Engineering topics
Pappa, Richard
Publications and source records attributed to Pappa, Richard.
Compact Telescoping Surface Array for Mars Solar Power
This paper describes a lightweight, large-area solar array concept for Mars surface power called the Compact Telescoping Surface Array (CTSA). The design is derived from the Compact Telescoping Array (CTA) proposed in 2015 for high-power spacecraft. The CTSA deploys horizontally from Mars landers, provides 1000 sq.m of solar cell area, and generates about 50-80 kW daytime and 10 kW nighttime power (from energy storage) near the equator with clear skies. The total mass is about 1500 kg, and the stowed volume is about 10 cu.m, equivalent to 200 W/kg and 30 kW/cu.m at 1 astronomical unit (AU) from the sun. These challenging mass and volume goals require compact, lightweight structures to deploy and tension thin solar cell blankets in the Mars 0.38 g gravity field. Other features include single-axis rotation for daily or seasonal sun tracking, dust shedding, and feathering in high winds and sufficient strength for sustained 40 m/s winds in dust storms and brief 100 m/s winds in dust devils (dynamic pressure of 120 Pa). Based on preliminary design and analysis reported in the paper, CTSA appears to be a feasible approach for 1000 sq.m-class Mars solar arrays that autonomously deploy from landers prior to human arrival.
Mars Surface Solar Arrays: Part 2 Power Performance
This presentation covers the modeling and power performance of high power Mars surface solar arrays needed to power a human Mars base.
Telescoping Solar Array Concept for Achieving High Packaging Efficiency
Lightweight, high-efficiency solar arrays are required for future deep space missions using high-power Solar Electric Propulsion (SEP). Structural performance metrics for state-of-the art 30-50 kW flexible blanket arrays recently demonstrated in ground tests are approximately 40 kW/cu m packaging efficiency, 150 W/kg specific power, 0.1 Hz deployed stiffness, and 0.2 g deployed strength. Much larger arrays with up to a megawatt or more of power and improved packaging and specific power are of interest to mission planners for minimizing launch and life cycle costs of Mars exploration. A new concept referred to as the Compact Telescoping Array (CTA) with 60 kW/cu m packaging efficiency at 1 MW of power is described herein. Performance metrics as a function of array size and corresponding power level are derived analytically and validated by finite element analysis. Feasible CTA packaging and deployment approaches are also described. The CTA was developed, in part, to serve as a NASA reference solar array concept against which other proposed designs of 50-1000 kW arrays for future high-power SEP missions could be compared.
Solar Array Structures for 300 kW-Class Spacecraft
State-of-the-art solar arrays for spacecraft provide on the order of 20 kW of electrical power, and they usually consist of 3J solar cells bonded to hinged rigid panels about 1 inch in thickness. This structural construction allows specific mass and packaging volumes of up to approximately 70 W/kg and 15 kW/m3 to be achieved. Significant advances in solar array structures are required for future very-high-power spacecraft (300+ kW), such as those proposed for pre-positioning heavy cargo on or near the Moon, Mars, or asteroids using solar electric propulsion. These applications will require considerable increases in both W/kg and kW/m3, and will undoubtedly require the use of flexible-substrate designs. This presentation summarizes work sponsored by NASA's Game Changing Development Program since Oct. 2011 to address the challenge of developing 300+ kW solar arrays. The work is primarily being done at NASA Langley, NASA Glenn, and two contractor teams (ATK and DSS), with technical collaboration from AFRL/Kirtland. The near-tem objective of the project is design, analysis, and testing of 30-50 kW solar array designs that are extensible to the far-term objective of 300+ kW. The work is currently focused on three designs: the MegaFlex concept by ATK, the Mega-ROSA concept by DSS, and an in-house 300-kW Government Reference Array concept. Each of these designs will be described in the presentation. Results obtained to date by the team, as well as future work plans, for the design, analysis, and testing of these large solar array structures will be summarized.
Solar Cell and Array Technology Development for NASA Solar Electric Propulsion Missions
NASA is currently developing advanced solar cell and solar array technologies to support future exploration activities. These advanced photovoltaic technology development efforts are needed to enable very large (multi-hundred kilowatt) power systems that must be compatible with solar electric propulsion (SEP) missions. The technology being developed must address a wide variety of requirements and cover the necessary advances in solar cell, blanket integration, and large solar array structures that are needed for this class of missions. Th is paper will summarize NASA's plans for high power SEP missions, initi al mission studies and power system requirements, plans for advanced photovoltaic technology development, and the status of specific cell and array technology development and testing that have already been conducted.
Development of Modal Test Techniques for Validation of a Solar Sail Design
This paper focuses on the development of modal test techniques for validation of a solar sail gossamer space structure design. The major focus is on validating and comparing the capabilities of various excitation techniques for modal testing solar sail components. One triangular shaped quadrant of a solar sail membrane was tested in a 1 Torr vacuum environment using various excitation techniques including, magnetic excitation, and surface-bonded piezoelectric patch actuators. Results from modal tests performed on the sail using piezoelectric patches at different positions are discussed. The excitation methods were evaluated for their applicability to in-vacuum ground testing and to the development of on orbit flight test techniques. The solar sail membrane was tested in the horizontal configuration at various tension levels to assess the variation in frequency with tension in a vacuum environment. A segment of a solar sail mast prototype was also tested in ambient atmospheric conditions using various excitation techniques, and these methods are also assessed for their ground test capabilities and on-orbit flight testing.
Bringing an effective solar sail design toward TRL 6
This document outlines the accomplishments of a Phase 1 effort to advance the technology readiness level of the concept from 3 toward a TRL of 6. The Phase 1 effort, the first of three proposed phases, addressed the design of the solar sail, its application to several missions currently under review at NASA, and developed a ground test plan to bring the technology toward a TRL of 6.
Bringing an Effective Solar Sail Design Toward TRL 6
Solar sails reflect photons streaming from the sun and convert some of the energy into thrust. This thrust, though small, is continuous and acts for the life of the mission without the need for propellant ( I ) . Recent advances in sail materials and ultra-low mass structures have enabled a host of useful missions utilizing solar sail propulsion. The team of L Garde, Jet Propulsion Laboratories, Ball Aerospace, and Langley Research Center, under the direction of NASA, has been developing a solar sail configuration to address NASA s future space propulsion needs. Utilizing inflatably deployed and Sub Tg rigidized boom components, this 10,000 sq m sailcraft achieves an areal density of 14.1 g/sq m and a characteristic acceleration of 0.58 mm/s . The entire configuration released by the upper stage has a mass of 232.9 kg and requires just 1.7 d of volume in the booster. After deployment, 92.2 kg of non-flight required equipment is jettisoned resulting in a sailcraft mass, including payload and control system, of 140.7 kg. This document outlines the accomplishments of a Phase 1 effort to advance the technology readiness level (TRL) of the concept from 3 toward a TRL of 6. The Phase 1 effort, the first of three proposed phases, addressed the design of the solar sail, its application to several missions currently under review at NASA, and developed a ground tes plan to bring the technology toward a TRL of 6.
Comparison of Modal Analysis Methods Applied to a Vibro-Acoustic Test Article
Modal testing of a vibro-acoustic test article referred to as the Aluminum Testbed Cylinder (ATC) has provided frequency response data for the development of validated numerical models of complex structures for interior noise prediction and control. The ATC is an all aluminum, ring and stringer stiffened cylinder, 12 feet in length and 4 feet in diameter. The cylinder was designed to represent typical aircraft construction. Modal tests were conducted for several different configurations of the cylinder assembly under ambient and pressurized conditions. The purpose of this paper is to present results from dynamic testing of different ATC configurations using two modal analysis software methods: Eigensystem Realization Algorithm (ERA) and MTS IDEAS Polyreference method. The paper compares results from the two analysis methods as well as the results from various test configurations. The effects of pressurization on the modal characteristics are discussed.
Estimation of full modal damping matrices from complex test modes
This paper describes the refinements of a previously published method for estimating a full modal damping matrix from complex test modes. It also documents application of the refined method to a structure where complex test modes were derived by the ERA method from multi-input random vibration test data. A numerical example based on simulated test data is presented to demonstrate the validity of the method. The application using real data was not successful, presumably because of noise in the small phase angles of the measured complex modes. Alternative test and data reduction procedures are suggested as possible remedies to the problem. A careful analysis of measurement and data processing errors should be made to examine basic feasibility before implementing the alternative procedures. The ability to estimate a full modal damping matrix is considered important for the preflight estimation of on-orbit damping, and for the synthesis of structural damping from substructure tests.