|Sývý Yakýtlý Roketler -
A gauche moteur à flux dérivé classique (RD-107),à droite moteur à flux
intégré (RD-253).(Dessin d'un auteur inconnu 1980)
Le moteur Russe RD-180 que l'on retrouve sur des
Fonctionnement Viking d'Ariane-1
Fonctionnement Vulcain d'Ariane-V
Le moteur Russe de tous les succés
Sistemi besleyen yakýt ve roket motoru yanma odasýnda oksitleyici: a - inert, b - pompa. 1 - yakýt tanký, 2 - meme karýþtýrma baþkaný 3 - gaz tüpleri yüksek basýnç, 4 - vanalar, 5 - oksitleyici tank, 6 - Soðutma, düþük basýnç 7 - gaz tüpleri, 8 - Pompalar 9 - türbini, 10 sýcak gaz - seçim türbin sürücüye.
Fýrlatma aracý Sputnik:
RD-107 þematik diyagramý
1 - Direksiyon odalarý;
2 - Kavþak açmak kamera direksiyon;
3 - Boru oksidan direksiyon odalarý;
4 - Boru Hatlarý direksiyon yakýt hücreleri;
5 - ana kamera;
7 - buhar-gaz jeneratörü;
8 - Türbin;
9 - Pompa oksitleyici;
10 - Yakýt pompasý;
11 - Basýnç sensörü, çekiþ kontrol sistemi;
12 - ana oksitleyici vana;
13 - Boru oksidan ana odalarý;
14 - yakýt ana vana;
15 - Boru Hattý yakýt ana kamera;
16 - Start-up ve hidrojen peroksit kesme vanasý;
17 - Basýnç azaltýcý;
18 - Pompa hidrojen peroksit;
19 - elektrikli sürücü ile Air diþli;
20 - Sývý azot pompa;
21 - sistemi ile tanklarý boþalma þok elektrik
Ýkinci aþamada motor RD-108
An Introduction to Rocketry
The first solid-fueled rockets were invented by the Chinese around the year 100. These early rockets worked by burning gunpower in a combustion chamber, and then directing the hot gas released out of a nozzle. In this way, the gas pushed the rocket through the air, like what happens when you blow-up a ballon and let it go. Fifteen-hundred years later, Isaac Newton would explain this with his Third Law of Motion: "For every action there is an equal and opposite reaction."
When the Europeans learned about rockets in the 19th century, they were quick to apply ther knowledge of chemistry to rocket design. The Europeans devised fuels more effective than gunpowder. Also, Europeans developed more efficent nozzles to channel the gases of the rocket. The most notable of these is the DeLaval nozzle, which is used in every rocket engine in use today. Gustav DeLaval was a Swedish engineer of French descent. He invented his nozzle design while he was working on steam engines. One of his designs for a steam turbine used jets of hot steam to turn itself. The faster the jets, the faster the turbine would spin, and the more power it would produce. Delaval found that the most effective way to get a high speed jet was with a nozzle that alternately converged and diverged:
The key to the DeLaval nozzle was this: as the nozzle narrowed, the jet's speed would increase. By carefully constructing the nozzle, the jet could be made to go supersonic just as it reached the nozzle throat. Now traveling faster than sound, the jet would move into the divergent section of the nozzle. Because the jet was supersonic, its speed would increase again as the nozzle diverged. However, if the jet was not supersonic by the time the nozzle began to diverge, its speed would decrease and the rocket would lose its thrust. Additionally, if the jet passed the sound barrier before reaching the throat, the narrowing walls would force it to slow down. Obviously DeLaval nozzles needed to be constructed exactly for their best performance.
In 1915, a yound man named Robert Goddard from Worcester MA, began experimenting with rockets. One of the problem that he found with the rockets of the time was that they were not very efficent. Only 2% of the energy released was used to accelerate the exhaust. Since a faster exhaust means more power, Goddard looked for effective ways to channel the exhaust. After reading about DeLaval's work, Goddard made one of the nozzles for a rocket he was building. When he tested it, the rocket had an efficency of 63%. This is far more efficent than any other engine. Steam engines can get up to 21%, and Diesels can reach 40%. Goddard realized that with such high efficentcies, rockets would be instrumental in probing the high atmostshpere and beyond. Goddard was able to get a grant from the Smithsonain to pursue this line of research. Unfortunately, America's entry into the First World War meant that Goddard would have to put his work on hold for awhile in the face of more pressing war problems.
After the war, Goddard returned to his rockets. He continued to experiment with various solid fuels for his rockets, but in 1922 he started designing a liquid-fueled rocket. Liquid-fueled rockets differed from solids in many ways, and posed serious technical challenges. Just by looking at a diagram of a liquid-fueled engine you can see how complex it is:
Looking more closely, you can see the parts of a rocket that we are familiar with: the combustion chamber and the nozzle. Up at the top of the diagram are the tanks which hold the fuel and the oxidizer. Everything else on the diagram is simply there to move the fuel and the oxidizer from their tanks to the combustion chamber. The oxidizer provides the oxygen for burning the fuel. In solid-fueled rockets the oxidizer is mixed in with the fuel. Liquid-fueled rockets, however, have to keep the fuel and oxidizer seperate. Some different types of oxidizers are liquid oxygen and hydrogen peroxide. Liquid-fueled rockets have several advantages over solids. They can vary the amount of thrust, they are reusable, and they can be restarted once they are shut off. Solids, on the other hand, burn completely and at a constant rate once they are lit.
Constructing liquid-fueled rockets is not an easy task. They burn at much higher temperatures than solids, and they require precision machines to keep them operating. It took Goddard four years to build his first flyable rocket. He tested it in March of 1926. For the first twenty-seconds of the test, the rocket sat on the ground, burning off fuel, until it became light enough and took-off to an altitude of 41 feet. It then promptly leveled off and flew into a neighbor's cabbage patch. In total, the rocket had been in the air for only 2.5 seconds. While unimpressive by today's standards, Goddard's test is considered the "Kitty Hawk" of rocketry.
In the years following Goddard's flight, rocketry evolved rapidly. Several designs were studied that moved away from chemical fuel entirely. Engineers looked at everything from ion engines to pulsed-nuclear propulsion. Throughout all of this, chemical rockets continued to get bigger and more powerful. Their development culminated in the first flight of the Saturn V in 1967. The Saturn V generated a million and a half times more thrust than Goddard's first rocket. It could send two Space Shuttle flights worth of payload to the Moon. Unfortunately, when the Apollo Program was canceled in 1972, the Saturn V was retired. No other rocket in operation today can match the performance of the Saturn V.
La propulsion chimique
C'est le système de propulsion actuellement utilisé en majorité : en effet,
c’est le seul système assez développé pour échapper à la gravité terrestre.
La poussée est produite par la réaction entre un carburant et un comburant,
appelés ergols. Cette réaction produit un gaz sous très haute pression, qui
est expulsé par l’intermédiaire d’une tuyère, pour produire la force de
poussée et propulser le vaisseau (La forme de la tuyère est un élément clé
pour la performance du système).
Le premier réacteur
Fonctionnement de la fusée à propergol
Très fiable, ne posant pas de problème de stockage et de
mise en oeuvre, ce type de fusée est très utilisé sur les petits engins. De
très nombreux types de propergol sont employés depuis la poudre noire
jusqu'au mélange perchlorate d'ammonium / aluminium des boosters la navette
spatiale ou d'Ariane 5 en passant par les poudres nitrocellulosqiues
fabriquées à partir de coton...
Fonctionnement de la fusée à propergol
La proximité d'un comburant et d'un carburant présente de
très grands risques d'explosion, l'accident le plus fréquent sur ce type de
moteur est la rupture des réservoirs entraînant rapidement une explosion (
c'est ce qui a causé l'accident de la navette spatiale Challenger en 1987 ).
Typical liquid propellant rocket motor (Hill and Peterson, 1992).
A hydrogen-oxygen rocket engine
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