Human astronauts are such a bother when it comes to space exploration. The space environment is pretty much the opposite of the conditions that humans evolved for, to the point where an unprotected human exposed to space will die horribly in about ninety seconds flat. Even given oxygen to breath, the human organism is quite insistent on a whole host of demands: food, water, comfortable temperature, gravity, absence of deadly radiation; the list goes on and on.
This is why NASA is so fond of robot space probes. Not only do robots not have any of those requirements, but there also is no problem with sending the probes on suicide one-way missions. Human astronauts would tend to complain about that.
But given organic non-cyborg astronauts, your spacecraft design is going to need a habitat module for the crew to live in, and all sorts of supplies to keep them alive. Since Every Gram Counts, it will be important to use every trick in the book to try and miminize the mass cost of all this.
The basic requirements for life support are:
- Breathing Mix: an atmosphere to breath, or the crew will rapidly suffocate. Oxygen must be added as it is consumed and carbon dioxide removed as it is exhaled.
- Water: for drinking and hygiene, or the crew will die of thirst.
- Food: for eating, or the last surviving cannibal crew member will starve to death.
- Waste Disposal: or the crew will perish in a sea of sewage.
- Temperature Regulation: or the crew will either freeze or roast to death, probably the latter.
- Radiation Shielding: or deadly radiation will take its toll.
- Artificial Gravity:
The first three requirements are called "consumables", since they are gradually used up by the crew. Each of those three can be controlled by either an "open" system or a "closed" system.
Open systems are ones where a supply of the consumable in question is lugged along as cargo, enough to last the for the planned duration of the mission. It is renewed by "resupply", by obtaining new supply from a resupply spacecraft, a base, or an orbital supply depot. Things can get ugly if the mission duration becomes unexpectedly prolonged, for instance by a meteor scragging the spacecraft's engine.
Closed systems are ones where the supply of the consumable in question are renewed by some kind of closed ecological life support system. Generally this takes the form of some sort of plants, who use sunlight to turn astronaut sewage and exhaled carbon dioxide into food plants and oxygen.
Note that requirements for consumables can be drastically reduced if some of the crew is placed into suspended animation.
If you want more data on life support than you know what to do with, try reading this NASA document. Otherwise, read on.
For some great notes on spacecraft life support, read Rick Robinson's Rocketpunk Manifesto essay.
As a very rough rule of thumb: one human will need an amount of mass/volume equal to his berthing space for three months of consumables (water, air, food). This was figured with data from submarines, ISS, and Biosphere II. Of course this can be reduced a bit with hydroponics and a closed ecological system. This also makes an attractive option out of freezing one's passengers in cryogenic suspended animation.
Eric Rozier has an on-line calculator that will assist with calculating consumables.
According to NASA, each astronaut consumes approximately 0.835 kilograms (0.560 cubic meters) of oxygen per day. They breath out 0.998 kilograms of carbon dioxide per day.
As a point of reference, a SCUBA tank is pressurized to about 250 bar i.e., 250 times atmospheric pressure. At that pressure, one person day of oxygen takes up about 0.00224 cubic meters.
Stored as liquid oxygen, 0.8 kilograms would take up about 0.0007 cubic meters. This requires extra mass for the cryogenic equipment to keep the oxygen liquid, but the volume savings are impressive.
So as far as pure oxygen goes, you take 0.8 kg for one person-day of oxygen, muliply it by the number of crewbeings on the ship, and then muliply it by the number of days in a standard mission (i.e., desired "endurance time" or time between supply stops) to discover the total oxygen mass requirement. Repeat with the volume figure for the total oxygen volume requirement.You'd be wise to add an additional reserve of about 25% to take account of pressurization of the hull, loss due to various mishaps, and general military paranoia.
However, this is just pure oxygen. This is insanely dangerous to use as the ship's atmosphere, the accident that killed the Apollo 1 crew proved that. In practice one uses a "breathing mix" of oxygen and another gas.
The Space Shuttle uses a 79% nitrogen/21% oxygen mix at atmospheric pressure (14.7 psi or 760 mm Hg). The shuttle space suits use 4.3 psi of pure oxygen, which means they have to prebreath pure oxygen while suiting up, or the bends will strike. Setting up the optimal breathable atmosphere is complicated.
In most space program, they use two pressure levels. Low Pressure (pure oxygen at 32.4 kPa) or High Pressure (breathing mix at 101.3 kPa, normal Terran atmospheric pressure).
Low pressure is attractive; since it uses less mass and the atmosphere will escape more slowly through a meteor hole. Unfortunately the required higher oxygen level make living in such an environment as hazerdous as chain-smoking inside a napalm factory. NASA found that out the hard way in the Apollo 1 tragedy. Since then NASA always uses high pressure, they use low pressure in space suits only because they cannot avoid it.
This does raise a new problem. There is a chance that the high-oxygen atmosphere will allow a meteor to ignite a fire inside the suit. There isn't a lot of research on this, but NASA seems to think that the main hazard is a fire enlarging the diameter of the breach, not an astronaut-shaped ball of flame.
The increased fire risk is one reason why NASA isn't fond of low-pressure/high oxygen atmospheres in the spacecraft proper. There are other problems as well, the impossibility of air-cooling electronic components and the risk of long-term health problems being two. Setting up the optimal breathable atmosphere is complicated.
A more annoying than serious problem with low pressure atmospheres is the fact that they preclude hot beverages and soups. It is impossible to heat water to a temperature higher than the local boiling point. And the lower the pressure, the lower the boiling point. You may have seen references to this in the directions on certain packaged foods, the "high altitude" directions. The temperature can be increased if one uses a pressure cooker, but safety inspectors might ask if it is worth having a potentially explosive device onboard a spacecraft just so you can have hot coffee.
Decompression sickness (also known as DCS, divers' disease, the bends or caisson disease) is one of the more hideous dangers of living in space.
It occurs when a person has been breathing an atmosphere containing inert gases (generally nitrogen or helium) and they move into an environment with lower pressure. This is commonly when they put on a soft space suit or the room suffers an explosive decompression.
It has all sorts of nasty effects, ranging from joint pain and rashes to paralysis and death. The large joints can suffer deep pain from mild to excruciating. Skin can itch, feel like tiny insects are crawling all over, mottling or marbling, swell, and/or suffer pitting edema. The brain can have sudden mood or behavior changes, confusion, memory loss, hallucinations, seizures, and unconsciousness. The legs can become paralyzed. Headache, fatigue, malaise, loss of balance, vertigo, dizziness, nausea, vomiting, hearing loss, shortness of breath, and urinary or fecal incontinence: the list just goes on and on.
Why does it happen? Well, imagine a can of your favorite carbonated soda beverage. Shake it up, and nothing happens. But when you open it, the soda explodes into foam and sprays everywhere. When you open the container of shaken soda, you lower the pressure on the soda fluid. This allows all the dissolved carbon dioxide in the soda to un-dissolve, creating zillions of carbon dioxide bubbles, forming a foam.
Now imagine that the carbon dioxide is nitrogen, the drink is the poor astronaut's blood in their circulatory system, and the foam is the deadly arterial gas embolisms. That's what causes the bends.
Please note that sometimes the bends can occur if one moves from one habitat to another that has the same pressure, but a different ratio of breathing mix (the technical term is "Isobaric counterdiffusion"). Spacecraft of different nations or models could use different breathing mixes, beware. In fact, rival astromilitaries might deliberately utilize odd-ball breathing mixes, to make life difficult for enemy boarding parties invading their ships.
The bends can be prevented by slow decompression, and by prebreathing. Or by breathing an atmosphere containing no inert gases. Slow decompression works great for deep-sea divers but NASA does not favor it for space flight. An atmosphere with no inert gases (pure oxygen) is an insane fire risk. NASA does not allow a pure oxygen atmosphere in spacecraft and space stations, but will allow it in space suit (in a desperate attempt to lower the suit pressure to the point where the astronaut can move their limbs instead of being trapped into a posture like a star-fish).
So NASA astronauts do a lot of prebreathing. This flushes nitrogen out of the blood stream. NASA uses Terra-normal pressure (14.7 psi) inside the Space Shuttle, but only 0.29 pressure (4.5 psi) with pure oxygen in the space suits. The prebreathing is officially called the In Suit Light Exercise (ISLE) Prebreath Protocol, and unofficially called the "Slow Motion Hokey Pokey".
The astronaut(s) enter the airlock, and the airlock pressure is reduced to 10.2 psi. They breath pure oxygen through masks for 60 minutes (because the air in the airlock contains nitrogen). They then put on their space suits and do an EMU purge (i.e., flush out all the airlock-air that got into the suit while they were putting it on, to get rid of stray nitrogen). The air inside their suits is now also pure oxygen. The airlock pressure is then brought back up to the normal 14.7 psi. They then do 100 minutes of in-suit prebreath. Of those 100 minutes, 50 of them are light-exercise minutes and 50 of them are resting minutes. "Light exercise" is defined as: flex your knees for 4 minutes, rest 1 minute, repeat until 50 minutes has passed. Thus "Slow Motion Hokey Pokey". Now they are ready to open the airlock and step into space.
The innovation was the 50 minutes of exercise. Without it, the entire protocol takes twelve hours instead of one hour and fifty minutes.
If the habitat module's pressure was 12 psi an astronaut could use an 8 psi space suit with no prebreathing required (a pity such suits are currently beyond the state of the art), and for a 4.5 psi suit the prebreathing time would be cut in half.
In case of emergency, when there is no time for prebreathing, NASA helpfully directs the astronauts to gulp aspirin, so they can work in spite of the agonizing pain
Please note that most of the problem is due to the fact that soft space suits have a lower atmospheric pressure than the habitat module. So this can be avoided by using a hard space suit or space pod.
All of the atmospheric controls will be on the life support deck.
On a related note, forced ventilation in the spacecraft's lifesystem is not optional. In free fall, the warm exhaled carbon dioxide will not rise away from your face. It will just collect in a cloud around your head until you pass out or suffocate. In Arthur C. Clarke's ISLANDS IN THE SKY the apprentices play a practical joke on the main character using this fact and a common match. In the image above the blue dome shaped flame is an actual candle burning in free fall. And in Clarke's "Feathered Friend", he talks about the wisdom of using an animal sentinel to monitor atmospheric quality. Specifically by using the tried and true "canary in a coal mine" technique.
And yes, on Skylab, the area around the the air vent got pretty disgusting quite quickly, as all the floating food particles and assorted dirt from the entire space station got sucked in. In some SF novels the slang name for the air vents is "The Lost and Found Department."
Unpleasant odors in the air is a problem, but there is not much one can do about it. After all, you can't just open up a window to let in some fresh air, not in the vacuum of space. NASA carefully screens all materials, sealants, foods, and everything else to ensure that they do not emit noticeable odor in the pressurized habitat sections of spacecraft and space stations. Such odors can quickly become overpowering in such tight quarters.
It is not enough to supply oxygen to breath, you also have to remove the carbon dixoide. Bad things happen if the CO2 levels rise too high. NASA says that each astronaut exhales 0.998 kilograms of carbon dioxide per day.
- 0.04 percent - Typical level in Terra's atmmosphere
- At 1 percent - drowsiness
- At 3 percent - impaired hearing, increased heart rate and blood pressure, stupor
- At 5 percent - shortness of breath, headache, dizziness, confusion
- At 8 percent - unconsciousness, muscle tremors, sweating
- Above 8 percent - death
NASA uses Carbon Dioxide Scrubbers. In the Apollo program spacecraft, NASA used lithium hydroxide based scrubbers, which fill up and have to be replaced.
You may remember all the excitement during the Apollo 13 disaster, when NASA learned the life-threatening dangers of non-standardization. The crew had to use the Command Modules' scrubber cartridges to replace the ones in the Lunar module. Unfortunately, due to lack of standardization, the CM cartridges would not fit into the LM life support system (CM's were square, LM were cylindrical). They had to rig an adaptor out of duct tape and whatever else was on-board.
In the Space Shuttle, NASA moved to a Regenerative carbon dioxide removal system. Metal-oxide scrubbers remove the CO2 as before. But when they get full, instead of being replaced, they can have the CO2 flushed out by running hot air through it for ten hours. Then they can be reused.
Meteors are probably nothing to worry about. On average a spacecraft will have to wait for a couple of million years to be hit by a meteor larger than a grain of sand. But if you insist, there are a couple of precautions one can take.
For larger ones, use radar. It is surprisingly simple. For complicated reasons that I'm sure you can figure out for yourself, a meteor on a collision course will maintain a constant bearing (it's a geometric matter of similar triangles). So if the radar sees an object whose bearing doesn't change, but whose range is decreasing, it knows that You Have A Problem. (This happens on Earth as well. If you are racing a freight train to cross an intersection, and the image of the front of the train stays on one spot on your windshield, you know that you and the engine will reach the intersection simultaneously. This example was from Heinlein's ROCKET SHIP GALILEO.)
(Ken Burnside used this concept in his starship combat game Attack Vector: Tactical. From the point-of-view of the target, the incoming missile will hit if it stays on one bearing and does not move laterally. So a game aid called a ShellStar is used to detect the presence of lateral motion.)
The solution is simple as well, burn the engine a second or two in any direction (That was from Heinlein's SPACE CADET). One can make an hard-wired link between the radar and the engines, but it might be a good idea to have it sound an alarm first. This will give the crew a second to grab a hand-hold. You did install hand-holds on all the walls, didn't you? And require the crew to strap themselves into their bunks while sleeping.
Having said that, Samuel Birchenough points out that anybody who has played the game Kerbal Space Program know that an object that is not on a fixed bearing can still hit you. If your spacecraft and the other object are in orbit around a planet, the object's bearing will be constantly changing up to the last few kilometers before the collision.
What if the meteor hits the ship and punctures the hull? An instrument called a Manometer will register a sudden loss of pressure and trigger an alarm. Life support will start high-pressure flood of oxygen, and release some bubbles. The bubbles will rush to the breach, pointing them out to the crew. The crew will grab an emergency hull patch (thoughtfully affixed near all external hull walls) and seal the breach. A more advanced alternative to bubbles are "plug-ups" or "tag-alongs". These are plastic bubbles full of helium and liquid sealing plastic. The helium is enough to give them neutral buoyancy, so they have no strong tendency to rise or sink. They fly to the breach, pop, and plug it with quick setting goo. Much to the relief of the crew caught in the same room with the breach when the automatic bulkheads slammed shut.
Now you have some breathing space to break out the arc welder and apply a proper patch.
The emergency hull patches are metal discs. They look like saucepan covers with a rubber flange around the edge. They will handle a breach up to six inches in diameter. Never slap them over the breach, place it on the hull next to the breach and slide it over. Once over the breach, air pressure will hold it in place until you can make more permanent repairs.
Assuming Terra-normal pressure and density inside, and zero pressure outside, the effective speed of the air whistling out the breach works out to a smidgen under 400 m/sec. Veteran rocketeers, vacationing on Terra, tend to have a momentary panic if they feel the wind. Their instincts tell them there is a hull breach.
∂m/∂t = A * sqrt( 2 * P * rho )
- ∂m/∂t = the rate (mass per unit time) at which air leaks into vacuum
- A = Area of the hole it's leaking through
- P = Pressure inside the room far from the hole
- rho = density inside the room far from the hole
More simply, assuming Terra-normal pressure and density,
whooshTime = ( gaspFactor * vol) / holeArea
- gaspFactor = 1.4 for 80% pressure, 4.3 for 50% pressure, 29 for 1% pressure.
- whooshTime = time for cabin pressure to drop to specified fraction of
- initial value (seconds)
- vol = volume of air in the cabin (yards3)
- holeArea = area of the breach (inch2)
(equation from GURPS:Lensman)
So if a posh passenger cabin of 20 cubic yards has a one square inch hole blown in the bulkhead by a wayward meteor, the inhabitants have an entire 86 seconds (about a minute and a half) before the atmospheric pressure drops to one-half.
Somebody in a space suit doesn't have that kind of time. The suit has a volume of approximately 0.03 cubic yards. A hole a quarter inch in diameter has a hole area of 0.05 square inches. As long as the suit's air tanks can keep up the loss the pressure won't drop. But once the tanks are empty, the pressure will drop by one-half in a mere 2.4 seconds.
Does this mean that crewpeople in a combat spacecraft will do their fighting in space suits? Probably not, for the same reason that crewpeople in combat submarines do not do their fighting while wearing scuba gear. The gear is bulky, confining, and tiring to wear. They will not wear it even though in both cases the vessel is surrounded by stuff you cannot breath. They may, however, wear partial-pressure suits. Those suits will only protect you for ten minutes or so, but in exchange you won't be hampered like you were wearing three sets of snow-suits simultaneously.
Instead, the ship's pressurized inhabitable section will be divided into individual sections by bulkheads, and the connecting airtight hatches will be shut. The air pressure might be lowered a bit.
NASA assumes that each astronaut consumes per day 0.617 kilograms of dry food and 3.909 kilograms of potable water (some mixed in with the food). Astronauts also use 26 kilograms of water per day for personal hygiene.
NASA also assumes that each astronaut excretes 4.254 kg of water per day due to various metabolic processes. For details see below. Some of this water can be reclaimed.
Ken Burnsides and Eric Henry figured that each person has a reserve of 10 liters of water, and requires somewhere between 0.1 and 0.25 liters of water per day to make up for reclamation losses. (Eric used 0.1, Ken used 0.25 mostly due to having worked in a sewage treatment plant)
NASA assumes that each astronaut consumes per day 0.617 kilograms of dry food and 3.909 kilograms of potable water. The food is to have an energy content of 11.82 MJ per astronaut per day.
For food, Eric and Ken ran numbers from the USS Wyoming.
150 man crew, 90 day cruise, 31,500 kg of food (9,000 kg frozen, 18,000 kg dry, 4,500 kg fresh). This is about 2.3 kg of food per man per day.
Frozen meat has a density of about 0.35 and 0.4 (which Ken determined experimentally with a kilo of frozen meat in a 2 liter pitcher in his sink). Frozen veggies were less, so split the difference and use 0.375. 9,000 kg takes up 24,000 liters.
Fresh foods have a density of roughly 0.25, due to air packed around the food by the packaging. 4,500 kg takes up 18,000 liters.
Dry and canned goods range from densities of 0.25 for flour and bread and 1.0 for canned goods. Split the difference and use 0.5. 18,000 kilos takes up 36,000 liters.
Total volume is 78,000 liters, or 78 cubic meters of food (1000 liters = 1 m3). Assume that we're off on our calculations and round up to 80 m3 as a reserve.
Storage, including refrigeration wastage is usually three times the space, but the Navy has a tradition of doing things in amazingly tight quarters. So we will merely double it, for 160 m3 to store our food.
Add about 1000 liters of water (water for 150 crew for 90 days, plus a reserve) which of course masses 1000 kg.
Add about 3,500 liters of compressed air (0.2 liters per person per day for 90 days, plus a reserve for general pressurization and a 20% safety margin) which masses 1050 kg.
Together air and water add about 5 m3.
There are alternate figures on life support in this document. It specifies the daily requirements of consumables per person as: 0.83 kg Oxygen, 0.62 kg freeze dried food (which would increase to 2.48 kg when the water was added), 3.56 kg water for drinking and food preparation, and 26.0 kg water for hygiene, flushing, laundry, dishes, and related matters. Note that the value for hygiene water is somewhat dependent on technology — if you have sonic showers and the like the requirements may be less.
William Seney notes that the NC State document specify oxygen consumption figures differ considerably from Eric and Ken's estimate. If we assume their value should be 48L per HOUR instead of per DAY (1.38 kg / day) it is much closer.
When the body uses glucose the reaction is:
C6H12O6 + 6 O2 => 6 CO2 + 6 H2O
so a slight excess of water is produced. According to the NC State document this works out to about 0.39L per person per day, which may be enough to replace losses.
For a real Spartan bare-minimum cruise, you can probably use a figure of one m3 per person per day. But this would not be recommended for a cruise of longer than 20 to 30 days. Morale will suffer. And don't even think about feeding your crew food pills.
The bare-minimum of consumables mass looks like 0.98 kg water, 2.3 kg food, and 0.0576 kg air per person per day. About 3.3 kg total, round it up to 4. People actually need 2.72 kg of water, but since food is 75% water, it contains an additional 1.72 kgs.
Our 90 day cruise now has about 165 m3 of bare essentials. Put in niceties like better cooking gear, spare clothing, toilet paper, video games, soda, luxury goods, and you are probably getting close to 240 m3. That will fit in a sphere 8 meters in diameter (about 25 feet).
A useful accounting device is the "man-day" or "person-day". If your ship has 30 person-days of food and oxygen, it can support: 30 persons for 1 day (30 / 30 = 1), 15 persons for 2 days (30 / 15 = 2), 3 persons for 10 days (30 / 3 = 10), or one person for 30 days (30 / 1 = 30). By the same math, a ship with 30 person-days of supplies facing a 10 day mission could support 3 persons (30 / 10 = 3).
So if the exploration ship Arrow-Back becomes marooned in the trackless wastes of unexplored space and is listed as having 20 person-weeks of life support, it makes it really easy for Mr. Selfish to do the arithmetic and figure that he will survive for twenty weeks instead of one if he murders the other 19 crew members. More democratically, if the rescue ship will arrive in 8 days (1.14 weeks), one can calculate that the supplies will stretch for an extra day with 17 crew members (20 / 1.14 = 17.5, round down to 17). The crew draws straws, and the unlucky two who get the short straws have the opportunity to heroically sacrifice themselves so that the rest of the crew may live.
If the spacecraft has no artificial gravity, you'd better include lots of spices and hot sauce. As the body's internal fluids change their balance, crewmembers will get the equivalent of stuffy noses. This will decrease the sense of taste. Food will taste bland like it does when you have a head cold, and for the same reason.
You'll need more space if you want to include hydroponics for fresh veggies. Roughly 800 liters of hydroponics per person per 'green meal' per week. This also helps CO2 scrubbing and crew moral. About 20 m3 per 25 men, or 120 m3 for our 150 man crew. 3 green meals per week takes about 600 m3.
On the topic of human metabolic waste, NASA assumes:
|Waste per astronaut per day|
|Dry Feces||0.032 kg|
|Fecal Water||0.091 kg|
|Dry Urine||0.059 kg|
|Urine Water||1.886 kg|
|Dry Perspiration||0.018 kg|
An attempt should be made to reclaim the water. 4.254 kg of water per astronaut per day is too much to just throw away.
Male astronauts will use approximately 28 grams per day of toilet paper, minimum. Female will use 64 grams per day, because unlike their male counterparts, they wipe after urination. There will be about 5.1 grams per day of waste clinging to the toilet paper.
More toilet paper is required than is necessary under one gravity since in microgravity the fecal material has no particular inclination to separate from the body.
Women experience menstruation for 4 to 6 days occurring every 26 to 34 days. The total amount of menses is about 113.4 grams, of which about 28 grams is solids and the rest is water. This is highly variable. Approximately 104 grams of menstrual pads or tampons are consumed each period, again highly variable.
Female crew members on the International Space Station use medication to prevent menstruation for up to six months, but this may not be acceptable for longer missions.
Naoto Kimura mentioned that "Oh-gee Whiz" would be a good brandname for space toilet.
NASA allocates 26 kilograms of water per astronaut per day for personal hygiene.
Bath and showers are very difficult in free fall. The crew will probably be reduced to sponge-baths or maybe a shower while zipped up in a bag. In Robert Silverberg's 1968 novel World's Fair 1992 he mentions "sonic showers" which use sound waves to remove dirt with no water required. And in Andre Norton's space novels, the bathing room is called the "fresher".
People who have gone camping are familiar with how surprisingly difficult it is to keep clean in the absence of running water. As do city-folk living in houses near a water main break who have to make do without tap water for a few days. You tend to take for granted the luxury of accessing unlimited amounts of water out of the faucet. In the space environment, water is strictly limited, and what water there is performs poorly as a cleansing agent in free fall.
Crew will probably be required to take showers "navy style", since wet navy ships also have limited water (non-salt water at least). You turn on the shower water to get your body wet. You then turn off the water to conserve it while you lather up with soap. Then you turn the water back on to rinse off.
Keeping the habitat module clean is also a challenge. Water is limited, water does not clean things very well in free fall, and the limited atmosphere prevents one from using any alternate cleanser that it toxic or has a disagreeable odor.
And as mentioned elsewhere, any free floating garbage tends to accumulate on the air-intake vents. The vents on the Skylab space station quickly became quite disgusting with random bits of rotting food and dust particles.
NASA directs that the temperature inside a habitat module should be from 291.5 K to 299.8 K with the nominal temperature 295.2 K. That's 18.4°C ⇒ 22°C ⇒ 26.7°C in metric (and 65°F ⇒ 72°F ⇒ 80°F for those poor benighted folk still using Imperial)
NASA assumes that each astronaut emits 11.82 MJ of heat per day.
This is the job of the Spacecraft Thermal Control Systems.
Temperature inside the habitat module is prevented from getting too cold by hull thermal insulation (to prevent the internal heat from escaping), and by removing heat using heat radiators.
Temperature inside the habitat module is prevented from getting too hot by hull thermal insulation (to prevent heat from the sun from entering), and by adding heat from sources such as electrical resistance heaters.
Radiation shielding has its own separate page.
You want to limit the acute dose of radiation to under 0.1 Grays, and the astronaut career chronic dose to under 4.0 Sieverts.
What this boils down to is supplying the habitat module with a small radiation shielded room called a storm cellar or biowell. It will need radiation shielding to the tune of 500 grams per square centimeter of surface. Since this very expensive in terms of mass, storm cellars will be as small as the designers think they can get away with. With the restriction that all the crew has to physically fit inside, and they might have to shelter there for several days.
If the spacecraft has a fission, fusion, or antimatter power plant or propulsion system, it will require an anti-radiation shadow shield to protect the crew.
If the spacecraft is a combat spacecraft who will have to face radiation from nuclear warheads and particle beam weapons, it is going to require lots of very massy armor.
Supplying artificial gravity has its own separate page.
So far the longest any astronaut has been in microgravity has been 437 days. NASA limits astronauts on the International Space Station to 180 day visits.
The main effects seem to be severe osteoporosis, loss of muscle mass, anemia, weakened immune system, and an increase in eye pressure. NASA astronauts have to exercise two hours a day to combat osteoporosis.
It is unknown what the minimum amount of artifical gravity is required for health.
Remember the fundamental rule of rocket design: Every Gram Counts.
The spacecraft will have to lug along inconveniently large masses of air, food, and water so that the astronauts can live. And if the ship runs out while in a remote location, the crew will be reduced to a castaways in a lifeboat situation drawing straws to see who dies. With the added constraint that castaways in a lifeboat at least have unlimited access to breathable air. The fact that consumables run out at all will limit the duration of any given mission.
Which explains NASA's burning interest in Closed Ecological Life Support Systems (CELSS). In theory the only input such a system needs is energy, either sunlight or some power source to run grow lights. The advantages are:
- The astronauts will have air, food, and water forever (or until the equipment breaks down or the energy input stops)
- After a certain mission duration, it will be cheaper (in terms of mass) to use a CELSS instead of transporting consumables. With a primitive CELSS this happens at about 145 days, increasing the efficiency will bring the break-even duration point lower. The mass of the CELSS is constant regardless of mission duration, the mass of consumables goes up with mission duration.
The main functions of a CELSS are:
- Turn astronaut's exhaled carbon dioxide into oxygen
- Turn astronaut poop and table scraps into food
- Turn astronaut pee and washing wastewater into drinkable water
The current lines of research focus on doing this the same way Terra's ecosystem does: by using plants. In order to make the CELSS hyper-efficient they have to use hyper-efficient plants. Which explains the focus on algae.
There are two methods of cracking CO2 into C and O2: low energy and high energy.
Low energy requires prohibitive amounts of biomass in plants. Data from Biosphere II indicate roughly seven tons of plant life per person per day, with a need for roughly 4 days for a complete plant aspiration cycle, so call it 25 to 30 tons of plant per crewman. With an average density of 0.5, each ton of greenhouse takes up about 2 cubic meters (m3).
High energy methods take up much less space, but (as the name implies) requires inconveniently large amounts of energy. It also results in lots of messy by-products and waste heat. Practically, it is easier to flush the CO2 instead of cracking it, and instead bringing along an extra supply of water to crack for oxygen. Water is universally useful with a multitude of handy applications, and takes less energy to crack than CO2.
For future Mars missions, it has been suggested that the life support system should utilize the Sabatier Reaction. This takes in CO2 and hydrogen, and produces water and methane. The water can split by electrolysis into oxygen and hydrogen, with the oxygen used for breathing and the hydrogen used for another batch of CO2. Unfortunately the methane accumulates, and its production eventually uses up all the hydrogen. The reaction does require one atmosphere of pressure, a temperature of about 300°, and a catalyst of nickel or ruthenium on alumina.
For emergency use, it would be wise to pack away a few Oxygen Candles. These are composed of a compound of sodium chlorate and iron. When ignited, they smolder at about 600°C, producing iron oxide (rust), sodium chloride (salt), and approximately 6.5 man-hours of oxygen per kilogram of candle. Molecular Product's Chlorate Candle 33 masses 12.2 kilos, cylindrical can dimensions of 16 cm diameter x 29 height, burns for 50 minutes, and produces 3400 liters of oxygen.
In THE MILLENNIAL PROJECT, Marshall Savage sings the praises of Spirulina algae. However, you'd best take the following with a grain of salt. There is often a long distance between the ideal and the real.
Anyway, Spirulina is apparently almost the perfect food, nutritional wise. A pity it tastes like green slime (though Savage maintains that genetic engineering can change the flavor). Spirulina is highly digestible since it contains no cellulose. It is 65% protein by weight and contains all eight essential amino acids in quantities equivalent to meat and milk. It also has almost all the vitamins, with the glaring exception of vitamin C (I guess rocketmen will become "limeys" again). It is also a little sparse on carbohydrates. Savage calculates that it will be possible to achieve production rates of 100 grams (dry weight) of algae per liter of water per day. It breaks down 6 liters of algae water per person, supplying both food and oxygen, while consuming sunlight (or grow-lights), CO2 and sewage. 6 liters of algae water will produce 600 grams of "food" (540 grams is 2500 calories, an average daily food requirement), 600 liters of oxygen, and consume 720 liters of CO2 and an unspecified amount of nutrient salts extracted from sewage. Since food is generally 75% water, 600 grams of dry food will convert into about 2.4 kg of moist food, which compares favorably with the 2.3 kg on the USS Wyoming.
NASA commissioned a study back in 1988 to determine how difficult it would be to cultivate Spirulina as part of a closed ecological life support system.
Dr. John Schilling mentions a possible pitfall:
There are other things you have to be mindful of when cultivating Spirulina. From the Swedish Medical Center:
SF writers with an evil turn of mind will see some interesting plot possibilites in these facts. The ship's food supply could become contaminated by an incompetent repair of the algae system utilizing lead pipes, an algae culture supplier with poor quality control, or deliberate sabotage.
The advantage of algae is that it can theoretically form a closed ecological cycle. This means that 6 liters of algae water, one human, some equipment, and sunlight can keep the human supplied with food and oxygen forever. Theoretically, of course. 0.006 m3 per person compared to 90 m3 per person is a strong argument for lots of green slime dinners for enlisted Solar Guard rocketmen. (Astro once said "I've been eating those synthetic concentrates so long my stomach thinks I've been turned into a test tube") Of course the Biosphere II fiasco shows how far we are from actually achieving a closed ecological cycle. Don't forget the 0.25 liters of water per person per day to make up for reclamation losses.
William Seney points out that as a luxury, some of the algae can be diverted to feed fish such as carp, catfish or tilapia for an occasional treat.
And you'd better keep the algae tanks far from the atomic drive. The last thing you want is for the little green darlings to mutate into something you can't eat. Or worse: something that is really inefficient at producing oxygen.
Christopher Huff begs to differ:
There were some figures in a report on a cruder life-support set up written in 1953. This used Chlorella algae, which isn't quite as good as Spirulina since it has an indigestible cellulose cell wall. The figures assume a Chlorella culture density of 55 grams per liter of water and a daily yield of 2.5 grams per liter. Savage's 100 grams per liter sounds a little optimistic, and 2.5 sounds a little pessimistic. The truth is probably somewhere in between.
At a yield of 2.5 g/l, to provide one rocketeer with 500 grams of food (instead of Savage's 600 grams) will require 200 liters of algae culture.
Urine is passed through an absorption tube to remove excess salt (which would kill the algae) but retaining urea and other nitrogen compounds the algae needs. Faeces are irradiated with ultraviolet to kill all bacteria and added to the urine. This is fed to the main algae tank along with pressurized carbon dioxide (previously removed from the air with calcium oxide). A pump sends a flow of algae culture to the growth trays under filtered sunlight. The culture then passes through a centrifugal separator on its way back to the main tank. The separator performs two functions:  removing excess gas to maintain a pressure equilibrium with the carbon dioxide injection and  periodically harvesting algae for food. Harvest will occur once a day, extracting 500 grams of algae from nine liters of culture per person. The pump will be controlled such that the algae on the average will experience two minutes of sunlight then three minutes in the darkness of the main tank before it starts the cycle anew.
A fresh batch of urine and faeces is added immediately after algae harvest, to give the algae twenty four hours to consume it. So by next harvest there is no human excretions contaminating the food (you hope).
Now for the answer you've been waiting for. Dr. Bowman estimates that the equipment will mass approximately 50 kg, plus 200 kg per man for algae culture. Since the equipment is such a small fraction of the total, mass savings depend upon getting the algae yield higher than 2.5 g/l. Such as Savage's 100 g/l Spirulina with 6 kg per man of algae culture.
Dr. Bowman points out that when one compares an algae system with merely stocking crates of food, the break-even point occurs at a mission of 145 days (about five months). Below this time it takes less mass to bring crates of food, as the mission duration rises above 145 days the algae tanks get more and more attractive.
You can find more interesting reading on the topic of life support here.
In NASA jargon, a closed environment life support system based on algae is called a "yoghurt box", one based on hydroponic leafy plants is called a "salad machine", and one based on a fish farm is called a "sushi maker".
Wastes have to be fed to the algae. But it would be nice to turn the astronaut poop into sterile chemicals first instead of infecting the algae tanks with E. coli bacteria. Not to mention the problem of reducing the useable form plant stalks, fish bones, chicken feathers, and other tough scraps. Not to mention all the plastic bag bits.
Enter the Supercritical water oxidation (SCWO) unit.
By placing water at temperatures and pressures above the thermodynamic critical point, it turns into a fluid that combines the worst properties of a blast furnance and sulphuric acid. You feed anything into one of these hellfire-in-a-box thingies and nothing is going to come out the other end except water, oxidized chemicals, and mineral ash. This happens at about 374.1°C and 22.12 Mpa.
The only estimates I've managed to find (Parametric Model of a Lunar Base for Mass and Cost Estimates by Peter Eckart) for a SCWO unit are:
- Mass: 150 kg per person being supported
- Expendibles required: 10 kg per person per year
- Volume: 0.5 m3 per person
- Power required: 0.36 kilowatts per person
- Heat load: 0.09 thermal kilowatts per person
- Liquid waste input: 27.18 kg per person per day
- Solid waste input: 0.15 kg per person per day
Waste products from the astronaut's septic tanks and tablescraps are run through the SCWO. The appropriate output chemicals are fed to the Spirulina., which multiplies in meters of transparent tubes run under filtered sunlight. Filtered because raw sunlight in outer space is quite deadly to algae, and it isn't too healthy for humans either.
There is more information on SWO units here. The first reference describes a facility with a volume of just over 20 cubic metres that can process 7.5L per minute, more than enough for a crew of 300. (30L/person/day - 20 hours a day). Thanks to William Seney for these link.
General Atomics has some developed some SWO units for waste disposal.
Other SF novels have suggested vats of yeast or tissue cultures of meat ("carniculture") to supplement food supplies. But unless they can re-cycle wastes from the crew, it seems more efficient to just carry more boxed food. Currently scientist can only grow tissue cultures as a single sheet of cells, making them thicker will require figuring out how to make them grow blood vessels to nourish all the cells. But some technicians figure that they can grow lots of meat cell sheets, then laminate the sheet layers together to approximate a slab of meat.
If you are trying a closed cycle with tissue cultures, you will have to deal with the problem of the Food Chain. Typically each higher level of the pyramid has one-tenth the biomass of the one below, for reasons you can read about in the link. What this means is that you will have to feed ten meals worth of algae to the meat tissue culture in order to produce one meal worth of meat. Even on Terra, this is the reason why meat is more expensive than vegetables.
Obviously the food chain effect also applies to diverting some of the algae to fatten up some fish as a special meal.
"Chicken Little" is a chicken breast meat tissue culture.
A shmoo is a fictional cartoon creature created by Al Capp, they first appeared in his classic comic strip Li'l Abner in 1948. Shmoos were prolific, required no food (only air), are delicious and nutritious, have no bones or other waste, and are eager to be eaten. (Ironically, they are the greatest menance to humanity ever known. Not because they are bad, but because they are good.)
Oddly enough, shmoos share many common traits with one-celled yeast. Yeast even looks a little like a shmoo. When a yeast cell senses the mating pheromone, it initiate polarized growth towards the mating partner, creating the characteristic outline of a shmoo. The process is called "shmooing", which shows that biologists have a sense of humor. As to the matter of the deliciousness of yeast, see the exerpt from Lucky Starr and the Oceans of Venus below.
The space environment is so inconvenient for human beings. There is so much that one has to bring along to keep them alive.
Life Support has to supply each crew member daily with 0.0576 kilograms of air, about 0.98 kilograms of water, and about 2.3 kilograms of (wet) food (less if you are recycling). Some kind of artificial gravity or a medical way to keep the bones and muscles from wasting away. Protection from the deadly radiation from solar storms and the ship's power plant and propulsion system. Protection from the temperature extremes in the space environment. Protection from acceleration. Medical support. And then there are the psychological factors.
Recently John Lumpkin and I were allowed the rare privilege of submitting questions to NASA astronaut Captain Stephen G. Bowen a couple of questions about life in the space environment.
The ability to put crew members to sleep for months at a time would be an awfully convenient thing to have. Such crew members would use air and food at a much reduced rate and would not be prey to interplanetary cabin fever or space cafard.
Hibernation or "cold-sleep" would mimic what bears and squirrels do in the winter. The crewmember would sleep and breath slowly. Food would be administered by an intravenous pump or the body's internal fat could be used. The crew member still ages, abet at a slighly slower rate.
Suspended animation, cryo-freeze, or cryogenic suspension is more extreme. The crewmember is frozen solid in liquid nitrogen. They do not breath, eat, nor age. Special techniques must be used to prevent the ice in the body's cells from freezing into tiny jagged knives shredding the organs. This is naturally more dangerous than mere hibernation. It is generally used for slower-than-light interstellar exploration, or to put a crewmember with an acute medical condition into stasis if the ship cannot arrive at a hospital for some months.
Hibernation was shown in the movies Alien, 2001, and 2010. In William Tedford's Silent Galaxy AKA Battlefields of Silence, interplanetary fighter pilots would sometimes find themselves out of fuel and on trajectories that would take years to return to a spot where they could be rescued. They would use hibernation to stretch their consumables and to sleep the time away.
Poul Anderson noted that there is probably a limit to how long a human will remain viable in cryogenic suspension (in other words they have a shelf-life). Naturally occuring radioactive atoms in the body will cause damage. In a non-suspended person such damage is repaired, but in a suspended person it just accumulates. He's talking about this damage happening over suspensions lasting several hundred years, during interstellar trips. This may require one to periodically thaw out crew members and keep them awake for long enough to heal the damage before re-freezing them.
Hibernation and suspension is often encountered in SF novels where large numbers of people have to be shipped, e.g., troop carriers, slave ships, and undesirable persons shipped off as involuntary colonists to some miserable planetary colony. Some passenger liners will have accomodations of First-class, Second-class, and Freeze-class (instead of Steerage). There is often a chance of mortality associated with hibernation and suspension. In some of the crasser passenger ships there will sometimes be a betting pool, placing bets on the number of freeze-class passengers who don't make it.
There are some maladies that afflict people who spend prolonged periods in microgravity, exposed to space radiation, and exposed to radiation from nuclear propulsion. These could be characteristic signs of space traveling old-timers.
The most obvious effect of microgravity is the astronaut's muscles atrophy and the shedding of calcium by their bones (1% to 1.5% per month, like osteoporosis). Being weak with brittle bones isn't lethal but presumably the astronauts at some point want to return home to Terra and still be able to walk. Science fiction literature is full of mandatory exercise to combat this, with "exercise credits" awarded for time spent under acceleration and in centrifuges. NASA astronauts on the International Space Station have to exercise two hours a day for this reason. Some astronauts (or colonists of low gravity planets and moons) might require man-amplifier prosthetics in order to walk under a full Terran gravity.
Naturally such space osteoporosis can lead to kidney stones, the agony of which is the closest a male will ever come to the sensation of giving birth. Space osteoporosis can also be combated by exercise.
Astronaut's eyes are especially vulnerable. Recently NASA made the horrible discovery that exposure to microgravity for six months or longer causes permanent damage to the eyes, similar to idiopathic intercranial hypertension. There is some evidence that this is due to enzyme polymorphisms that increases astronaut vulnerability to bodily fluid shift in free fall.
Don't forget that astronauts who eat more than fifty grams per day of spirulina algae from your closed ecological life support system, they run the risk of developing gout. That could be Old Poor Astronaut Syndrome.
And a science fictional favorite is the microgravity adapted astronaut who when on Terra has a tendency to let go of glasses of water in mid air, expecting them to float.
The two main effects of radiation on an astronaut are  cancer and  death by radiation sickness. You are unlikely to encounter an old astronaut suffering from  unless you like to visit graveyards. But the probability is high that most old astronauts will have undergone treatment for cancer at one time or another. Probably several times. NASA tries to avoid this by ensuring that there are no old astronauts. NASA has strict career limits on astronaut radiation exposure.
Secondary effects of radiation are skin ulceration and blindness due to cataracts scarring. High-mass, high-charged (HZE) cosmic rays might accelerate the development of Alzheimer's disease. Radiation also lowers the immune system (chromosomal aberrations in lymphocytes), but it can recover.
Atomic rocketeers on board an atomic rocket will also without fail have a package of potassium iodide tablets on their persons at all times. Why? If the reactor core is breached, the mildly radioactive fuel and the intensely radioactive fission fragments will be released into the atmosphere. While none of the fission fragment elements are particularly healthy, Iodine-131 is particularly nasty. This is because ones thyroid gland does its level best to soak up iodine, radioactive or not. Thyroid cancer or a hoarse voice from thyroid surgery might be common among atomic rocket old-timers. The tablets prevent this by filling up the thyroid first, before the Iodine-131 arrives. The instant the reactor breach alarm sounds, whip out your potassium iodide tablets and swallow one.
Space Adaptation Syndrome aka "drop sickness" is a kind of motion sickness caused by weightlessness. Outer space sea-sickness, so to speak. Symptoms include dizziness, fatigue, nausea, vomiting, and an inability to care about anything but your own private world of pain. The joke is drop sickness makes you feel like you are going to die, and you are actually looking forwards to it.
About half of new astronauts suffer from drop-sickness when they first travel into space. Of those who suffer, 50% have mild symptoms, 40% have medium, and 10% have severe. The most severe that NASA ever recorded was that of Senator Jake Garn in 1985. They jokingly use the "Garn scale", where 1.0 Garn is the worst.
Drop sickness usually goes away after two to four days exposure to free fall. Occasionally there is a relapse, which can happen at any time. When suffering from drop sickness, be careful not to rapidly turn or shake your head. This will make the fluid in the inner ear slosh and make things much worse.
Novice NASA astronauts do not take motion-sickness medication on their first trip into orbit. It is considered better for them to be miserable for a day or two but actually adapt to become immune. This is also the reason NASA never schedules EVAs for the first two days of a mission.
Having said that, NASA astronaut always put on a transdermal dimenhydrinate anti-nausea patch when suiting up in a space suit, because throwing up inside a suit can be fatal. A little dramamine is much better than suffocating to death in a vomit-filled helmet.
Drop sickness can be avoided if the spacecraft or station has artificial gravity, though that creates more problems.
Several SF novels point out the dangers inherent in cooping up people in a tin can surrounded by vacuum for months at a time. They will be prey to "space cafard" (i.e., deep space cabin fever, what the French Foreign Legion called "the beetle"). The only solutions seem to be [a] put them in the suspended animation freezer, [b] drug them, or [c] keep them busy, busy, busy! (a bi---, er, ah complaining spacer is a happy spacer) The first officer can assign some worthless busy-work, like a once daily nose to stern ship inspection for micro-meteor holes. One might think that the same problem would be faced by the crew on a military submarine, but as it turns out the analogy is inexact. Christopher Weuve says:
A more constructive approach (for officers) is a huge stockpile of study-spools and daily home-work in such topics as higher mathematics, astronavigation, and nuclear physics. Plus other non-space related subjects just to keep the mind flexible. There will also be an active schedule of cross-training, e.g., the astrogator learning how to maintain an atomic drive unit. You never know when knowledge of a job outside of your specialty could prove vital in an emergency.
And the sergeant in charge of the enlisted men will have to know when to turn a blind eye to the home-made moonshine "still" hidden on Z deck and the floating poker and dice games. Gambling and rocket-juice will combat boredom. As will other forms of recreation.
In the anime Planetes, they recognize the fact that having male and female crew members cooped up in close quarters for weeks at a time can cause certain tensions. When stocking a spacecraft for a mission, one officially required item is a selection of erotic magazines. This allows the crew members to take care of the problem in solitary fashion.
Obviously there are problems with confining too many astronauts in a too-small habitat module for prolonged periods of time with not enough sleep and practically no privacy. Add pressure from ground control to work the astronauts to death coupled with boredom and you have a real recipe for blood floating all over the module. At least in an Arctic research station a researcher close to snapping can step outside for a breath of fresh air. Not so the astronaut
Cosmonaut Valery Ryumin, twice Hero of the Soviet Union, quotes this passage from The Handbook of Hymen by O. Henry in his autobiographical book about the Salyut 6 mission: “If you want to instigate the art of manslaughter just shut two men up in a eighteen by twenty-foot cabin for a month. Human nature won't stand it.”
This was sort of hinted at by the 1999-2000 Russian Sphinx-99 experiment. This enclosed six crewmembers in a simulated space station for six months. About two months into the experiment there was a bloody fist-fight between two of the Russian crewmembers. Shortly thereafter the Canadian female crewmember (Dr. Judith Lapierre) was dragged off camera by the Russian commander and forcibly french-kissed despite her vigorous protests. In two separate incidents.
And then there is the Break-Off effect. This was first reported before the dawn of space travel, by high altitude military airplane pilots. It was a type of psychological dissociative anomaly, a feeling of detachment. Most pilots felt peaceful, a few euphoric, and about a third were panic-stricken.
It was thought this would also happen with astronauts. But in the 1970's when cosmonauts and astronauts actually started flying the problem seemed to disappear.
It wasn't until recently that it became clear the Break-Off effect did not disappear in astronauts. What disappeared was the astronauts reporting it. Astronauts are in constant terror of being grounded, so they developed a "lie to fly" culture. The last thing they are going to do is report to the flight surgeons some scary mental breakdown that will get them grounded faster than a teenage girl staying out five hours past her curfew.
During the Apollo missions, some astronauts reported how the vision of Earth as the big blue marble caused a sudden cognitive shift in awareness. They suddenly saw Earth as a fragile ball of life where national boundaries became unimportant. A writer named Frank White coined the term The Overview Effect, and wrote a popular book on the topic in 1987. You can find some quotes about the effect here.
And there are some psychologists who suspect that the Break-Off Effect and the Overview Effect are one and the same.
A NASA technician said "If you treat vacuum as you would poison gas you won't go far wrong."
How does space kill you? Let me count the ways. Face it, the human body was not designed to properly function in the vacuum of space. At a rough guess a person can survive space exposure as long as they are placed back inside a pressured atmosphere within 90 seconds. After that time, death might be unavoidable. You will only have about ten seconds before you become unconscious. Dr. Geoffrey Landis has an analysis here. There are some more links on the topic of explosive decompression here.
And anybody who's seen 2001 A Space Odyssey knows that a human exposed to vacuum is not going to pop like a balloon.
In order of lethality the effects are:
If you take glass of water, and lower the air pressure, the temperature point at which the water boils is lowered as well. This is why cake mixes have high altitude instructions: the watery part has a lower boiling point/maximum temperature than normal so it takes longer to cook. If you are living in a habitat module with a pure oxygen breathing mix, the pressure will be at about 32.4 kPa (80% normal Terran atmospheric pressure). Here too the cake mixes will take longer to cook since water boils at 70° C, and your tea will always be lukewarm.
What I am leading up to is the Armstrong Limit. You see, if the pressure drops to 6.3 kPa, water will boil at 37° C. Which just happens to be normal human body temperature. The saliva will boil off your tongue, the tears will boil off your eyes. If you become so frightened that you pee in your pants, that will boil as well. The same goes for poop but that's a horrible image I just don't want to think about.
The blood will boil in your veins too, were it not for the fortunate fact that your skin will pressurize your vascular system enough to prevent that unhappy state of affairs. This is why soft suits can get away with not pressurizing your body.
Naturally astronauts will not commonly be constantly exposed to 6.3 kPa. Much more likly they will briefly encounter it as the pressure plummets to zero kPa, as all the breathing mix goes rushing out a deadly tear in their space suit or a major breech in the hull of the habitat module.
But in any event if your saliva starts to boil, be aware that you have only ten seconds to get to safety before you lose consiousness, and 80 additional seconds for your buddies to drag you into somewhere pressurized before you die. Be quick or be dead.
A morbid but necessary fixture that nobody talks about will be the "C-Chute" (from the Isaac Asimov story with the same name). "C" is short for "Casualty". A dead body will quickly contaminate the air of the lifesystem, so there has to be a way to jettison the dear departed. Also of concern is the effect on crew morale. Personnel will be prone to morbid thoughts while their crewmate(s) mortal remains are lying in the next cabin. There will probably be a tradition of laying the dead to rest within twenty-four hours of death.
It will be important to have an already established protocol for laying the dead to rest. In the movie Conquest of Space they did not have such an established protocol, and the results were ugly. During an EVA astronaut Andre Fodor is killed by a meteor. Not knowing what to do, they leave the body out there still on the safety line.
You can see the surviving crew start to freak out as they try to ignore their dead friend floating outside the porthole. Finally one of them cracks and starts to scream at the body. That's when the captain suddenly wakes up to the vital necessity of laying to rest the dear departed. Say a few words, and push the body off into space. Don't bother trying to push it into collision course with the Sun, it takes far too much delta V and if the course is only a tiny bit off the body will just sling-shot around and head off to the Oort cloud.
Somebody suggested using the spacecraft's rocket exhaust to cremate the body. Tuyu explains why this is not a good idea: