AAE 490:ERV Human Factors Preliminary Design Analysis Sherri Spreadbury

Human Factors Overview Consumables Life Support Space Environment Radiation Hazards Thermal Control

Consumables 200 days worth of dry food/nonperishable items ~5 Tonnes of water ~2/3 Tonnes of nitrogen/argon ~1 Tonne of breathing oxygen (1kg/person/day for 5 people)

Life Support Four options are possible: open loop, physical/chemical, bioregenerative, and cached stocks of consumable materials. The open loop option is the simplest to implement but typically the most expensive in terms of the mass required. For this option, life support materials are constantly replenished from stored supplies as they are used. The physical/chemical option is typical of the systems used in current spacecraft and relies on a combination of physical processes and chemical reactions to scrub impurities from the air and water. This system has been tested on board orbiting space stations and the space shuttles.

Life Support The bioregenerative option uses higher plant life species to provide food, revitalize air, and purify water. This type of approach is technically embodied in the concept of a Controlled Ecological Life Support System, although it is often described colloquially as a “greenhouse system.” The cached stocks option makes use of the ISRU (in- situ resource utilization ) equipment already in place for manufacturing propellants to also make usable air and water for the crew. Trace amounts of the constituents of usable air and water will be by-products of the propellant manufacturing process. Capturing and storing these impurities as well as oversizing some of the production processes can allow the crew to at least augment other elements of the life support system.

Space Environment It is a known fact that the human body undergoes certain changes when exposed to extended periods of weightlessness- changes that are most debilitating when the space traveler must readapt to gravity. The most serious known changes include cardiovascular deconditioning, decreased muscle tone, loss of calcium from bone mass, and suppression of the immune system. There has been some success with long periods of daily exercise to maintain cardiovascular capacity and muscle tone, but monotonous and time-consuming exercise regimes affect the efficiency and morale of the crew. The longest continuous stay in space by a U.S. astronaut is the 181 days of Shannon Lucid the longest stay by a Russian cosmonaut is 366 days.

Radiation Hazards First and most dangerous is the probability of a solar proton event (SPE) which is likely to occur during any Mars mission. Solar proton events can rise to the level where an unshielded person can acquire a life threatening radiation dosage. Galactic cosmic rays, the other radiation hazard, occur in small numbers, are very energetic, and can cause deleterious effects over a long period of time. Exposure to cosmic radiation could induce an additional 3 percent lifetime risk of cancer (curable or incurable). Possible remedies include design shielding materials, radiation protectant materials, and SPE monitoring and warning systems for the Mars crew.

Radiation Hazards Using a mission radiation calculation(MIRACAL) program developed by NASA Langley the amount of effective spacecraft shielding needed can be calculated. For the solar flares a 25 g/cm 2 storm shelter can be used for a standard Mars mission. The galactic cosmic rays can be reduced by having the crew spend a fraction of its day in the storm shelter. One possibility is to build the astronauts sleeping quarters into the storm shelter. In March of 1999 scientists studying data from Japanese Yohkoh satellite announced a new technique for early detection of Coronal Mass Ejections, the most energetic type of solar eruption. Could provide 2-4 days warning as opposed to 1 hour.

Thermal Control Direct Sun: 300 o F Cold Space: -459 o F Electronics and humans generate heat Possible remedies White paint Multi-layer insulation Adjustable louvers Radiators/ Heat Exchangers Coolant systems

Future Work Find more data on possible structures to reduce amount of radiation to the crew. Find out systems and consumable lifetimes since the ERV will be in a state of standby for ~4 years. More detailed information on the amount and type of consumables needed. Write program once numbers are found.

References “Destination Mars” Yuri Semyenov and Leonid Gorshkov Science in the USSR July-Aug 1990 pp “Mars Exploration Strategies: A reference program and comparison of alternative architectures” AIAA , David Weaver and Michael Duke. “Radiation Exposure Predictions for Short-Duration Stay Mars Missions” by Scott A. Striepe, John E. Nealy and Lisa C. Simonsen; NASA Langley Research Center, Hampton, Virginia “The Reference Mission of the NASA Mars Exploration Study Team.” Stephen J. Hoffman, Editor and David L. Kaplan, Editor; Lyndon B. Johnson Space Center, Houston, Texas, July