128. How big was Skylab?
It was about one hundred feet long and weighed eighty tons. The space inside was about the same as a three-bedroom house (12,500 feet).
Skylab was launched by a modified moon rocket (Saturn V), which was as tall as a thirty-three story building (330 feet) and weighed a little over six million pounds.
129. How long did it take to build Skylab?
About six years.
130. What did Skylab cost?
Skylab cost $2.6 billion over a seven-year development period.
131. How much did your space suit cost?
About $400,000.
132. What kind of spacecraft did you use to go up to Skylab?
We went up to Skylab in a special Apollo-type command and service module. The command module separated from the service module just before reentry.
Overall, it was about the size of a travel-trailer (35 feet long, 12.8 feet in diameter) and weighed 30,000 pounds. The cabin volume—the space inside the command module for the astronauts—was about the same as the inside of a station wagon.
The command module was shaped like a cone. The conical shape was similar to the shapes of the earlier Mercury and Gemini spacecraft. The heat shield covered the curved base of the cone. The overall shape was adopted because the designers had experience with it and were confident it could accomplish reentry following the return from the moon as well as reentry from Earth orbit.
133. What was the heat shield made of?
On Mercury, Gemini, and Apollo spacecraft, it was made of a silicon compound chemically similar to sand. These heat shields actually burned away or flaked off (ablated) during reentry.
The maximum heat shield temperature was 5200°F during Earth orbit reentry and approximately 8000°F during lunar return reentry.
134. After reentry, how much did the chutes slow down the command module? How fast were you dropping on the parachute at splashdown?
The parachutes opened at ten thousand feet above the ocean and slowed our descent to about twenty miles per hour at splashdown (about thirty feet per second).
135. How big was the rocket that launched you into orbit?
The Saturn IB was about 225 feet tall and weighed 1,300,000 pounds.
136. What kind of metal was your spaceship made of?
Most of the metal in the structure of spacecraft and rockets is aluminum. Where high strength is needed, steel, titanium, and other alloys or composite materials may be used.
137. How many pieces are in the rocket (spacecraft, Skylab)?
The large Saturn V moon rocket had hundreds of thousands of parts in the three major sections (stages). The Apollo command module had over 2,000,000 parts; Skylab had about 150,000 parts.
138. How many people work for NASA?
Approximately 21,380 (as of January 1985).
139. How fast did you go?
We traveled at a speed of 17,500 mph (about five miles per second) while on Skylab, at an altitude of 270 miles (415 km) above the Earth’s surface.
We circled the Earth over 1,200 times during the eighty-four days we were in space, which adds up to 34,500,000 miles.
140. Did you hit any meteoroids? What would happen if you did hit one?
Yes, but all were very small, the size of a tiny speck of dust. We had special test surfaces mounted outside on Skylab which were called micro-meteoroid samplers. Tiny meteoroid particles made miniature craters when they hit some of the samplers. A meteoroid larger than a pin head (1⁄16 inch diameter or larger) would probably burn a hole in the wall of a spacecraft. Assuming no one was hit by the tiny fragments, the worst problem arising from the hole would be a loss of air. The larger the meteoroid, the worse the problem. The hazard from meteoroids is actually very small.
141. How did you generate electricity?
On Skylab, large surfaces called solar arrays were covered with small devices (solar cells) which converted sunlight into electricity. Part of the electricity generated on the sunlit side of the Earth was stored in batteries for use on the night side. The command module used fuel cells which combined oxygen and hydrogen to generate electricity and water. The Space Shuttle also uses fuel cells.
A fuel cell is a device that combines two chemicals to produce electricity. Spacecraft fuel cells combine oxygen and hydrogen gases to produce electricity and drinking water. A fuel cell is like a cheese sandwich, with two porous metal plates (the slices of bread) on each side and a chemical (the cheese) in between. Oxygen is forced in through one plate and hydrogen through the opposite plate. The oxygen and hydrogen gases combine on the inside of the sandwich to form water. The water is removed as it is formed and piped to the drinking water supply. During this chemical process, a flow of electrons occurs between the plates to create a capability to deliver electricity to the spacecraft power system. The chemical (cheese) in the sandwich is a strong alkaline solution. Spacecraft fuel cells currently in use employ potassium hydroxide as the chemical filler for the fuel cell sandwich.
142. How did you heat the spacecraft?
When required, electrical heaters warmed air that was circulated through Skylab. Most of the time, though, the need was to cool the spacecraft, because a lot of heat was produced by electrical and electronic equipment as well as by sunlight on the sides of the spacecraft.
143. What kind of lights did you have?
On Skylab we had over eighty light fixtures that used fluorescent bulbs.
144. Did you grow any plants on Skylab?
Dr. Gibson grew rice plants on our mission. The purpose was to determine the growth rate and direction of stem growth in weightlessness. A light was shone on the plants continually, in an attempt to make the stems grow straight toward the light, but they sort of turned and twisted as they grew. It really looked strange.
145. Did you use plants to control the amount of carbon dioxide expired by crewmen?
On Skylab, we did not use plants to remove carbon dioxide, but this may be possible in the future. This technique may be used on long space missions to other planets, on a permanent moon base, or in a space colony.
146. How did you control the carbon dioxide level in the spaceship atmosphere? How could you tell what it was?
On Skylab, we used a device called a molecular sieve to trap and remove carbon dioxide exhaled by crewmen. Air was forced through the sieve, a device manufactured by pressing metal powder into a cake or solid block. The spaces between the powdered metal particles were large enough to let nitrogen and oxygen pass through, but not the large molecule of carbon dioxide. We had an instrument to tell us the concentration level of carbon dioxide in the air.
Our command module used a different system. A chemical, lithium hydroxide, was used to absorb the carbon dioxide. The Space Shuttle also uses this method.
147. How much radiation exposure did you get?
I got a total of forty rems, which is about twelve hundred times what I would have received on the Earth’s surface during the same eighty-four day period. This was about one-quarter the maximum allowable dose. I received most of it while outside Skylab on space walks.
The radiation was measured by personal dosimeters, also called film badges, that were carried on our clothing and space suits. There were also two other instruments used from time to time for measuring radiation levels at special locations inside Skylab.
148. Where does space begin?
Earth is really a part of space, but we tend to think in terms of “outer space” as beginning at some distance away from the Earth. We in the United States say that a person has been “in space” if he goes more than fifty miles above the Earth (approximately 265,000 feet). However, during reentry, the spacecraft actually starts to “feel” the Earth’s atmosphere at about seventy-five miles above the surface of the Earth (about 400,000 feet). We call this altitude the “entry interface.” There are all sorts of practical terms of reference for everyday flight-planning purposes. We might say that we enter outer space when nature’s rules of orbits h
ave much greater influence on the vehicle than do nature’s rules of travel in the atmosphere.
149. What does it look like when you’re going up?
As the rocket climbs vertically, the sky gradually turns from blue, to dark blue, then to dark violet, and finally to jet black. As the rocket gradually noses over to a level path, it is possible to see the Earth’s horizon and the Earth. It is very surprising the first time you see the horizon because the layer of air, our Earth’s atmosphere, looks so thin. I used to think of it as a thick blanket, but now I think of it as a thin sheet. If one could imagine an apple as big as the Earth, 99% of the atmosphere would be thinner than the skin of the apple.
150. What keeps you in orbit?
A British scientist named Newton gave a very good explanation of an orbit back in the seventeenth century. Suppose you are standing at the North Pole of the Earth and looking south toward Canada and the United States. Further, suppose you can throw a ball as fast as you desire and that air drag doesn’t exist. First, you throw the ball and see it land in Hudson Bay, Canada. Not satisfied, you wind up and throw it faster and see it land in Lake Michigan. The third ball is even faster, and you see it land in the Gulf of Mexico. The fourth ball is faster yet and falls in Argentina. Finally, you really put your back into it and the ball doesn’t even touch the surface of the Earth as it goes over the Antarctic and the South Pole. As you stand there considering what happened to the ball, it suddenly whizzes past your shoulder from behind you and streaks toward the south again. What happened is, you threw it hard enough to send it all the way around the Earth. In other words, you put it into orbit. It is actually falling, but it is going so fast that its path of fall is the same as the curvature of the Earth. If there were no air resistance and the Earth a uniform spherical mass, the ball would continue to “fall,” or orbit, indefinitely. This is why a spacecraft can stay in orbit for a long time without running the engines. It is actually “falling” and is still being pulled by Earth’s gravity, but its great speed keeps it from taking a path that would cause it to hit the Earth’s surface.
The orbital lifetime of a satellite depends on several factors—its distance or altitude above the Earth (moon, planet, sun, etc.), the shape of the orbit, the density of the atmosphere, and, perhaps, the shape and density of the satellite. For example, the Earth is in orbit around the sun and it will remain in orbit around the sun for billions of years. A satellite in orbit above the Earth at an altitude of about one hundred miles will only stay in orbit for several months. Skylab was in orbit at an altitude of 270 miles and it stayed up for six years.
151. Don’t the rocket engines pollute the atmosphere and space?
Many rockets use hydrocarbon- or petroleum-derived fuels in the first stage, and some pollutants are produced. The upper stages usually employ liquid hydrogen and liquid oxygen which are very clean, so very little pollution is caused in the Earth’s upper atmosphere or in space. The attitude rockets and orbital maneuvering engines on the orbiting vehicle cause a small amount of pollution in the form of oxides of nitrogen.
152. How much pollution is caused by a launch?
For the Space Shuttle, many tons of aluminum oxide (AlO2) and hydrochloric acid (HCl) are produced by the solid rockets. The liquid propellant engines in the Orbiter produce virtually no pollution. All rocket engines utilize combustible propellants and there are exhaust products. Some of the products are considered pollutants; others are not. For example, the exhaust products from hydrogen-oxygen used by the Shuttle’s main engines are water, plus some free oxygen and hydrogen; the exhaust products from RP1 (kerosene) and LOX (liquid oxygen) used in the first stage of a Saturn rocket include carbon monoxide, carbon dioxide, water, carbon, and some unburned kerosene (hydrocarbons). The engines used in orbit to control attitude and make adjustments to the orbit and for deorbit use nitrogen tetroxide (N2O4) and monomethyl hydrazine (CH3NHNH2). The products of combustion of these propellants include oxides of nitrogen, carbon monoxide, carbon dioxide, ammonia, water, and free hydrogen, oxygen, and nitrogen.
153. What good is it to look down at the Earth? Give me one example of something you saw that did some good on Earth.
NOTE: This was not a hostile question; it was asked by a student to force me to explain the practical value of Earth observations—it turned out he wanted to become an astronaut.
I reported a branch of the New Zealand current near the Chatham Islands that was previously unknown to exist. This report was challenged by ground teams who thought I had made a mistake in reporting the location. I later verified it on a subsequent orbit and ships were dispatched by the Australian Navy. They confirmed my report. This was important because it was a new fishing area unknown. Currents carry plankton which is the base of the ocean food chain (the “bread of the sea”). Small organisms are eaten by larger ones and this process continues until commercial food fish are present.
Our crew was the first to receive formalized training to prepare us to make deliberate visual observations for specific purposes. Although our training was limited, it did give us a good idea of what information the scientists wanted. We observed the growth cycle of crops in Australia and Argentina, structural (geologic) fault lines in many areas, weather effects, and ocean surface phenomena, and we studied several desert and arid areas.
Based upon observations of the Sahel, a broad region spanning the continent of Africa south of the Sahara Desert, I theorized that enormous quantities of dust were being carried high into the atmosphere and far out to the sea. Six months later, automated satellites verified that dust clouds travel over vast distances. Satellite photos were used to observe the movement of a dust cloud from Africa all the way to the Caribbean sea.
Not only is observing the Earth an enjoyable aesthetic experience, but it also has immense practical value.
154. I read in a book that there were cracks in the interstage structure of the rocket that took you into space. Is this true?
Yes, there were “stress corrosion” cracks in the interstage trusses that connected the two stages of our Skylab-4 booster. These cracks could only be seen with a magnifying glass.
155. Wasn’t this a bit risky?
The stress corrosion cracks weren’t considered to be a serious problem and were only discovered during detailed inspection following replacement of cracked fins on our rocket. Our launch had been delayed a week for the fin replacement and when we were told about the stress corrosion cracks I remarked to Jerry Carr that we ought to name our booster rocket “Humpty Dumpty” because they were finding so many cracks in it. Later, Jerry casually mentioned our proposed name to the launch pad manager who had been working around the clock supervising the repair work crews who had accomplished the fin replacement and inspection work. He didn’t appear to find the remark amusing.
The next morning we were atop the rocket in our spacecraft waiting for launch. In between the many checks we were confirming with the launch director, he would read “Good Luck” messages from the different teams that had participated in our training and launch preparation. It was rather nice and helped pass the time. Finally, the launch director said, “I have one final message,” and Jerry Carr said, “Go ahead.” The launch director read it slowly: “To the crew of Skylab 4, Good Luck and Godspeed—signed: All the King’s horses and all the King’s men.” We had a good laugh and thanked the repair team for all their hard work. It somehow seemed reassuring to know they had a good sense of humor.
156. Did you have 100% oxygen in the space station?
No. Skylab had a mixture of 75% oxygen and 25% nitrogen at a total pressure of five pounds per square inch (about 35% sea-level pressure).
157. What was it like during reentry?
Our reentry began in darkness. Before we even felt the slowing effect of the atmosphere, the spacecraft became surrounded by a faint white “cloud.” As the air friction increased, the white cloud changed to pink, then deepened to rose, and finally became a fiery mix of orange and red with streaks of brigh
t red particles from the heat shield in the trail of hot gases behind the spacecraft. As the thrusters fired to roll the spacecraft for corrective maneuvers, the rocket plumes caused wild swirls in the hot gases, and the patterns of flame seemed to spiral crazily along the edges of the wake of fire. The whole thing lasted about four minutes, during which we were subjected to a peak force about four times our own weight. It was such a fascinating and beautiful display that I didn’t even notice the build-up of heavy force on my body. Then it seemed like it was suddenly over, and we were falling down through 100,000 feet in a gradually steepening trajectory. The rest was just procedures—the real fun was over.
158. How do you stay cool and comfortable during reentry heating?
The heat shield is a very effective insulation material, so very little heat passes through to the inside. Even though the temperature may reach 8,000°F on the heat shield, the inside of the spacecraft remains comfortable.
159. What did it feel like when you entered gravity again?
Everything felt very heavy, including our own bodies. I picked up a three-pound camera just after splashdown and it felt like it weighed fifteen or twenty pounds. When I rolled over on my side in the spacecraft couch to pick up the camera, it felt like one side of my rib cage was collapsing onto the other. These exaggerated impressions of heft and weight only lasted a few days and, for the most part, disappeared completely in less than a week.
160. Did you have any difficulty adjusting to gravity again?
There were several incidents that I found disconcerting:
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