Rocket Definition and 78 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. H

    Conservation of Momentum of Rocket Exploding after Takeoff

    -Solved for vf using equation 3 to get 20.0m/s (speed before explosion) then solved for the distance to reach the explosion using equation 4, to get 20.0m, which felt wrong having the same numbers but that may just be coincidence. -Found the distance travelled of the lighter piece using 530m -...
  2. NODARman

    Change of ellipse while accelerating the rocket

    When the rocket accelerates in space does its trajectory which is an ellipse change in size and not the focal points because the Earth is still in one of two and also the current height doesn't increase, right?
  3. B

    The Traditional Bernoulli Eqn Derivation of Rocket Exhaust Velocity

    If you've seen it, they chose one point in the combustion chamber and the other in the exhaust nozzle. I think they're assuming that we have a gas both places. They say that the pressure in the nozzle is atmospheric pressure, or it you're in outer space, zero. That makes perfect sense...
  4. H

    I Image for increase in gravitational potential energy in radial field

    A question to physicists: What sort of real world scenario / image would *best* depict the increase in gravitational potential energy in a radial field? Would a rocket traveling through the Earth's atmosphere suffice or are there better alternatives? This image would have to be relevant to the...
  5. C

    A 2.0x10^4 kg rocket has a rocket motor that generates….

    I tried A with the solution of 9.73 and 8.69 both wrong.
  6. G

    I Centrifugal Effects During Rail Launch

    I’m writing a 3DOF sim for a rocket. I’m having a hard time visualizing centrifugal effects from the Earth's rotation on the rocket while it is moving along the rail (acceleration > 0). I know that once it has left the rail I no longer need to account for it since it’s in the ECI frame and...
  7. O

    B Untraditional Space Travel

    If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low Earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle. Assuming the launch vehicle...
  8. Sagittarius A-Star

    I What is the force on a scale in the following Rocket scenario?

    [Moderator's note: Spin-off posts from previous thread have been included in this new thread. Also, the OP's re-post of the scenario for discussion has been moved to this top post for clarity.] Yes. Physically, scales measure a force (and indirectly the energy) in their frame. Consider the...
  9. Zenon

    What is the relationship between a rocket and Inverted Pendulum?

    I'm doing my homework about the Inverted Pendulum and I'd like to know how a rocket flies and why it's related to an Inverted Pendulum.
  10. F

    Rocket moving away from the Earth

    I first began to identify the various events in the problem. I call the rocket ##S'## and the Earth ##S##. Sending signal Tail signal reflection Head signal reflection Tail signal return Head signal return For the Earth I know that: ##t_4 = T## ##t_5 = T + \Delta T## Since the two events...
  11. D

    DV Calculation clarification (rocket booster)

    When calculating the dV available from a rocket booster, the below calculation is used: (ISP . g) . ln(Mass when full/Mass when empty) Is 'g' always equal to 9.81 in this equation, or do you use the actual gravitational acceleration that the booster will experience, at it's given altitude, to...
  12. G

    A rocket and its gas exhaust velocity

    This isn't right, is it? -\dfrac{GM}{R}+\dfrac12 v^2=-\dfrac{GM}{R+h} v=\sqrt{\dfrac{GM}{R}}\left( 1-\sqrt{\dfrac{R}{R+h}}\right) He's doing energy conservation. The mechanical energy at the Earth's surface is equal to the energy when the speed is 0.
  13. M

    B Is there an analytical solution to this equation?

    So I've derived the rocket equation in empty space and with constant gravity. Now I am interested in adding air resistance. I'm aware that there are 2 different models as if 0<Re<1 then F_drag=k*v and if 1000<Re<30000 then F_drag=1/2*A*rho*CD*v^2. And for my purpose the second model is most...
  14. 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...
  15. Physyx

    How to model a rocket equation from the derivative of momentum?

    I am using the derivative of momentum (dp/dt) with Newton’s 3rd Law with the gravitational force of Earth. F - [Force of gravity on rocket] = dp/dt F - (G * m_e * m_r / r2 ) = v * dm/dt + ma F = Force created by fuel (at time t) G = Gravitational Constant m_e = Mass of Earth m_r = Mass of...
  16. F

    Solving the Rocket Pendulum Fallacy?

    I have been researching the rocket pendulum fallacy and have gotten into some spirited debate on the subject. If I understand correctly... 1. if the thrust is perfectly in line with the centerline (and no outside forces act on the craft other than gravity) it does not matter where the source...
  17. bob14

    Solving a Second-Order Nonlinear Differential Equation

    Homework Statement Hi, I'm trying to calculate the formula for the position vs. time of a rocket landing from an altitude of 100km. I'm neglecting a lot of forces for simplification but basically, I want to solve ##F_{net} = Drag - mg##. Homework Equations Drag Force: D = ## \frac {C_dAρv^2}...
  18. G

    Rocket equation without infinite small variables

    Hey, I'm tutor for theoretical physics for first year students and I found a question that I couldn't answer so far. It's about the rocket equation. I tried to derive the acceleration without using infinite small variables, but somehow there is one term left that shouldn't be there. In the...
  19. R

    Find the initial velocity of a water rocket (mass changes)

    Homework Statement Find the initial velocity of the boost phase (when water is coming out). Here is everything I know - Mass of rocket with no water is 0.13kg, mass of rocket with water is 1.1kg. The total length of the rocket is 0.48m. The time to the maximum point is 3.46 seconds, and total...
  20. T

    Forces - Space Shuttle Takeoff Calculations

    Homework Statement [/B] The total mass of a space shuttle and its launch vehicle is M=2000t. a) What must be the minimum size of the thrust force, to make the rocket move? b) The actual thrust of the rocket is F=30MN. What is its acceleration in the beginning? c) Assume that a mass of a...
  21. S

    I Multistage continuous Rocket Eqn

    So if you have a rocket let's say that discards all the structural and engine mass continuously at zero velocity that is relative to the rocket until only the payload is traveling at the final velocity - then what will the equation of motion will look like? we can neglect the drag and...
  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. Julian Erickson

    I Rocket-Jet Hybrid, Rocket + Ramjet

    I read that a thrust augmentor can significantly increase the efficiency of a jet engine ( Now from my understanding, the thrust agumentor is sort of like a ramjet. Only, in this case, the cold air is being sucked in along with the hot air...
  24. G

    I ##F=\dot{p}=\dot{m}v+m\dot{v}## and Galilean invariance

    Hi. In Newtonian physics, total mass is conserved, but open systems can obviously gain or lose mass, such as a rocket. But how can the term ##\dot{m}v## be Galilean invariant?
  25. S

    I Fission source as "rocket"

    Looking at a humble smoke detector - a metal plate with some alpha source on one side. I guess the fission products / apha etc emitted in one direction are absorbed into the metal, and the opposite direction go into space. So there should be a minute net force ? Would that be useful as a "sail"...
  26. L

    Relative velocity of exhaust in Ideal Rocket Equation

    In this derivation of the Ideal Rocket Equation (, they use the fact that ##V_e = V - v_e##, or that the velocity of the exhaust in the observer frame ##V_e## is the velocity of the rocket ##V## minus the speed of...
  27. 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...
  28. BlackholeGirl

    NASA [NASA] Cosmological projects instead of space exploration

    NASA decided to stop *WFIRST and concentrate on Mars project (send humans to Mars). What do you think about it? In my opinion, since a lot of ventures have begun space developments such as SpaceX and this proves that rockets make money, NASA should tackle WFIRST. Generally, we cannot earn...
  29. 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...
  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. Franz Rojas Ayala

    Maximum pressure for a combustion chamber

    Greetings All! I am not sure if this is the correct place to post this, but I think that since rocket fuel is considered a chemical reaction, this sections seems appropriate. Right, to the topic. Me and my team from the spaceflight society are looking forward to building a hybrid rocket fuelled...
  32. J

    Height From Hangtime

    Homework Statement We are doing water rockets and I don't know how to calculate the height it went from it's hang time. It's total hang time was 7.35 seconds, and I know it's vertical acceleration was -9.8m/s^2 from gravity, and I'm assuming I need to first find out it's initial velocity, since...
  33. D

    Finding the Coefficient of Drag for Partial Parachutes

    Hey Guys, I'm on a rocket team at my university and we are attempting to figure out the force of opening acting on some of our parachutes. Typically this is done using the following equations, in particular, the one in the top right corner. This is where our trouble begins. In the Recovery...
  34. A

    B Supersonic rockets

    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,
  35. B

    A rocket on a cart is fired to go through a hoop

    Homework Statement A 300 g rocket is on a cart that is rolling to the right at a speed of 2 m/s. The rocket engine, when it is fired, exerts an 6 N thrust on the rocket. Your goal is to have the rocket pass through a small horizontal hoop that is 18 m above the launch point. At what horizontal...
  36. S

    Launching a rocket from high altitude

    I have a project where I will be launching a rocket from a high altitude weather balloon. I am planning on launching the rocket at around 70Km or even higher. My main concern is the igniter not being able to ignite the engine because of the low amount of oxygen. Is there any way around this...
  37. 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...
  38. EL_bob

    Magnetic assisted rocket engine

    Hello everybody! I have been thinking about something for a while now. I would like to make a magnetic nozzle for a rocket engine. Basically, I would like to ionize the hot and high pressure gaz in the combustion chamber and then use a strong magnetic field to adjust the nozzle throat...
  39. H

    Simple Water Rocket

    I'm going to make a water propelled pop bottle rocket for a competition. The bottle holds 1.5 liters and we are going to fill some amount of it with water and pressurize it to 75 psi. When triggered, water will come out of the hole in the cap and propel the rocket. The rocket is perfectly...
  40. Jared

    Need help finding energy for escape velocity

    Homework Statement The gravitational potential energy of a certain rocket at the surface of the Earth is -1.9x10^12 J. The gravitational potential energy of the same rocket 300km above the Earth's surface is -1.8x10^12 J. Assume the mass of the rocket is constant for this problem. A) How much...
  41. J

    Rocket Engine: Centripetal Force to Vector thrust

    Hey guys, I'm new to the forum and I have a question that has stumped several of the professors at my school. My idea is to use an electric motor with a solid rocket engine on a thrust stand to spin the exit cone. The concept would make use of centripetal force to increase the pressure of...
  42. doktorwho

    Explosion and momentum

    Homework Statement A rocket is fired from from the ground at initial velocity of ##v_0## and at an angle ##\theta##. At its highest height it splits into 2 parts of equal masses. The first part is fired straight up and at velocity ##v_0/2##. Find the angle and intensity of the second part...
  43. A

    How to calculate force exerted by ground

    Homework Statement Force exerted by the ground on the rocket Mass of the Rocket = 1500kg Duration of landing impact = 0.04 s Velocity at time of impact = 175 m/s Distance traveled = 30km Time taken to complete journey = 6 minutes Acceleration due to gravity = 9.8 m/s^2 Homework Equations...
  44. M

    Rocket meaning - definition

    I was wondering if there is an actual definition given by a recognised organisation over what is meant by the word "rocket". In case there is not, I wanted to reflect upon what do we really mean when we say rockets.
  45. 1oldman2

    Space Stuff and Launch Info

    Due to the constant never ending supply of "cool stuff" happening in Aerospace these days I'm creating this thread to consolidate posts every time something new comes along. Please feel free to add random information if its relevant. So to start things off here is the SpaceX Dragon launch coming...
  46. T

    Calculating combustion temperature of mixture

    Hey guys, I'm trying to write a small article that very simply explains some of the math involved with a rocket engine. I'm not looking for a very accurate answer so I tried the following method 1) Stoichiometry on the fuel which was sugar and saltpeter and their respective enthalpies of...
  47. J

    Speed of Hydrogen combustion out of a tube?

    Hello, I was curious about how to calculate how fast the escape velocity of hydrogen out of a tube/cylinder would be. Once end of the cylinder is closed, the other is open, obviously. Assume the cylinder is full of hydrogen at 1 atm. My thought is that you could use PV=NRT to calculate the...
  48. defaultusername

    Lagrange Multipliers / Height of a Rocket

    Homework Statement I am going to paste the problem word for word, so you can have all the exact information that I have: You’re part of a team that’s designing a rocket for a specific mission. The thrust (force) produced by the rocket’s engine will give it an acceleration of a feet per second...
  49. Andy24

    Coefficient of Drag on a model rocket

    Hello everyone, I am predicting the altitude of a model rocket based on some testing I did where I found the impulse of a little single stage model rocket motor. I am wondering how to incorporate drag into my calculations to make it more accurate. I know D=Cd*rho*v^2*A and I can definitely find...
  50. M

    B How do I calculate the apogee of a rocket before launch?

    Is there any equation in order to know how high my rocket will go, before launching it? I suppose that if there is any, it will not take into account air drag and others, and there is no need for that. I just one to know an approximate, I am making a summer project with some friends and we had...