G. Ron Chen, Ph.D., Associate Professor, UH
Jane Malin, Ph.D., JSC
Mike Dowell, Ph.D., Post-Doctoral Fellow, UH
THE RED PLANET MARS glows a little brighter in the
night sky after millions of people saw images from the Mars Pathfinder. These images,
showing the Sojourner robot moving across the Martian landscape, generated great
excitement. Over the next few years, more robots will be sent to Mars. However, the
mission that most often captures the public's imagination is sending humans to live on
Mars.
While movies and television portray space travel as simple, in reality many problems will occur during the two years required for a human mission to Mars. Recent problems on the Mir space station help to illustrate some of the difficulties that humans might encounter during the trip, but little is known about the difficulties that may arise while living on the surface of Mars. To discover more about these difficulties and acquire operational experience, NASA's Advanced Life Support program is building the Bioregenerative Planetary Life Support Systems Test Complex (BIO-Plex).
Dr. Jane Malin, NASA specialist in biotechnology, studies a system to help solve problems of waste disposal in space and on Earth.
BIO-Plex is a ground research facility that will be used to evaluate and experiment with life support systems that may become part of a Mars planetary base. These systems must grow, harvest, and process plants for food and oxygen for the crew, provide carbon dioxide and nutrients for the plants, and purify water for both the crew and plants.
Construction of the BIO-Plex is proceeding in two stages. The configuration for the initial stage consists of three chambers, an interconnecting tunnel, and an airlock. The three chambers include a biomass production chamber, habitation chamber, and life support chamber. Each chamber is 4.6 meters in diameter and 11.3 meters in length with two floors and a stairway. The initial stage accommodates tests of 120 days in which approximately 50 percent of the crew diet will be produced in the biomass production chamber. The majority of these crops are grown hydroponically.
The final stage of construction will add an additional biomass production chamber and a laboratory chamber. This stage will accommodate tests designed to produce 90 to 95 percent of the crew diet. Currently, the first biomass production chamber and the habitation chamber have been constructed and are being outfitted with equipment at NASA's Johnson Space Center.
Tests with the stage 1 configuration begin in the year 2000. The duration of the BIO-Plex tests will be from 120 to 425 days with four people in a crew. Two crews will occasionally occupy the complex concurrently for short periods of time to simulate the arrival of a new crew to replace an existing crew in a planetary base on the surface of Mars.
The BIO-Plex Test Facility
BIO-Plex Activities
BIO-Plex life support systems must manage many duties including water recovery, air
regeneration, environmental temperature regulation, electrical power utilization, and food
production. These systems need both low-level control software to supervise each of the
individual systems and high-level planning and scheduling software to integrate the
overall operation of these systems. In addition, the high-level software must reduce the
workload and expertise required of the crew and maximize the use of limited resources
required by these systems.
Investigators are studying requirements for the scheduling functions of high-level monitoring and control software. Because of the closed-loop nature of this application, resource management is a major concern in scheduling software. Scheduling software must reduce peak demands for electrical power and other resources while efficiently allocating resources and ensuring a safe environment.
The scheduling problem is complicated by the sheer number of systems requiring electrical power. For example, each biomass production chamber has approximately 90 square meters of area for growing crops, including wheat, soybeans, rice, and lettuce. There are eight individual growth bays in each chamber with a total of 576 lights. Current plans allow for each of these lights to be turned on and off individually based on the ages and types of plants in each growth bay. In addition, the habitation and life support chambers have over 70 systems requiring electrical power. These systems include common household items such as a stove, dishwasher, and ceiling lights. Other, more specialized items required include dew point sensors, a carbon dioxide analyzer, and an incinerator. The final BIO-Plex testbed configuration will require an estimated 700 systems to supply electrical power requirements.
While some of these systems run continuously, many systems will be turned on and off during a typical day on Mars. This project has created a discrete-event simulation computer program to compute the amount of electrical power required throughout a typical day inside the BIO-Plex for a crew of four people. Input to the program is a listing of the devices running during the simulation. Information for each device includes the required power and a daily schedule specifying when each device is to be turned on and off.
The power simulation graph illustrates the output of the program. The device list includes equipment in the habitation and life support chambers plus the interconnecting tunnel. Approximately 70 devices are included in the schedule with more than 200 device events occurring on an average day. A device event is the occurrence at which a piece of equipment is turned on or off.
Results of the simulation display the power required for a schedule of device events. In addition, the peak electrical demand for the schedule is also computed. While items can conceivably be computed by hand, the 70 devices used in this simulation require an input file exceeding 500 lines of text.
Planning software can use the results to evaluate potential schedules and identify periods of high electrical power demand. In addition, crews desire the capability to change schedules. Consequently, resource allocation must be analyzed after each schedule change to ensure that enough power remains to execute the new schedule. Scheduling in this domain must take into account other limited resources such as the availability of carbon dioxide, oxygen, and available crew time.
Future work will examine the feasibility of adding these resources to the discrete-event simulation program.
Power Simulation Graph
References
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Office of Life and Microgravity Sciences and Application, NASA, Washington, D. C., Feb.
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Supply and Recovery in the ALSS Project," Annual Report presented to Rick
Eckelcamp, NASA-Johnson Space Center, July 25, 1995.
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IEEE Trans. on Aerospace and Electronics Systems 30 (1995): 414-29.
D. Misir, H. A. Malki and G. R. Chen. "Design and Analysis of a Fuzzy
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Systems Human-Rated Test Facility," Technical Report, NASA-JSC, Houston, TX.
K. E. Lange and C. H. Lin. "Requirements Definition and Design Considerations,"
document CTSD-ADV-245, Crew and Thermal Systems Division, NASA-JSC, Houston, TX, Dec.
1996.
BIO-Plex Habitation Chamber
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