Advanced Life Support Power Reduction

Cory K. Finn

This research involves modeling of the power and energy usage of regenerative life support systems suitable for exploring the Moon and Mars. System energy integration and energy reuse techniques are being investigated, along with advanced control methods for efficient distribution of power and thermal resources. The high power requirements associated with food production and overall closed regenerative system operation remain as a critical technological challenge. Optimization of individual processors alone will not be sufficient to produce an optimized system. System studies must be used in order to improve the overall efficiency of life support systems.

Designs are being developed that match sources of waste heat, such as crop lighting and solid waste processing systems, with processes that can use this waste heat, such as water processing, food processing, food preparation, and heating of shower water, dish wash water or clothes wash water. Using energy integration techniques, optimal system heat exchange designs are being developed by matching hot and cold streams according to specific design principles. For various designs, the potential savings for power, heating and cooling are being identified and quantified, and estimates are being made of the emplaced mass needed for energy exchange equipment.

Advanced control system designs are also being developed that allow for more efficient distribution of resources, such as system cooling water or electrical power, in order to reduce system power requirements. More efficient energy usage can be achieved by allocating power and thermal resources in a dynamic fashion. Advanced control techniques, such as market-based control, can be used in order to smooth out system thermal and power loads. Reductions in the peak loading will lead to lower overall requirements. The controller dynamically adjusts the use of system resources by the various subsystems and components in order to achieve the overall system goals. A typical system goal would be the smoothing of power usage and/or heat rejection profiles, while maintaining adequate reserves of food, water, oxygen, etc., and not allowing excessive build-up of waste materials. Initially, computer simulation models are being used to test various control system designs. The most promising of these will be tested using a laboratory-scale life support system testbed at Ames Research Center.

Energy balance models are being developed to support both the energy integration and the dynamic resource allocation work. These models leverage off of existing mass flow models of regenerative life support systems developed at Ames Research Center. The heat exchange designs and control schemes developed as part of this NRA research will be provided to Johnson Space Center for use in the development of the ALS Systems Integrated Test Bed (also known as BIO-Plex) and in the design of flight hardware for Moon or Mars missions.

Currently, energy integration techniques are being applied to the life support problem. Several potential designs that would be suitable for various Mars missions have been selected for application of the energy integration analysis. Life support data have been collected, and an optimized heat exchange design has been developed for each scenario. For each design, the potential savings in energy and cooling has been estimated.

In addition to the energy integration work, advanced control system designs are being developed that allow for more efficient distribution of electrical power. A dynamic model of the BIO-Plex air loop has been created and serves as a platform for the development of active power management strategies. Several resource allocation objectives have been defined and tested. One objective that was considered was to reallocate power as needed to the various life support processors to eliminate surges in power usage over time. However, the reallocation of power was subject to constraints. For example, material storage levels needed to be maintained, as well as atmospheric conditions within the life support chambers. This power management system has been demonstrated using the simulation model and performed reasonably well. A second objective that has been and continues to be investigated is to smooth the demand for power throughout the system over time.