Space Chronicles: Facing the Ultimate Frontier (22 page)

Some people seem to believe that we just strap the astronauts to a rocket and fire them to the Moon. Fact is, a lot of image reconnaissance goes into planning these journeys. For example, in 1966–67 five Lunar Orbiter spacecraft were sent to study the Moon and photograph possible landing sites. The photograph of what became Apollo 11’s landing site is now part of the Lunar Orbiter Image Recovery Project at the NASA Ames Research Center. Fast forward four decades, and the NASA’s Lunar Reconnaissance Orbiter, the LRO, returned its first images of the Apollo 11 landing site, with the lunar module still sitting right there, casting a long, distinctive shadow. LRO is the next step in returning astronauts to the Moon—it’s a robotic scout that’s helping to find the best places to explore. Future images will be even better. And by the way, those images are publicly available, so you can show them to anyone who somehow continues to believe we faked it all.

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ASA operates on our hearts, on our minds, on the educational pipeline—all for one-half of one cent on the tax dollar. It’s remarkable how many people think NASA’s budget is bigger than that. I want to start a movement where government agencies get paid the budget people think they’re getting. NASA’s budget would rise by a factor of at least ten.

That people think NASA’s budget is huge is a measure of the visibility of every NASA dollar that gets spent. An extraordinary compliment that I wouldn’t give up for anything, lest we stop advancing in all the areas Americans have come to value in the twentieth and twenty-first centuries.

For me, an interesting feature about NASA is its ten centers scattered across the country. If you grow up near one of them, you have either a relative or a friend who works for NASA. Working for NASA is a point of pride in those communities, and that sense of participation, of common journey, is something that makes this agency an enterprise for the entire nation, not simply for the select few.

Some engineers and administrators and other workers from the Apollo era still work at NASA today—though likely not for much longer. We are destined to lose them. Many, many people besides the astronauts contributed in essential ways to the Apollo era. Think of it as a pyramid. At the base are thousands of engineers and scientists, laying the groundwork for the Moon voyages. As you work your way up the pyramid, the astronauts are at the top—the brave ones putting their lives at risk. But in doing so, they place their trust in what the rest of that pyramid provides. And what sustains the base of that pyramid, keeping it broad and sturdy, is inspiration of the coming generation.

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CHAPTER TWENTY-ONE

HOW TO REACH THE SKY
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n daily life you rarely need to think about propulsion, at least the kind that gets you off the ground and keeps you aloft. You can get around just fine without booster rockets simply by walking, running, rollerblading, taking a bus, or driving a car. All those activities depend on friction between you (or your vehicle) and Earth’s surface.

When you walk or run, friction between your feet and the ground enables you to push forward. When you drive, friction between the rubber wheels and the pavement enables the car to move forward. But try to run or drive on slick ice, where there’s hardly any friction, and you’ll slip and slide and generally embarrass yourself as you go nowhere fast.

For motion that doesn’t engage Earth’s surface, you’ll need a vehicle equipped with an engine stoked with massive quantities of fuel. Within the atmosphere, you could use a propeller-driven engine or a jet, both fed by fuel that burns the free supply of oxygen provided by the air. But if you’re hankering to cross the airless vacuum of space, leave the props and jets at home and look for a propulsion mechanism that requires no friction and no chemical help from the air.

One way to get a vehicle to leave our planet is to point its nose upward, aim its engine nozzles downward, and swiftly sacrifice a goodly amount of the vehicle’s total mass. Release that mass in one direction, and the vehicle recoils in the other. Therein lies the soul of propulsion. The mass released by a spacecraft is hot, spent fuel, which produces fiery, high-pressure gusts of exhaust that channel out the vehicle’s hindquarters, enabling the spacecraft to ascend.

Propulsion exploits Isaac Newton’s third law of motion, one of the universal laws of physics: for every action, there is an equal and opposite reaction. Hollywood, you may have noticed, rarely obeys that law. In classic Westerns, the gunslinger stands flat-footed, barely moving a muscle as he shoots his rifle. Meanwhile, the ornery outlaw that he hits sails backward off his feet, landing butt first in the feeding trough—clearly a mismatch between action and reaction. Superman exhibits the opposite effect: he doesn’t recoil even slightly as bullets bounce off his chest. Arnold Schwarzenegger’s character the Terminator was truer to Newton than most: every time a shotgun blast hit the cybernetic menace, he recoiled—a bit.

Spacecraft, however, can’t pick and choose their action shots. If they don’t obey Newton’s third law, they’ll never get off the ground.

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ealizable dreams of space exploration took off in the 1920s, when the American physicist and inventor Robert H. Goddard got a small liquid-fueled rocket engine off the ground for nearly three seconds. The rocket rose to an altitude of forty feet and landed 180 feet from its launch site.

But Goddard was hardly alone in his quest. Several decades earlier, around the turn of the twentieth century, a Russian physicist named Konstantin Eduardovich Tsiolkovsky, who earned his living as a provincial high school teacher, had already set forth some of the basic concepts of space travel and rocket propulsion. Tsiolkovsky conceived of, among other things, multiple rocket stages that would drop away as the fuel in them was used up, reducing the weight of the remaining load and thus maximizing the capacity of the remaining fuel to accelerate the craft. He also came up with the so-called rocket equation, which tells you just how much fuel you’ll need for your journey through space.

Nearly half a century after Tsiolkovky’s investigations came the forerunner of modern spacecraft, Nazi Germany’s V-2 rocket. The V-2 was conceived and designed for war, and was first used in combat in 1944, principally to terrorize London. It was the first rocket to target cities that lay beyond its own horizon. Capable of reaching a top speed of about 3,500 miles an hour, the V-2 could go a few hundred miles before plummeting back to Earth’s surface in a deadly free fall from the edge of space.

To achieve a full orbit of Earth, however, a spacecraft must travel five times faster than the V-2, a feat that, for a rocket of the same mass as the V-2, requires no less than twenty-five times the V-2’s energy. And to escape from Earth orbit altogether and head out toward the Moon, Mars, or beyond, the craft must reach 25,000 miles an hour. That’s what the Apollo missions did in the 1960s and 1970s to get to the Moon—a trip requiring at least another factor of two in energy.

And that represents a phenomenal amount of fuel.

Because of Tsiolkovsky’s unforgiving rocket equation, the biggest problem facing any craft heading into space is the need to boost “excess” mass in the form of fuel, most of which is the fuel required to transport the fuel it will burn later in the journey. And the spacecraft’s weight problems grow exponentially. The multistage vehicle was invented to soften this problem. In such a vehicle, a relatively small payload—such as the Apollo spacecraft, an Explorer satellite, or the space shuttle—gets launched by huge, powerful rockets that drop away sequentially or in sections when their fuel supplies become exhausted. Why tow an empty fuel tank when you can just dump it and possibly reuse it on another flight?

Take the Saturn V, a three-stage rocket that launched the Apollo astronauts toward the Moon. It could almost be described as a giant fuel tank. The Saturn V and its human cargo stood thirty-six stories tall, yet the three astronauts returned to Earth in an itty-bitty, one-story capsule. The first stage dropped away about ten minutes after liftoff, once the vehicle had been boosted off the ground and was moving at about 9,000 feet per second (more than 6,000 miles per hour). Stage two dropped away about ten minutes later, once the vehicle was moving at about 23,000 feet per second (almost 16,000 miles per hour). Stage three had a more complicated life, performing several episodes of fuel burning: the first to accelerate the vehicle into Earth orbit, the next to get it out of Earth orbit and head it toward the Moon, and a couple more to slow it down so that it could pull into lunar orbit. At each stage, the craft got progressively smaller and lighter, which means that the remaining fuel could do more with less.

From 1981 to 2011, NASA used the space shuttle for missions a few hundred miles above our planet: low Earth orbit. The shuttle has three main parts: a stubby, airplanelike “orbiter” that holds the crew, the payload, and the three main engines; an immense external fuel tank that holds more than half a million gallons of self-combustible liquid; and two “solid rocket boosters,” whose two million pounds of rubbery aluminum-based fuel generate 85 percent of the thrust needed to get the giant off the ground. On the launchpad the shuttle weighs four and a half million pounds. Two minutes after launch, the boosters have finished their work and drop away into the ocean, to be fished out of the water and reused. Six minutes later, just before the shuttle reaches orbital speed, the now-empty external tank drops off and disintegrates as it reenters Earth’s atmosphere. By the time the shuttle reaches orbit, 90 percent of its launch mass has been left behind.

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ow that you’re launched, how about slowing down, landing gently, and one day returning home? Fact is, in empty space, slowing down takes as much fuel as speeding up.

Familiar, earthbound ways to slow down require friction. On a bicycle, the rubber pincers on the hand brake squeeze the wheel rim; on a car, the brake pads squeeze against the wheels’ rotors, slowing the rotation of the four rubber tires. In those cases, stopping requires no fuel. To slow down and stop in space, however, you must turn your rocket nozzles backward, so that they point in the direction of motion, and ignite the fuel you’ve dragged all that distance. Then you sit back and watch your speed drop as your vehicle recoils in reverse.

To return to Earth after your cosmic excursion, rather than using fuel to slow down, you could do what the space shuttle does: glide back to Earth unpowered, and exploit the fact that our planet has an atmosphere, a source of friction. Instead of using all that fuel to slow down the craft before reentry, you could let the atmosphere slow it down for you.

One complication, though, is that the craft is traveling much faster during its home stretch than it was during its launch. It’s dropping out of a seventeen-thousand-mile-an-hour orbit and plunging toward Earth’s surface, so heat and friction are much bigger problems at the end of the journey than at the beginning. One solution is to sheathe the leading surface of the craft in a heat shield, which deals with the swiftly accumulating heat through ablation or dissipation. In ablation, the preferred method for the cone-shaped Apollo-era capsules, the heat gets carried away by shock waves in the air and a continuously peeling supply of vaporized material on the capsule’s bottom. For the space shuttle and its famous tiles, dissipation is the method of choice.

Unfortunately, as we all now know, heat shields are hardly invulnerable. The seven astronauts of the Columbia space shuttle were cremated in midair on the morning of February 1, 2003, as their orbiter tumbled out of control and broke apart during reentry. They met their deaths because a chunk of foam insulation had come loose from the shuttle’s huge fuel tank during the launch and had pierced a hole in the leading shield that covered the left wing. That hole exposed the orbiter’s aluminum dermis, causing it to warp and melt in the rush of superheated air.