Lawrence C. Greer

MISSE7: Building a Permanent Environmental Testbed for the International Space Station

The Materials on the International Space Station Experiments (MISSE) provide low‐cost material exposure experiments on the exterior of the International Space Station (ISS). The original concept for a suitcase‐like box bolted to the ISS to passively expose materials to space has grown to include increasingly complex in situ characterization. As the ISS completes construction, the facilities available to MISSE experiments will increase dramatically. MISSE7 is the first MISSE to take advantage of this new infrastructure. In addition to material exposure, MISSE7 will include characterization of single‐event radiation effects on electronics and solar cell performance in LEO. MISSE7 will exploit the ISS Express Logistics Carrier power and data capabilities and will leave behind a MISSE specific infrastructure for future missions.

Excavation on the Moon: Regolith Collection for Oxygen Production and Outpost Site Preparation

The development of a robust regolith moving system for lunar and planetary processing and construction is critical to the NASA mission to the Moon and Mars. Oxygen production may require up to 200 metric tons of regolith collection per year; outpost site development may require several times this amount. This paper describes progress in the small vehicle implement development and small excavation system development. Cratos was developed as a platform for the ISRU project to evaluate the performance characteristics of a low center of gravity, small (0.75m x 0.75m x 0.3m), low-power, tracked vehicle performing excavation, load, haul, and dump operations required for lunar ISRU. It was tested on loose sand in a facility capable of producing level and inclined surfaces, and demonstrated the capability to pick up, carry, and dump sand, allowing it to accomplish the delivery of material to a site. Cratos has demonstrated the capability to pick up and deliver simulant to a bury an inflatable habitat, to supply an oxygen production plant, and to build a ramp.

Cooperative multi-agent mobile sensor platforms for jet engine inspection - concept and implementation

Cooperative behavior algorithms utilizing swarm intelligence are being developed for mobile sensor platforms to inspect jet engines on-wing. Experiments are planned in which several relatively simple autonomous platforms will work together in a coordinated fashion to carry out complex maintenance-type tasks within the constrained working environment modeled on the interior of a turbofan engine. The algorithms will emphasize distribution of the tasks among multiple units; they will be scalable and flexible so that units may be added in the future; and will be designed to operate on an individual unit level to produce the desired global effect. This proof of concept demonstration will validate the algorithms and provide justification for further miniaturization and specialization of the hardware toward the true application of on-wing in situ turbine engine maintenance.

Initial results from the second Forward Technology Solar Cell Experiment

The success of the first Forward Technology Solar Cell Experiment (FTSCE) which flew as part of the 5th Materials on the International Space Station Experiments (MISSE-5) [1,2,3], led to a follow on experiment, FTSCE II. This experiment is currently operating on the International Space Station (ISS) as part of MISSE7. Solar cells are characterized with I–V curves. The test cells include current and next generation triple-junction production cells from Emcore and Spectrolab as well as advanced inverted metamorphic (IMM) and other thin film III–V cells from Emcore, Spectrolab and MicroLink Devices, Inc. Other thin film technologies include, advanced amorphous silicon concepts from United Solar Ovonic and a Copper Indium Selenide based two-cell string from Dutch Space. In this paper, The FTSCE II experiment is described and current status presented.

In-flight performance of III-V multi-junction solar cells from the Forward Technology Solar Cell Experiment

The Materials on the International Space Station Experiments (MISSE) present a unique opportunity in space science by offering a low-cost platform to expose materials directly to the space environment on the International Space Station (ISS). MISSE experiments consist of a “suitcase” like package known as the “Passive Experiment Carrier” (PEC) that can be carried by astronauts and mounted externally to the ISS. The 5th MISSE payload (MISSE-5) contained both passive and active experiments. The Forward Technology Solar Cell Experiment (FTSCE) on MISSE-5 measured current-voltage (I–V) characteristics on 36 solar cells of various types. Over 1500 I–V curves were recorded on each cell during a 13-month period. This paper analyses the results for all the III–V multi-junction cells flown, including state-of-the-art space qualified cells and next generation metamorphic cells.

A dust characterization experiment for solar cells operating on Mars

During the Viking and Pathfinder missions to Mars, significant amounts of dust accumulated on the spacecraft. In Pathfinders case, the dust obscured the solar panels on the lander and the rover degrading their output current. The material adherence experiment aboard the Pathfinder rover quantified the rate of decrease in short circuit current at 0.28% per day. This rate is unacceptably high for long duration missions. In response, NASA has developed the Dust Accumulation and Removal Technology (DART) experiment. DART has 3 instruments for characterizing dust settling out of the atmosphere and tests two methods to keep dust from settling on solar cells.

Results from real-time laser speckle-shift strain measurement system

A real-time two-color laser speckle-shift strain measurement system based on the technique of Yamaguchi was designed, built, and tested at room temperature. This noncontact 1-D system detects surface strain in a structural fiber as it is pulled in a tensile test machine. Inter- ference or speckle patterns from the laser-illuminated fiber test specimen are recorded. As the fiber is pulled, its speckle pattern shifts in proportion to the strain, translational, and rotational components of the sample de- formation. Shifting speckle patterns are detected using two linear CCD arrays with image processing performed in realtime by a hardware cor- relator. Surface strain is detected in fibers with diameters on the order of 100 mm and can be resolved to 20 mm/m. This system was designed to be robust and compact and generally does not require surface prepara- tion of the structural fibers.

Design and Operation of a Fast, Thin-Film Thermocouple Probe on a Turbine Engine

As a demonstration of technology maturation, a thin-film temperature sensor probe was fabricated and installed on a F117 turbofan engine via a borescope access port to monitor the temperature experienced in the bleed air passage of the compressor area during an engine checkout test run. To withstand the harsh conditions experienced in this environment, the sensor probe was built from high temperature materials. The thin-film thermocouple sensing elements were deposited by physical vapor deposition using pure metal elements, thus avoiding the inconsistencies of sputter-depositing particular percentages of materials to form standardized alloys commonly found in thermocouples. The sensor probe and assembly were subjected to a strict protocol of multi-axis vibrational testing as well as elevated temperature pressure testing to be qualified for this application. The thin-film thermocouple probe demonstrated a faster response than a traditional embedded thermocouple during the engine checkout run.

Low Earth Orbit Space Environment Testing of Extreme Temperature 6H-SiC JFETs on the International Space Station

This paper reports long-term electrical results from two 6H-SiC junction field effect transistors (JFETs) presently being tested in Low Earth Orbit (LEO) space environment on the outside of the International Space Station (ISS). The JFETs have demonstrated excellent functionality and stability through 4600 hours of LEO space deployment. Observed changes in measured device characteristics tracked changes in measured temperature, consistent with well-known JFET temperature-dependent device physics.

Materials on the International Space Station Experiment-5, Forward Technology Solar Cell Experiment: First On-Orbit Data

First on-orbit data from the forward technology solar cell experiment (FTSCE) are presented. FTSCE is housed within the 5th Materials on the International Space Station Experiment (MISSE-5), and currently resides on the exterior of the ISS. A range of solar cell technologies are included in the experiment including triple junction (3J) InGaP/GaAs/Ge solar cells from several vendors, thin film amorphous Si and CuIn(Ga)Se2 cells, and next-generation technologies like single-junction GaAs cells grown on Si wafers and metamorphic InGaP/InGaAs/Ge triple-junction cells. Measured current vs. voltage (IV) curves from on- board experiments are analyzed. All of the solar cell technologies are showing nominal performance with no obvious signs of degradation