¡SkyCaramba! Weekly astronomy blog for the week ending July 19, 2014
It’s hard to believe there was a time when some people doubted any object could maneuver in space. Only science fiction characters traveled to other planets. Even sending a machine above the atmosphere to do any work seemed imaginative. Some people thought that if humans ever succeeded in putting objects in space, those objects would travel along paths determined by external forces and the laws of physics. They were sure there was no way to steer a spacecraft in the vacuum of space.
Isaac Newton understood that for every action there is an equal and opposite reaction. Push away the water with your palms in a swimming pool or bath tub. Even though you move the water, it feels like the water is trying to push back. Indeed, it is! That makes it possible to swim in deep enough water.
Air is a lot less dense than water. So you can push it out of the way a lot easier. But gravity pulls you downward through air a lot faster too. That’s why even the best human swimmers can’t flap their arms fast enough to fly. To get anywhere on land, a person must push against the earth and experience the push back that results in walking, running, or jumping.
Now suppose you’re in a vacuum with no planet or anything else beneath you. With nothing to push against, how would you get anywhere unless you were already moving toward that place? With a little thought, it seems absurd that one can steer in space. On January 13, 1920, the New York Times published an editorial dismissing the idea as something no one with a high school education could seriously consider.
The newspaper had reacted to a paper Robert H. Goddard published a day earlier. The famed scientist and inventor had already worked for at least 13 years with various types of rockets. We would liken many of them to toys today. But in his 1920 work, Goddard calculated what it would take to make a rocket go high enough and fast enough to escape Earth’s gravity and land on the moon. The New York Times said it was one thing for Jules Verne to entertain people with a story, but such a fantasy “is not so easily explained when made by a savant who isn’t writing a novel of adventure”.
With a little more thought, we can understand that a rocket in space certainly does have something to push against that will push back on it. The stuff is called rocket fuel. Not only is it pushed away, it is burned to release a tremendous amount of energy. Pushing that mass and energy away and out the rocket’s exhaust tube is the action. The equal and opposite reaction is that material pushing the rocket forward or in whatever other direction is opposite.
Goddard never stopped believing. However, vindication didn’t come during his lifetime. He died in 1945. The first artificial satellite reached orbit in 1957 and an object landed on the moon two years later. Then, in 1969 as Apollo 11 carried the first people who would walk on the moon on the journey to it, the New York Times published a retraction.
After “further investigation and experimentation”, the paper’s hard nosed skeptics were satisfied that “it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere”. In all likelihood, all the editors had long outgrown their skepticism or left the paper. But reputable newspapers admit their mistakes—even many years later.