Maio 10, 2006
On June 3, 1965, Edward H. White stepped outside his spacecraft and let go. Twenty-three minutes later, when he was ordered to reenter his Gemini capsule, he said, Its the saddest moment of my life. After paying a small fortune to reach one of the most spectacular places in creation, with the experience that enthralled astronaut Edward White at arms length, few will be content to look through a small window and stay inside!
It is no surprise that NASA and other serious space agencies dont focus on or facilitate extra vehicular activity (EVA) work (or play!) Many sailors cant swim, and submarines dont normally carry SCUBA gear. It takes a different attitude to want to face a novel environment with minimal equipment, and a different mindset to master its challenges.
SCUBA diving has become a large and important business, particularly at the Caribbean resorts. But this would never have happened if the undersea gear described by John D. Craig in his 1938 book Danger Is My Business remained the standard. The traditional Hard Hat diving dress, with its pumps and hoses, was awkward to use and dangerous. Many dangers were caused by the system itself and only partially eliminated by upgrades. Jacques Cousteau had a better idea, and launched the affordable systems used by recreational divers today.
Going outside in space will not be done by the untrained. But you dont survive SCUBA diving without proper preparation and training either, yet millionsof all ageshave completed certification training. Space EVA is in almost all ways safer than SCUBA diving. Admittedly, both hypothetical and historic problems need to be addressed before this fact can be accepted, which this article will do.
Consider, for starters, that visibility underwater is seldom more than ten meters (and no more than that for one swimmer trying to find another on a choppy surface). In a few seconds, a buddy can be lost with no references or communication. In orbital space you will actually be visible for hundreds of thousands of meters, with flawless communication and differential GPS position data accurate to less than a centimeter. You face no unexpected currents, no unknown obstacles, and no sharks!
Next, get rid of the idea that one slip will cause you to drift away into space. That is more or less true in interplanetary space, but not in low Earth orbit! You wont drift very far, even if you try, and cant hide from those who are prepared to bring you back. If you jump off a space stationlet alone slip off a handholdyou place yourself in an independent orbit which will intersect the spacecraft orbit once or twice every 90 minutes. An energetic jump could carry you three kilometers away before you find you are cycling back again as if you are personally attracted to the space station. When you realize that one liter of liquid oxygen can supply your needs for 48 hourstwo full daysyou can relax and wait for help. Multiple tiny radio transmitters are sufficient to monitor your condition and motion while the lifeguard prepares to pick you up.
The lifeguard, as mentioned, relates to a historic problem. If one plans on minimal EVA, then little is spent on facilities or training to make it safe and easy. If it is highly desirable (like swimming at a beach resort) a modest expense for personnel, facilities, and training can make it a safe and economical activity for hundreds of visitors. In this case, automatic monitoring and even retrieval using remote control are feasible.
Space is, of course, not cold. The deep oceans are coldnear freezing with the high heat conductivity of water sucking heat from divers. Mountaintops are cold, with frigid air, wind chill to augment heat loss, and snow and ice waiting to capture large quantities of heat. None of these are present in space, and sunlight is predictable. Space blankets (the thin aluminized plastic film) work really well in space and transform a user wrapped in one into a virtual Thermos bottle. A human wrapped in such a blanket, in space near Pluto, would overheat from his own metabolic heat production and need to unwrap part of his body. White paint (for maximal cooling), black paint (to capture sunlight), and the space blanket provide tremendous power to control temperature in space, with predictable performance.
Meteor impacts are for fiction. An online NASA article (Impact Damage of LDEF Surfaces) treats a 0.7-mm aluminum sphere (the size of a poppy seed) as a typical dangerous impactor. At 10 kilometers per second this can penetrate spacecraft walls 2.5 mm thick, not as a deeply-penetrating super bullet but by producing a 5-mm diameter, hemispherical crater which will break through at the bottom when the impactor, and a larger portion of the target, are vaporized. A larger particle can punch a clean hole through this thickness of material, or leave a proportionally larger crater in thicker material. Seven such objects walloped the large LDEF satellite during its 5.75-year mission. (Plastic materials dont seem to be more deeply penetrated.) A thinly-clad space diver could have such an object take a pea-sized bite out of his flesh once in 700,000 hours of EVA. Few of these would be life-threatening, even without helmets and other protection.
The largest damage crater to be expected for a human-sized target in 10,000 EVA hours would be less than 1 mm diameter (and 0.5 mm deep): at worst a painful bug bite, unless stopped by clothing 0.5 mm thick. Everyone who steps out onto a terrestrial beach faces far greater hazards.
Radiation is possibly worse (in effect, but not in intensity) in orbit compared to exposure in a high-flying aircraft or on a mountaintop, but astronauts are not conspicuously impacted by it. Solar flare radiation storms are the exception, but are far rarer than terrestrial stormsjust stay inside.
EVA has earned the reputation as a difficult exercise, to be avoided whenever possible. Part of this results from poorly-designed equipment, resembling antique diving gear. It works, as did the old diving dress, but it can be improved. A greater part of the difficulty results from procedures and systems designs.
Considering the difficulties created by high air pressure and nitrogen gas, it is astonishing that NASA elects to maintain sea-level pressure, 21 % oxygen conditions in the ISS. The obvious reason is so that any and all fire safety and medical questions could be sidestepped, with normal air supplied. This does not eliminate fire dangers, and only swaps one set of medical problems for another, but it can be used to end discussion of these issues.
Less political organizations can take a different approach. Note that a great many people live in reduced pressure (few in fact live at sea level, most are hundreds or thousands of feet above this altitude). Twenty million live in Mexico City, about 2.4 kilometers above sea level, with 28% less atmospheric pressure. Airline passengers handle 24% to 36% reduction in air pressure routinely. More than 200,000 people live in Lhasa, Tibet at 3,800 meters, with 42% less than sea level air pressure. And regular trucking and bus transportation flows over Karakoram Pass, at 5,575 meters with less than 50% of sea level air pressure.
It does in fact take several days to prepare people to handle the lowest of these pressures and function well in them. Yet more than a few days are presently spent preparing people to fly into orbit and this will remain true for a number of years. Virtually no time is spent preparing to ski in Vail or Breckenridge Colorado, where the upper bowls approach 4,000 meters. This is several hundred meters above the level where the FAA requires oxygen masks, but skiers never wear them. One night is often preparation enough to face the 40% reduction in air pressure.
The problem is that while spacesuits with 3.5 psi pure oxygen are practical and easy to work in, suits pumped to 15 psi are nearly as rigid and inflexible as automobile tires. The 3.5-psi oxygen, as used in Mercury, Gemini, and Apollo spacesuits, is more than enough for respiration. However, when one transitions from normal atmospheric pressure to low pressure, all the nitrogen dissolved in the body and blood tries to bubble out like the CO2 in warm champagne. This causes the painful, and potentially fatal, divers bends, also known as Caisson Disease (from underwater tunneling). To avoid this, one has to breathe pure oxygen for hours before going into the lower pressure. Oxygen also dissolves in fluids, but is rapidly consumed by the body. The nitrogen goes nowhere unless it is gradually transferred to the lungs and breathed out. This transition is complicated by the fact that breathing pure oxygen at 14.7 psi can cause oxygen toxicity, including convulsions. Too much causes one problem, too little causes another.
A quick fix is to pretend that you are a skier and get used to 60% air pressure. At this pressure oxygen toxicity never happens, and you can breathe pure oxygen all day (and probably for years: many people breathe enhanced medical oxygen for a very long time). Such a procedure is being tried by NASA on the ISS, but not by reducing the stations air pressure. Rather, astronauts are camping out in the airlock, where they can breathe reduced-pressure oxygen overnight in preparation for EVA. It doesnt take a rocket scientist to see that there are better approaches when one is designing an orbital resort.
On the other hand, one admittedly cant learn to swim in space. With training, the useless floundering of a neophyte in water can be turned into useful propulsion. The addition of swim fins makes this a lot more efficient, and these are standard for divers. But training or simple aids wont help in space at all. It takes a really sophisticated piece of hardwarea can of Dust-Offto produce useful results. I expect that maneuvering with these, and more powerful hand-steered thrusters, will become a popular sport. Spare cans guarantee that the user wont be helpless. Yet even these simple systems will require training.
The neophyte will be aided by automatic systems. Tumbling can be stopped by the user himself with a panic button, or by a lifeguard by radio control. The reaction jets can use a small cylinder of CO2, mini-valves, and the gyro system from a stabilized camcorder. To be maximally effective, the user must be trained like a skydiver to assume a spread eagle position whenever tumbling may be a problem. This position minimizes rotation (the opposite of a skaters tuck to accentuate spinning) and it positions wrist and foot reaction jets for maximum effect. A lifeguard, notified by computer monitors, could shut down the neophytes manual controls, stop his tumbling, and bring him slowly back to the station by radio controlwhile speaking reassuring words.
The ability to execute graceful swoops and turns near a space station is akin to three-dimensional skiing, which at its best includes seemingly effortless sweeps of motion. In this case the snow-covered mountains are replaced by the face of a planet rolling past and framed by the black of space. For that half of each orbit in darkness, cities and highways on Earth sparkle and glow with lights, and behind the space station, with its luminous strips, the stars shine without blinking. Weightless play is fun, but the walls keep getting in the way. The human spirit longs to soar! Few will be able to resist innovative expression in dance which ballet can only approximate. Going inside will be a sad time, as it was for astronaut White, but these tourists can look forward to their next time out.
Richard Speck is president of Micro-Space, Inc.