I always thought the airlock doors on Star Trek: Deep Space Nine were pretty cool, kind of steam punkish with their great big gear teeth in the age of warp drives and teleportation. Yesterday, since I was feeling under the weather, I amused myself by thinking about how they might work. Since you have these great big gear teeth, and since the doors rotate as they are opening or closing, you might think those gear teeth have something to do with how they operate. You could control the motion of the door with a two racks, one on the top and one on the bottom, like so:
To roll the door into the closed position, the bottom rack would stay fixed and the top rack would move. Once the door was in position, both racks would move in opposite directions to spin the door. I'm thinking there would be a screw thread around the outside of the door that would be used to firmly clamp the sealing surface. This could work. You would need something to get the threads started. Careful positioning of the start of the threads might be all you need, and since the door is captive and isn't going anywhere besides back and forth in its slot, it should be reliable.
However, the racks will need to be quite long. They would need to be twice as long as the door is wide. In addition, the top rack would need to travel twice the width of the door so it would need a space four times as long as the door width. That might be okay on a giant space station, but it would be problematic on something smaller like a space ship.
One way to make it more compact would be to have three motors with pinion gears spaced equidistantly around the circumference. The motors would be mounted on slides. We wouldn't need to actually spin the door until it was in position to close, but it wouldn't hurt.
This isn't the best video, he doesn't really spend much time on what SpaceX is likely to do with their Starship, but there is a load of good background information.
Emergency Training Averts Airlock Disaster on MIR Science Channel
There isn't much to this video, but it gives you a sample of how, when small things go wrong they can leave you in the lurch. You should probably be brushing up on your Russian. Even if you don't go to space, it can help you with negotiating bribes and/or defending yourself against criminal charges in Congress.
I've been thinking about long term survival in outer space and now I'm thinking about how our exploration / exploitation of the moon might proceed.
There was an episode of Star Trek (at least I think it was Star Trek) wherein we are told the story of a colony that was established on a planet and due to some misfortune they ran short of supplies. A relief mission was sent, but failure to communicate meant the colony believed it would not arrive soon enough to save them. The leader of the colony then caused half of the colony to die which meant there were enough supplies for the remaining people to survive. Shortly thereafter the relief mission arrived, which meant the leader was pilloried as a mass murderer. If the relief mission had been delayed as expected, he would have been lauded as a hero for saving half of the colony.
I think it was an episode of Star Trek, it was a long time ago and my memory is a little fuzzy about the details, but it brought home to me the idea of how dependent space travelers are going to be on their space ship. Earthbound explorers always had air to breath, and if you were on land you could generally find water to drink. Food can be problematic, but is often obtainable. Space travelers need to ensure they have an adequate supply of all three because there isn't going to be any air, water or food wherever they are going.
If we are going to establish a base on the moon, we are going to want to construct a factory for producing rocket fuel. I don't know how that will go, maybe some whiz kid will come up with a fancy probe they can jam in the ground and with a proper application of electricity will produce oxygen or methane directly from moon rocks. I suspect it will probably be more like earth bound mining operations: skip loaders driving around on the surface, picking up loads of rocks and carting them back to the big rocket-fuel-making-machine. Wheeled machines will no doubt need to be brought 'inside' occasionally for repairs and maintenance. To do this, we are going to need an airlock.
Now the maintenance garage could act as airlock, but it means that every time anyone comes in or goes out, all the air will have to pumped out of the garage, which would take some time. Even if we could generate enough air from moon rocks, it wouldn't be prudent to just vent the whole shop's atmosphere. You might need that air.
So I am proposing a tunnel of airlocks. Each segment would be maybe one hundred feet long with a door at each end. The doors would be like conventional garage doors so that would take up the least amount of space inside the tunnel. The one hundred foot length would allow the skip loader to drive along slowly while the doors closed in back and opened in front. Each segment would be kept at a pressure that was one PSI below the previous segment. When you open the door between two segments with a difference of one PSI, there is not going to be a whole lot of air moving from one chamber to the other. Even if they were to completely equalize during the time the door is open, it is not going to amount to a great quantity of air.
When you get to the last chamber the air pressure will be somewhere between one and two PSI, which is not very much. If you can afford to vent that small quantity of air to the vacuum, you can dispense with the vacuum pumps you would need to evacuate that last chamber, and since the chamber is fairly large and pressure is already so low, it would probably take a very long time, time when the skip loader could be working.
So the tunnel would 1400 feet long, You might be digging it through rock, or you might make it out of plastic and erect it on the surface, or you might use a combination of both. I'm thinking any kind of substantial moon base would need to be inside one of those lava tube caverns that might be lurking below the surface. Being underground would protect you from radiation. You are going to need a tunnel to get to the surface. If the cavern could be sealed, and you could make enough air, you might possibly be able to pressurize the whole cavern, a cavern big enough to build a city. In any case, you could use an similar airlock tunnel just to carry personnel and supplies between the cavern and the surface.
P.S. Evidently, the meaning of the term 'skip loader' has changed. I ask YouTube for 'skip loaders' and I get pictures of tractors equipped with a back hoe and front end loader. To me, a skip loader has four large wheels and a large shovel on one end, much like the machine in the video. Normal skip loaders are taller, the one in video has been squashed so it will fit in a tunnel which is exactly what we would want on the moon.
Update December 2021. I was feeling under the weather yesterday, so I amused myself by thinking about airlocks and I remembered this post and thinking that the amount of pressure on the doors between adjacent sections of the tunnel would not be very much, and then I did some rough calculations and I realized that it's actually going to be quite a large amount of pressure. For instance, a ten foot square door would have 100 square feet of surface area which translates to 14,400 square inches, so with a pressure differential of one PSI you are going to have 14,400 pounds of pressure which is seven tons. The doors might need to be made of unobtanium, but they are going to need to be very stout.
I read Artemis a couple of weeks ago and it got me started thinking about long term living on the moon. If we are going to have a base there, we are going to need a regular rocket-to-the-moon service, at least monthly, preferably weekly. I mean ol' Elon's getting pretty good at puttin' rockets up, and since he reuses them the only cost is fuel, which is just natural gas, which is dirt cheap, and oxygen, which he takes out of the air, so it's free. Once they get this regular service going, the cost of going to the moon is going to be too cheap to meter (as they once promised us about nuclear power). Okay, it ain't gonna be cheap, but we should be able to afford it.
Anyone, if we can get that far, we are going to have people living on the moon for days going on weeks, and given what happens to a body hanging out in the International Space Station for a long time (it's bad), we can probably expect similar effects on the moon. One way to compensate would be to build a centrifuge. I proposed building a train that would travel in a circular tunnel at high speed. The long radius would reduce the difference in force between the head and feet and so should be similar enough to the Earth's gravitational field that there would be no ill effects.
But that would be a major engineering project. Even if you could deliver a tunnel digging machine to the moon, it would likely take ten years finish digging the tunnel. We aren't going to want to wait ten years before we start sending people to the moon, so we need something a little smaller. You can generate enough force to simulate gravity with a small cylinder, you just have to spin it faster. However, if you are standing, there is going to be a large difference in force between your head and feet. However, if you are lying down, the difference in force between the tip of you nose and the back of your head, or the tip of your big toe and your heel, is going to be minimal. It might not be very good for working, but it would be just fine for sleeping. And spending eight hours a night in a full G environment might be enough to keep you healthy enough to return to Earth without suffering the ill effects of 'gravity sickness'.
So we take an empty fuel tank, locate an empty lava tube, drag the tank down underground into the lava tube, mount the tank on a couple of big bearings, fill it with air and beds and you've got your one Gee bunkhouse. Shoot, big as those lava tubes are, you could take the whole front end of SpaceX's Starship down there. It would already have everything you need: air, power, water, waste management (yes, we will need lavatories even on the moon), an airlock and beds.
(The whole point of going underground is to reduce the effect of radiation which is pervasive outside of the Earth's magnetic field. Domes on the surface can be covered with dirt, but a spinning cylinder is going to need some kind of structure to protect it. If a natural cave could be located, that would be perfect.)
Problem with caves on the moon is that they are devoid of air. And even if you could find one that could be sealed (perhaps by coating the interior with some kind of polyurethane), depending on moon rocks for the air you breath (don't you dare move, you rocks you) might not be prudent. Better to have a self contained air-supply, and that means air locks.
This centrifuge isn't the only thing going to need airlocks. Space ships are going to need them, regular moon domes are going to need them. Airlocks are basically a box with two doors. Domes connected with pressurized corridors won't necessarily need airlocks, but they will need pressure doors in case somebody springs a leak. I look forward to seeing what kind of doors they are going to use for moon houses.
50 years ago a Russian made the first space walk. They had a couple of problems. It's a miracle they survived. I mean 10 G's of force? Motherboard has the story. Now they have made a movie about it (trailer above). It will be released next month. Via Posthip Scott.
When I was a teenager with a driver's license, my friends and I would go to the Mid-Ohio racetrack to watch the Can-Am / Group 7 cars race. In those days Jim Hall and his Chaparral and McLaren were the ones to watch. Their cars were built along the same lines as the Ford GT40, except without a roof. The important part, as far as I was concerned, was that they were all using big, 7 liter, all aluminum V-8 engines from Detroit. America, hoo-rah!
Watching an episode of The Grand Tour a couple of weeks ago and they're talking about some exotic mobile, and Richard Hammond mentions that the people who buy these million-dollar go-fast toys have, on average, 64 other cars, which means they need a warehouse to keep them in and a staff to wrangle them (keep them clean and prepped and ready for the next time you want to take one for a spin). Or maybe you don't need a warehouse, you can just distribute them among your umpteen houses with their ten car garages. Whatever. You get the picture, we're talking the upper echelons of the one percenters here.
Now you might think that all this is a ridiculous waste of time and money, and from a pragmatic, go-to-work-and-save-your-pennies point of view, it is. On the other hand, all this activity employs a fair number of talented people, and most of their work is being done by hand, so they aren't putting their efforts into mass producing stuff that will put other producers out of work. It's really part of the entertainment industry, which in some respects is kind of like the defense industry: it absorbs a large chunk of money and produces very exotic stuff that no one really needs, but everyone wants, sort of. I mean it would be nice to have your own supersonic jet aircraft / race car, wouldn't it?
Lewis Hamilton and Jenson Button are real-life race car drivers. Alexander Armstrong is an actor. Not often you see race-car drivers with speaking roles, or at least that's the way it used to be. I suppose with zillions of dollars at stake, you might invest a little effort in polishing their public personas. And make no mistake, zillions of dollars are at stake. McLaren was fined $100 million for some kind skullduggery. The company is private, so they don't have to tell anybody how much they are worth, but I suspect it is somewhere north of $2 billion.
Still looking into this business of figuring out which way is north, I wander into Wikipedia's article on Gyroscopes, where I found this passage about London Moment. It reads like something out of Science Fiction:
A London moment gyroscope relies on the quantum-mechanical phenomenon, whereby a spinning superconductor generates a magnetic field whose axis lines up exactly with the spin axis of the gyroscopic rotor. A magnetometer determines the orientation of the generated field, which is interpolated to determine the axis of rotation. Gyroscopes of this type can be extremely accurate and stable. For example, those used in the Gravity Probe B experiment measured changes in gyroscope spin axis orientation to better than 0.5 milliarcseconds (1.4×10−7 degrees) over a one-year period.[41] This is equivalent to an angular separation the width of a human hair viewed from 32 kilometers (20 mi) away.[42]
The GP-B gyro consists of a nearly-perfect spherical rotating mass made of fused quartz, which provides a dielectric support for a thin layer of niobium superconducting material. To eliminate friction found in conventional bearings, the rotor assembly is centered by the electric field from six electrodes. After the initial spin-up by a jet of helium which brings the rotor to 4,000 RPM, the polished gyroscope housing is evacuated to an ultra-high vacuum to further reduce drag on the rotor. Provided the suspension electronics remain powered, the extreme rotational symmetry, lack of friction, and low drag will allow the angular momentum of the rotor to keep it spinning for about 15,000 years.[43]
A sensitive DC SQUID is able to discriminate changes as small as one quantum, or about 2 ×10−15 Wb, is used to monitor the gyroscope. A precession, or tilt, in the orientation of the rotor causes the London moment magnetic field to shift relative to the housing. The moving field passes through a superconducting pickup loop fixed to the housing, inducing a small electric current. The current produces a voltage across a shunt resistance, which is resolved to spherical coordinates by a microprocessor. The system is designed to minimize Lorentz torque on the rotor.[44][45]
Gravity Probe-B Gyroscope
"the polished gyroscope housing is evacuated to an ultra-high vacuum" Heh. It means they opened the airlock door.
Space suits are a pain. There are only a couple of reasons to have them. One is if you need to go outside when you are in space. These days this is typically only done to make repairs. Another is to send images of a man in a spacesuit back home so the public can see that we actually have men in space. The last is in case of emergency and something goes wrong with your spaceship. Space suits are difficult to make, to put on, to work in. If there was any way to avoid using them we would.
Maybe there is. In Neal Stephenson's Anathem, our hero, along with his cohort, don some spacesuits that were designed 6,000 years ago. One of the features of these suits was they didn't have any gloves. The arms of the suits ended in a small sphere that had room for your hand to flex. On the outside of this ball was mounted a mechanical hand and on the inside was a control for this hand. You manipulate the control on the inside and the mechanical hand on the outside echos your movements. No glove required.
If you are going to use a remote manipulator, there is no reason to have it mounted adjacent to the control. Given the speed of electronic communication, anywhere within a thousand miles would be just fine. You get farther away than that and the delay due to lightspeed is going to be noticeable.
The remote manipulator is key. I don't know if hands are really the best devices for manipulating other objects, but they are most versatile ones we have and we are certainly accustomed to them. Modeling remote manipulators on hands is probably our best bet. Arms are much easier and much simpler to build and control. From an amazed perspective, hands are wonderfully complex. From an engineering perspective, hands are horribly complex. The work being done with prosthetics is making the most progress. (There's even Lego versions out there.)
Once you have a decent remote manipulator there is no reason to go outside your spaceship anymore, which got me to thinking that instead of individual space suits, maybe what we need is individual space ships. Space is a dangerous place. You are in constant danger of being struck by a deranged bit of matter that will poke a hole through you and your ship as if you were cheesecake. If you have a group of people, everyone having their own ship could increase the group's odds of surviving such a collision. An individual might be lost, but the group would survive.
You would want an airlock on your personal ship so you could visit other people in your party, but you wouldn't want too many people to all be in one place at one time to the avoid the possibility of catastrophe. For a large group of people you would need an airlock hall so several people could dock their ships at the same time.
Originally I was envisioning these personal space ships to be like escape pods, maybe the size of a mini-van, just big enough for you to carry out daily chores without tying yourself in knots. Then I got to thinking that these are going to be for long term habitation, so they should be self sufficient, with power, lights, hydroponic gardens, recycling, reaction mass and engines. So now I'm thinking something along the size of a destroyer.
Update May 2018 replaced one missing picture and then another when Blogger "fixed" some old mystery stuff.
One of my big ideas to improve traffic in cities is to build layers in central downtown areas. Vehicles would be confined to dedicated lower levels and pedestrians would have the top level all to themselves. If vehicles were powered by electricity, there should be no problem with fumes. However, I do not see the internal combustion engine going away anytime soon. In this case, we would need to provide ventilation for these lower levels.
One way to do this would be to build "smokestacks". These would be very similar to the smoke stacks used by coal burning furnaces: essentially tall, hollow pipes. The bottom end would be open to the levels used by the motor vehicles and the top would be open to the sky. Natural convection would cause the air (laden with fumes from the engines) to rise through these pipes and empty out into the air hundreds of feet up. Fresh air would be drawn in from the surrounding area at ground level. This would ensure a supply of fresh air for the people on these lower levels.
On multi-story buildings you may have noticed that they invariably have two sets of doors at each entrance, something like an airlock. Or they may have revolving doors. The reason for this is that with tall buildings the elevator shafts act like air ducts, and without some restraint, air comes in off the street and flows up the elevator shafts. The effect is so strong that it will make something of a windstorm, and in the winter a great deal of heat is lost to air going out of the top of the building. The two sets of doors help keep this breeze from starting.
Our smokestack takes advantage of this phenomena. Of course blowing the fume laden air out the top does not really do anything to reduce pollution, it just spreads it out over a larger area. But there might be something more we could do.
Imagine a smoke stack made of glass, about one hundred feet in diameter and five hundred feet high. Now line the inside wall with planters planted with green plants. Perhaps build a framework inside the stack to support more planters. Add automatic irrigation. Giving the stack a large diameter and a relatively small opening at ground level should reduce the velocity of the air to levels that would not damage the plants.
Now when the air flows up through the anti-smoke stack, it runs into the leaves of plants, where it may interact. This interaction could reduce the amount of pollution in the air. So besides providing fresh air to the vehicle occupants on the lower levels, it would also reduce the amount of pollution being generated by those vehicles. The plants would act something like a filter to clean the air coming through this pipe.
An embellishment would be to integrate this filter pipe into a building. You could make the pipe into a building by surrounding the central pipe with layer of rooms. Each floor would be circular with a circular hole cut in the center. However, if we do that, then there would not be much light to support plant growth at the lower levels of the central pipe. Lining the inside surface with mirrored glass could help with that.
Here is a video about solar updraft power project. It has a couple of features in common with my "anti-smoke stack", though it is an order of magnitude larger. Plans are being made to build one in Spain and one in Australia.
Update April 2015: Replaced video on account of the old one disappeared. I think it's the same video, though.
I have a couple of ideas on how airlocks might be improved. Both would remove more air more quickly than any current airlocks. Of course the only airlock we have right now is on the Space Shuttle, so the comparison is a bit unfair. They would add some complexity and mass, so the only place they would be useful would be where the air and time they saved would be worth the cost of boosting the extra material into space. Being as the cost of boosting the material is currently a couple of orders of magnitude greater than the cost of the material, we can neglect the cost of actually building these devices.
The first device would use large plastic bags to force the air in the chamber out. The collapsed bags would line two opposing walls of a airlock. Inflated with air, they would meet in the middle and completely fill the chamber. To operate, a space suited person would stand in the middle of the chamber facing one of the bag lined walls with arms and legs spread. Evacuation of the chamber would begin. The bags would be inflated with perhaps double the current atmospheric pressure. This will encourage the air in the chamber to leave. When a satisfactory amount of air had been evacuated from the chamber, the pressure in the bags would be relieved, and the bags would drawn back to the walls by the means of straps attached to the insides and/or outsides of the bags. The bags would need to be made of a tough material to withstand the pressures involved. The tougher the bags, the higher the pressures could be and the quicker the airlock could be cycled. We would want to be careful not to exert too much pressure on the person in the lock, we would not want any crushing injuries. It would be nice if the bag could be made of a transparent material to alleviate any feelings of claustrophobia.
The second device is simply a large diameter, long cylinder attached to the airlock. The cylinder would have about ten times the volume of the airlock. When the people entered the airlock, a piston in the cylinder would be next to the chamber. The other side of the piston would be vacuum. When the airlock was sealed, the piston would be released. The air in the chamber would expand and push the piston to the far end of the cylinder. The opening between the airlock and the cylinder would be sealed and the airlock could be opened to space. We would lose perhaps ten percent of the air with each cycle, but it would be very quick, a matter of seconds at most.
Baring a breakthrough in physics, sending human beings anywhere in space beyond the moon is going to take a very long time. Even a trip to mars will take a year just to get there. Given this situation I think it would be a good idea if we got started with building a space habitat where we could learn how to live in space, not just survive. All the ideas I have seen about building a ship to go to Mars all look like they come from cheapskates. The bare minimum of equipment, the bare minimum of shielding, just enough that the crew, if they are lucky, will survive. It looks like a recipe for disaster. We should take a page from the Victorians and building something that could survive most anything the universe can dish out. Building a habitat at Lagrange point L4 (never mind L5, everyone else has already talked L5 to death) would give us a chance to see what it is really like to operate in space.
Lagrange Point Habitat
I am thinking we would want a sphere about one mile in diameter. Spin it at a rate of one revolution per minute and you would have one gravity of acceleration at the largest radius. I like the idea of making the surface of the sphere out of foot thick steel, but this may not be the right choice. The skin of the sphere will have several functions:
Keep air and water vapor inside
Keep dangerous radiation outside
Absorb and/or deflect meteors and other debris
Hold itself together, i.e. have some structural integrity
To do all this may require several layers of various materials and in fact may be a hundred feet thick and honeycombed with access passages. One thing to remember is that we probably are not going to want much on the outside of the skin near the equator. The skin at the equator will be traveling at about 200 miles per hour. Anything that is attached there that loses its grip is going to leave very quickly.
A large diameter cylinder would be fitted to the inside of the sphere and concentric with axis of spin. It would take up one third to one half of its' length. This would give us a large surface of even gravity on which which to house our people. A cylinder a third of a mile long and one mile in diameter would give us about one square mile of "land": 640 acres. We should be able to do something with this, perhaps farm, or even raise cows. The area between the cylinder and the skin of the sphere could be used for water tanks. In case of a breech of the hull, large valves could be opened into these tanks and quickly drain any surface water into the tanks before it all evaporated into space. Water in these tanks could also be transferred around the diameter of the sphere to compensate for any imbalance.
The large diameter offers several advantages:
Low gravity gradient. There would little difference in the apparent force of "gravity" as you changed elevation. For instance there would a negligible difference between your head and your feet, and the difference would still be small for an elevation change of 100 feet.
Slow spin rate. I would hope that an angular velocity of one revolution per minute would minimize any problems with vertigo either for permanent residents or visitors. As far as I know there is no way to tell. Research and testing will be necessary.
High linear velocity. The high linear speed of 200 MPH means that any motion in the vessel, like walking, will have a minimal effect on your perceived weight. Running, either with or against the rotation, will no doubt have a noticeable effect, though it should be something most people should be able to deal with.
Wide open spaces. Having a "ceiling" a thousand feet in the air would give people a feeling of wide open spaces like they have on the Earth's surface. It might help prevent attacks of agoraphobia in people returning to Earth, and attacks of claustrophobia in people arriving at the habitat.
Large volume of air. This means that we can survive small leaks until they are found and a small amount of anything unpleasant or noxious would be diluted to the point where it is harmless.
A smaller diameter cylinder would also be fitted into the sphere, also concentric with axis of spin. This cylinder would be much smaller in diameter, perhaps a couple of hundred feet. This cylinder would be used for docking of cargo and passenger vehicles. This ends of the cylinder would be doors. Since the entire cylinder would be exposed to vacuum, the surface of this cylinder would need to have many of the same attribute as the surface of the sphere. The doors at the end of the cylinder would span perhaps a quarter of the diameter of the cylinder. Vessel docking would be accomplished by:
contact with a long probe which would stabilise the vessel's position and relative velocity.
with the aid of the probe the vessel would be maneuvered into position directly outside the sphere and in-line with its' axis of rotation
a cage-like frame would close about the vessel and be secured
the cage would be drawn into the sphere
the cage, and the contained vessel, would be spun up to match the sphere's rotation
the cage would be moved sideways, relative to the axis to a docking berth
We could have two kinds of berths. One would just hold the cage, and could provide an airlock for crew and passengers. The other could be enclosed so that it could be pressurized. A vessel a mile in diameter can expect to have a fair amount of traffic coming and going. Having this central cylinder devoted to docking would allow incoming vessels to enter at one end, be docked along the walls, and exit through the other end. A continuous stream of traffic could beaccommodated this way.
In most cases docking could be carried out in vacuum, but there will be cases where bringing the vessel into a pressurized chamber would make things easier. Emergency would be one case, and external repairs would be another. It is easier to build and seal a small door rather than a large door. If vessels where constructed as long cylinders, then they could enter a pressurized chamber through a relatively small door. So pressurized docking chambers would be cylinders perhaps three times the diameter of a vessel and slightly longer.
We would probably not need to accommodate winged vessels like the space shuttle. We would be a long ways from anyplace where wings would be useful. The expense of boosting them this far out would be very hard to justify. However, if this structure is going to be a mile in diameter, just how big are the ships going to be? Right now I find it difficult to imagine anything larger than about 30 feet, but I have seen numerous engineering projects that had to be revised to accommodate the bigger, larger and more powerful.
At one point I was thinking that sand would be the perfect material to use for shielding the outer skin of the sphere. Easy to transfer, simply pour from one container to another. Good for absorbing impacts from micrometeorites and cosmic rays. And it could be used as a raw material. Apply enough heat and you get oxygen and silicon. Oxygen is always handy for air breathing mammals. Problem is any small holes in the "underside" of the containing vessel would let the sand drain out and be lost. There are ways to compensate, like putting a chamber below the sand to catch any that leaks out, and allow maintenance to plug whatever holes show up in the floor of the sand chamber.
