Elements of Design Review for Space Systems Nasa
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Nov 13, 2000 -- Many of usa stuck on World wish we could join (at least temporarily) the Expedition ane coiffure aboard the International Space Station (ISS). Floating effortlessly from module to module, looking down on Globe from a scenic height of 350 kilometers.... It'due south a dream come true for innumerable space lovers.
Right: An artist'south rendering of the ISS as it currently appears.
Only be careful what you wish for! Living on the Space Station likewise means hard work, cramped quarters, and... what's that scent? Probably more than outgassing from a scientific experiment or, worse yet, a crewmate.
With 3 to 7 people sharing a minor enclosed book on the nonetheless-growing Infinite Station, air management is critical.
Life support systems on the ISS must not simply supply oxygen and remove carbon dioxide from the cabin's atmosphere, but also prevent gases similar ammonia and acetone, which people emit in small quantities, from accumulating. Vaporous chemicals from science experiments are a potential run a risk, besides, if they combine in unforeseen ways with other elements in the air supply.
Then, while air in space is undeniably rare, managing information technology is no pocket-sized problem for ISS life support engineers.
In this 2nd article in a serial about the practical challenges of living in space, Science@NASA examines how the ISS will provide its residents with the breath of life.
Making oxygen from water
Virtually people tin can survive only a couple of minutes without oxygen, and low concentrations of oxygen can crusade fatigue and blackouts.
To ensure the prophylactic of the coiffure, the ISS will have redundant supplies of that essential gas.
"The main source of oxygen volition be water electrolysis, followed by Otwo in a pressurized storage tank," said Jay Perry, an aerospace engineer at NASA's Marshall Space Flight Center working on the Eastwardnvironmental Control and 50ife Support Southwardystems (ECLSS) project. ECLSS engineers at Marshall, at the Johnson Infinite Eye and elsewhere are developing, improving and testing principal life support systems for the ISS.
Nearly of the station's oxygen will come from a process chosen "electrolysis," which uses electricity from the ISS solar panels to split water into hydrogen gas and oxygen gas.
Left: The ISS'south first crew -- Neb Shepherd, Sergei Krikalev and Yuri Gidzenko -- aboard the Space Station. During their 4-month stay, the coiffure will rely on the Station'due south hardware to provide breathable air.
Each molecule of h2o contains two hydrogen atoms and ane oxygen atom. Running a electric current through water causes these atoms to separate and recombine as gaseous hydrogen (Htwo) and oxygen (Oii).
The oxygen that people breathe on Earth also comes from the splitting of water, but it's not a mechanical process. Plants, algae, blue-green alga and phytoplankton all split water molecules as role of photosynthesis -- the process that converts sunlight, carbon dioxide and water into sugars for food. The hydrogen is used for making sugars, and the oxygen is released into the atmosphere.
"Eventually, it would be groovy if nosotros could utilize plants to (produce oxygen) for usa," said Monsi Roman, chief microbiologist for the ECLSS project at MSFC. "The byproduct of plants doing this for us is nutrient."
Yet, "the chemical-mechanical systems are much more meaty, less labor intensive, and more reliable than a plant-based system," Perry noted. "A plant-based life support system pattern is soon at the basic research and demonstration stage of maturity and in that location are a myriad of challenges that must be overcome to make information technology viable."
Hydrogen that's leftover from splitting h2o will exist vented into space, at least at commencement. NASA engineers have left room in the ECLSS hardware racks for a automobile that combines the hydrogen with excess carbon dioxide from the air in a chemical reaction that produces h2o and methyl hydride. The water would help replace the h2o used to make oxygen, and the methane would be vented to space.
Right: The oxygen that humans and animals exhale on Earth is produced by plants and other photosynthetic organisms such every bit algae.
"We're looking to close the loop completely, where everything will be (re)used," Roman said. Various uses for the marsh gas are being considered, including expelling it to help provide the thrust necessary to maintain the Space Station'southward orbit.
At present, "all of the venting that goes overboard is designed to be non-propulsive," Perry said.
The ISS will as well take large tanks of compressed oxygen mounted on the outside of the airlock module. These tanks will exist the primary supply of oxygen for the U.S. segment of the ISS until the chief life support systems make it with Node 3 in 2005. Later on that, the tanks will serve every bit a fill-in oxygen supply.
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Last week, while the crew were waiting for activation of a water electrolysis machine on the Zvezda Service Module, they breathed oxygen from "perchlorate candles," which produce O2 via chemical reactions within a metal canister.
"You've got a metallic canister with this textile (perchlorate) packed inside information technology," Perry explained. "They shove this canister into a reactor and and so pull an igniter pivot. One time the reaction starts, it continues to burn down until it'southward all used." Each canister releases enough oxygen for one person for one twenty-four hours.
"It'due south really the same engineering science that's used in commercial aircraft," he continued. "When the oxygen mask drops downwards, they say to yank on information technology, which actuates the igniter pin. That'due south why you take to requite it a tug to begin the menstruation of oxygen."
Keeping the air "clean"
At present, carbon dioxide is removed from the air by a machine on the Zvezda Service Module based on a textile chosen "zeolite," which acts as a molecular sieve, according to Jim Knox, a carbon dioxide control specialist at MSFC.
The removed CO2 will be vented to space. Engineers are also thinking of ways to recycle the gas.
In add-on to exhaled COii, people also emit small amounts of other gases. Methane and carbon dioxide are produced in the intestines, and ammonia is created past the breakdown of urea in sweat. People also emit acetone, methyl booze and carbon monoxide -- which are byproducts of metabolism -- in their urine and their jiff.
Activated charcoal filters are the primary method for removing these chemicals from the air.
Above: This diagram shows the catamenia of recyclable ("regenerative") resources in the Space Station'due south Environmental Control and Life Support System (ECLSS).
Maintaining a healthy atmosphere is made fifty-fifty more complex by the dozens of chemicals that volition be used in the science experiments on board the ISS.
"In a xxx year period, there could be whatever number of unlike types of experimental facilities on board that could have any number of chemical reagents," Perry said.
Some of these chemicals are probable to be hazardous, especially if they're allowed to combine in unforeseen means, Perry said. Keeping these chemicals out of the air will exist vital for the crew'south health.
When the Space Station was first being designed, NASA engineers envisioned a centralized chemical-treatment arrangement that would manage and contain all the chemicals used for experiments. Simply such a system proved to be too complex.
"The ability for the Station to provide generic monitoring capability to try to cover the wide spectrum of chemicals that 15 plus years of basic enquiry volition require -- plain that's not something that the Station itself tin can provide," Perry said.
"It really made much greater sense that each experimental facility on board the lab module would provide its own containment of its (chemicals), substantially maintaining responsibility for the chemicals from cradle to grave," Perry said.
Left: An illustration showing the location of Node 3, where the ECLSS life support equipment will be housed. Notation that the Station components in the line of sight to Node 3 are transparent in this paradigm.
A safety review for each proposed experiment will decide the level of containment that the rack-mounted experiment facilities must provide. In the issue of a release, the crew will seal off the contaminated module and then follow procedures for cleanup, if possible.
But conscientious planning and well-designed hardware should minimize the run a risk of this scenario, enabling the coiffure of the Space Station to exhale easy.
Web Links
International Space Station -- NASA's Web folio for the International Space Station
Anatomy of the Space Station -- a PDF file with a labeled, exploded view of the International Infinite Station
Wheels in the Sky -- Science@NASA article about humanity's dreams of a space station from the scientific discipline fiction fantasies of the Nineteenth Century to Wernher von Braun'south catalytic vision in the 1950s
Advanced Life Support Web Folio -- from the Johnson Infinite Flight Center
Environmental Control and Life Back up Systems -- describes the life support systems being adult at Marshall Space Flight Center
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| For lesson plans and educational activities related to breaking science news, delight visit Thursday'due south Classroom | Author: Patrick L. Barry Production Editor: Dr. Tony Phillips Curator: Bryan Walls Media Relations: Steve Roy Responsible NASA official: Ron Koczor |
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Source: https://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/
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