R.E. Freeland

ODISSEE — A proposal for demonstration of a solar sail in earth orbit

Abstract A recent pre-phase-A study conducted cooperatively between DLR and NASA/JPL concluded that a lowcost solar sail technology demonstration mission in Earth orbit is feasible. Such a mission, nicknamed ODISSEE ( O rbital D emonstration of an I nnovative, S olar S ail driven E xpandable structure E xperiment), is the recommended approach for the development of this advanced concept using solar radiation pressure for primary propulsion and attitude control. The mission, proposed for launch in 2001, would demonstrate and validate the basic principles of sail fabrication, packaging, storage, deployment, and control. The demonstration mission scenario comprises a low-cost ‘piggy back’ launch of a sailcraft with a total mass of about 80kg on ARIANE 5 into a geostationary transfer orbit, where a 40m × 40m square sail would be deployed. The aluminized sail film is folded and packaged in small storage containers, upon release the sail would be supported by deployable light-weight carbon fiber booms. A coilable 10m central mast is attached to the center of the sail assembly with a 2DoF gimbal, and connected to the spacecraft. Attitude control is performed passively by gimbaling the central mast to offset the center-of-mass to the center-of-pressure generating an external torque due to solar radiation pressure, or actively using a cold-gas micro-thruster system. By proper orientation of the sail towards the Sun during each orbit, the orbital energy can be increased, such that the solar sail spacecraft raises its orbit. After roughly 550 days a lunar polar flyby would be performed, or the sail might be used for orbit capture about the Moon. On-board cameras are foreseen to observe the sail deployment, and an additional science payload could provide remote sensing data of the Earth and also of previously not very well explored lunar areas.

System Concept For A Moderate Cost Large Deployable Reflector (LDR)

A study was carried out at the Jet Propulsion Laboratory during the first quarter of 1985 to develop a system concept for NASAs Large Deployable Reflector (LDR). This new system concept meets the primary scientific requirements and minimizes the cost and development time. The LDR requirements were investigated to determine whether or not the major cost drivers could be significantly relaxed without compromising the scientific utility of LDR. In particular, the telescope wavefront error is defined so as to maximize scientific return per dollar. Major features of the concept are a four-mirror, two-stage optical system; a lightweight structural composite segmented primary reflector; and a deployable truss backup structure with integral thermal shield. The two-stage optics uses active figure control at the quaternary reflector located at the primary reflector exit pupil, allowing the large primary to be passive. The lightweight composite reflector panels limit the short wavelength operation to approximately 30 pm but reduce the total primary reflector weight by a factor of 3 to 4 over competing technologies. System optical performance is calculated including aperture efficiency, Strehl ratio, and off-axis performance. On-orbit thermal analysis indicates a primary reflector equilibrium temperature of less than 200 K with a maximum gradient of =°C across the 20 m aperture. Weight and volume estimates are consistent with a single Shuttle launch and are based on Space Station assembly and checkout.

Technical Approach For The Development Of Structural Composite Mirrors

Light weight, high precision, low cost structural composite mirrors have tremendous potential for enabling affordable space telescope systems. The Large Deployable Reflector (LDR) is an example of such a system. It is a 20 meter diameter, earth orbiting submillimeter telescope. Its technology requirements are for panels that are from 1 to 2 meters in size with areal densities of 5 to 10 Kg/m2 and surface figure precision of a few microns. JPL and the Hexcel Corp. have entered into a joint technology activity, sponsored by the NASA Precision Segmented Reflector (PSR) Program, for the development of such mirrors. Highly specialized manufacturing and materials processing techniques have been developed by Hexcel for the production of high precision, light weight and low cost composite mirrors. JPL has developed an analytical simulation capability for composite mirrors that characterizes their mechanipal and thermal performance in terms of the materials properties and configurations. This capability is the basis of detail panel designs for thermal stability, test simulation, test/analysis correlation and projection of performance for specific applications. This combination of capabilities from both organizations has resulted in the development of graphite/epoxy mirrors up to 1.0 meter in size with surface precision of a few microns rms while weighing only 6 Kg/m2. This paper describes that development program. The PSR Panel Program, over a four year period is for mirrors up to 1.5 meters with surface precision and LDR orbital thermal stabilities on the order of one micron.

Mobile communications satellite antenna flight experiment definition

Abstract There are classes of application that collectively require a variety of different types of large-aperture space antennas. Fortunately, there are a number of different deployable antenna concepts that have tremendous potential for such applications. However, these concepts vary in maturity from flight-proven designs to extremely innovative configuration definitions. But these promising concepts lack sufficient demonstrations of maturity to be seriously considered in the large size range for immediate application. The reason for this situation is an extremely limited space flight data base in addition to the technical limitations and great costs associated with meaningful ground testing of large, flexible, precision space structures. The user community of such structures, especially the commercial organizations interested in providing a Mobile Communications Satellite (MSAT) on a profit-making basis, will require significant demonstrations of technology readiness prior to application commitment. Such demonstrations will probably be based on a combination of extensive ground testing and subsequent space flight experiments. The Communications Division of the National Aeronautics and Space Administration (NASA) Office of Space Science and Applications sponsored a study at the Jet Propulsion Laboratory (JPL) to determine the technical feasibility and cost of a Shuttle-based flight experiment specifically intended for the MSAT commercial user community. The experiment will include demonstrations of technology in the areas of radio frequency (RF), sensing and control, and structures. This paper summarizes the results of the structural subsystem study. These results include experiment objective and technical approach, experiment structural description, structure/environment interactions, structural characterization, thermal characterization, structural measurement system, and experiment functional description.

Development of structural composite mirror technology for submillimeter space telescopes

Abstract Lightweight, low-cost, high-precision mirrors are needed to support a number of near-term and far-term submillimeter, space-based astronomical telescopes. These telescopes will range in size from 3 to 20 m, and will possibly be larger. They will utilize mirrors varying from 1 to 2 m in size and from 1 to 3 μm rms in surface precision; they will operate in an orbital thermal environment somewhere between 100 and 200 K. The Precision Segmented Reflector (PSR) program, sponsored by the NASA Office of Aeronautics, Exploration and Technology (OAET), was formulated and implemented specifically to develop the telescope technologies associated with future NASA missions. A major element of that program is the development of lightweight structural composite mirrors, which is the subject of this paper. The most significant technology challenges associated with the development of these highly specialized mirrors are (a) the processing and manufacturing required to produce high-precision, lightweight mirrors and (b) the determination of materials and structural mirror configurations that produce the thermal stability needed for specific classes of applications. These challenges have been addressed by a joint partnership between the Jet Propulsion Laboratory (JPL) and the Hexcel Corporation during the 4-year PSR program. This paper describes the technical approach used for the design, manufacturing, testing, and analytical simulation of lightweight graphite/epoxy mirrors. This program has produced (a) 1.0 m graphite/epoxy panels with areal densities of 7 kg/m 2 and as-manufactured surface precision near 1 μm rms, (b) 0.5 m panels with figure changes of μ m rms for temperature reductions of 100 K, (c) analytical performance-prediction capability with submicron accuracy relative to panel thermal distortion, and (d) a unique thermal vacuum test facility for structural composite mirrors.