6.2 Consumables and Life Support

6.2 Consumables and Life Support

Brandon R. Abel

6.2.1 Introduction

Human Factors associated with the first human mission to Mars is vital to the survivability of the crew. However, there are many concerns with such a mission since none of this duration has ever been attempted with a manned crew. Questions in regards to consumables, life support, recycling, and others must be addressed to keep the mass penalties to a minimum. The following gives solutions for such problems.

6.2.2 Crew Size

The size of the crew is a critical decision for a human mission to mars. This decision will have an enormous impact on the mass of the vehicle and thus the ability for the mission to be successful. Of course, the objective while selecting the crew size is to try to maximize the number of humans on the surface of Mars. This will allow for increased ability for exploration, science experimentation, and redundancy of backgrounds. Also, for such a complicated mission and requiring the use of such complex hardware, a larger crew is needed in order to complete the mandatory tasks for the survivability of the mission itself. A trade off must be made, however. Additional crewmembers mean a larger penalty on mass and volume, and for the first mission to Mars, having an entire colony may not be necessary.

We feel that four crewmembers is an optimum number for such a mission.1 There are many advantages in selecting a crew of this size. First, this is probably the least number of crew that can successfully complete the mission without enormous risks to the success and survivability of the crew itself. Also an even number of people means that no one crew member will be alone for an extended period of time. On the other hand, the mass penalties for this number should be relatively small. Due to the nature of the mission, which is mainly testing the feasibility of making the trip, an enormous crew is not necessary. The other types of missions will follow in the footsteps of such an initial mission.

6.2.3 Crew Make-up

Crew make-up is also an important consideration for such an initial mission to Mars. Not only will these crewmembers need to be experts in each one of their respective fields, they must also be well versed in other fields for redundancy on the trip. A mission such as this will have the luxury of drawing from the best minds and bodies on the planet. These individuals will truly be unparalleled by many standards.

With a crew size of only four, many disciplines will be sacrificed during the mission. The mission cannot have the luxury of having an expert in every relevant field as some may have hoped. However, considering that individuals being so well versed in multiple disciplines, along with the fact that they will have contact with Earth for much of the mission, they should have the knowledge they need for any conceivable situation.

The crew will consist of two members who will specialize in the systems, operations, and maintenance of the vehicle itself. This covers pilot, engineer, mechanic, etc. The other two crewmembers will specialize specifically in the different science areas. These two will cover topics such as geology, biology, chemistry, etc. They are responsible for all the exploration and discoveries on the surface of Mars.2

6.2.4 Schedule

A mission to Mars will put the astronauts through rigors much like the space shuttle and Apollo astronauts; however, they will be there for a much longer period of time. This will require considerable more flexibility in the schedule and less strenuous working hours than some astronauts may be used to. It should be much like a normal working schedule on Earth.

One small consideration is the difference between the Martian day and a day on Earth. Mars revolves around its axis approximately once every 24.5 hours. This means that the astronauts will have to adjust their working day to this time frame so that they will always be able to work in daylight. Table 6.2.1 shows a flexible time allocation for the average working day.

Table 6.2.1 Scheduled Time Allocation

Allocated Item / Hours
Work / 8
Maintenance / 1
Meetings/Reports / 1.5
Sleep / 8
Eat / 1.5
Hygiene / 1
Exercise/Health / 1
Personal / 2.5

Another notable fact is that there will be 2.5 hours of communication from Mars to Earth available to the crew each Martian day. This is distributed between 1.5 hours of business and 1 hour of personal communication for the crew.

6.2.5 Consumables

The consumables for a mission to Mars may be one of the most important elements of such a mission. The nominal amount of food, water, and oxygen used by humans is determined by multiple sources and averaging these amounts.

Recycling consumables is the only way to successfully make a mission to Mars. From multiple resources and references, it is determined that we will be able to recycle water at a 90% rate and oxygen at least at an 86% rate. By using these abilities, tens of thousands of kilograms in mass can be saved.

The amount of consumables the average human needs for this mission was compared using a variety of sources. We averaged the amount from each source, and using engineering judgment, finalized the amounts of food, water, and oxygen our astronauts will receive.1,3,4,5,6 Also, we did the same thing with regards to recycling percentages. Table 6.2.2 shows the final average of consumables during the mission, along with the recycling percentages.

Table 6.2.2 Consumable rates and percentages

Item / Rate (kg/person/day) / Percent Recyclable
Food / 0.62 / 0
Potable Water / 4 / 90
Hygiene Water / 25 / 90
Oxygen / 0.8 / 86

The Habitation module (Hab) must contain enough consumables to last an entire free return abort scenario. Although this does not include the complete nominal amount of consumables needed for such an event, the crew will have 100% of the potable water and oxygen, but only 50% of the hygiene water they will need after they miss Mars. Even though this may be uncomfortable for the crew, it will be safe and ensure survival while saving approximately 3000 kg. Table 6.2.3 shows the amount of consumables the Hab will require.

Table 6.2.3 Hab Consumables

Item / Mass (kg) / Volume (m^3)
Food / 1984.0 / 16.99
Potable Water / 1280.0 / 1.28
Hygiene Water / 4220.0 / 4.22
Oxygen / 716.8 / 3.19
Totals / 8200.8 / 25.68

The Earth Return Vehicle (ERV) will contain enough consumables to last the entire trip home with added redundancy. Since the vehicle will never touch the face of Mars, this reduces the risk involved with the mission. The crew will have 100% of all consumables on the return trip. Table 6.2.4 shows the amount of consumables the ERV requires.

Table 6.2.4 ERV Consumables

Item / Mass (kg) / Volume (m^3)
Food / 446.4 / 3.82
Potable Water / 368.0 / 0.37
Hygiene Water / 2300.0 / 2.30
Oxygen / 206.1 / 0.92
Totals / 3320.5 / 7.41

The Crew Transfer Vehicle (CTV) will carry consumables needed for seven days. This includes food, water and oxygen. There will be no recycling capabilities with this vehicle. Table 6.2.5 shows the consumables the CTV requires.

Table 6.2.5 CTV Consumables

Item / Mass (kg) / Volume (m^3)
Food / 17.4 / 0.15
Water / 112.0 / 0.11
Oxygen / 22.4 / 0.10
Totals / 151.8 / 0.36

6.2.6 Life Support Systems

The design of a life support system is crucial to the success of a human mission to Mars. After comparing different types of life support systems, it was found that a life support system composed of physical-chemical processes will be the most durable and cost effective system for our mission.7,8 This was chosen over a biological system, in which plants purify water and produce oxygen and food, because the physical-chemical system requires much less power and volume and is a more proven technology.

Both the HAB and ERV will incorporate the same life support system and specifications, thus reducing the cost significantly. Table 6.2.6 shows the mass and volume of the life support systems with the vehicles.

Table 6.2.6 Life Support Systems9,10,11

Item / Mass (kg) / Volume (m^3)
Atmospheric Recycling / 560 / 1.0
Pressurization System / 720 / 2.0
Fire Suppression / 100 / 0.0
Internal Thermal Control / 610 / 1.0
Water Recycling / 770 / 0.5
Waste Management / 190 / 0.5
Medical / 100 / 1.0
Extra / 200 / 1.0
Totals / 3250 / 7.0

6.2.7 Power Inputs

The power input for the life support systems is critical to the survivability of the crew. Because the crew cannot afford to take all the consumables necessary to sustain them without recycling, the power necessary for the recycling systems is absolutely necessary. The power for these systems is calculated using multiple trade studies, finding the average power inputs of similar systems, and sizing them for the oxygen and water requirements. Table 6.2.7 shows the power inputs required for the specific life support systems.

Table 6.2.7 Power Inputs

Item / Power (W)
Atmospheric Recycling / 3800
Pressurization System / 500
Fire Suppression / 50
Internal Thermal Control / 4100
Water Recycling / 300
Waste Management / 250
Totals / 9000

6.2.8 In Situ Propellant Production

The In Situ propellant production plant has the advantage of having the ability to produce water and oxygen as by-products. Therefore, the mission can use this production system to account for some oxygen and water that is not necessarily needed to launch off the Earth; only the hydrogen feed stock to make it. Also, if some hydrogen is not used and needed for the production of the propellant, this provides the life support systems some needed extra redundancy for consumables while on the surface of the planet. Another advantage of such an idea is that they will be able to ensure the plant has successfully made this before the crew launches from the surface of Earth, so little added risk is involved.

The consumables necessary for the stay on Mars account for the hygiene water not given to the crew in case of a needed free return abort scenario. However, it is optimal that they have the full amount of water and oxygen when they make it to the surface, and thus the extra water and oxygen is needed. Also, the free return consists of a shorter time frame than the travel time to Mars and the stay on the planet.

The In Situ production plant must have the capability to produce an extra 3476 kg of H2O and an extra 32 kg of O2.

Using the In Situ propellant production plant for this extra water and oxygen will also be applicable to future missions considering the technology has been demonstrated as effective. Therefore, future missions cannot only use the same technology but on a much larger scale for the production of water and oxygen for future Mars colonies.

6.2.9 Medical

The crew on a mission to Mars will have to take an inherent risk given the fact that there will be no hospital or emergency room available. In fact, many of the possible treatments for health risks to humans will not be available to the crew because of the severe mass and volume penalties these would incur. Also, given the small size of the crew, no full time doctor can be a crewmember on board. However, every crewmember should be trained in the standard CPR and trauma skills, and there should be some sort of crewmember with medical technician training.

The required medical cares necessary for a space mission depends upon two factors, the mission duration and mission type. Given the mission type and duration, the types of injuries and illnesses that may occur can be predicted. The characteristics of the illnesses and injuries important for our design are described below.

First, the probability of the occurrence of disease or injury can be determined through historical data from the Mercury, Gemini, Apollo, space shuttle, and space station missions. However, this mission will have the luxury of using the most highly trained and healthy people on the planet. Therefore, selection and pre-screening will decrease on most of the risks due to illness.

Also, if the time for a certain disease has a long incubation period, these problems need not even be dealt with. However, if the disease does have a short incubation time, it must be efficiently and accurately dealt with on the vehicle. Next, the equipment available to the crew must have the capabilities for diagnoses of the level of an injury or illness in order to allow for adjustments to any specific workloads or changes in lifestyle.

Then, the vehicle must have the necessary room for recuperation time. Finally, the medical facility must have the ability to treat any of these diagnoses or provide the best alternative method of treatment if no equipment is available.

Considering these factors, most of the equipment needed will mainly focus on trauma, injury, and illness of various sorts. These will range from splints to Band-Aids to burn treatments to normal pain medications.

Table 6.2.8 shows the necessary equipment and systems to keep the crew healthy.

Table 6.2.8 Medical Equipment Requirements

Equipment Requirements
Data Base and Communications Capabilities
Manage and store medical information and crew health records.
Inventory of medical supplies and pharmaceuticals.
Two way voice and visual communications between the module
and supplemental medical support facilities outside the module.
Environmental Monitoring Equipment
Particaulate substances.
Microbial contamination of air, water, and surfaces.
Volatile contaminants of the atmosphere.
Potential water supply contaminants.
Module and biological radiation exposure.
Physiological Monitoring Equipment
Cardiovascular.
Pulmonary.
Metabolic.
Renal.
Muscular and skeletal.
Body Fluids.
Advanced Life Support
Laboratory
Hematology.
Clinical Chemistry.
Urine Analysis.
Microbiology.
Diagnostic Imaging
Countermeasures
Exercise equipment.
Physiological monitoring equipment.
Pharmaceuticals.
Pressure devices to counteract the effect of fluid shifts in zero gravity.
Surgery/Anesthesia Equipment
Dental Care Equipment
Intravenous Fluid Injection Supplies and Equipment
Sterile water.
Fluids containing medications, electrolytes, or nutritional substances.
Blood or blood products.
Hyperbaric Treatment Facilities
Pharmaceuticals
Central Supply
Physician's Instruments
Safe Haven Medical Design Requirements
Facilities For Processing and Storage of a Deceased Crew Member

Table 6.2.9 is a flexible list of the medical equipment needed for the mission to Mars.

Table 6.2.9 Medical Equipment List

Items in Emergency Medical Kit
Airway
Oral airway
Tracheal tube w/ atylet
Laryngoscope
Pertrach Kit
Comox resuscitator
Ambu Bag
Antiseptics
Alcohol wipes
Bandages
Ace Bandage
Bandaids
Kling
Sponges
Telfa pads (4 x 4s)
Wounds pack
Burns
Silvadene cream (silver sulfadiazine)
Decongestants
Afrin nasal spray
Diagnostic Equipment
Blood Pressure cuff
Stethoscope
Eye Treatment
Tearisol eye drops (artificial tears)
Motion Sickness
Phenergan, oral
Scop/Dex
Pain Medications
Ascriptin (aspirin)
Tylenol (acetaminophen w/ codeine)
Miscellaneous
Scissors
Tweezers
Tape (generic adhesive - medical)
Steri-Strip skin closure
Penlight

6.2.10 Exercise

The physical health of the crew is critical, although the amount of exercise may not be important given the artificial gravity created by the tether throughout the mission. However, exercise equipment will be necessary for additional physical fitness, and as a redundancy.

6.2.11 Miscellaneous

A study such as this cannot fully account for all necessary items needed for normal human living. Because of this, a 200 kg and 1 m3 allotment has been given for the unthinkable. These will include things such as toothbrushes, playing cards, and notebook paper.

6.2.12 Future Considerations

The existing HAB and ERV modules will have the capabilities to be modified for the use of five crewmembers instead of the planned four. Therefore, in future missions, more crew will be able to be transported to Mars with little loss in mass penalties. The reason this will work is due to the fact that we will not use the free-return abort methods in the future. This free-return abort scenario will not be an option, and we can make all of our water and oxygen on the surface of the planet. Therefore, without any mass penalties, we can sustain life of five humans instead of four.

6.2.13 Risk Considerations

A human mission to Mars carries with it enormous risks. Risks involved with the life support of the crew are critical. One great risk involved with such a system is the amount of water and oxygen needed to be recycled. If such a system would break down and the redundancy and repairs could not suffice, then this would be catastrophic to the crew. However, some of this risk is reduced by the double redundancy in breathable oxygen supplied for the crew. If one tank did burst, there would still be enough oxygen for the crew to live. Finally, the only way to reduce the risk is to test and retest all of the systems on this craft before it becomes operational.