David Lichodziejewski

DEVELOPMENT AND GROUND TESTING OF A COMPACTLY STOWED SCALABLE INFLATABLY DEPLOYED SOLAR SAIL

Solar sails reflect photons streaming from the sun and transfer momentum to the sail. The thrust, though small, is continuous and acts for the life of the mission without the need for propellant. Recent advances in materials and ultra-low mass gossamer 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 the NASA In-Space Propulsion office, has been developing a scalable solar sail configuration to address NASA’s future space propulsion needs. The baseline design currently in development and testing was optimized around the 1 AU solar sentinel mission. Featuring inflatably deployed sub-Tg rigidized beam components, the 10,000 m 2 sail and support structure weighs only 47.5 kg, including margin, yielding an areal density of 4.8 g/m 2 . Striped sail architecture, net/membrane sail design, and L’Garde’s conical boom deployment technique allows scalability without high mass penalties. This same structural concept can be scaled to meet and exceed the requirements of a number of other useful NASA missions. This paper discusses the solar sail design and outlines the interim accomplishments to advance the technology readiness level (TRL) of the subsystem from 3 toward a technology readiness level of 6 in 2005. Under Phase 2 of the program many component test articles have been fabricated and tested successfully. Most notably an unprecedented section of the conically deployed rigidizable sail support beam, the heart of the inflatable rigidizable structure, has been deployed and tested in the NASA Goddard thermal vacuum chamber with good results. The development testing validated the beam packaging and deployment. The fabricated masses and structural test results of our beam components have met predictions and no changes to the mass estimates or design assumptions have been identified adding great credibility to the design. Several quadrants of the Mylar sail have also been fabricated and successfully deployed validating our design, manufacturing, and deployment techniques. The team of L’Garde, Ball Aerospace, JPL, and LaRC has developed a highly scalable solar sail configuration to meet the in-space propulsive requirements of many of NASA’s future missions, while dramatically lowering launch costs. Phase 2 of the program has seen much development and testing of this design validating design assumptions, mass estimates, and predicted mission scalability. Under Phase 3 the program will culminate in a vacuum deployment of a 20 m subscale test article at the NASA Glenn Plum Brook 30 m vacuum test facility to bring the TRL level as close to 6 as possible in 1 g. This focused program will pave the way for a flight experiment of this highly efficient space propulsion technology.

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 (1) . 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 m 2 sailcraft achieves an areal density of 14.1 g/m 2 and a characteristic acceleration of 0.58 mm/s 2 . The entire configuration released by the upper stage has a mass of 232.9 kg and requires just 1.7 m3 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.

VACUUM DEPLOYMENT AN D TESTING OF A 20M SOLAR SAIL SYSTEM

Solar sails reflect photons streaming from the sun and transfer momentum to the sail. The thrust, though small, is continuous and acts for the life of the mission without the need for propellant. Recent advances in materials and ultra -low mass gossamer structures have enabled a host of useful missions utilizing solar sail propulsio n. This paper discusses the Phase 3 accomplishments of a 3 -phase 33 -month collaboration between L’Garde, Ball Aerospace, JPL, and NASA LaRC under the direction of the NASA In -Space Propulsion office to develop solar sails and to raise the technology readi ness level ( TRL ) to as close to 6 as possible though ground testing of large scale solar sail test articles . A comprehensive review of the program accomplishments to date finds the overall TRL level now in the 5 to 6 range which has increased from around 3 at the beginning of the program. This comprehensive ground test program included material, component, subsystem, system, and finally launch environment and thermal vacuum deployment tests . In conjunction FEA models were developed and validated with gr ound test data resulting in highly credible analysis techniques able to bridge the gap between ground test results and future large scale flight articles. This focused program will pave the way for a flight experiment of this highly efficient space propuls ion technology.

Finite Element Analysis and Test Correlation of a 10-Meter Inflation-Deployed Solar Sail

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASAs future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive phased test plan is currently being implemented to advance the technology readiness level of the solar sail design. These tests consist of solar sail component, subsystem, and sub-scale system ground tests that simulate the vacuum and thermal conditions of the space environment. Recently, two solar sail test articles, a 7.4-m beam assembly subsystem test article and a 10-m four-quadrant solar sail system test article, were tested in vacuum conditions with a gravity-offload system to mitigate the effects of gravity. This paper presents the structural analyses simulating the ground tests and the correlation of the analyses with the test results. For programmatic risk reduction, a two-prong analysis approach was undertaken in which two separate teams independently developed computational models of the solar sail test articles using the finite element analysis software packages: NEiNastran and ABAQUS. This paper compares the pre-test and post-test analysis predictions from both software packages with the test data including load-deflection curves from static load tests, and vibration frequencies and mode shapes from vibration tests. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were uncertainties in the material properties, test conditions, and modeling assumptions used in the analyses.

SPIRAL WRAPPED ALUMINUM LAMINATE RIGIDIZATION TECHNOLOGY

Aluminum Laminate is the most mature space inflatable/rigidization technology; it has been flow on the early echo balloons in the 1960s and most recently on L’Garde’s Orbital Calibration Sphere in 2000, all with very successful results. Several recent programs at L’Garde have further developed and enhanced the technology, the enhanced ITSAT solar array, and the Techsat 21 deployable boom (Figure 1). The structural performance of the design has been significantly improved with the addition of an external helically wound filament to absorb the hoop stress during rigidization. A new sheath deployment technique, developed for Techsat 21 program, offers a unique and mass efficient way to controllably deploy a structure incorporating this technology. Though limited in thickness, this rigidization technique has many uses for small to medium sized structures. L’Garde has designed, fabricated, and tested many tubes incorporating this new design. This paper will review the history of

INFLATABLE RIGIDIZABLE SOLAR ARRAY FOR SMALL SATELLITES

With today’s high launch costs, and tightening launch opportunities, low mass, cost, and packaged volume can determine the mission feasibility. L’Garde has developed the Inflatable Torus Solar Array Technology (ITSAT) to supply power to the growing fleet of small satellites in the 1kW class making forays into the space market. The ITSAT configuration with low mass and stowage volume and the inherent reliability of inflatably deployed structures is an excellent solution for these low power applications. The ITSAT is able to provide power densities more typical of a much larger system, despite its small scale.

Ground Testing a 20-Meter Inflation Deployed Solar Sail

Solar sails have been proposed for a variety of future space exploration missions and provide a cost effective source of propellantless propulsion. Solar sails span very large areas to capture and reflect photons from the Sun and are propelled through space by the transfer of momentum from the photons to the solar sail. The thrust of a solar sail, though small, is continuous and acts for the life of the mission without the need for propellant. Recent advances in materials and ultra-low mass gossamer structures have enabled a host of useful space exploration missions utilizing solar sail propulsion. The team of L Garde, NASA Jet Propulsion Laboratory (JPL), Ball Aerospace, and NASA Langley Research Center, under the direction of the NASA In-Space Propulsion Office (ISP), has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. The 100-m baseline solar sail concept was optimized around the one astronomical unit (AU) Geostorm mission, and features a Mylar sail membrane with a striped-net sail suspension architecture with inflation-deployed sail support beams consisting of inflatable sub-Tg (glass transition temperature) rigidizable semi-monocoque booms and a spreader system. The solar sail has vanes integrated onto the tips of the support beams to provide full 3-axis control of the solar sail. This same structural concept can be scaled to meet the requirements of a number of other NASA missions. Static and dynamic testing of a 20m scaled version of this solar sail concept have been completed in the Space Power Facility (SPF) at the NASA Glenn Plum Brook facility under vacuum and thermal conditions simulating the operation of a solar sail in space. This paper details the lessons learned from these and other similar ground based tests of gossamer structures during the three year solar sail project.

Structural Analysis and Test Comparison of a 20-Meter Inflation-Deployed Solar Sail

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive test program was implemented to advance the technology readiness level of the solar sail design. These tests consisted of solar sail component, subsystem, and sub-scale system ground tests that simulated the aspects of the space environment such as vacuum and thermal conditions. In July 2005, a 20-m four-quadrant solar sail system test article was tested in the NASA Glenn Research Center s Space Power Facility to measure its static and dynamic structural responses. Key to the maturation of solar sail technology is the development of validated finite element analysis (FEA) models that can be used for design and analysis of solar sails. A major objective of the program was to utilize the test data to validate the FEA models simulating the solar sail ground tests. The FEA software, ABAQUS, was used to perform the structural analyses to simulate the ground tests performed on the 20-m solar sail test article. This paper presents the details of the FEA modeling, the structural analyses simulating the ground tests, and a comparison of the pretest and post-test analysis predictions with the ground test results for the 20-m solar sail system test article. The structural responses that are compared in the paper include load-deflection curves and natural frequencies for the beam structural assembly and static shape, natural frequencies, and mode shapes for the solar sail membrane. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were unmeasured initial conditions in the test set-up.

Propulsive Reflectivity and Photoflexibility: Effects on Solar Sail Performance and Control

Surface quality and sail shape are primary influences on the thrust and passive attitude stability of solar sails. Further, sail membrane stress greatly affects structural mass, influencing the true performance and navigation parameter of interest, acceleration. In 2001, L’Garde quantified the surface quality of 0.9 µm metallized Mylar at zero stress using bi-directional reflectance tests, and developed a method to vector sum and reduce all the data at a given incidence angle to just two data parameters for the reflected force component, “Propulsive Reflectivity” and “Propulsive Zenith.” The results showed excellent propulsive performance even at zero membrane stress, freeing L’Garde to design the lightest possible structure, and giving us a solid experimental basis for performance predictions and navigation design. Sail shape, on the other hand, is generally shallow enough that thrust and mass are not greatly affected relative to a flat plate. However, relatively large moments appear at off-normal attitudes, affecting control. The dominant, stabilizing influence of effective shuttlecock is modified by an effect dubbed “photoflexibility.” As the ultra-thin membrane has essentially zero flexural stiffness, and as the applied solar force is a strong function of local membrane solar attitudes, sail shape changes with attitude, altering the applied moment about the sail center, the center of mass of the quadrant, and the beam bend.

STRUCTURAL ANALYSIS OF AN INFLATION- DEPLOYED SOLAR SAIL WITH EXPERIMENTAL VALIDATION

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive phased test plan is currently being implemented to advance the technology readiness level of the solar sail design. These tests consist of solar sail component, subsystem, and sub-scale system ground tests that simulate the vacuum and thermal conditions of the space environment. Recently, two solar sail test articles, a 7.4-m beam assembly subsystem test article and a 10-m four-quadrant solar sail system test article, were tested in vacuum conditions with a gravity-offload system to mitigate the effects of gravity. This paper presents the structural analyses simulating the ground tests and the correlation of the analyses with the test results. For programmatic risk reduction, a two-prong analysis approach was undertaken in which two separate teams independently developed computational models of the solar sail test articles using the finite element analysis software packages: NEiNastran and ABAQUS. This paper compares the pre-test and post-test analysis predictions from both software packages with the test data including load-deflection curves from static load tests, and vibration frequencies and mode shapes from structural dynamics tests. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were uncertainties in the material properties, test conditions, and modeling assumptions used in the analyses.