for outer planetary, deep space missions. While the majority of spacecraft have relied on photovoltaics for primary power, the drastic reduction in solar intensity as the spacecraft moves farther from the sun has either limited the power available (severely curtailing scientific operations) or necessitated the use of nuclear systems. A desire by NASA and the scientific community to explore various bodies in the outer solar system and conduct “long-term” operations using smaller, “lower-cost” spacecraft has renewed interest in exploring the feasibility of using photovoltaics for missions to Jupiter, Saturn and beyond. With recent advances in solar cell performance and continuing development in lightweight, high power solar array technology, the study determined that photovoltaics is indeed a viable option for many of these missions.

Inflatable lenses for space photovoltaic concentrator arrays

This work presents a new stretched lens array (SLA), as a concentrator array used in the space environment. The recent improvements in the lens, solar cell, photovoltaic receiver, rigid panel structure, and complete solar array wing are described. In addition to excellent durability in the space environment, the SLA provides outstanding wing-level performance.

The mini-dome Fresnel lens photovoltaic concentrator array: current status of components and prototype panel testing

For 12 years, ENTECH and NASA Lewis have been developing Fresnel lens solar concentrator technology for space power applications. ENTECH provided the point-focus mini-dome lenses for the PASP+ array, launched in 1994. These silicone lenses performed well on-orbit, with only about 3% optical performance loss after 1 year in elliptical orbit, with high radiation, atomic oxygen, and ultraviolet exposure. The only protection for these silicone lenses was a thin-film coating provided by OCLI. ENTECH also provided the line-focus lenses for the SCARLET 1 and SCARLET 2 arrays in 1995 and 1997, respectively. These lenses are laminated assemblies, with protective ceria glass superstrates over the silicone lens. In March 1997, ENTECH and NASA Lewis began development of inflatable Fresnel lenses, to achieve lower weight, smaller launch volume, reduced cost, less fragility and other advantages. This paper summarizes the new concentrator approach, including key program results to date.