Sunjammer: A Solar Sail Demonstration

The NASA Engineering and Safety Center (NESC) was established in 2003 (after the Columbia accident) to provide an independent technical resource for the resolution of challenging technical problems (through the use of studies, analysis, tests, etc.) for NASA programs and projects. Since its inception, NESC has completed nearly 1000 technical assessments for NASA’s Human Exploration and Operation Mission Directorate (HEOMD), Science Mission Directorate (SMD), Space Technology Mission Directorate (STMD), and Aeronautics Research Mission Directorate (ARMD). Of the SMD related assessments, several were for the resolution of technical problems, analysis, or studies related to NASA’s astrophysics missions in various phases of the project from design to operation. Some of the recent examples of NESC technical support for NASA astrophysics missions have been for: Hubble Space Telescope (HST), Chandra X-ray Observatory (CXO), Fermi Gamma-ray Space Telescope, Kepler Space Telescope, Transiting Exoplanet Survey Satellite (TESS), James Webb Space Telescope (JWST), and Laser Interferometer Space Antenna (LISA). In this paper, we outline some of the technical challenges faced by these astrophysics missions and describe how NESC contributed to their resolution. The case studies cover a wide range of disciplines involving space telescopes, detectors, lasers, and attitude control systems. These efforts include innovative solutions for extending the life of the missions, technical resolution of challenging problems, strategies for risk mitigation, and failure investigations combined with lessons learned reports to advance discipline knowledge, enhance NASA capabilities, and avoid future problems.

The focus of this research is to develop a vision guided autonomous system for simulated structure assembly on distant planets/moons. This concept supports NASA’s Space Technology Mission Directorate (STMD) by enabling autonomous structure or habitat assembly. To accomplish this, simulated building materials shaped as bricks are used to assemble structures in a similar fashion as on earth. The bricks would be produced via additive manufacturing from the in-situ environment, which is not the focus of this research. This is an alternative methodology to many of the NASA 3D Printed Habitat Centennial Challenge concepts; it is accomplished by mounting a robot arm atop a mecanum drive robotic platform. The mecanum base enables the system to traverse omni-directionally over the terrain while the robot arm provides material manipulation abilities. To counter the changing work conditions, a vision system provides flexible peripheral input. The system would travel to the approximate build location then the vision system would provide guided input for the automated assembly. Each subsystem provides flexibility to simulate a scenario of being deployed on a distant planet/moon while the appropriately sized construction blocks allowed the rover to build a structure piece by piece.

The National Aeronautics and Space Administration (NASA) Centennial Challenges Program, part of the Space Technology Mission Directorate (STMD), addresses key technology needs of NASA and the nation, while facilitating new sources of innovation outside the traditional community. This is done by the direct engagement of the public at large, through the offering of Congressional authorized prize purses and associated challenges developed by NASA and the aerospace community and set up as a competition awarding the prize money for achieving the specified technology goal.

Personnel from NASA's MSFC have been investigating the feasibility of an advanced propulsion system known as the Electric Sail (E-Sail) for future scientific exploration missions. This team initially won a NASA Space Technology Mission Directorate (STMD) Phase I NASA Innovative Advanced Concept (NIAC) award and then a two-year follow-on Phase II NIAC award in October 2015. This paper documents the findings from this three-year investigation. An Electric sail, a propellant-less propulsion system, uses solar wind ions to rapidly travel either to deep space or the inner solar system. Scientific spacecraft could reach Pluto in ~5 years, or the boundary of the solar system in ten to twelve years compared to the thirty-five plus years the Voyager spacecraft took. The team's recent focuses have been: 1) Developing a Particle in Cell (PIC) numeric engineering model from MSFC's experimental data on the interaction between simulated solar wind and a charged bare wire that can be applied to a variety of missions, 2) Determining what missions could benefit from this revolutionary propulsion system, 3) Conceptualizing spacecraft designs for various tasks: to reach the solar system's edge, to orbit the sun as Heliophysics sentinels, or to examine a multitude of asteroids.

Design, modeling and experimental investigation of a novel solar sail with high area-to-mass ratios for efficient solar sailing

Despite decades of old theoretical foundation and all the efforts of space researchers, until very recently there were surprisingly few attempts to build and fly large solar sails in space. Germany’s Deutschen Zentrum fur Luft-und Raumfahrt (DLR) took particular interest in solar sail technology in the 1990s and fabricated one of the first large-scale ground-based engineering model sails. The Russians demonstrated in space a spinning 20-m mirror, called Znamya, from their Progress resupply vehicle after it completed its mission to the Mir space station in 1993. Though technically a mirror, the technologies used were essentially the same that would be required to build a solar sail. The Planetary Society, working with the Russians, developed a sail and would have demonstrated the technology in space had the rocket not failed during a launch attempt in 2005. The Japanese are also developing solar sails. In August 2004, an S-310 suborbital rocket launched from the Uchinoura Space Center in Kagoshima, Japan, and deployed two types of solar sail materials to validate both the materials and their deployment in space. The Japanese sail experiment was a success, though it was not a demonstration of a free-flying solar sail that could be used for deep-space exploration. In 2005, NASA built and tested on the ground two 20 m solar sails, each using very different technical approaches.

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 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.

The concept of using photon pressure for propulsion has been considered since Tsiolkovsky in 1921. In fact, Tsiolkovsky and Tsander wrote of 'using tremendous mirrors of very thin sheets' and 'using the pressure of sunlight to attain cosmic velocities' in 1924. The term 'solar sailing' was coined in the late 1950s and was popularized by Arthur C. Clarke in the short story Sunjammer (The Wind From the Sun) in May 1964. The National Aeronautics and Space Administration (NASA) used sailing techniques to extend the operational life of the Mariner 10 spacecraft in 1974-1975. A problem in the control system was causing Mariner 10 to go off course. By controlling the attitude of Mariner 10 and the angle of the solar power panels relative to the Sun, ground controllers were able to correct the problem without using precious fuel. Once thought to be difficult or impossible, solar sailing has come out of science fiction and into the realm of possibility. Any spacecraft using this method would need to deploy a thin sail that could be as large as many kilometers in extent. Candidate sail materials should be: 1) strong, 2) ultra-lightweight (density of a few g/sq m), 3) able to be folded or crushed until deployed, 4) subject to minimal sagging or stretching, and 5) resistant to ionizing radiation, such as galactic and solar particles (electrons and protons), x-rays, ultraviolet light, and magnetically trapped charged particles. Solar sails must be resistant to each of these types of radiation.

Terminology is always treacherous—one field’s jargon contradicts another’s unstated assumptions—but we must now make a distinction between solar sails and lightsails. The solar sail is pushed by photons from the Sun, while the lightsail is usually much larger and driven by man-made light, microwaves, or perhaps some kind of particle beam. This distinction isn’t exclusive, though, because even before we’ve launched the first free-flying solar sail, the mission planners for The Planetary Society’s Cosmos i have plans to demonstrate both photon and microwave propulsion on the same sail. Nor is size an absolute criterion, for solar sails can be vast in their own right. The early solar sail designs NASA studied for the Halley’s Comet rendezvous reached 640,000 square meters, fully a half-mile to the side.

A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semimajor axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail that provides the heliostability needed to maintain a passive “sun-pointing” attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5000 km. Numerical results characterize the expected performance, leading to (for example) an increase of for a small device at geostationary Earth orbit.

A study was performed in conjunction with the In Space Technology Investment Area of NASA's Marshall Space Flight Center to investigate potential applications of solar sails to Mars missions. While solar sails have been proposed as possible candidates for several missions, including Geostorm and a Polar Observer mission, Mars has often been overlooked as a potential destination. It was found that solar sails may have potential in Mars observation missions with smaller payloads. Sail aerocapture maneuvers also show an improvement in payload delivery capability. This study has shown that solar sail spacecraft rival chemical interplanetary probes to Mars and may have applications in future Mars exploration.

Understanding of what is achievable with solar-sail technology around planetary bodies is in its infancy. The seemingly simple problem of transferring from one circular orbit to another circular orbit with a solar sail around a planet is yet to be fully characterized. This work aims to start filling that gap by analyzing the coplanar patched multirevolution circular-to-circular (PMC2C) transfer. The PMC2C transfer is a continuous sequence of single-revolution circular-to-circular (SC2C) transfers, where each SC2C transfer is optimized for the achieved radius change in one orbital revolution. Then, the radius change and transfer time of a PMC2C transfer is obtained as the aggregation of the individual SC2C increments. To generalize to all initial geometries, hundreds of PMC2C transfers must be computed, which is not feasible in practice. To bypass this problem, the so-called patched method is proposed. The patched method uses a semianalytical approach to estimate the radius change and the transfer time of the PMC2C transfers, effectively removing the need for numerical optimization. Dimensionless in nature, the patched method can be used for any sail design around any planet orbiting a star. With this tool, early mission design is greatly simplified; hundreds of trajectories can be analyzed in a matter of minutes. In addition, the generalized formulation reveals the best and worst orbital geometries and initial epochs to start a PMC2C transfer, improving general knowledge of how to “sail” around planets.

A High-Efficiency and Versatile Reconfigurable Intelligent Surface Design Paradigm with Novel Topological Representation

Solar sailing is a novel technology that is still in its infancy, with great potential for a large number of missions that are not possible with conventional spacecraft. The degree of controllability of solar sail with constrained control inputs in artificial Lagrangian orbits is evaluated in this paper, using a method to compute the degree of controllability via system discretization. The results reveal that the controllability of solar sail varies depending on the location in the artificial Lagrangian orbits, as well as the constrained control inputs of the sail, which give us more quantitative information to better understand the characteristics of solar sail, and may help to improve the design of solar sails for future space missions.

Base editing enables the high-throughput screening of genetic variants for phenotypic effects. Base editing screens require the design of single guide RNA (sgRNA) libraries to enable either gene- or variant-centric approaches. While computational tools supporting the design of sgRNAs exist, no solution offers versatile and scalable library design enabling all major use cases. Here, we introduce BEscreen, a comprehensive base editing guide design tool provided as a web server (bescreen.ostendorflab.org) and as a command line tool. BEscreen provides variant-, gene-, and region-centric modes to accommodate various screening approaches. The variant mode accepts genomic coordinates, amino acid changes, or rsIDs as input. The gene mode designs near-saturation libraries covering the entire coding sequence of given genes or transcripts, and the region mode designs all possible guides for given genomic regions. BEscreen enables selection of guides by biological consequence, it features comprehensive customization of base editor characteristics, and it offers optional annotation using Ensembl's Variant Effect Predictor. In sum, BEscreen is a highly versatile tool to design base editing screens for a wide range of use cases with seamless scalability from individual variants to large, near-saturation libraries.