What is Rockets: Definition and 135 Discussions

A rocket (from Italian: rocchetto, lit. 'bobbin/spool') is a projectile that spacecraft, aircraft or other vehicles use to obtain thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellant carried within the rocket. Rocket engines work by action and reaction and push rockets forward simply by expelling their exhaust in the opposite direction at high speed, and can therefore work in the vacuum of space.
In fact, rockets work more efficiently in space than in an atmosphere. Multistage rockets are capable of attaining escape velocity from Earth and therefore can achieve unlimited maximum altitude. Compared with airbreathing engines, rockets are lightweight and powerful and capable of generating large accelerations. To control their flight, rockets rely on momentum, airfoils, auxiliary reaction engines, gimballed thrust, momentum wheels, deflection of the exhaust stream, propellant flow, spin, or gravity.
Rockets for military and recreational uses date back to at least 13th-century China. Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology for the Space Age, including setting foot on the Earth's moon. Rockets are now used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight, and space exploration.
Chemical rockets are the most common type of high power rocket, typically creating a high speed exhaust by the combustion of fuel with an oxidizer. The stored propellant can be a simple pressurized gas or a single liquid fuel that disassociates in the presence of a catalyst (monopropellant), two liquids that spontaneously react on contact (hypergolic propellants), two liquids that must be ignited to react (like kerosene (RP1) and liquid oxygen, used in most liquid-propellant rockets), a solid combination of fuel with oxidizer (solid fuel), or solid fuel with liquid or gaseous oxidizer (hybrid propellant system). Chemical rockets store a large amount of energy in an easily released form, and can be very dangerous. However, careful design, testing, construction and use minimizes risks.

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  1. .Scott

    Artistically Ornated Atmosphere

    That Life Science article is entitled "SpaceX rockets keep tearing blood-red 'atmospheric holes' in the sky, and scientists are concerned". The article suggests "astronomy and communications" as potential "unrecognized problems". Also from the articles: As a non-expert, non-scientist, I think...
  2. W

    B Newton's second law -- rockets

    I am having difficulty understanding the information below. In the second line it states that F=0 as there is no external force on the system. However it later calculates acceleration of the rocket. How can Force=0 if there is acceleration? (This is the first time I have encountered the...
  3. J

    Optimal Size of Rocket Engine Nozzle for Vacuum Performance

    I'm interested in how rocket engines perform in a vacuum. My first impression is that an atmosphere is needed for the action/reaction to push against in order to get forward movement. I saw a demonstration using a long balloon attached to a long length of string stretched across a room. When the...
  4. .Scott

    Methalox Rockets: First Attempts, Future Plans

    Per Spacenews.com: It appears that Zhuque-2, built by the Chinese firm Landscape, failed to reach orbit yesterday. That was the first attempt to reach orbit using methane/oxygen boosters. However, more methalox orbital attempts are coming soon: * Relativity, a Long Beach, CA company that uses...
  5. BarChen

    Become a Propulsion Engineer - Learn to Work with Rockets & Spacecraft

    Hi guys, I'm about to start my degree in a few months and I know what field I want to major in but I don't know what track I should take. In the future I want to work with rockets and spacecraft engines, I want to help develop the new generation. Correct me if I'm wrong but it's called a...
  6. H

    Which sub-forum would be suitable for asking Q. related to rockets?

    If I need to ask doubts about very basics of rockets and satellites, for example about what basically Ramjet and Scramjet are, which sub-forum should be suitable.
  7. D

    Exploring Electron Rockets for Interstellar Travel

    Hi all, Why not build an electron rocket? Why won't this idea work? Seems like someone could just hitch an electron gun onto a spaceship. Boom! Electron Rocket. I was thinking about ion thrusters. These use ions to achieve thrust. They are problematic for achieving a high delta V because...
  8. P

    Conservation of energy in Gravitation

    Suppose a rocket is moving at radial velocity vr and tangential velocity vt in the Sun's gravitational field. At some time, the rocket enters the gravitational field of Mars (with the above mentioned velocities), and gravitation effects due to the Sun can be ignored. After more time, the rocket...
  9. A

    Collision time between two rockets in one rocket's frame....

    While attempting this question , velocity of ##B## wrt ##A## ,##u'_x=\frac{u_x-v}{1-u_xv/c^2}## where ##u_x=-0.6c,v=0.8c## comes out to be ##-0.945c## (approaching).. The distance between ##A## and ##B## seen by ##A## at ## t=0## is ##d=\sqrt(1-.8^2)4.2×10^8## comes out to be ##252*10^6m##...
  10. A

    Do Nations Need USA Launch Permission for Rockets?

    When other countries are launching rockets into space do they have to get permission from USA for the launch? i.e. China, Iran, India, Japan, Do they just simply coordinate with the local airspace to avoid any conflict or do they actually have to attain a launch permission from a body in USA.
  11. E

    Traveling to Mars with plasma rockets

    Plasma-powered rockets could reduce the travel time to Mars by roughly half. https://theconversation.com/traveling-to-mars-with-immortal-plasma-rockets-58705
  12. Robert DeVries

    Trouble with fluid thermodynamics and nuclear thermal rockets

    Summary:: In need of help determining the exhaust velocity of a rocket nozzle given temperature and propellant molar mass Greetings and salutations! My name is Robert DeVries, world builder extraordinaire. I have come with questions in search of answers. So for the last few days I've been...
  13. M

    Bernoulli's Equation and water rockets

    So I'm playing around with some water rockets and I'm trying to figure out how fast the exhaust velocity of the water is. I've had an experimental approach using high fps camera to record and analyse (using tracker) the exhaust velocity. I'm using a 0,5 l soda bottle with 0,085 L ; 0,135 ; L...
  14. C

    Is Specific impulse indicative of performance as a gun propellant?

    Black powder has specific impulse of around 80s, while rocket candy has up to 130s of specific impulse. Does that mean I could replace the propellant in a BP cartridge with 80/130 of the weight in rocket candy and obtain the same performance in an idealized gun? (as in without considering...
  15. M

    Investigating Motion of Rockets & Satellites: Advanced Mechanics Depth Study

    Homework Statement: Hi, I just got my first year 12 assignment which is a depth study of advanced mechanics. I had one idea of investigating the motion of rockets and satellites. I could even do something with circular motion or projectile motion, taking air resistance into consideration. I...
  16. W

    How many rockets would it take....

    The world is ending bla bla bla. :) The core question is, how many rockets can launch at the same time around the entire earth. Doesn’t matter if the atmosphere is destroyed after, anyone left behind is already dead. What matters is getting as many people off the planet at the same time. I can...
  17. sweet springs

    I Transverse inertial motion of rockets in acceleration

    Hello. I have a question on inertial motion transverse to gravity force, e.g. blocks of dry ice floating on the smooth and flat floor on Earth. For simple mathematics I explain my problem in Rindler case. Let a group of N rockets gather at origin (0,0,0,0) of a IFR and let them start...
  18. X

    Engine design -- Fusion powered rockets

    I found this interesting engine design on the internet. It is one of the most powerful and largest machines human have ever designed. It is a fusion powered propulsion device, it uses “heavy fusion technology” which can use any elements lighter than Fe-56 as power source. Is this design feasible?
  19. A

    So how is it accelerating (two rockets in space)

    Assume that there are 2 rockets in deep space or a place where there is nothing around to compare their motion to. Rocket A starts its thrusters but the observer in rocket A doesn't know about it. So my question is, if rocket A is considered to be stationary by the observer then how can he...
  20. P

    Calculations on a fireworks rocket?

    So I'll soon be writing an assigntment on the physics and chemistry behind firework rockets and that's why I'm here! I've already prepared for the chemistry part but when it comes to the physics part then I am a bit lost. Bare in mind that I'm supposed to learn something new (myself) and explain...
  21. Benjamin Fogiel

    A rocket burns out at an altitude h above the Earth's surface

    Homework Statement A rocket burns out at an altitude h above the Earth's surface. Its speed v0 at burnout exceeds the escape speed vesc appropriate to the burnout altitude. Show that the speed v of the rocket very far from the Earth is given by v=(v02-v2esc)1/2 Homework Equations KEf-KEi=Ui-Uf...
  22. S

    Why are rockets tethered before takeoff

    Hi there, Recently i was watching some rocket launches and was wondering why they are tethered before takeoff, after some searching i found out that they are used to keep a constant supply of fuel to replace the part that boils off. But is there any other uses for such tethers?
  23. R

    Steering rockets in space by shifting CM

    So, I'm investigating a certain way of steering a rocket in space for my first undergraduate research project. Essentially, the idea is to control the location of some mass located on a horizontal track perpendicular to a rocket, so that when the mass is moved, the center of mass of the rocket...
  24. C

    What is the combustion efficiency of liquid fuel rockets?

    How efficiently is the fuel burned in a typical liquid fuel rocket engine? I've heard numbers ranging from 95% to below 50%.
  25. T

    B Why do rockets explode so easily when they tip over?

    I've seen the SpaceX fail videos, even when they tip over on water the rockets still explode. Why?
  26. D

    I Why do rockets turn horizontally so soon after launch?

    My 12 year old asked me this question. I have a MS in Mechanical Engineering, so I can usually answer his physics questions, but this one stumped me. When lifting off, why do most rockets turn close to horizontal almost immediately? Of course we know they need mostly horizontal speed to...
  27. Kevin

    Pressure Gradient for Nitrous Flow

    Hello everyone, I am currently working on an undergraduate club team for the Intercollegiate Rocket Engineering Competition. I am attempting to do a calculation to determine the pressure needed in a vessel leading to another pressurized combustion chamber to achieve a desired mass flow rate...
  28. chandrahas

    What makes rockets expensive?

    Rockets are quite expensive and it takes about 2000 to 10000 dollars to place 1 pound into orbit. So I was wondering: Is the size or the fuel mass of a rocket a big concern or will it be of no help economically if we make smaller rockets with less fuel mass for the same amount of payload...
  29. Rednecknav

    I Calculating Energy to Remove Space Debris from Earth Orbit

    How much energy needs to be be expended to throw a non operating satellite (or other space trash) out of orbit (L4 or L5) or L2 into deeper space... thus minimizing space debris in Earth orbit. I could only find formulas for getting an object INTO orbit... Background of question: we were...
  30. C

    Rockets approach: time they meet w.r.t. rocket A?

    This is an IB problem from November 2017. Two rockets are separated by 6E8m (2 sec x c, or two light-seconds), w.r.t. Earth, and are approaching Earth from opposite directions. Rocket A approaches from left at 0.6c. Rocket B approaches form right at 0.4c. According to Earth, when do they...
  31. A

    B Ride a Supersonic Rocket: Can You Hear Your Friend?

    if you and your friend ride a supersonic rocket , do you can listen to your friend voice ? I mean if you travel faster than sound will you can hear anything ,It's difficult to imagine. And thanks so much,
  32. S

    B How do rockets propel themselves up?

    Well, first thing, I am new to this forum and it looks pretty good and I'm looking forward to reading more from it and post more questions. Well rocket propeling (or anything that uses some material to propel up when shooting it down) seems pretty straight forward at first, you have some gas...
  33. J

    B Is it always better to use multi stage rockets?

    Hello all! I was wondering if there is a scenario, where a single stage rocket will be superior to a multi-stage rocket, and if so, why? i'm under the impression that multi stage is always better, but i don't think that is entirely correct. Good day to you all
  34. J

    Multi-stage Vs. single stage rockets

    Homework Statement Hello all I have to show why there advantageously can be employed multi-stage rockets Homework Equations How do i do this best, a graph/plot? The Attempt at a Solution i have done some calculations for a single stage rocket and a multistage rocket, but how can i show this...
  35. J

    Graph of multi-stage rockets

    Homework Statement Show why it is advantageous to use multistage rockets Homework Equations - 3. The Attempt at a Solution [/B] Hello there I have to show why using multi stage rockets are an advantage, i have done som calculations for a 2. stage rocket and a singel stage, with the same...
  36. J

    Advantages of Multistage Rockets: Calculating the Benefits with an Example

    Homework Statement Assess why there can advantageously be used multistage rockets, with a calculation example. Homework Equations - The Attempt at a Solution [/B] Hello all, i need to show why it is an advantage to use multistage rockets, with some mathematical proof, and I am a bit lost. I...
  37. michaeldk

    Pendulum fallacy - hovering rockets, still applies?

    Hi all! I've come here to seek your expertise because I've ran into a bit of a heated discussion (well, heated from the other side ;-) about rockets, hovering and center of gravity. Basically people are referencing to the pendulum fallacy when I say that a rocket which is hovering would be...
  38. ramzerimar

    Books on structures of rockets and spacecraft?

    I've been looking after some good books dealing with structural engineering of rockets and spacecraft s in general. I know that Rocket Propulsion Elements is a good book on rocket science, but I'm looking not only for propulsion but more specifically for structural design (loads, stress...)...
  39. Minestra

    Kinematics Problem with Rockets

    Homework Statement In Example 2.6, we considered a simple model for a rocket launched from the surface of the Earth. A better expression for a rocket's position measured from the center of the Earth is given by Y(t)=(RE3/2+3(√g/2)REt)2/3 where RE is the radius of the Earth (6.38 ✕ 106 m) and g...
  40. kolleamm

    B Near C Speed Rockets: Time Dilation & The Twin Paradox

    Suppose we had two rockets traveling in opposite directions at 0.99c each. Would a rocket in one frame of reference see the other traveling at 1.98c? The argument would be that we would observe the rocket going slower, since time would slow down at near c speeds but who does the time slow...
  41. Astronuc

    RIP Bob Ebeling - Engineer of Shuttle Booster Rockets

    Challenger Engineer Who Warned Of Shuttle Disaster Dies http://www.npr.org/sections/thetwo-way/2016/03/21/470870426/challenger-engineer-who-warned-of-shuttle-disaster-dies Thanks, Bob, you did right!
  42. C

    A rocket ship leaves earth at a speed 0.6c. When a clock....

    Homework Statement A rocket ship leaves Earth at 0.6c. The clock of the rocket says 1hr has elapsed. (a.) According to the earth clock, when was the signal SENT? (b.) According to the earth clock, how long after the rocket left did the signal arrive BACK on earth? (c.) According to the rocket...
  43. T

    How long does it take for a rocket to lift off the ground?

    Homework Statement A rocket with an initial mass of 60,000kg ignites its engines and burns fuel at a rate of 300 kg/s with an exhaust velocity of 2220 m/s. How long after the engines start does the rocket lift off the ground? Homework Equations From Newton's second law F = Ma this equation can...
  44. C

    Rockets and inverted pendulums

    Hi, I can´t understand how a rocket is not flipped over by the thrusters (especially without finns). I know this is a general misconception of how a rocket works, but it seams intuitive that it would behave like a inverted pendulum, since the force works below the center of mass, of the rocket...
  45. SteveManPhy076

    Theoretical Floating Cities

    Could there perhaps ever be floating cities? If we could get the type of technology that sends rockets into space, and have the boosters running at a constant and equal velocity inversely, could this cause anything to levitate? If so, would this even be habitable? Considering that the fumes...
  46. Gbl911

    Compression Nozzles on Model Rockets

    I am doing a experiment with model rockets to see if a added compression nozzle on a model rocket would make the engine perform better. As you can see in this picture there is a small clay nozzle immediate to the propellant. This is the same place that you put the igniter. My experiment is...
  47. pioneerboy

    Quit undergrad physics -- Wishes and options? Advice please

    Hello everyone, I am brand new here in the PhysicsForum and this is my very first message. So it's apleasure to meet likeminded people sharing the same interest and probably also profession. The latter is also the reason why I finally registered in this forum and I sincerely hopethat I am given...
  48. Basimalasi

    What is the characteristics of the flow in Hot-water rockets

    So I'm trying to make a Hot-Water Rocket. But I want to make the necessary thermodynamics calculations first. What kind of flow will it be in such systems I think it's obviously going to be an unsteady flow but is it uniform or not? I also would love if you guys linked me to unsteady...
  49. E

    How rockets take curved paths in space (absent gravity)

    This might have been answered before but it's something that has been bothering me. A rocket in space will move in a straight line. If I apply thrust, it still moves in a straight line unless I apply the thrust in a different direction. So unless I have rocket nozzles attached to the side...