Everything that is shipped into space is likely to become waste of one kind or another. This project looked at waste processing options and their impact on life support. About 40,300 kilograms (kg) of life support commodities are required for a crew of six for a year (yr). This is a lot of mass to supply and generates a similar mass of waste to be disposed of. Fortunately, much of this waste mass is recoverable, though at a cost of requiring some additional resources to process the waste. One example of a recoverable resource is water. Water is resupplied to the International Space Station (ISS) at a rate of approximately 3,500 kg/yr in its current configuration.

This project developed a model that calculated system impacts for varying mission types. System impacts are estimated in mass units as equivalent system mass (ESM). Estimates of initial and time-dependent ESM and break-even times for different life support options are shown in table 1 for a Mars surface mission with a crew of six people. The picture is less clear for ISS itself, in low Earth orbit, because much of the water is supplied from the Shuttle fuel cells and would otherwise be dumped.

Using ALS technologies, the time-dependent mass would be about 18,800 kg/yr. About 16,700 kg/yr of this would appear as waste that would have to be dealt with during the mission. This waste would be of a variety of types, including expended (ORU’s), gases (notably carbon dioxide [CO2]), liquids (waste hygiene water, urine), and solids (trash, feces).

Our models and resulting analyses were used to produce the official ALS Research and Technology Development (R&TD) Metric (Drysdale and Hanford, 2002, JSC 47787, and earlier revisions) released by NASA Johnson Space Center (JSC). The metric used is calculated by dividing the ESM for a specified mission using ISS technology (ESM_ISS) by the ESM for the same mission using ALS technology (ESM_ALS): metric = ESM_ISS / ESM_ALS. The values of the metric for the missions considered are given in table 2.

For some mission scenarios, inedible biomass is a significant issue. A biomass production estimate was developed with Dr. Raymond Wheeler, YA-E4, for biomass and waste production for each of the selected ALS crop plants. From this crop model and the design of the plant production system for the BIO-Plex (Barta, 1996), the cost effectiveness of each of the crop plants was calculated. Using the diets given in the Baseline Values and Assumptions Document (BVAD), excluding those crop plants that were shown to be not cost-effective and using crop production rates from the BVAD, a plant waste data model for a crew of six was developed. The food closures (dry-weight basis) for the missions considered were calculated to be: Mars transit, 13 percent; Mars surface exploration mission, 13 percent; and a Mars base, 29 percent.

The waste model (draft for Mars missions) is summarized in table 3. The missions are further defined in Stafford, Levri, and Drysdale (2001), the ALS SIMA Reference Missions Document, JSC 39502.

Key accomplishments:

• Numerous publications and reports identifying model results were generated and presented (publication list available upon request).
• Plant waste models for ISS missions and Mars missions were calculated.

Key milestones:

• Results of this work are being presented at international conferences, including the International Conference on Environmental Systems (San Antonio, July 2002) and the Committee on Space Research (COSPAR) conference (Houston, August 2002).

Contact: Dr. R.M. Wheeler (Raymond.Wheeler-1@ksc-nasa.gov), YA-E4, (321) 476-4273
Participating Organization: Boeing (A.E. Drysdale and S. Maxwell)