Newton's Laws of Motion are:
Newton's Laws are all contained in a more general principle called conservation of momentum. Momentum is mass times velocity, and in a system that is not disturbed from outside, the total momentum stays constant. Thus:
Suppose you are standing on very slick ice. You weigh 50 kg. You fire a 1 gram (.001 kg) bullet at 1000 m/sec. Its momentum is .001 x 1000 = 1 (the units are kg-m/sec, if you're curious). To keep the total momentum of the original system zero, you have to acquire -1 momentum. Since you weigh 50 kg, your velocity will be -1/50 or -.02 m/sec. You will start sliding backward on the ice at 2 centimeters per second. This is why a rifle has a kick.
As an aside, what matters are instantaneous changes. Once the bullet leaves the gun, it's no longer part of your system, and what happens to it doesn't affect you. You don't feel a momentum change when the bullet strikes its target. Likewise, when friction eventually slows your slide on the ice, that doesn't affect the bullet. Okay, go back to what you were doing.
Rockets and jets work according to Newton's Third Law. They fire mass out at high speed and acquire velocity in the opposite direction. Thus, we can dispel one common myth about rockets and jets: they do not need something to push against. A rocket does not take off because it is pushing against the ground, nor does a jet fly because it is pushing against the air. They move because they are expelling exhaust gases at high speeds. If you like, the rocket or jet is pushing mass away, and the mass is pushing back (equal and opposite reaction.)
Rockets and jets expel mass by burning fuel. A rocket differs from a jet in that a jet gets the oxygen for combustion from the atmosphere, and a rocket carries oxygen in some form with it. Thus rockets can function outside the Earth's atmosphere; jets can't.
When a rocket or jet takes off, it has to carry all its remaining fuel with it. Most of the mass of the Space Shuttle is fuel, and most of that is used to get the remaining fuel off the ground. The miles-per-gallon fuel efficiency of the Space Shuttle in its first foot off the ground is pretty terrible!
Satellites travel elliptical paths with the center of the Earth at one focus (A below - Kepler's First Law, again). Anything shot from the surface of the Earth, a baseball, say, or a cannonball, travels an elliptical path, but the ellipse soon intersects the surface of the Earth again. Ballistic missiles do the same thing except their ellipses intersect the surface of the Earth thousands of kilometers away. Nothing shot directly from the surface of the Earth can go into orbit; it will either fall back to Earth again or, if it's moving fast enough, escape completely.
Objects stay in orbit because of a balance between inertia, that would cause them to keep moving in a straight line, and gravity, that would pull them down. Isaac Newton conceived of artificial satellites (B below). He pointed out that a cannon on a high enough mountain and firing ever faster cannonballs could fire them to greater and greater distances. If fired with a great enough velocity, the curvature of the cannonball's path would be equal to that of the Earth and the cannonball would circle the Earth.
To get into orbit, you have to climb Newton's mountain first (C). Rockets are launched into orbit by launching them vertically to get them above the atmosphere, then accelerating them horizontally to reach orbital velocity. It takes 29,000 km/hour to do this in low Earth orbit. You get 1670 km/hour of this for free thanks to the Earth's rotation. That's why most satellites are launched eastward.
The Chinese invented both gunpowder and rockets over a
thousand years ago. Gunpowder is sulfur, carbon (charcoal) and
saltpeter (sodium nitrate - NaNO3). The oxygen for combustion
comes from the saltpeter.
(The reaction is something like: S + C + 8NaNO3 = SO2 + CO2 + 8NO2 + 4Na2O)
Chinese rockets were used for celebrations and in warfare for psychological rather than destructive reasons.
The British encountered somewhat more dangerous rockets in India in the mid 1700's and began designing their own. The standard design was the Congreve rocket, which looks like the stereotypical Fourth of July skyrocket scaled up. It was a cylinder with a conical nose and a stabilizing tail stick that also served to support it. The "rockets' red glare" in the Star Spangled Banner were Congreve rockets. The military advantage of rockets is that, unlike cannon, they have no recoil, so can be launched in large numbers from a small ship. Throughout the 19th and 20th centuries rockets were used occasionally as artillery, more often for illumination, signaling, and occasionally carrying rescue lines and messages.
It is a remarkable fact that just about every major theoretical question regarding spaceflight was worked out in advance by amateur enthusiasts long before the technology was available. The decision to put the Apollo spacecraft into lunar orbit and use a detachable lander was, in all practical respects, made before World War II. The three leading pioneers in rocket technology were Konstantin Tsiolkovsky, Robert Goddard and Hermann Oberth
Konstantin Tsiolkovsky (1857-1935), a Russian schoolteacher, was virtually unknown outside Russia for many decades, but worked out just about every major theoretical problem connected with space travel. He is the theoretical father of space flight.
|Robert Goddard (1882-1945) had his epochal vision of space travel in 1898 during the reign of Queen Victoria, and as Carl Sagan notes in Cosmos, "before anyone had ridden in an airplane or listened to a radio". Truly a remarkable goal for the time, all the more so for being able to carry much of it out. When one of his early lectures was ridiculed in the media, Goddard shunned publicity. Nevertheless he attracted funds and support from several sources, notably aviation pioneer Charles Lindbergh. Goddard launched the first liquid-fueled rocket and developed most major principles of rocket guidance. Goddard developed the rocket into a practical device.|
Goddard's first prototype of 1926 is shown above.
Hermann Oberth was the only one of the three pioneers to live to see the full fruition of his ideas. In contrast to Goddard, Oberth and the German rocketry program hyped rocketry to the fullest to raise funds and support. They found allies in the German military, with fateful results. Oberth can be considered the father of ballistic missiles.
In summary, Tsiolkovsky made rocketry theoretically possible, Goddard built the hardware, and Oberth made rockets operational. There were, of course, many other people contributing.
Future historians may well see World War II as a tremendous watershed. Films set in the 1930's have an antiquated look about them; films set in World War II seem modern. World War II saw the advent in at least prototype form of computers, radar, jet aircraft, nuclear weapons, and missiles.
All the major powers developed and used rocket weapons in World War II, mostly as light artillery. The German rocket program was dramatically different. Set up at Peenemunde on the Baltic coast, its purpose was to develop the first strategic rocket weapons.
The first German V weapon (V for Vergeltung: retaliation) was the V-1, a small pilotless jet aircraft that carried an explosive warhead and fell to Earth when it ran out of fuel. It traveled slower than the speed of sound, could be tracked on radar, and although it was faster than most aircraft, radar warnings enabled the British Royal Air Force to intercept them and shoot them down regularly. The V-1 was the famous "buzz bomb", so called for the sound its engines made in flight.
The V-2 was a true rocket. It was about 15 meters long and two in diameter and looked exactly like the standard depiction of rockets in popular media of the time. It reached speeds of 5,000 km/hour, altitudes of 150 km (well outside the atmosphere) and ranges of several hundred kilometers. The V-2 traveled faster than sound, came down steeply, and hit without warning. None were ever intercepted. At the height of the V-2 campaign, they were actually causing more casualties than the famous Blitz of 1940-41. But by this time, Germany was clearly losing and the V-2 did not have the desired psychological effect. After D-Day, V-2's were also fired at Allied facilities on the mainland, especially at the port of Antwerp in Belgium. The other casualties of the V-2 were the slave laborers who built the rockets and rocket factories. More people may have died building the V-2 than died from its use as a weapon.
In one incident that would do credit to Hollywood, the Polish underground, acting in concert with the British, got to a crashed V-2 before the Germans, pushed it into a river to hide it, then removed key components and smuggled them to British Intelligence for analysis.
As the Allies closed in, the German rocket program fled the advancing Russians and most of the key personnel, including Werner von Braun, surrendered to American forces.
The Germans, British and U.S. were all working on jet aircraft before or during the war, but only the Germans fielded an operational weapon. Had it appeared early on, it would have been devastating, but the German jets only appeared in small numbers near the end of the war, the Germans did not fully realize their potential, and German production facilities were in no shape to sustain the manufacture of enough jets.
The Germans had conceived of most of the elements of a modern missile program, if only on the drawing board. They experimented with underwater missile launches, developed an air-to surface missile that actually sank several ships, and were thinking of orbital launches and intercontinental missiles.
Although rocketry captured the news headlines in the late 1950's, many of the technical advances that made spaceflight possible came from the testing of high-performance aircraft. Tom Wolfe's book, The Right Stuff is a marvelous account of the connections between flight testing and early space exploration. The title refers to the fact that a military jet pilot has about a 25 per cent chance of being killed in his career, and pilots cope with this by cultivating a superstition of having "the right stuff" that will protect them from harm. The 25 per cent figure, by the way, does not include combat; it is the fatality rate due to accidents and malfunctions.
Chuck Yeager's pioneering supersonic flight was cloaked in secrecy, but after publication of Wolfe's book he became something of a celebrity. Of course, long before then he was a superstar among aviation enthusiasts. Occasionally the universe does serve up justice. The culmination of the research in aeronautics was the X-15, one of the most successful research aircraft ever flown. It flew about 200 times, reaching altitudes of 67 miles and speeds of 7,000 km/hour.
The Spaceflight video and writings by Wolfe and others hint that the better approach of the X-15 was aborted by the rush to get a human into space quickly, an error that was only recently corrected with the Space Shuttle. The maximum velocity of the X-15 was only about one-fourth that required to reach orbit, and 1000 km/hr of that was provided by the B-52 that carried it. Since energy increases as velocity squared, the X-15 would have required 16 times as much fuel to reach orbit, plus the fuel needed to lift the additional fuel. It would be too heavy to carry on a B-52, increasing fuel demands still more. Also, the X-15 had no life support for extended stays in space and had room for only one person. By the time we reconfigure the X-15 to be a viable orbital spacecraft, it would need a heavy booster to reach orbit, something developed to support the manned space program. The reality is that the Space Shuttle requires both the aeronautical knowledge developed by the X-15, plus the vertical lift technology of the manned space program.
|The core of the Sputnik 1 launcher was an early ICBM, the SS-6. Its warhead was removed, an extra oxygen tank added in its place, and four additional boosters added around the outside.|
Everyone knows that the Russians developed their space program by employing captured German scientists after World War II. Everyone is wrong! Both the Russians and the U.S. built V-2's immediately after the war - it was the only operational military missile in the world. The Russians used captured Germans to build their V-2's but kept them tightly sequestered from their main rocketry program. They were well treated and returned to Germany in the early 1950's. And how do we know this? Because we debriefed them after their return.
However, the often repeated story that the Soviet missile program (which in a relatively short time led to the world's first intercontinental ballistic missile and soon thereafter to Sputnik, the pioneering artificial satellite) had been the work of German rocket engineers taken into the Soviet Union after the war, is just plain nonsense. Wernher Von Braun's development team, which had fathered thc V-2, had left its Peenemunde rocket center on the Baltic before the Red Army arrived and was ultimately captured by the United States Army in southern Germany. The Soviet Army did draft a number of production engineers from the subterranean plant in the Harz Mountains back into service after the war to get the V-2 production moving again. Most of these men were indeed moved to the Soviet Union later, but, being production rather than development people, they could contribute little to more advanced missile concepts. There were a few first-class development engineers among them, but according to their own accounts (published years later), they were merely asked to offer their own ideas for possible technological improvements without being given access to secret Soviet plans for the future. Under these conditions, the work of the former Peenemunde men in the Soviet Union was mainly in support of the evaluation and improvement of the V-2. By 1953 all of them had been repatriated to Germany.
Why has the myth of the Soviet dependence of the Germans persisted even though the truth has been in the open literature for years? Because it's what we want to believe.. Following World War II, Americans tended to believe that "American know-how" would inevitably triumph. After the launch of Sputnik I, Americans were dumbfounded and simply could not believe that the supposedly backward Russians had gotten there first. The need for an explanation, plus the all-too-ready tendency of the American public to believe in conspiracies, accounts for the durability of the myth.
The real hero of the Soviet space program was Sergei Korolev. Known as the "chief designer", his existence and identity were tightly guarded secrets in the Soviet Union during his lifetime. He was an early pioneer of the Soviet rocketry movement and was, in effect, a prisoner of his own brilliance, not permitted to travel abroad or appear in public. He was further eclipsed by premier Nikita Krushchev's insistence on taking the glory of the Russian space program for himself. In his final years he fell from grace because of his clashes with Krushchev, but by then Soviet space technology was well established.
"Sputnik", by the way, is a blend of three Russian roots: "s" means "with", "put" means "path", and "nik" meaning "one who does something"; in other words, someone who travels the same path with you. It can mean "satellite" but also "fellow traveler". It's accurate to refer to the Communist nations of Eastern Europe as satellites, but it carries a different connotation in Russian.
|Looking at the world in 1957, the U.S. and Russia faced two different strategic challenges. We were consumed by fears of Russian advances in Europe and Asia, but the Russians had no bases close to the contiguous U.S (Cuba didn't become Communist until 1960). At that time there were no ballistic missile submarines. We, on the other hand, had military forces in Germany, Turkey, Japan, and many other places close to Russian soil, plus a huge advantage in aircraft carriers. A map centered on Russia shows them hemmed in by hostile forces. We can't entirely blame them for being a bit paranoid.|
In 1950, the Russians actually were well ahead in the race to develop the hydrogen bomb and we got there first only because of a breakthrough by physicist Edward Teller. The Russian bombs were huge; ours were smaller, plus we believed we could make them even less massive. With huge bombs and a long way to enemy territory, the Russians were forced to develop massive rocket boosters capable of lifting enormous loads. We, on the other hand, preferred to rely on bombers and our skill at miniaturization to make smaller weapons requiring less massive rockets. Thus, when the first satellites were launched, the Russian satellites were measured in tons and ours in kilograms.
President Eisenhower is often disdained by intellectuals for presiding over a rather bland period of U.S. history. Eisenhower did indeed fail badly by not reining in Joe McCarthy, but in some other ways he was well ahead of his time. More than anyone else he warned of the dangers of the Military-Industrial Complex and tried to avert a U.S.-Soviet arms race. He tried to allay public fears of a "missile gap", but with little effect.
Cruise missile is a term most of us associate with the Persian Gulf War, but in fact the first cruise missile was the V-1. In the late 1940's and early 1950's, much of the U.S. missile effort was devoted to cruise missiles before it was finally decided they were not effective delivery systems (then) for intercontinental nuclear warfare. This factor further slowed U.S. development of heavy missiles.
The U.S. Army had come to Eisenhower in 1956 with a plan to launch a satellite, but Eisenhower insisted that U.S. space exploration be civilian. U.S. scientists were confident of launching a satellite before 1957 was out. Project Vanguard was scheduled for launch in December, 1957, and, to the horror of a nationwide news audience, toppled over and exploded on the launching pad.
The Army plan had already been dusted off and given the go-ahead after the launch of Sputnik I. The satellite and upper stages were designed, built and launched in the incredibly short time of three months. The first U.S. satellite, Explorer I, was launched into orbit on January 31, 1958.
The next few years were gloomy ones for American space enthusiasts. Launch failures were frequent. Soviet failures, many far more catastrophic than any we experienced, were hidden for decades behind a thick veil of secrecy. In retrospect, it was never more than a year or so between some Soviet success and the U.S. equaling or surpassing it, but, speaking as one who lived through that time, it seemed like forever.
Illustrations of Important Rockets and Spacecraft
Created 31 January 1998, Last Update 10 April 1998
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