Paul M. Stella

Design and performance of the MER (Mars Exploration Rovers) solar arrays

The Mars Exploration Rovers (MER) program posed a significant engineering and technology challenge. Now that the Rovers have operated beyond their original design life of three months by nearly a factor of four it is clear that the challenge was met and far exceeded. A key to the success of MER has been the enhanced power provided by the cruise and Rover solar arrays. Benefiting from a nearly 50% improvement in cell efficiency compared to the single junction GaAs cells used on Pathfinder, the MER designs were subject to many constraints both in design and in operation. These constraints included limited available panel area, changing illumination levels and temperatures, and variable shadowing, atmospheric conditions and dust accumulation for the rovers. This paper will discuss those constraints and their impact on the design. In addition, flight data will be provided to assess the performance achieved during the mission.

Photovoltaic options for solar electric propulsion

During the past decade, a number of advances have occurred in solar cell and array technology. These advances have lead to performance improvement for both conventional space arrays and for advanced technology arrays. Performance enhancements have occurred in power density, specific power, and environmental capability. Both state-of-the-art and advanced development cells and array technology are discussed. Present technology will include rigid, rollout, and foldout flexible substrate designs, with silicon and GaAs solar cells. The use of concentrator array systems is also discussed based on both DOD and NASA efforts. The benefits of advanced lightweight array technology, for both near term and far term utilization, and of advanced high efficiency, thin, radiation resistant cells is examined. This includes gallium arsenide on germaniun substrates, indium phosphide, and thin film devices such as copper indium diselenide.

The performance of advanced solar cells for interplanetary missions

Recent advances in space solar cell technology have produced substantial increases in Air Mass Zero (AM0) efficiency. Since these cells have been developed primarily for Earth orbiting missions, little is known of their behavior at distances far from the Sun. In order to better define the photovoltaic performance of arrays for deep space missions, JPL has completed initial measurements on a number of advanced cells under a variety of LILT (low intensity, low temperature) conditions. These include high efficiency silicon, and multi-junction III-V devices. The test results show that multi-junction cells suffer from LILT degradation and that at 5AU (approximately the solar distance of Jupiter), efficiency advantages over high efficiency silicon are minimal. Silicon cells optimized for 3-6 AU operation not only equal the efficiency available from 2 and 3 junction cells, but also tend to be more uniform.

Thin film GaAs for space-moving out of the laboratory

In 1991, NASA-JPL completed the APSA (Advanced Photovoltaic Solar Array) program, demonstrating a lightweight deployable flexible array wing capable of 130 W/kg specific performance, a substantial improvement over conventional flight hardware. The design was based on the use of thin (55 microns) silicon or thin (100 microns) GaAs/Ge solar cells. Further array performance enhancements will require the implementation of a new advanced solar cell. An effort has been initiated to develop array fabrication methods for use of ultrathin high efficiency large area thin film GaAs cells. Flexible substrate modules have been assembled for thermal cycle testing.<<ETX>>

Advanced Photovoltaic Solar Array Program status

The Advanced Photovoltaic Solar Array (APSA) Program for spacecraft is discussed. The objective of the program is to demonstrate a producible array system by the end of this decade with a beginning-of-life (BOL) specific power of 130 W/kg at 10 kW as an intermediate milestone toward the ultimate goal of 300 W/kg at 25 kW by the year 2000. The near-term goal represents a significant improvement over existing rigid panel flight arrays (25 to 45 W/kg) and the first-generation flexible blanket NASA/OAST SAFE I array of the early 1980s, which was projected to provide about 60 W/kg BOL. The prototype wing hardware is in the last stages of fabrication and integration. The current status of the program is reported. The array configuration and key design details are shown. Projections are shown for future performance enhancements that may be expected through the use of advanced structural components and solar cells.<<ETX>>

Latest Developments in the Advanced Photovoltaic Solar Array Program

In 1985, the Jet Propulsion Laboratory (JPL), under sponsorship from the NASA Office of Aeronautics, Exploration and Technology (OAET), initiated the Advanced Photovoltaic Solar Array (APSA) Program to demonstrate a producible array system by 1990 with a specific power greater than 130 W/kg at a 10 kW (BOL) power level. This establishes an intermediate near-term goat in anticipation of the eventual need by the year 2000 for an array with a specific power of 300 W/kg at a power level of 25 kW (BOL). The near-term goal represents a significant improvement over existing rigid panel flight arrays (20 to 40 W/kg), the first-generation flexible blanket NASA/OAET SAFE I array of the early 1980s which was projected to provide about 66 W/kq (BOL), and the proposed flexible blanket arrays for Space Station Freedom at 40 W/kg (BOL). The latest program phase completed fabrication and initial functional testing of a prototype wing representative of a full-scale 5 kW (BOL) wing (except truncated in length to about 1 kW), with weight characteristics that could meet the 130 W/kg (BOL) specific power goat using thin silicon solar cell modules and weight efficient structural components. This paper continues the status reporting on the program presented in the last three IECEC symposia. The wing configuration and key design details are reviewed along with results from key component-level and wing-level tests. Projections are shown for future performances enhancements that may be excepted through the use of advanced solar cells and structural components. Performance estimates will be shown for solar electric propulsion orbital transfer missions through the Van Allen radiation belts. The latest APSA program plans are presented.

Advanced photovoltaic solar array - Design and performance

This paper reports on the development of an ultralightweight flexible blanket, flatpack, foldout solar array design that can provide 3- to 4-fold improvement on specific power performance of current rigid panel arrays and a factor of two improvement over a first-generation flexible blanket array developed as a forerunner to the Space Station Freedom array. To date a prototype wing has been built with a projected specific power performance of about 138 W/kg at beginning-of-life (BOL) and 93 W/kg end-of-life (EOL) at 12 kW (BOL) for a 10-year geosynchronous (GEO) mission. The prototype wing hardware has been subjected to a series of system-level tests to demonstrate design feasibility. The design of the array is summarized. The major trade studies that led to the selection of the baseline design are discussed. Key system-level and component-level testing are described. Array-level performance projections are presented as a function of existing and advanced solar array component technology for various mission applications. 8 refs.

JUNO - Photovoltaic Power at Jupiter

This paper summarizes the Juno modeling team work on predicting the Juno solar array performance at critical mission points including Juno Orbit Insertion (JOI) and End of Mission (EOM). This report consists of background on Juno solar array design, a summary of power estimates, an explanation of the modeling approach used by Aerospace, a detailed discussion of loss factors and performance predictions, a thermal analysis, and a review of risks to solar array performance

The Mars surface environment and solar array performance

January, 2010, marked the 6th anniversary for MER. This also marked the completion of more than three Martian years of solar array operation on Mars. During the spring of 2010, the MER rovers broke the RTG powered Viking Lander record for robotic operations on the Mars surface. Not only has a wealth of scientific information been obtained from MER but also a large quantity of data regarding factors that impact solar array performance. These include measurement of atmospheric dust, i.e., the atmospheric tau value. Additionally, dust buildup and removal from the solar array surfaces has been tracked. It is expected that the data from the rovers will enhance the prediction of future Mars surface solar array performance. Seasonal and annual trends have been identified. The results of these parameter analyses will be presented to assist in the design of future Mars surface solar power systems, both rover and stationary.

Early mission power assessment of the Dawn solar array

NASAs Discovery Mission Dawn was launched in September 2007. Dawn will be the first to orbit two asteroids on a single voyage. The solar array for the Dawn mission will provide power under greatly varying illumination and temperature conditions. Dawns ion propulsion system (IPS) will provide the spacecraft with enough thrust to reach Vesta and Ceres and orbit both. The demanding mission would be impossible without ion propulsion — a mission only to the asteroid Vesta (and not including Ceres) would require a much more massive spacecraft and, a much larger launch vehicle.