The First Scientific Concept of Rockets for Space Travel by Robert Godwin Part 5
From The Space Library
Contents |
A Journey Through Space - 1861
We know that Leitch arrived in Boston after the beginning of hostilities in early 1861. We also know he then subsequently embarked for Scotland. In his essay on Clark he talks about being on the steamer so we can perhaps assume that he wrote his treatise on Clark during the crossing. It appeared in Good Words in the July 1861 issue (Good Words was now a monthly) and it was followed in August by an explanation of his work with bees. [1] This would suggest that these works predated his next essay which would return him to the world of astronomy and appeared in Good Words in the September issue. Perhaps he also wrote it during the crossing, or perhaps it was composed before leaving Canada. All we can know for certain is that it was written after the summer comet of 1860 but wasn’t ready for publication that year, but it was finished by the time he returned to Glasgow in autumn of 1861. It seems improbable that he had time to write it during his first few months of tenure at Queens, but not impossible. The timing couldn't have been better. The demand for Good Words was now flying high. The noted review periodical The Bookseller writing in September 1861 on the state of the competition between the hoard of magazines being published stated, "...the only one that is progressing is Good Words, which appears to devour all others." [2]
The September essay in Good Words would be entitled “A Journey Through Space” and this time Leitch was to outdo himself.[3]
He began by making a quick summary of how important the spirit of man is, even when faced with the immensity of the cosmos. His argument, couched in wholly Christian terms, was that despite the work of astronomy constantly revealing humans to be smaller and smaller, the result in his mind at least, was how important this made us. This same notion was articulated more than a century later by noted science writer Arthur C. Clarke who submitted that if humans are alone in the universe, or not; the confirmation of either fact would be equally astounding.
Using his most eloquent prose Leitch then decided to elevate his reader to a place outside of the usual observation post of planet Earth and take them on a tour of the universe.
The Rocket for Space Flight
“Though the facts and deductions of astronomy sufficiently bring out the immensity of the universe, as contrasted with our world, still it is difficult to realise the truth; our thoughts will obstinately cling to our globe, and the images of grandeur will still be, our terrestrial seas and mountains. Let us, however, attempt to escape from the narrow confines of our globe, and see it, as others see it, from a different point of view. Let us take a nearer survey of other orbs and systems, and see what impressions they produce, as compared with that received from the platform of the earth.
“But what vehicle can we avail ourselves of for our excursion? Must we be altogether dependent on the fairy wings of imagination, or can we derive aid from some less ethereal agencies? It was long the fond wish of man to soar above this terrestrial scene, and visit other planets. In the infancy of physical science, it was hoped that some discovery might be made that would enable us to emancipate ourselves from the bondage of gravity, and, at least, pay a visit to our neighbour the moon. The poor attempts of the aeronaut have shown the hopelessness of the enterprise. The success of his achievement depends on the buoyant power of the atmosphere, but the atmosphere extends only a few miles above the earth, and its action cannot reach beyond its own limits.
“The only machine, independent of the atmosphere, we can conceive of, would be one on the principle of the rocket. The rocket rises in the air, not from the resistance offered by the atmosphere to its fiery stream, but from the internal reaction. The velocity would, indeed, be greater in a vacuum than in the atmosphere, and could we dispense with the comfort of breathing air, we might, with such a machine, transcend the boundaries of our globe, and visit other orbs.
“Instead, however, of torturing our imagination to conceive of a rocket device, which would eclipse the performances of all flying machines, let us take one of nature’s rockets as the material aid to our imaginary flight. Let us follow the course of some comet in its wanderings across our system. A rocket, held fast, with its fiery stream directed against a strong wind, very well represents the telescopic appearance of a comet, when in the neighbourhood of the sun. The luminous particles shoot out from the nucleus of the comet, precisely as the sparks issue from the rocket-tube, and they are thrown back as a strong wind would throw back the fiery stream of the rocket.”
This remarkable opening volley by Leitch seems at first blush to overthrow a century of space history. The paragraph highlighted above in bold type offers no opportunity for misinterpretation. It is succinct and self explanatory. Leitch knew that the reaction forces implicit in the rocket made it the only engine which would work in space, and it would work better in space.
These two facts are in direct contravention of the accepted history of this subject. There are two slightly different but similar reasons why a rocket’s velocity is “greater in a vacuum than in the atmosphere”. They both involve the impeding nature of air molecules.
Newton's Laws
If a rocket accelerates away from the earth, the air around it gradually gets thinner and becomes less of an encumbrance to its flight, but if the rocket continues to get faster it has to push more air out of the way. Eventually a balance is achieved where the density of the air and the accelerating rocket hit a point where the two are at their most contentious. In the parlance of NASA this moment is called “Max Q” or maximum aerodynamic pressure. From that point onwards the air pressure declines and the rocket continues into the vacuum of space. All the time becoming more efficient because it is no longer being impeded by the air.
It seems that Leitch was clearly aware of the effect of a vacuum on things in flight. He states as much in his essay about the moon. “Think how strange life must be in the moon without an atmospheric medium… Armies in battle array do not hear the boom of the cannon, though rifled arms, from the low trajectory of the ball, must acquire a fatal precision and range.” His last word is critical, “range”. From this we can see that he understood that a vacuum removes this hindrance to forward flight. There is no “Max Q” in space.
The other reason that a vacuum improves the efficiency of the rocket is more subtle, but also important. The whole notion of a “reaction” engine is that if you throw mass in one direction it causes movement in the opposite direction. In the case of the rocket the “mass” is hot gas coming out of the rocket nozzle. The faster you can push the hot gas out of the nozzle the faster your rocket moves in the opposite direction. However, when you fire a rocket in the atmosphere at sea level the hot gas has to fight the air pressure around the nozzle. As the rocket ascends, this pressure declines steadily until the rocket reaches space. Evidence of this can be seen during any major rocket launch; as the rocket gets higher the plume of its exhaust widens as the air pressure declines.
This is where the argument began for those who did not understand Newton’s third law. The rocket naysayers argued that without air pressure to push against, the rocket wouldn’t move. Therefore it couldn’t be used in space.
However, we can see from his own words that Leitch clearly understood that this was not the case. “The rocket rises in the air, not from the resistance offered by the atmosphere to its fiery stream, but from the internal reaction.”
Quite clearly Leitch spells out the explanation for why the lack of air in space is a boon not an impediment. In space there is no air to inhibit the rapid flow of the exhaust. It would take another six decades before Robert Goddard would prove this through experimentation.
Leitch’s description is worded in such a way to suggest that this was not even an important revelation to him. With very little effort the reader could be persuaded that this was something Leitch had discussed previously and had simply dismissed as so improbable that he gave it very little further consideration. However his comment about “torturing his imagination” suggests otherwise. His knowledge of projectiles is implicit.
Earlier Efforts
Certainly there were earlier references to rocket flight, but the few that exist were apocryphal or satirical, or simply written by people who had no understanding of why this might work. The oft-cited Chinese adventurer Wan Hu, with his rocket propelled chair, is almost certainly an example of complete fiction; very likely created in the early 20th century. Then there is the French satirist Cyrano De Bergerac. Born in 1619, Cyrano was a soldier in the French army who was well known for his outrageous tales. It is of interest to note that Cyrano wrote two hilarious satires about space travel. The Comical History of the States and Empires of the Moon (1656) and The Comical History of the States and Empires of the Sun (1662). The single most significant contribution made by Cyrano would be his proposal to actually use rockets as a method of propulsion to send his protagonist (himself) to the moon. However, Cyrano did not hit upon this idea due to any exceptional scientific awareness or belief in its viability. An alternative method that he proposed was to fill bottles with dew, and then simply by strapping the bottles to his belt, he was miraculously lifted skyward by the inevitable action of the sunlight on the dew. Isaac Newton’s revelations were still 25 years in the future.
There can be no such misinterpretation of Leitch’s words. He not only very clearly understood how a vacuum was an impediment to any form of winged flight, but as an expert astronomer, he was also well-versed in Newtonian physics. Most remarkably he showed a very clear understanding of the dynamics of gasses in a vacuum and in an atmosphere. He dismissed the fumblings of the “aeronaut” (at that time a reference to balloonists, as this was 42 years before the Wright Brothers) and concluded that the rocket would far outstrip any other flying vehicle. Click here for Part 6
