Sunday, December 5, 2010

The International Space Station

 This month was my turn to present something to my writer's group (we each do two a year).  This is a diverse and distinguished group, and sometimes I wonder whether I really belong.  Our common interest is what used to be called Natural Science, with an emphasis on geography.  Some are scientists, and some are not.  There is one engineer.  They are not pilots.  Well, we had one pilot (my student, of course) who left to become Dean of a university in Texas.  Another's mother was a pilot, in the 1950s, but we never seem to connect when I try to take him flying.

This means that I have simplified some of the scientific and engineering material.  Anyone who has tried to do this knows how difficult it is to balance correctness with simplicity.  One thing I would like is for those who know more about the ISS than I do to point out any inaccuracies or mistakes.

Most of my presentations are not aviation-related.  For example, I have written about the etymology of animal names, naturalist Carl Akeley, mapping of the Great Basin, and the dust bowl.

The ISS is not really aviation-related, either, because rocket science is not aerodynamics.  But I feel that there is a strong relationship.  With no apologies, here's what I said.




iPhone Picture of ISS, November, 2010

For the past few months, when conditions have been favorable, I have gone out in the evening or early morning to watch the International Space Station (ISS) fly over. A few people have come out with me to see it once or even twice, but I've watched it dozens of times. The repetition has permanently changed my perception of the Earth's place among the stars.

The Space Station is full of contradictions. It doesn't travel among the stars; instead it barely skims above the Earth's surface. It is often closer to me than Denver, but it is impossibly far away. From the perspective of Voyager 2, which at a distance of 15 light hours or so is out of our solar system, the distance from the ISS to Earth amounts to a rounding error. It travels at about 17,500 miles per hour, but it does not go anywhere. It is not a flying machine, although pilots seems to love it, and the astronauts are generally pilots. Few astronauts are scientists, but the ISS is billed as a science laboratory.

It is a bureaucratic boondoggle, a tool in search of a need, the creator of its own necessity. My rational, political side sneers. But I still go outside to watch it pass over.

Some people marvel at skyscrapers, or bridges, or tunnels. Some go out of their way to see the great dams, or the Great Wall of China. My high school had a policy by which students on the Honor Roll could skip one day each term; I used an honors holiday to tour the first Boeing 747 to land in Boston. The ISS is a source of wonder and, to some, inspiration. After all, how many 1,000,000 pound objects can you see moving?

Consideration of the ISS takes many forms: scientific, engineering, political, psychological, medical, to start the list. Any one of these would take more than an evening to discuss.

I think the most important of these is that the ISS is in space. While I suppose that some might find the station itself pleasing to look at, its beauty for me lies in its perspective on the planet. The inside -- I've toured mockups and watched videos -- has the cubicle look of an Air Force base. But no Air Force base I've visited has such a good view out the window.

Orbital Mechanics

The science of the Space Station is, without sarcasm, rocket science, and one of the first things one must understand about rocket science is that in space everything you know about the physical world is wrong. Everything you know either depends on gravity or on the atmosphere. And while objects in orbit are influenced by the Earth's gravity, once in orbit everything in your world is falling together, so there is no perception of relative motion. When an astronaut lets go of a fork, it appears to hang there as they fall together. This much is amusing. But now consider a fuel tank. If you put a valve at the bottom of the tank, the valve and the fuel will continue to fall together, so the fuel will not flow. This is a serious engineering problem.

Sleeping astronauts are in danger of suffocating in the bubble of exhaled carbon dioxide that builds up over the course of the night. On Earth, the CO2 falls to the floor, but in microgravity it just hangs there. Sleep areas must be well ventilated. Nothing is left on the bedside table. The bubbles in a carbonated drink won't rise to the surface, and a popped champagne cork would lead to a plume of champagne that continued until it hit a wall.

Salt and pepper shakers make no sense. A pepper mill without gravity is a sneezing fit waiting to happen.

Whatever else happens in our world happens in reference to up. But on the ISS there is no well-defined ``up." Astronauts refer to the nadir, meaning toward the Earth, and the zenith, meaning away. But there is no up.

Newton's insight that a falling apple and the Moon both respond to the same force seems a commonplace to us, but actually encompasses a remarkable breadth of vision. While Kepler had derived the laws of orbital mechanics empirically, there is an air of mysticism about Kepler's work, and much of it contained mutually-cancelling errors. But Newton started at a simple and reasonable assumption, the inverse square law, and derived the consequences.

Newton's First Law of Motion is that every object in motion tends to stay in that state of motion unless an external force is applied. When you throw a ball, you apply an external force, but as soon as you let go the ball continues to move in the same direction at the same speed. Actually, that would be the case without gravity; but the external force of gravity changes the motion of the ball.

When the engines on a rocket stop, the rocket continues to go in the same direction at the same speed, so by the First Law the rocket should continue in a straight line away from the Earth. But, again, gravity takes over. That initial velocity makes a big difference; a rocket that was launched straight up would just fall straight down, although unless launched from the North or South pole it would land someplace different because the Earth would have moved during the flight.

When the rocket stops, it needs to be going in the right direction and at the right speed. In addition, the rocket sitting on the launch pad is already in motion, due to the rotation of the Earth. At the equator, the Earth is rotating at a little over 1,000 miles per hour, while at 45 degrees north the speed is reduced to about 745 mph. That's why launch sites are clustered as near to the Equator as possible; Arianspace, a European consortium, launches from French Guiana, very close to the Equator.

STS-124 Altitude

What's remarkable is that many space shuttle launches include a descent. For example, 5:38 into the launch of STS--114, the shuttle had reached an altitude of 67.57 miles, and was travelling at 8,649 mph. It then descended to 63.71 miles over the next 2 minutes or so, accelerating to 15,596 mph, nearly doubling its speed. The engines were cut off at 8:34, with the shuttle going 17,609 mph at an altitude of 65.14 miles.

The Orbital Plane

A launch trajectory defines a plane in space, and the spacecraft cannot leave that plane without a large expenditure of energy, which means a large expenditure of fuel. This is part of the reason that missions requiring rendezvous have a ``launch window;" the target must be in position when the vehicle gets there, and the vehicle has little ability to adjust.

The ISS orbital plane is tilted about degrees from the Equator, which means that the station passes over most of the inhabited regions of the earth. The station always stays in the same plane, while the Earth rotates below, so it appears in different parts of the sky depending on the relative geometry.

Orbital Mechanics

Orbital maneuvering is another realm in which everything you know is wrong. We are accustomed to thinking of flying machines, with the exception of balloons, having the ability to maneuver any which way. Add thrust to go faster, add drag to go slower.

But an aircraft turns by aerodynamic forces. Filmmakers expect the audience to know this intuitively, so they show spaceships banking in order to turn. This makes no sense in space. The only way to turn is to apply thrust to the side of the orbit, parallel to the Earth. This is far more expensive than turning an airplane, and most of the spacecraft that we have launched have extremely limited ability to turn. Maneuvering consists of moving faster or slower so that the space craft is at the intersection of two orbits at the same time as its target.

Kepler's Laws, as refined by Newton, lock an unpowered satellite's speed to its altitude. Higher speed satellites must be in lower orbits. A satellite in low Earth orbit passes under one in geosynchronous orbit about 16 times each day.

The Atmosphere

Although the sensible atmosphere only goes up to about 100,000 feet, there are enough stray molecules in low Earth orbit, and the ISS is so big, that atmospheric drag is a factor in operations. Each collision with a molecule uses a little energy, so not only is the Space Station falling in the Newtonian sense, it is falling in the colloquial sense of losing altitude. In one 24-hour period last week, the station lost 78 meters in altitude; some days it loses 200 meters.

The remedy is to dock with a Russian ``Progress" module and use its engine to boost the orbit. A reboost last Wednesday added 1.77 km of altitude. This took 7m38s. The Shuttle and Soyuz spacecraft also act as boosters.

Of course a reboost disturbs all of the microgravity experiments.

Station Attitudes

Orbital boost means that the station has to be pointed in the right direction. The Progress or Shuttle is docked to the station in a rigid way, and its thrust must point to the nadir.

What about at other times? What, exactly, is the right direction?

The debate about which way a spacecraft should point began with project Mercury, the single seat ``space capsule" of the 1960s. Airplanes have a preferred direction that minimizes atmospheric drag, and maximizes the effects of thrust. But there is not enough drag in low Earth orbit to make aerodynamic design effective. And spacecraft don't use thrust in the conventional sense; they merely fall, with style.

The flights of John Glenn (Friendship Seven) and Scott Carpenter (Aurora Seven) were plagued with flight control issues. There was no problem with the path of the ship; that had been determined through Laplace's calculations a century earlier. But there was a problem keeping it pointed in the so-called ``right direction", with the astronaut facing forward, his head at the zenith. From a navigational standpoint, the only time that the ship's attitude really mattered was when the engine was fired to start reentry. In Carpenter's case, an instrument failure forced him to fly the re-entry maneuver manually, and he landed over 200 miles from the planned area.

(The Mercury capsule had three different attitude control systems, and astronauts got confused and used fuel from two or more simultaneously; this contributed to the control problems.)

The next flight, Wally Schirra in Sigma Seven, featured long periods of ``drifting and dreaming"; Schirra allowed the spacecraft to point in whatever direction it pleased for long periods of time.

Schirra depended on batteries for electric power, but the ISS uses massive solar panels, so it can't just drift. Its solar panels are the size of a football field, and create noticeable atmospheric drag. They must be pointed so the sun hits them, but this is difficult. There are two basic schemes. The less intuitive one is inertial; the space station is always oriented the same way with respect to the stars. The more intuitive one is the opposite of Schirra's flight: the same side of the station is always pointed toward the Earth, kind of like an airplane. NASA says that this orientation is best for microgravity experiments, but I'm not seeing this intuitively. Keeping this attitude does not require thrusters; momentum wheels are used, which, owing to the gryoscopic property of rigidity in space, keep the station pointed correctly.

Earth's Shape and Composition

While everything that we do happens in reference to up, the concept of up is more complicated than it appears. In geodesy -- the study of the Earth's surface and composition -- there are three common definitions of ``up," and they don't quite agree. Latitude is the complement of the angle between up and the Pole.

The first complication is that the world is not flat. Anyone who doubts this needs to spend an evening or two watching the space station and the many other satellites in orbit. But the Earth is not a sphere, exactly. It's wider at the equator than at the poles, and it's slightly pear--shaped.

One way to measure the vertical is to use the line through you and the center of the Earth. This is called geocentric latitude. Following that line is surely ``up," but how could you ever measure it?

Another measure is the normal -- the perpendicular -- to the tangent plane at your location. We call it geodetic latitude. This is slightly different from the first, in a measurable way, because the Earth is not a perfect sphere.

The final measure is the direction of gravity, which is called astronomical latitude. As [former member] explained last spring, the Earth is not homogeneous, and so a plumb line is attracted -- measurably if you're careful enough -- toward the denser part. The Rockies are less dense than the iron-rich regions around the Great Lakes, so a plumb line in Kansas tilts just a little to the northeast. A satellite feels the same pull as the plumb line.

This is more of a problem for the Global Positioning System satellites than for the ISS. People use GPS to measure in centimeters, so the satellite orbits are measured with at least that precision. Following the orbits with that precision is the full-time mission at Schriever Air Force Base.

By the way, the ISS has GPS receivers, but these are not a primary navigational tool. There's no need to navigate; it's not going anywhere.

Astronauts

First let me make a statement of conflict of interest. I applied to the astronaut program about 1990. My application didn't even make the first cut.

The astronauts are cheerful overachievers, traditional leaders. I'm sure that some of them are characters, but the public face is cheerful and loyal. Most have a military background, and military morale seems to require extreme loyalty to one's platform. F-18 pilots think they have it better than F-16 pilots, who are much better than F-15 pilots, who are far superior to F-18 pilots. Submarines are more effective than aircraft carriers which are obviously superior to Air Force Bases which are far superior to submarines.

And so there is no surprise in hearing astronauts praise the Shuttle, or the Space Station. With some of them a critical ear can detect the cant, but in a few their joy and wonder sound genuine.

Wisdom on the choice of a crew for a long expedition has been passed down from expedition leader to expedition leader. Before departing to cross the North Pole in the airship Norge, Amundsen told Byrd that ``[m]en are the doubtful quantities in the Antarctic. The most thorough kind of preparation, the shrewdest plan, can be destroyed by an incompetent or worthless man." An unnamed British explorer from Robert Falcon Scott's ill-fated expedition to the South Pole told Byrd ``The first man who starts trouble of a disloyal nature deserves the worst death you can think of."

The crew eats breakfast and dinner together, then go about their daily business. It's probably a lot like the Air Force labs where I
have spent some time. Some tasks are solitary, some take two people.

But then they have free time. Free time means looking out the window. It seems that everywhere one turns in the station, there is a laptop, and I wonder how many YouTube videos get watched. TV is difficult, because the station moves too quickly to track any ground or in-orbit stations; presumably there is internet upload.

The skeleton crew aboard the ISS last weekend had the weekend ``off." I'm not quite sure what that means. I can imagine writing a novel during the off time, or studying Spanish, or working on a software project; but what about the plastic hobbies? You can't build a chair or install a weathervane.

Lately, some of the astronauts have been using Twitter. Some ``get it", others don't. Twitter allows 140 characters in a message, so flexibility and improvisation are in order. Soichi Noguchi, a Japanese astronaut, is a talented photographer (photos only require a few characters), and had the advantage that 140 characters of Japanese carry a lot more information than 140 characters of English. Doug Wheelock, who commanded expedition 25, didn't get it, and his messages were always truncated.

But Wheelock is active in ham radio; hams live in their own universe and always have something to talk about.

Many just keep their heads down and do their work. What is their work exactly? It's mundane housekeeping, space-style. Here's what happened on Thanksgiving. Inspecting the aerosol filters for the oxygen generators. Transferring data from body sensors or other experiments for downlink. Toilets need lots of maintenance; toilet issues appear frequently.

One cosmonaut worked on preparing the Soyuz capsule that would return him and two astronauts to Earth on Friday.

There are also training sessions with the various robotic arms; this sounds like real astronaut work!

Pilots and the ISS

While I have done no formal research, it is easy to imagine that many pilots are ``fans" of the ISS. It is certainly the case that many of the astronauts are ``fans" of flying.

In the space shuttle, two astronauts sit ``up front", the Commander and the Pilot. The Commander is really the pilot, and the Pilot is really the copilot. The Commander flies the shuttle to its landing, although there is a tradition that the Pilot is allowed to handle the controls for a few seconds, during a non-critical moment.

The computers fly the shuttle for takeoff.

Everyone else in the shuttle is a Mission Specialist, and Mission Specialists do not handle the flight controls. Remarkably, many Mission Specialists list flying as a hobby, and hold advanced ratings. But this is a hobby, not part of the job.

Still, the pilot personality is probably a good fit for this kind of mission. More specifically, the professional pilot personality is a good fit; the amateur pilot personality is not. This division of pilots into personality types is certainly crude, and the division is independent of whether a pilot is paid to fly. The professional pilot loves every aspect of flight, while the amateur finds some of the details to be tedious and boring. The amateur jumps in and goes, while the professional enjoys the process of preflight preparation.

Preflight preparation for an astronaut is pretty extensive, too, measured in months or years rather than minutes.

Each ISS Expedition has a Commander, a Commander-to-be, and a handful of Flight Engineers. There is no pilot! The Space Station has no cockpit. The Space Station does not fly: it falls with style.

Rendezvous and docking seem to be much more like flying. Military pilots and glider pilots routinely rendezvous with other aircraft, although we do not touch each other. There are some differences from ordinary formation flight due to orbital mechanics, but a delicate touch is required in any event. The Shuttle docking is apparently hand-flown, while the Soyuz and Progress dockings are flown by the computer.

I have a simulator program for docking; I succeed about every other time. Watching a Soyuz docking live, though, I was impressed with the simulator's accuracy.


Scientific Value

The scientific mission of the ISS is, to a large extent, self-generated. Many experiments focus on the effect of long-term spaceflight on the human body; in other words, we need the ISS in order to study the ISS. Other experiments have focused on combustion, crystal growth, and microbial development. I am excessively judgmental, but my impression is that the science is pretty weak. The real achievement is in the engineering.

Cultural Value

I think the right cultural context for considering the ISS is that of polar exploration. The metaphor is brought home by the naming of crews to the ISS: Expedition 25 ended last week, and Expedition 26 will begin soon (the crews overlap so the station is not left empty).

While Scott's Terra Nova Expedition of 1911 tried a ``new" technology in the form of ponies and motor sledges, Amundsen's expedition relied on proven techniques for travel on the ice. Amundsen did no science, making his task much easier.

(When hiking in the Rockies I often think about the men who carried heavy surveying equipment along the same trails.)

Since Amundsen, exploration has been driven by new technology. Byrd's Arctic and Antarctic expeditions exploited something new, the airplane. Nuclear propulsion enabled the submarine Nautilus to reach the north pole.

But orbit is not a place.

In each case, resupply and logistics are major hurdles. Amundsen marked his caches carefully, while Scott did not, and Scott starved to death. The ISS has been resupplied by the Shuttle and by various Russian craft. The current political climate  makes refurbishing of the Shuttles impossible; the penultimate mission is planned for this month. But the political climate in Russia strikes me as less-than-stable, although the presence of Russians on the station would seem to guarantee some kind of will to resupply.

Scott and Byrd had corporate sponsors; only Byrd's third Antarctic expedition had government support. NASA now is moving toward supporting commercial space efforts. Byrd and Amundsen bought supply ships on the open market, so there is plenty of precedent, but in that sense they were using existing technology, not developing new technology. The closest we have to private space travel, barring a few eccentric billionaires who bought their way onto Soyuz missions, is Sir Richard Branson's Virgin Galactic effort. Virgin Galactic has built a space port in New Mexico and a suite of aircraft modeled after Burt Rutan's Space Ship One. A mother ship ( White Knight Two) carries the space ship Space Ship Two to around 50,000 feet, where it is dropped. The rockets are fired and the space ship leaves the atmosphere and climbs to ``at least 110 km." For reentry, an innovative feathering arrangement is deployed, and once into a thick enough atmosphere the wings are unfeathered and the ship becomes a glider.

I wonder if the Virgin Galactic enterprise will be attractive to microgravity researchers. For $200,000 and a few days' training, a researcher could get 4 minutes of microgravity

Conclusions

When the conditions are right, an Earth-bound observer can watch the station pass into eclipse. In these conditions it is especially bright. I watch it turn from hot white to dusky red as it reaches twilight, and then it disappears.

Imagine what it looks like from inside.


Blow-up of iPhone photo of ISS

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