What is Rocket: Definition and 999 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. S

    Find the amount of work done against gravity in moving a 150kg rocket

    I started by calculating the energy at the Earths surface, which is just -G(150)(6 x 10^24)/(6400 x 10^3) = -0.9 x 10^10, and calculating the energy at the orbit radius, E = -G(150)(6 x 10^24)/(18000 x 10^3) = -3.4 x 10^9, then doing some subtraction we have -3.4 x 10^9 - (-0.9 x 10^10) = 5600 x...
  2. U

    B What limits a rocket's max speed if in space drag is zero?

    What limit rocket max speed if in space drag is zero? If drag is zero and thrust is constant that mean rocket accelerate all the time?
  3. N

    Help with final year uni course selection for defense and rocket industry

    TL;DR Summary: Help with final year courses that will help for defense and rocket industry. Hello , what extra courses would be best to help with knowledge in defense/rocket industry as a mechanical engineer in final year. I am going to do thermofluid specilisations for my final year and I am...
  4. P

    Ionizing Atmosphere on the nose of a rocket, missile or aircraft to reduce drag

    I heard of a strange engineering concept that was mentioned to me by someone who claimed to be a retired aerospace engineer. It was a guy I met on the internet so I took what he said to me with huge grain of salt. He said something to me that I barely comprehend and I haven't heard from this...
  5. S

    B Launch of a rocket - its initial displacement and velocity

    so then when we model the velocity of the motion of a rocket (e.g., in a mathematics report), is it reasonable to assume that the initial velocity equals zero? I also apologise for my lack of information if I made a huge mistake in my question 🙏🏻
  6. R

    Rocket propelled by a beam of photons

    Before the engine is switched off: $$P_{Initial rocket} = (m_{i}c, 0)$$ $$P_{photons} = (E/c, -p_{photons})$$ where E is the energy of the photons and ##p_{photons}## is the 3 momentum of the photons. Rocket after engine switched off: $$P_{Final rocket} = (m_{f}c, m_{f}v)$$ By conservation of...
  7. JoeDGreat

    What is the rocket's initial acceleration?

    Help me solve... I'm getting errors here..
  8. S

    B Another special relativity related "paradox"

    Full disclosure: I have asked this question on stackexchange too, but I think I didn't frame my question properly there, which probably led to misunderstandings and complicated answers. Plus some comments there led me to refine the question a bit so I hope it's in a good state now. I am new to...
  9. F

    Why is the thrust equation same under gravitational force?

    The homework statement isn't exactly as is mentioned above. The actual problem statement is as follows: This is problem 3.8 from John R. Taylor's Classical Mechanics; however, my question is not related to the main problem itself but one particular aspect of it. Now, in the same textbook (John...
  10. C

    I Aircraft guidance question: Effect of mounting sensors at the CG vs on the Tail

    Hi, Can I someone please explain to me, the moment behaviors of having something fixed on CG vs on Tail in a rocket? are there any benefits of having a Sensor on CG than fixed on the tail? Thank you
  11. T

    Water Rocket Science Project by Tanguy: Reach 11,2k m/s!

    Hi ! I'm a French student in Terminale (12th grade equivalent) and I have to do an oral presentation of 5min (Grand Oral) for my baccalauréat linked with my professional project. As I want to become an engineer in astrophysics, I want to talk about water rocket and the theoretical possibility to...
  12. P

    Rocket thrust equation in under-expanded nozzle

    Hello, so the thrust equation goes like: F = (m dot)*v_e + A_e*(p_e - p_a), where F ... thrust [N] m dot ... mass flow rate [kg/s] v_e ... velocity of exhaust [m/s] A_e ... area of the exit nozzle plane [m2] p_e ... pressure of the exhaust at the exit of the nozzle [Pa(a)] p_a ... ambient...
  13. R

    Where in orbit should a rocket fire to escape with minimum ΔV

    I am really lost on how to deal with this. Since this is an elliptic orbit, the mechanical energy is negative. For the rocket to escape orbit, we have to get the mechanical energy to be equal to or greater than zero. I thought at first that it would escape in the perigee, since that's where the...
  14. L

    B Model rocket physics: Why doesn't the motor go through the nose cone?

    For those who have built those small model rockets, please help me understand a very very simple physics problem that i for some reason do not fully get. Why is it that the motor tube does not have a retention ring on it, to prevent the motor from flying out the nose cone? i know it cant be...
  15. A

    Rocket acceleration problem: confused about Newton's 2nd Law

    TL;DR Summary: I approach a rocket acceleration problem using two approaches: F=d(m*v)/dt and F=ma. The resulting differential equations are different. What am I doing wrong? We have a ship with a mass-reaction rocket engine floating in space. The initial mass of the ship (including fuel) is...
  16. L

    Finding the terminal velocity of a model rocket from a list of velocities

    Ok, i have some rocket data from a 20,000 foot launch. I have the times, altitudes, and velocity at said time. Is it possible to find the terminal velocity from this long list of numbers? I tried graphing the velocities to see where the curve flattens out, since usually that is where terminal...
  17. J

    B Speed of light and this Accelerating Rocket scenario

    Hello, I have a question linked to gravity and speed of light : According to the Special Theory of Relativity, the speed of light cannot be exceeded because it would need an infinitive energy to accelerate the relativistic mass of a moving objet (a space craft for example) : indeed if the...
  18. P

    B Calculating Fuel Efficiency of Rocket Going Near c

    How would you calculate the fuel efficiency of a rocket (around 10 tonnes) going near the speed of light?
  19. gleem

    Rocket Lab's Neutron Rocket

    The Neutron is the rocket that Rocket Lab intends to compete with SpaceX's Falcon9. Still in development Rocket Lab is planning to use composites for tankage and airframe. Didn't SpaceX try this for the Falcon but abandoned it in favor of proprietary stainless steel...
  20. L

    I Measuring Model Rocket Velocity: Is it Possible?

    Question, if i record a video of a model rocket launching, and then falling, is it possible to get the actual (or extremely close) velocity every 1 second? thanks
  21. L

    Impact force of model rocket with parachute

    I just launched a 2.2kg model rocket that stands about 5 feet tall and has a airframe that is 4 inches in diameter. I am trying to find how much the impact force is when the rocket hits the ground at 16MPH. Whats the best approach? Momentum? KE? or something else:) thanks
  22. Ahmad Sadek

    B Can a rocket flame be controlled by a magnetic field?

    An idea came to my mind after I saw the plasma reactor and how the plasma floats through a magnetic cage that prevents the nuclear reactor from melting, to make a magnetic cage that prevents the rocket engines from melting while they are working. Is this possible, or does it take a critical...
  23. 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 -...
  24. StellarisVoid

    Help with building a school rocket

    Hello, I attend a physics club at my school and now, we are building rockets until winter. I need some help because I really want to beat the GCSE students. We are in self chosen teams and the winner is who gets their rocket the highest(hopefully it will go high enough so we can't see it) I have...
  25. Astronuc

    The Future of Rocket Propulsion, What To Do About Emissions

    https://www.bbc.com/future/article/20220713-how-to-make-rocket-launches-less-polluting
  26. heyhey281

    Is this rocket equation right?

    I tried to use conservation of momentum I only want to know if the equation I came up with is correct and if not, why?
  27. gggnano

    Can I make a rocket by mixing aluminum + iodine (+ water catalyst)?

    Basically it's a well known reaction, many kids on youtube make it for the views: I am thinking, since AlI3 sublimes can it be put in say tungsten bottle (is this even a thing??) and then used as a rocket the same way Na+H2O or HCL+Al rockets are used - the gas escapes? This phase...
  28. N

    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?
  29. L

    B This rocket physics problem seems unrealistic

    Ok, so here is what i am trying to do. Find apogee of a model rocket i built using a C motor, then i need to calculate terminal velocity, but something is not adding up, i get a really really high apogee, almost a mile. STAGE 1: I have a c6-7 rocket motor which provides 10N-s of impulse, and...
  30. Rikudo

    A rocket ejecting mass

    I have a question. If we assume that ##dm## is positive, is the answer supposed to be different from the one when we regard the ##dm## as negative? 1. If I assume that ##dm## is positive: By using momentum conservation, we will get $$mv=(m-dm)(v+dv)+dm (v-u)$$ simplify the equation $$m \,dv=dm...
  31. Rikudo

    Rocket Escape Velocity from the Earth-Sun system

    I have a difficulty when making the energy-conservation-equation for the second step. When making the equation, we need to know the exact position (measured from the sun) of the rocket after it is freed from the Earth gravitation. But, where exactly does the rocket free from Earth...
  32. G

    B Andy Weir's "Hail Mary": Question About Relativistic Rocket

    I am reading Andy Weir's Hail Mary. There was a part about relativity: it wrote, that a relativistic interstellar ship had lots of spare fuel, because the mission planners actually ignored relativity, and thought travel will be Newtonian. Am i wrong to think, that is nonsense, and the opposite...
  33. Ozen

    Why Not Titanium Alloy Rocket Engine Nozzles?

    Industry standard right now is a copper alloy (usually an aluminum bronze) inner liner to promote heat transfer to the coolant channels and the walls of the channels and outer liner are usually made of an INCONEL alloy, usually either 625 or 718. But INCONEL is VERY expensive and heavy. The...
  34. anorlunda

    Scott Manley's Video: Pulsed Rocket Drives

    Scott Manley makes some excellent videos. This is a thought provoking one about several futuristic rocket engine concepts. Note in the video that many of the drives are pulsed. I'm wondering if there are any SF stories incorporating those ideas. I'm thinking of the ergonomics for the...
  35. E

    I Modeling a Bottle Rocket: Analyzing the Maximum Altitude

    Edit: I've been catching errors I've made in the transcribing the formulas into latex ( not errors I made in the actual model..yet ). There may be more. I did this in one sitting. I've been trying to model a bottle rocket (water propellant, compressed air fuel) and my model seems ok for a...
  36. C

    A rocket on a spring, related to potential/kinetic energy

    Part A) So from a force diagram we can see that the only two forces acting in our system are the spring force(positive y axis) and the weight of the rocket(negative y axis), which means the spring force is equal and opposite to the weight force. The weight is simple enough ##12* 9.8=117.6N##...
  37. LCSphysicist

    Rocket ejecting mass in a direction perpendicular to its velocity

    That was my approach: $$P_f - P_i = [(m-dm)(v + dv) + dm(u+v+dv)] - [m(v)]$$ $$= mdv - dmv + dmu + dmv = mdv + dmu = 0$$ Since the variation of the rocket's velocity is perpendicular to itself, $$ dv = v d \theta => m v d \theta + dm u = 0$$ So we have $$\frac{dm}{m} = \frac{-v d \theta}{u}$$...
  38. V

    Trouble with a Rocket Propulsion question (Variable Mass & Momentum)

    I chose to set the upwards direction to be positive and dM/dt = R = 190 kg/s, so I can solve the problem in variable form and plug in. With the only external force being gravity, this gives M(t) * dv/dt = -M(t) * g + v_rel * R where M(t) is the remaining mass of the rocket. Rearranging this...
  39. P

    Engineering Velocity Decay Curve for a Rocket

    I am trying to solve the problem below. I have previously calculated from 0 to 4 seconds how far the rocket will travel in each second. I am stuck now as to how to start this problem. I have searched but unable to find the answer. Do i need to rearrange this? A is currently 14 which does not get...
  40. PainterGuy

    Time dilation and length contraction for a rocket

    Hi, It's not a homework but still thought to post it here as advised in the past. A rocket is going to leave Earth's surface and it is decided that a data pulse encoding emission time of pulse will be sent every second from Earth station to the rocket, and the rocket would do the same. The...
  41. wnvl2

    I Relativity paradox: rocket landing in a cylinder

    A rocket has length L with a separate head on top. The rocket lands in a cilinder on Earth with height L with speed v. From the point of view of the rocket, the cylinder undergoes a Lorentz contraction. The rocket will therefore collide with the bottom of the cilinder and damage it. From the...
  42. greg_rack

    Rocket Design: Egg-Safe Landing Plan

    DISCLAIMER: I am not entirely sure whether I should open this thread here or in #general, but I will try! :') Hi guys, I am a freshman in aerospace engineering and i have taken part into a competition consisting in engineering a rocket so that it reacher 1km altitude and manages to touch back...
  43. E

    New type of rocket propulsion design, and why it might not work?

    Hi, *Excuse the crude visualization and possibly imprecise description - I'm not a rocket scientist :) So, I have a friend that has come up with a "new" concept for a rocket propulsion design, and although I have a hunch that it might not work better than existing designs I cannot really...
  44. 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...
  45. Astronuc

    Rocket possible collision with Moon

    https://arstechnica.com/science/2022/01/an-old-falcon-9-rocket-may-strike-the-moon-within-weeks/ https://www.projectpluto.com/temp/dscovr.htm
  46. ColeridgianHam

    Total flight time of rocket

    I calculated the time for the velocity before ground impact, which is v = -189.23 and the velocity at end of engine burn time, which is 120.996. I also calculated the max altitude (y = 1826.94), and the time to reach the max altitude was t = 23.0823 seconds. So from this information, I did: t =...
  47. S

    Distance between rocket and object

    Speed of rocket after moving 0.5 km = ##\sqrt{u^2-2gh}=\sqrt{120^2 - 2 \times 9.81 \times 500}=3\sqrt{510}## m/s Then I try to consider conservation of momentum to find the speed of the object after being released. Total momentum before the object is released = total momentum after the object...
  48. D

    B Propellantless Rocket: Unleashing the Power of Breit-Wheeler

    Hi, I've posted recently about multiphoton Breit-Wheeler matter production. The goal I had in mind for producing a large quantity of positrons and electrons was so that a rocket could make its own propellant without having to carry any propellant along with it. Ultimately, the goal being to...
  49. Father_Ing

    Rocket motion in space

    Consider a rocket with mass ##m## in space is going to move forward. In order to do so, it needs to eject mass backwards. Let the mass that is ejected has velocity ##u## relative to the rocket. What is the equation for the final velocity? It is said that after ##dt## second, the rocket will...
  50. T

    I Is the classical ideal rocket thrust equation correct?

    Hello! I have recently found this fascinating article: https://zenodo.org/record/3596173#.YJ1ttV0o99B The author claims that classical equation for rocket thrust in incorrect because F is not equal to ma for a changing mass. Neither my professors nor me can see any errors. Do you think this...
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