|William Surles “Bill” McArthur, Jr., (Colonel, USA, Ret.) NASA Astronaut. (Photo courtesy of NASA)|
ENR spoke with NASA astronaut, Col. William Surles (Bill) McArthur, Jr., on Aug. 8, the day the Atlantis Crew left the training facility at the Johnson Space Center to head to the launch pad at the Kennedy Space Center in Cape Canaveral, Florida, for the launch of the next mission to the International Space Station. It is scheduled for a launch window that opens at the end of the month.
McArthur is a veteran of two trips to the station, once an assembly mission in 2000, when construction was just getting started, and most recently, as one of two astronauts on board for six months, from Sept., 30, 2005 to April 8, 2006—a mission of 189 days, 19 hours and 53 minutes. After exchanging pleasantries and information about our respective families, including discussion of the astronautic ambitions of this editor’s own daughter, a university senior who has turned toward the study of biology instead, we got to work, but not until McArthur had put his recruiting hat on.
MCARTHUR: You tell your daughter we need biologists in the space program and tell her to come on down. With our plans to send people to Mars, I think somebody with some experience in biology is going to be well qualified to be there. If, in fact, as we are convinced there was water on Mars at one time, I think it is likely we will find signs of life.”
ENR: Is the ISS a construction project?
MCARTHUR: It is absolutely that.” I had the good fortune to actually visiting the ISS twice, once on a vehicle assembly mission, at which point it was relatively small, and then again recently. It was exciting the first time, but not nearly as impressive as it is now.
In its very current configuration, which is extremely impressive, you look at it and you realize that we have had a lot of people contributing small parts to create something that is truly awe-inspiring. It is quite a beautiful vehicle now.
On the most recent visit, we had the opportunity to do two spacewalks, one of which was on the U.S. segment, and another where we went from as far forward as you could go from the U.S. segment, to the end of the aft section.
It was awesome. It gave you a much greater appreciation for what a remarkable feat it is already, a sense you don’t get on the inside. On the inside it is just a marvelous facility, but we spend so much time inside you start to take it for granted.
Hopefully, we were the last two-person crew. We did our EVAs, (Editor’s note: Extra-Vehicular Activities, or space walk) just as previous crews had done, but the Station had no crew on the inside.
ENR: How do you move yourself across the structure?
MCARTHUR: We did all the translation hand over hand. In 2000, I always had a death grip on the handles, but last year I felt more secure, relaxed on the outside.
ENR: What are the consequences if you let go?
MCARTHUR: We always have a safety tether we are attached to. On the U.S. side it’s 85 ft. We have retractable leash, you know those dog leashes? Like that. We just call it a safety tether, that is attached to what we think is a location that makes sense.
When we did our EVA in Russian space suits, we moved using the Russian protocol. When we are using the U.S. retractable safety tethers, you do have a sense of security knowing that if you “fall off” quote, unquote, you will be dragged back 85 ft.
At a worksite, if we want to use both hands, we used a work-tether at the worksite. I would have one or two additional tethers besides the safety tether. It would be so inconvenient—and a little embarrassing—if you did lose your grip and were retracted by the tether!
The Russians use two safety lines. One is a bungee and the other is a meter and a half long. You are always attached at two points, either the two hooks, or, if you are translating, you reposition the hooks one at a time, and while the one hook is released you hold on with the other hand.
Another technique, for real time protection, is to have two safety tethers attached to different handrails, so if there was a structural failure of the handrail, you still have the other.
You can get quite comfortable being out there, again, because deeply ingrained in us is our protocol.
ENR: But is it construction?
MCARTHUR: Our robotic arms are cranes. We are maneuvering large structures—10, 000, 15,000, 20,000-pound structures, and we are attaching them, bolting them into place, doing wiring and plumbing; that sounds a lot like construction to me.
ENR: Have you ever done terrestrial construction?
MCARTHUR: Just around the house.
ENR: What about the image of the tree that was placed on the ISS in December 2000? That’s a time-honored construction symbol for celebrating the completion of the highest part of a structure. Do you know about it? Was it a symbol of that?
MCARTHUR: It absolutely was put up as a topping-out symbol, and I took it down in November, last year. The tree was embroidered on a protective cover that was part of a device called a floating potential probe. We have a metal structure that is orbiting the earth and is passing through the earth’s magnetic field…if you take a conductor and pass it through a magnetic field you can generate potential.
ENR: I’ll bet!
MCARTHUR: Well, the FPP dissipates any electrical energy that is generated with the metal structure of the station. The Christmas tree was embroidered on the fabric of the cover of the FPP, but the FPP wasn’t designed to be in space that long. There are four trusses with solar arrays. The one on the top of the station now is the main solar array, and one of the last assembly tasks is to move that to a different location… the FTP unit gets in the way of moving some of the remaining truss elements, so we discussed disassembling it and bringing it back inside, but there was some discussion about O1 contamination, so we decided to remove it and throw it away intact.
ENR: You threw it overboard?
MCARTHUR: I discarded it retrograde… I gave it a very small amount of deceleration—about a foot-and-a-half per second. It’s not a pure vacuum at 220 miles. It’s low earth orbit. Believe it or not, there are some particles of oxygen that get all the way up there. It causes some drag in low earth obit, 1 millionth of a G, but over time, any object in low earth orbit, over time, will de-orbit. The space station, every day, descends anywhere from 70 to 100 meters.
ENR: I read somewhere it causes a fair amount of stress on the structure when it is boosted back into higher orbit.
MCARTHUR: Yes. Also, with the pressurized volumes, put together end-to-end, its pretty long and skinny, so to avoid vibrations we have limitations or constraints, like on the frequency at which we exercise. If I am doing bench presses, I can do only one every three seconds.
ENR: To Prevent setting up harmonics? The soldiers marching over the bridge?
ENR: We heard there were some problems with that when the first solar panels were unfurled. A vibration pattern started as it came out in jerks and they had to break it off. What did they call it…?
MCARTHUR: “Stiction.” There were some problems with the solar arrays and ‘stiction.’”
ENR: Are we working out techniques and capabilities that will be useful for interplanetary construction/?
MCARTHUR: I think it will, we are looking that we may have to do some assembly on orbit for a vehicle to go to Mars. We may have to do some reconfiguration on orbit. Is it going to require spacewalks? I don’t think we have made those decisions yet.
We may use berthing, spacewalks, all the technologies that we are evaluating that we have gained a lot of experience with, with the International Space Station.
ENR: How heavy are the suits you wear? We have heard they weigh in at about 730 lbs., astronaut, life support and tool belt included.
MCARTHUR: The suits we wear to work outside are about 250 pounds.
Suits on the shuttle for assent and re-entry, if you throw in the parachutes and everything, weigh 70 or 80 lbs. They’re pretty heavy, which is something that really makes you enjoy being in microgravity. To include the person inside you are talking in the neighborhood of 500 pounds.
ENR: Just wearing them must be pretty tiring.
MCARTHUR: It is very fatiguing. The assembly itself sometimes creates resistance on your motions, but a pretty significant problem is that the suit rigidizes as a function of the internal pressure.
The soft goods, the arms, fingers of the gloves, our legs, as the suit pressure increases relative to the external pressure, every motion you make encounters resistance caused by the pressure of the suit.
For 30 minutes its not a big deal… at the end of 6 hrs the fatigue level can be quite extreme. With the Russian suits, the pressure is at almost 6 psi. With the U.S. suits, it’s a little over 4.
ENR: Are there improvements on the horizon?
MCARTHUR: We have looked to see if there are other designs, but right now the way we address it is by exercising our upper body, shoulders, forearms and hands.
ENR: Does the space station make noises?
MCARTHUR: The most obvious one is we rely on a pretty sophisticated air conditioning system, if you will, to revitalize the atmosphere. One major contribution to the noise is just the air circulating. But there are other sounds; any rotating machinery makes pretty distinct sounds, valves opening and closing. One of the things I thought was important was to be able to identify those sounds when I heard them, and anything I couldn’t identify or that was unfamiliar, I would contact ground control to find out what system just cut in.
ENR: What about structural noises? Creaks and groans?
MCARTHUR: I can’t recall the snaps and groans and pops. Others have reported sounds they couldn’t identify, but I never have heard them. Not even during reboost, but knowing it, if you listen very carefully, you could hear the engines, thrusters that were installed on the re-supply vessel.
There is no throttling on the thrusters, no ignition. They are either full on or full off.
ENR: I understand the range of the orbit is between 220 and 250 miles. When you get a boost, do you go up 30 miles?
MCARTHUR: No, nothing like that. Normally you are adjusting the elevation by a few kilometers.
ENR: Thank you very much for taking the time to talk to us about this, and good luck with your missions.
MCARTHUR: You’re welcome. All the best to your family, and tell your budding biologist that we absolutely need biologists in the astronaut program.