With Mars the closest it's been in almost 60,000 years, planning a manned trip to the "red planet" seems alluringly close. In fact, projects are underway for evaluating the feasibility of such a trip at a 12-by-12-ft research facility in New Mexico. The Laboratory Biosphere Project in Santa Fe, NM, is a unique research project looking into the possibilities of growing and sustaining food crops to support long-term space and planetary missions.

The Laboratory Biosphere Experimental Chamber is a cylindrical steel vessel with an internal capacity of 1,200 cubic ft. It is connected to a variable volume chamber (the "lung") which, depending on temperature and humidity conditions within the total system, varies in volume between zero and 400 cubic ft. This gives a total volume for both chamber and lung together of between 1,200 and 1,600 cubic ft.

Critical Real-time Data

With the chamber designed for testing plant growth in extreme environments, constant monitoring of the HVAC systems is critical. Real-time data is needed to assist the system in reacting to variances. "The atmospheric temperature and humidity control system is the most critically monitored technical component of Laboratory Biosphere," Abigail Alling, CEO, Biosphere Foundation said. "The 2CP5 Texas Instruments' pressure transducers constantly report critical pressure data from the compressors' refrigerant lines to the computer watchdog system. Control actions are taken based on this data."

The 2CP5 pressure transducers for this project, donated by Texas Instruments, are used to monitor both high and low variances in the A/C loop. An Ohio-based firm, Design Services Network, recommended using the transducers along with Copeland compressors. The pressure transducers sit in the refrigerant lines leading to and from compressors and AHUs (which were custom built by a sheet metal shop in Albuquerque to the head engineer's special design specifications). The transducers provide continual feedback to the monitoring system and collect real-time data for this experiment, allowing a better understanding of the overall management of this contained environment.

The pressure transducers connect to National Instruments (NI) Fieldpoint hardware controlled by NI's LabVIEW software. Three banks of LabVIEW Real-Time embedded FieldPoint control modules are used to monitor all of the environmental variables inside the chamber and control and monitor external support systems. For example, the LabView Software can read constant data from transducers and trip an alarm if pressure readings are too high or low. Continuous readings can be seen worldwide at www.biospherefoundation.org.

"There have been a few times where pressure transducers have been critical to controlling the environment," said Bill Dempster, chief engineer, Laboratory Biosphere Project. "In one instance, a low pressure reading tripped an alarm in our control system alerting us to unsuitable conditions, and we were able to take control actions before it became a serious issue.

Without this system, there could have been frosting in the coils, which would block airflow. Ultimately, temperature control would have been lost."

Space-grown Wheat And Soy?

System tests began in April and May of 2002. These tests, which checked performance of the lights, HVAC, and other mechanical systems, also provided initial clues as to the way the complex system would operate. After two further experiments, where plant life was monitored for 65 days, then nearly three months, the Biosphere Project now boasts successful experiments in growing wheat and soybeans with another project currently in progress testing sweet potato growth, which is thought to be a crucial dietary component for inclusion in remote or extreme environments.

Knowledge gained from this chamber is a direct precursor to the Mars on Earth project which will construct and operate an Earth-based prototype Mars Base Biosphere that will be a test-bed for developing life support systems for an inhabited Mars mission. The development of this Mars Base Modular Biosphere will play a major role in determining the feasibility of maintaining humans in a self-sustaining system on Mars.

"This project is one example of how a component as small as a pressure transducer can make a major impact on a sensitive HVAC system that cannot afford to fail," Alling added. "TI's transducers, Copeland's compressors, and the monitoring system from National Instruments all are key components to this successful HVAC system and to our research project."ES