Duration Space Missions Research Articles

Advanced fault tolerant computing for future manned space missions

Planet Mars has been at the focal point of astronomical attention. As we enter the next millennium, Mars will play a key role in humanity's successful expansion into heliocentric space. Future Mars space transportation will require reliable operations over a lifespan of years. Unlike other long life deep space missions, human Mars operations require real-time masking of critical faults. This paper discusses Mars stringent baseline requirements and constraints and presents fault-tolerant approaches, techniques, and design building block strategies that include standby redundancy, reconfigurable voting, backup sparing, and graceful degradation. The contemporary approach and recognized inadequacies of their application to long duration space missions will be discussed. Certain problems will be identified and viable solutions offered. Various aspects of fault tolerant designs and implementations are discussed including component selection, radiation tolerance, high-density packaging technology, computational integrity, and fault coverage. Architectural solutions that can make systems affordable such as open systems, standardization, and ease of validation will be highlighted. The paper concludes with a technology demonstration plan to achieve the desired baseline requirements and goals.

Erosion resistance and durability improvement of polymers and composites in space environment by ion implantation

Spacecraft designers use polymers and polymer-based composite materials extensively in electrical, thermal, and structural applications to address both weight and performance demands. Without protection from the deleterious effects of the space environment, in particular hyperthermal atomic oxygen (HAO), these materials suffer accelerated erosion from chemical interaction and experience a loss of mass and deterioration of performance. High dose implantation at energies in the 10–100 keV range using ions of metal or semiconductor materials was used as a method of modifying the surface of these polymeric materials to produce changes that can yield dramatic improvements in space environmental durability. The results of this study show that computer modelling of the ion implantation process combined with reasonable fluence estimates give a good basis for the choice of implantation conditions. This study presents the results for high-performance materials including Kapton ®, Mylar ®, PEEK, Lexan ®, and PEEK/carbon fibre composites using X-ray electron spectroscopy, scanning electron microscopy, and other surface analysis techniques, before and after treatment. The results show that implantation of silicon and aluminum (singly, binary, or in combination with boron) or yttrium implantation produces a stable, protective oxide-based layer following exposure to HAO. The improvement in chemical resistance of these materials assures performance without deterioration in long duration space missions and shows promise for improvement in terrestrial performance in highly reactive oxidative environments.

Accumulation and effect of volatile organic compounds in closed life support systems

Bioregenerative life support systems (BLSS) being considered for long duration space missions will operate with limited resupply and utilize biological systems to revitalize the atmosphere, purify water, and produce food. The presence of man-made materials, plant and microbial communities, and human activities will result in the production of volatile organic compounds (VOCs). A database of VOC production from potential BLSS crops is being developed by the Breadboard Project at Kennedy Space Center. Most research to date has focused on the development of air revitalization systems that minimize the concentration of atmospheric contaminants in a closed environment. Similar approaches are being pursued in the design of atmospheric revitalization systems in bioregenerative life support systems. In a BLSS one must consider the effect of VOC concentration on the performance of plants being used for water and atmospheric purification processes. In addition to phytotoxic responses, the impact of removing biogenic compounds from the atmosphere on BLSS function needs to be assessed. This paper provides a synopsis of criteria for setting exposure limits, gives an overview of existing information, and discusses production of biogenic compounds from plants grown in the Biomass Production Chamber at Kennedy Space Center.

Bright light as a chronobiological countermeasure for shiftwork in space

Work-rest schedules during long duration space missions involve several factors which could disrupt sleep and circadian temporal organisation: (1) displacement of sleep due to two-shift operations; (2) planned or unplanned schedule changes due to operational requirements; (3) social and light Zeitgebers different from those on earth; (4) changes in the gravitational exposure. Timed bright light treatment has the potential to accelerating adaptation to schedule changes. Four male subjects were exposed to two sessions of 11 d of simulated microgravity (6 ° head down tilt bedrest) with 6-h extensions of the wake period on 2 days (12-h phase delay). In a blind crossover design, subjects were exposed to bright light (> 3500 lux) for 5 h on each of the 2 shift days and the following day, at times either expected to accelerate the adjustment to the phase delay (experimental condition) or to have no phase shifting effect (control condition). Sleep was recorded polygraphically, the circadian system was monitored by recordings of heart rate and body temperature, and by collection of urine (electrolyte and hormone excretion). Only the rhythms of 6-hydroxymelatoninsulphate and potassium excretions showed significantly enhanced adjustment under the experimental condition. Different rhythms Actapted to the 12-h delay at different rates, comparable to those observed after time zone shifts. Sleep was shorter in simulated weightlessness than in normal ambulatory age-matched subjects, consistent with the shorter sleep durations characteristic of space flight. These results confirm the disruptive effects of wake-rest schedule shifts on sleep and circadian rhythms. Contrary to our initial hypothesis, 5-h exposures to bright light finishing at the time of the circadian temperature minimum were not more effective at accelerating adjustment to a 12-h schedule delay than exposures coinciding with the temperature maximum. We conclude that, while bright light may accelerate adjustment to work-rest schedule delays, any such effect seems to be largely independent from the timing of the light exposure.

RESPONSE OF THREE SWEET-POTATO CULTIVARS GROWN IN NFT TO DIFFERENT IRRADIANCE LEVELS

The effects of light intensity on three sweetpotato cultivars [Ipomoea batatas (L.) Lam] were evaluated in growth chambers, as part of NASA's Closed Ecological Life Support Systems (CELSS) program for long duration space missions. Vine cuttings of `TI-155', `GA Jet', and TUJ1 were grown using nutrient film technique (NFT) in a modified half Hoagland's solution with a 1:2.4 N:K ratio in channels (0.15×0.15×1.2 m). Plants were exposed to irradiance levels of 360 or 720 umols m-2s-1 with an 18/6 photoperiod in a randomized complete block design with two replications. Temperature was set at 28:22 lightdark and RH was 70%. Differences in plant response to were more related to cultivars than the effect of light intensity. Storage root number (8) fresh, (786 g/plant) and dry weights (139 g/plant) were highest for `TI-155' while foliage fresh and dry weights were highest for `TUJ1' when averaged across light levels. TI-155' (921 g/plant) and `GA Jet' (538 g/plant) produced greater yields at higher irradiance. `TUJ1' produced a higher yield (438 g/plant at the lower intensity compared to 219 (g/plant) at the higher intensity, suggesting this cultivar could produce storage roots in similar conditions in a CELSS.

ALTERING NUTRIENT SOLUTION N:K RATIO TO INCREASE YIELDS OF SWEETPOTATO GROWN IN NFT

The effects of altering, nutrient solution N:K ratio on growth of `TI-155' sweetpotato [Ipomoea batatas (L.) Lam] was evaluated in a greenhouse, as part of NASA's Closed Ecological Life Support Systems (CELSS) program for long duration space missions. Vine cuttings of `TI-155', were grown using nutrient film technique (NFT) in a modified half Hoagland's solution in channels (0.15×0.15×1.2 m). Plants were grown for 42 days in a culture solution in which N was doubled (6 mM) in order to accelerate foliage growth after which treatment N:K ratios of 1:2.4, (control) 1:4.8, and 1:7.2 were initiated. A randomized complete block design with 4 replications was used. The number of storage roots/plant increased linearly as K was increased in the solution. Storage root fresh and dry weights, growth rate (g m-2 d-1), fibrous root dry weight, foliage fresh and dry weights, and edible biomass index (root mass/total plant mass), though not significant all increased as K was increased in the nutrient solution. Nutrient solution analyses showed that K uptake was greatest in plants at the highest K level, while nitrate uptake was steady over the duration of crop growth regardless of treatments.

An assessment of habitat pressure, oxygen fraction, and EVA suit design for space operations

At high cabin pressure [e.g. 1013 hPa (14.7 psi) 21% O 2] there are serious issues relative to specification of suit pressure and the need for prebreathing. A high pressure suit will be costly but use of the existing, flexible suit requires up to 6 h of prebreathing. Or one could use a cabin pressure of 700 hPa (10.2 psi) prior to extravehicular activity (EVA) in order to use the existing suit with only 1 h of prebreathing. If these normal cabin pressures and O 2 levels are utilized, existing physiological and medical databases apply, providing a known basis for evaluating effects of long duration space missions. If a 345 hPa (5 psi), 70–100% O 2 atmosphere is adopted the existing suit can be used with no prebreathing required. However, there is no reference database on physiological effects under the conditions of lower pressure and higher O 2 concentration. This paper considers the major issues involved in defining habitat pressure, O 2 fraction, and EVA suit design for operations in space. A preliminary model for evaluating habitat/suit pressure and O 2% strategies is presented.

Operational and Human Factors Implications of Physiological Deconditioning in Long Duration Spaceflight

A major factor in determining the success of any manned long duration space mission will be how well the human body can endure the microgravity environment. Data collected from long duration space missions conducted by both the United States and the former Soviet Union have shown that almost every system in the human body is adversely affected by microgravity. These adverse affects, taken individually or in concert, can have operational implications for a long duration space mission. Data collected to date indicate that significant human factors complications could arise due to the deconditioning of the musculoskeletal, cardiovascular and hematological systems that occur in a microgravity environment, resulting in decrements in overall astronaut performance. This paper examines some of these deconditioning effects, their immediate operational implications and possible countermeasures.

Achieving and documenting closure in plant growth facilities

As NASA proceeds with its effort to develop a Controlled Ecological Life Support System (CELSS) that will provide life support to crews during long duration space missions, it must address the question of facility and system closure. Here we discuss the concept of closure as it pertains to CELSS and describe engineering specifications, construction problems and monitoring procedures used in the development and operation of a closed plant growth facility for the CELSS program. A plant growth facility is one of several modules required for a CELSS. A prototype of this module at Kennedy Space Center is the large (7m tall × 3.5m diameter) Biomass Production Chamber (BPC), the central facility of the CELSS Breadboard Project. The BPC is atmospherically sealed to a leak rate of approximately 5% of its total volume per 24 hours. This paper will discuss the requirements for atmospheric closure in this facility, present CO 2 and trace gas data from initial tests of the BPC with and without plants, and describe how the chamber was sealed atmospherically. Implications that research conducted in this type of facility will have for the CELSS program are discussed.

Man in space: The use of animal models

Animals have traditionally preceded man into space. During animal and human travels in space over the past almost 30 years, numerous anatomical, physiological, and biochemical changes have been observed. In order to safely qualify humans for extended duration space missions, scientific research needs to be performed. It may be possible to achieve many of these research goals with flight crews serving as experimental subjects; however, to do this with human subjects alone is impractical. Therefore, the use of animal surrogates as experimental subjects is essential to provide the missing information on the effects of spaceflights, to validate countermeasures, and to test medical treatment techniques which will be necessary for long duration missions. This research to assure human health, safety, and productivity in future extended duration space flights will include flights on NASA's Space Shuttle, unmanned biosatellites, and the Space Station Freedom.

Gas transfer in microgravity fermentations

Fermentations performed under microgravity conditions may be used in future long duration space missions for recycling expendable life support materials. These fermentations will differ from similar fermentations performed at one gravity in the manner in which gas transfer in the fermentor is carried out.

A Reliable Spaceborne Memory with a Single Error and Erasure Correction Scheme

A program for the development of a highly reliable memory has been underway for a number ofyears at ESTEC. Plated wire and ferrite core spaceborne memories have been developed and qualified, and the more recent advent of low power LSI memory devices has made the semiconductor memory an attractive proposition for spaceborne applications. These technologies are briefly discussed and compared. However, in common with the previous solutions, the reliability of a semiconductor memory even when protected by a conventional single error correction scheme, did not meet the requirements of long duration space missions.

Predicting Annealing of Lithium-Doped Solar Cells during Long Duration Space Missions

A mathematical model has been developed which predicts the annealing kinetics of electron, proton, and neutron damage in lithium-doped silicon solar cells. The model to be presented uses the diffusion-limited reaction theory modified to account for excess lithium consumption and varying defect capture radius. Experimental data from short term radiations with 1 and 10 MeV electrons, 0.25, 1.0, and 2.0 MeV protons, and reactor neutrons are shown for comparison with calculated annealing curves. Data from a 24-month real time test in a simulated space environment of vacuum, Compton electrons, 100 keV protons, and UV radiation are also presented to illustrate the success of the model in predicting long term effects in cells where simultaneous damage introduction and annealing is occurring. These data are particularly interesting because they indicate that 1) the annealing of electron and proton damage is similar and apparently involves the same lithium-defect interactions, 2) that the annealing of neutron damage, while its annealing kinetics are similar and can be described by the same mathematical model as electron and proton damage, involves different defect-lithium interactions and the neutron annealing appears to be independent of prior cell histories in electron and proton environments, and 3) irradiations in combined environments of electrons and low-energy protons produce synergistic effects that are not predicted by any current damage models in both conventional cells and lithium doped cells.

Physicochemical methods for the synthesis of potential foods

Potential foods synthesis for long duration space missions by physiochemical methods, discussing regeneration of carbohydrates from metabolical waste carbon dioxide and electrolytic byproduct hydrogen

Leisure and recreation in long duration space missions.

Leisure activities pursued during long range space missions should not be considered by planners as merely a way of filling in time. Current astronaut selection procedure tends to favor those who in leisure time in a spacecraft will spontaneously pursue mission-oriented activities, making the most of whatever facilities are available. With provision of an appropriate climate and opportunity, encouragement can be given to furtherance of the creative use of leisure for self-development of the persons involved. Provision should be made for both active recreation, as in hobbies, communal games, and even music making, and for passive enjoyment as in listening to recorded music and radio, watching television and movies, and reading. Provisision for exercise programs is also required.

Space environment simulator for materials studies at NASA Ames.

Space environment simulator for analysis of spacecraft material reliability during long- duration space mission

Space Maintenance of Nuclear Rocket Propulsion Vehicles

Long duration space mission success could depend upon the extent to which the crew can perform work outside the spaceship. Study results presented show that space suits are not the whole answer. Evaluation of worker requirements leads to a maintenance capsule concept. Capsule application is depicted in contrasting situations: Repair of meteoroid damage, a minor but vital task which can occur anywhere on the spaceship; and nuclear engine replacement, a task of major proportions.