System-Level Analysis of Food Moisture Content Requirements for the Mars Dual Lander Transit Mission 2004-01-2364
To ensure that adequate water resources are available during a mission, any net water loss from the habitat must be balanced with an equivalent amount of makeup water. For a Mars transit mission, the primary sources of makeup water will likely involve water contained in shipped tanks and in prepackaged food.
As mission length increases, it becomes more cost effective to increase system water closure (recovery and generation) than to launch adequate amounts of contained water. This trend may encourage designers to specify increased water recovery in lieu of higher food moisture content. However, food palatability requirements will likely declare that prepackaged foods have a minimum hydration (averaged over all food types). The food hydration requirement may even increase with mission duration. However, availability requirements for specific emergency scenarios may declare that determined quantities of water be provided in tanks, rather than as moisture in food. As a result, the cost effectiveness of increased water closure must be balanced against the palatability characteristics of hydrated food as well as the emergency availability of water in shipped tanks, while considering crew quality of life and system-level risk.
This study addresses one piece of the water supply design puzzle by examining the need for makeup over a range of configurations for a life support system. A calculation is performed to determine the necessary food moisture content if all needed makeup water were stored in prepackaged food. This paper examines the need for makeup water as it depends upon the configuration of the rest of the life support system. Conversely, one may examine how the need for a particular processor depends upon the quantity of available makeup water.
The Dual Lander Transit Mission was selected for study because it has been considered by the NASA Exploration Office in enough detail to define a reasonable set of scenario options for system configuration. Depending on mission abort scenarios, the life support system in the Transit Vehicle of the Dual Lander mission may need to provide up to 600 days' worth of contingency supplies (including food and water), in addition to supplies for 180-day transit legs both to and from Mars. Thus, the mission duration considered for system design can be vastly different from the nominal scenario duration. As a result, the Transit Vehicle is an excellent focal point for illustrating the trades between water closure, food palatability and water availability.
Mass balance results for the Transit Vehicle show that if all needed makeup water were stored in prepackaged food, moisture contents would be similar to those of Shuttle/ISS food, unless carbon dioxide reduction were implemented to recover some of the water used for oxygen generation via electrolysis. Possible implications of this result on system design are discussed in the “Conclusions and Discussion” section of this paper.
This study also illustrates the concept that there are multiple, reasonable life support system scenarios for any one particular mission. The need for a particular commodity can depend upon many variables.
It is important to note that the results in this paper are highly theoretical; only very general design recommendations can be made based upon the results of this study alone.