Ground and on-orbit command and data handling architectures for the Active Rack Isolation System microgravity flight experiment

The Active Rack Isolation System [ARIS] International Space Station [ISS] Characterization Experiment, or ARIS-ICE for short, is a long duration microgravity characterization experiment aboard the ISS. The objective of the experiment is to fully characterize active microgravity performance of the first ARIS rack deployed on the ISS. Efficient ground and on-orbit command and data handling [C&DH] segments are the crux in achieving the challenging objectives of the mission. The objective of the paper is to provide an overview of the C&DH architectures developed for ARIS-ICE, with the view that these architectures may serve as a model for future ISS microgravity payloads. Both ground and on-orbit segments, and their interaction with corresponding ISS C&DH systems are presented. The heart of the on-orbit segment is the ARIS-ICE Payload On-orbit Processor, ARIS-ICE POP for short. The POP manages communication with the ISS C&DH system and other ISS subsystems and payloads, enables automation of test/data collection sequences, and provides a wide range of utilities such as efficient file downlinks/uplinks, data post-processing, data compression and data storage. The hardware and software architecture of the POP is presented and it is shown that the built-in functionality helps to dramatically streamline the efficiency of on-orbit operations. The ground segment has at its heart special ARIS-ICE Ground Support Equipment [GSE] software developed for the experiment. The software enables efficient command and file uplinks, and reconstruction and display of science telemetry packets. The GSE software architecture is discussed along with its interactions with ISS ground C&DH elements. A test sequence example is used to demonstrate the interplay between the ground and on-orbit segments.     

Biosphere 2 Test Module: a ground-based sunlight-driven prototype of a closed ecological life support system.

Constructed in 1986, the Biosphere 2 Test Module has been used since the end of that year for closed ecological systems experiments. It is the largest closed ecological facility ever built, with a sealed variable volume of some 480 cubic meters. It is built with a skin of steel spaceframes with double-laminated glass panels admitting about 65 percent Photosynthetically Active Radiation (PAR). The floor is of welded steel and there is an underground atmospheric connection via an air duct to a variable volume chamber ("lung") permitting expansion and contraction of the Test Module's air volume caused by changes in temperature and barometric pressure, which causes a slight positive pressure from inside the closed system to the outside thereby insuring that the very small leakage rate is outward. Several series of closed ecological system investigations have been carried out in this facility. One series of experiments investigated the dynamics of higher plants and associated soils with the atmosphere under varying light and temperature conditions. Another series of experiments included one human in the closed system for three, five and twenty-one days. During these experiments the Test Module had subsystems which completely recycled its water and atmosphere; all the human dietary needs were produced within the facility, and all wastes were recycled using a marsh plant/microbe system. Other experiments have examined the capability of individual component systems used, such as the soil bed reactors, to eliminate experimentally introduced trace gases. Analytic systems developed for these experiments include continuous monitors of eleven atmospheric gases in addition to the complete gas chromatography mass spectrometry (GCMS) examinations of potable, waste system and irrigation water quality.     

Development and research program for a soil-based bioregenerative agriculture system to feed a four person crew at a Mars base.

For humans to survive during long-term missions on the Martian surface, bioregenerative life support systems including food production will decrease requirements for launch of Earth supplies, and increase mission safety. It is proposed that the development of "modular biospheres"--closed system units that can be air-locked together and which contain soil-based bioregenerative agriculture, horticulture, with a wetland wastewater treatment system is an approach for Mars habitation scenarios. Based on previous work done in long-term life support at Biosphere 2 and other closed ecological systems, this consortium proposes a research and development program called Mars On Earth(TM) which will simulate a life support system designed for a four person crew. The structure will consist of 6 x 110 square meter modular agricultural units designed to produce a nutritionally adequate diet for 4 people, recycling all air, water and waste, while utilizing a soil created by the organic enrichment and modification of Mars simulant soils. Further research needs are discussed, such as determining optimal light levels for growth of the necessary range of crops, energy trade-offs for agriculture (e.g. light intensity vs. required area), capabilities of Martian soils and their need for enrichment and elimination of oxides, strategies for use of human waste products, and maintaining atmospheric balance between people, plants and soils.     

“Modular Biospheres” – New testbed platforms for public environmental education and research

This paper will review the potential of a relatively new type of testbed platform for environmental education and research because of the unique advantages resulting from their material closure and separation from the outside environment. These facilities which we term “modular biospheres”, have emerged from research centered on space life support research but offer a wider range of application. Examples of this type of facility include the Bios-3 facility in Russia, the Japanese CEEF (Closed Ecological Experiment Facility), the NASA Kennedy Space Center Breadboard facility, the Biosphere 2 Test Module and the Laboratory Biosphere. Modular biosphere facilities offer unique research and public real-time science education opportunities. Ecosystem behavior can be studied since initial state conditions can be precisely specified and tracked over different ranges of time. With material closure (apart from very small air exchange rate which can be determined), biogeochemical cycles between soil and soil microorganisms, water, plants, and atmosphere can be studied in detail. Such studies offer a major advance from studies conducted with phytotrons which because of their small size, limit the number of organisms to a very small number, and which crucially do not have a high degree of atmospheric, water and overall material closure. Modular biospheres take advantage of the unique properties of closure, as representing a distinct system “metabolism” and therefore are essentially a “mini-world”. Though relatively large in comparison with most phytotrons and ecological microcosms, which are now standard research and educational tools, modular biospheres are small enough that they can be economically reconfigured to reflect a changing research agenda. Some design elements include lighting via electric lights and/or sunlight, hydroponic or soil substrate for plants, opaque or glazed structures, and variable volume chambers or other methods to handle atmospheric pressure differences between the facility and the outside environment.     

Integration of lessons from recent research for “Earth to Mars” life support systems

Development of reliable and robust strategies for long-term life support for planetary exploration must be built from real-time experimentation to verify and improve system components. Also critical is incorporating a range of viable options to handle potential short-term life system imbalances. This paper revisits some of the conceptual framework for a Mars base prototype which has been developed by the authors along with others previously advanced (“Mars on Earth^®”) in the light of three years of experimentation in the Laboratory Biosphere, further investigation of system alternatives and the advent of other innovative engineering and agri-ecosystem approaches. Several experiments with candidate space agriculture crops have demonstrated the higher productivity possible with elevated light levels and improved environmental controls. For example, crops of sweet potatoes exceeded original Mars base prototype projections by an average of 46% (53% for best crop) ultradwarf (Apogee) wheat by 9% (23% for best crop), pinto bean by 13% (31% for best crop). These production levels, although they may be increased with further optimization of lighting regimes, environmental parameters, crop density etc. offer evidence that a soil-based system can be as productive as the hydroponic systems which have dominated space life support scenarios and research. But soil also offers distinct advantages: the capability to be created on the Moon or Mars using in situ space resources, reduces long-term reliance on consumables and imported resources, and more readily recycling and incorporating crew and crop waste products. In addition, a living soil contains a complex microbial ecosystem which helps prevent the buildup of trace gases or compounds, and thus assist with air and water purification. The atmospheric dynamics of these crops were studied in the Laboratory Biosphere adding to the database necessary for managing the mixed stands of crops essential for supplying a nutritionally adequate diet in space. This paper explores some of the challenges of small bioregenerative life support: air-sealing and facility architecture/design, balance of short-term variations of carbon dioxide and oxygen through staggered plantings, options for additional atmospheric buffers and sinks, lighting/energy efficiency engineering, crop and waste product recycling approaches, and human factor considerations in the design and operation of a Mars base. An “Earth to Mars” project, forging the ability to live sustainably in space (as on Earth) requires continued research and testing of these components and integrated subsystems; and developing a step-by-step learning process.     

Gravisensing: ionic responses, cytoskeleton and amyloplast behavior.

In Zea mays L., changes in orientation of stems are perceived by the pulvinal tissue, which responds to the stimulus by differential growth resulting in upward bending of the stem. Gravity is perceived in the bundle sheath cells, which contain amyloplasts that sediment to the new cell base when a change in the gravity vector occurs. The mechanism by which the mechanical signal is transduced into a physiological response is so far unknown for any gravity perceiving tissue. It is hypothesized that this involves interactions of amyloplasts with the plasma membrane and/or ER via cytoskeletal elements. To gain further insights into this process we monitored amyloplast movements in response to gravistimulation. In a pharmacological approach we investigated how the dynamics of plastid sedimentation are affected by actin and microtubule (MT) disrupting drugs. Dark grown caulonemal filaments of the moss Physcomitrella patens respond to gravity vector changes with a reorientation of tip growth away from the gravity vector. MT distributions in tip cells were monitored over time and MTs were seen to accumulate preferentially on the lower flank of the tip 30 min after a 90 degree turn. Using a self-referencing Ca2+ selective ion probe, we found that growing caulonemal filaments exhibit a Ca2+ influx at the apical dome, similar to that reported previously for other tip growing cells. However, in gravistimulated Physcomitrella filaments the region of Ca2+ influx is not confined to the apex, but extends about 60 micrometers along the upper side of the filament. Our results indicate an asymmetry in the Ca2+ flux pattern between the upper and side of the filament suggesting differential activation of Ca2+ permeable channels at the plasma membrane.     

Atmospheric dynamics in the "Laboratory Biosphere" with wheat and sweet potato crops.

Laboratory Biosphere is a 40-m3 closed life system equipped with 12,000 W of high pressure sodium lamps over planting beds with 5.37 m2 of soil. Atmospheric composition changes due to photosynthetic fixation of carbon dioxide and corresponding production of oxygen or the reverse, respiration, are observed in short timeframes, e.g., hourly. To focus on inherent characteristics of the crop as distinct from its area or the volume of the chamber, we report fixation and respiration rates in mmol h-1 m-2 of planted area. An 85-day crop of USU Apogee wheat under a 16-h lighted/8-h dark regime peaked in fixation rate at about 100 mmol h-1 m-2 approximately 24 days after planting. Light intensity was about 840 micromoles m-2 s-1. Dark respiration peaked at about 31 mmol h-1 m-2 at the same time. Thereafter, both fixation and respiration declined toward zero as harvest time approached. A residual soil respiration rate of about 1.9 mmol h-1 m-2 was observed in the dark closed chamber for 100 days after the harvest. A 126-day crop of Tuskegee TU-82-155 sweet potato behaved quite differently. Under a 680 micromoles m-2 s-1, 18-h lighted/6-h dark regime, fixation during lighted hours rose to a plateau ranging from about 27 to 48 mmol h-1 m-2 after 42 days and dark respiration settled into a range of 12-23 mmol h-1 m-2. These rates continued unabated until the harvest at 126 days, suggesting that tuber biomass production might have continued at about the same rate for some time beyond the harvest time that was exercised in this experiment. In both experiments CO2 levels were allowed to range widely from a few hundred to about 3000 ppm, which permitted observation of fixation rates both at varying CO2 concentrations and at each number of days after planting. This enables plotting the fixation rate as a function of both variables. Understanding the atmospheric dynamics of individual crops will be essential for design and atmospheric management of more complex CELSS which integrate the simultaneous growth of several crops as in a sustainable remote life support system.     

Reduced minimum configuration fiber optic gyro for land navigationapplications

Further cost reduction of the fiber optic gyroscope is necessary to meet the economic requirements of land navigation systems. Previous concentration was on the reduction of the number of splices and component improvements in the open-loop minimum configuration. Now non-essential components and splices are eliminated. The source-detector coupler is not part of the Sagnac interferometer, and serves solely to direct light from the interferometer into the output photodetector. Many commercial laser diodes incorporate a back-facet photodetector to monitor laser intensity. The signal returned from the Sagnac traverses the laser, and can be detected at this photodetector. The gyro signal can be distinguished from the laser signal by the bias modulation applied in the interferometer. Configuring a gyro in this manner eliminates a directional coupler and the separate photodetector, as well as up to two fiber splices in an all-fiber gyroscope. A production, open-loop fiber optic gyroscope has been modified to demonstrate this principle. The gyroscope exhibits performance comparable to the conventional minimum configuration     

Geometric aspects of long-term noncoherent integration

Long-term integration is defined as integration, perhaps interrupted, over time periods long enough for targets to move through volumes in space resolvable by the radar. Because the motion of the target is unknown prior to detection, long-term integration must be performed along multiple paths representing plausible target paths. The geometry of such a set of integration paths affects detection performance in several ways. The simplest implementation of long-term integration, using constant radial velocity paths, is investigated. The effects of path geometry on detection is quantified and optimized for a target whose motion is nearly radial but otherwise unknown