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LEAF-Lite (Laser Enhanced Arc-Jet Facility) is a radiative laser heating facility that has been added to the 60 MW Interaction Heating Facility (IHF) convective plasma arc-jet located at NASA Ames Research Center. Together, these two systems can simulate both convective and radiative heating at heat fluxes reaching 551 W/cm2 by simultaneously combining a highest measured heat flux of 160 W/cm2 convective and 391 W/cm2 radiative heating on a 152-mm x 152-mm wedge model configuration. Adding radiant heating to an existing convective facility better simulates Earth atmospheric entry from hyperbolic lunarreturn speeds. The radiative heat is provided by multiple 50-kW CW IR lasers, which is nearly uniform across the illuminated surface with a total variation less than 6%, while the convective heat is provided by a high enthalpy plasma arc-jet. In a later phase, the facility will expand to test panel test articles of 432-mm x 432-mm and provide 100 W/cm2 of radiative heating in a plasma convective flow environment. The paper describes this new combined heating capability, its current testing conditions, and the unique application of the laser system with respect to the Orion test flight lunar orbits.

The concept of a mobile offshore base (MOB) reflects the need to stage and support military and humani- tarian operations anywhere in the world. A MOB is a self- propelled, modular, floating platform that can be assembled into lengths of up to 2 km, as required, to provide logistic support to US military operations where fixed bases are not available or adequate. It accommodates the take-off and landing of C17 aircraft, and can be used for storage, as well as to send resources quickly to shore. In most concepts, the structure is made of three to five modules, which have to perform long-term station-keeping in the presence of winds, waves, and currents. This is usually referred to as dynamic positioning (DP). In the MOB, the alignment is maintained through the use of thrusters, connectors, or a combination of both. In this paper, we consider the real-time control of scaled models of a MOB. The modules are built at the 1 : 150 scale, and are kept aligned by rotating thrusters under a hierarchical hybrid control scheme. This paper describes a physical testbed developed at the University of California, Berkeley, under a grant from the US Office of Naval Research, for the purpose of evaluating competing MOB control concepts.

The Mobile Offshore Base (MOB) is a large, self-propelled, floating, pre-positioned ocean structure formed of three to five modules and reaching up to 1,500 meters in length. The alignment of the modules is maintained through the use of thrusters and/or connectors. A simulation framework has been used to provide evaluation of different control strategies. We have conducted experiments in which three 1:150 scale modules are kept aligned by pivoting thrusters and form a miniature runway. This paper addresses lessons learned in the course of the MOB project.

The mobile offshore base (MOB) will consist of a number of large semi-submersible modules connected together to form a runway approximately 2 km long. In order to conduct model-based testing of such a system with reasonably sized models, it is necessary to use models with a very small scale. In this paper, we outline the design and characterization of a 5 cm diameter azimuthing thruster unit designed for use on a 1:150 scale model of a MOB module. Experimental results are presented regarding thrust performance, thrust response dynamics, thrust level stability and repeatability, effects of pontoon proximity and azimuth angle relative to pontoon, and effects of advance velocity. The results indicate that the thruster performs well and is suitable for use in model-testing applications.

In support of the SPRITE concept, an integrated data acquisition system has been developed and fabricated for preliminary testing. The data acquisition system has been designed to condition traditional thermal protection system sensors, store their data to an on-board memory card, and in parallel, telemeter to an external system. In the fall of 2010, this system was integrated into a 14 in. diameter, 45 degree sphere cone probe instrumented with thermal protection system sensors. This system was then tested at the NASA Ames Research Center Aerodynamic Heating Facility's arc jet at approximately 170 W/sq. cm. The first test in December 2010 highlighted hardware design issues that were redesigned and implemented leading to a successful test in February 2011.

Over the last few years, staff from Lawrence Livermore National Laboratories and the NASA Ames Research Center have been collaborating on the inspection of various Thermal Protection System (TPS) articles (both test and flight) using X-ray computed tomography (CT). The work presented here shows how this powerful non-destructive inspection technique can be used to help understand the performance of TPS materials and designs. Three applications of before-and-after imagery are discussed in detail, including lessons learned, new insights, and questions remaining to be answered. These examples illustrate the promise of X-ray CT as an important technology deserving of routine application to research, development and production of thermal protection systems.

Small Probe Reentry Investigation for TPS Engineering (SPRITE) is a novel concept for a comparatively low-cost means of certifying thermal protection system (TPS) materials for spaceflight. By developing a fully instrumented small-scale test platform that can be tested both in arc-jet facilities and in flight, SPRITE promises to improve the ground-to-flight traceability of TPS qualification programs by implementing the NASA “test-like-you-fly” policy. This paper discusses the design and manufacture of the proof-of-concept SPRITE test articles, development and capabilities of the SPRITE flight-like data acquisition system, and fidelity of the design tools used in the effort. With the successful completion of this stage of the SPRITE project, the next test article to be built will have a hemispherical backshell as originally designed for flight stability. Unlike the initial proof-of-concept probes, TPS for the next test article will be scaled according to current margins policies for arc-jet testing at relevant flight-like aerothermal environments. At the conclusion of the ground test campaign, SPRITE probes will be ready for flight testing and, ultimately, acceptance into future mission planning where they will contribute to more affordable access to space for both large and small science payloads.

Thermal protection materials used in spacecraft heatshields are subjected to severe thermal and mechanical loading environments during re-entry into earth atmosphere. In order to investigate the reliability of PICA tiles in the presence of high thermal gradients as well as mechanical loads, the authors designed and conducted solar-tower tests. This paper presents the design and analysis work for this tests series. Coupled non-linear thermal-mechanical finite element analyses was conducted to estimate in-depth temperature distribution and stress contours for various cases. The first set of analyses performed on isolated PICA tile showed that stresses generated during the tests were below the PICA allowable limit and should not lead to any catastrophic failure during the test. The tests results were consistent with analytical predictions. The temperature distribution and magnitude of the measured strains were also consistent with predicted values. The second test series is designed to test the arrayed PICA tiles with various gap-filler materials. A nonlinear contact method is used to model the complex geometry with various tiles. The analyses for these coupons predict the stress contours in PICA and inside gap fillers. Suitable mechanical loads for this architecture will be predicted, which can be applied during the test to exceed the allowable limits and demonstrate failure modes. Thermocouple and strain-gauge data obtained from the solar tower tests will be used for subsequent analyses and validation of FEM models.