Questions tagged [propulsion]
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313 questions
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Why does that screw-propelled vehicle steers opposite to common sense?
Watching videos of screw-propelled vehicles, I came across this one, where at some point (2:15 to 2:40) there's one weird steering/yaw reversal:
While driving forward in a swamp, thrust comes from ...
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Radioisotope Direct Kinetic Propulsion (using alpha particles)
Edit: instead of using neutrons emitted from a rod, could it instead use alpha particles emitted from a sheet, the radioisotope perhaps being the commonly used plutonium 238. This sheet either ...
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Hall Effect Thruster electric field explain
I am trying to understand how a hall thruster work.
My understanding is that, first the cathode emits electrons. The electrons get trapped by the magnetic field (Br) and start swirling around at high ...
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Why do rockets need such powerful engines? [duplicate]
The starship catch between the two arms has been all over the internet. And it made me wonder, why do rockets need such powerful engines?
Although I am very comfortable with math, I barely know any ...
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Why the exhaust pressure should be equal to ambient pressure? (Part 2) [closed]
I'm asking a follow-up question to J. Pipiskin's post: Why the exhaust pressure should be equal to ambient pressure?.
TRF's answer shows a plot of normalized thrust vs exhaust-to-ambient pressure ...
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Steep missile turn during launch?
I know this might be a pretty basic and easy question, but I've started to wonder about missile aerodynamics and how they work. I recently saw a video of a Tomahawk Cruise missile launch (linked below)...
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Why do the hydrogen-based jet engines create propulsion?
Theoretically, the jet engines create propulsion because of the pressure in the combustion chamber that creates force that pushes the rocket.
But when hydrogen combustion is conducted, 2 hydrogen ...
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Ion propulsion and coronal discharge
Most model ion thrusters use pointed ends on their negative ends instead of their positive ones. Why is this? Wouldn't the lower rate of coronal discharge from the positive end be made up for by the ...
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A theoretical experiment about gravity and propulsion
An observer travels in a spherical ship drifting through space. The observer cannot 'see' anything outside the ship.
At some time, the ship approaches a massive object P and describes an hyperbolic ...
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3-stage rocket payload problem [closed]
A rocket goes to the sky, and undergoes 3 stages. I want to find the payload of it.
In stage 1, 80% of the mass is the fuel, 10% of the mass is dry mass, and 10% is the remaining rocket. Similarly, in ...
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Problem with equation of thrust in a system of variable mass
The equation for force on a system of variable mass (e.g. a rocket thrust equation) is
$$F=-u\frac{\mathrm{d}m}{\mathrm{d}t}$$
where $u$ is the velocity of the escaping gases with respect to the ...
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How significant is the parabolic arch effected with an incline versus a decline in angle versus a decline in angle . For example throwing a dart
A dart players height can vary as can the height in which they raise their arm to aim.
Is there less parabolic arch when throwing at the same strength from above the target compared to below, due to ...
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Tsiolkovsky rocket equation assumptions
From what I understand, the elementary derivation of the Tsiolkovsky rocket equation makes the assumption that mass is lost as a linear function of time.
Why do we make this assumption? Does it follow ...
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Would a photon engine work?
So as far as I know for a body to move in space it needs to accelerate using it's mass because there is nothing else to push against. And as far as I understand, basically, the photon engine is an ...
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Can nuclear material be detonated with light?
In this question https://space.stackexchange.com/questions/65842/nuclear-solar-reflective-plasma-drive I propose a question to use the light from the sun to start a nuclear chain reaction to propel a ...
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Are there very high voltage very low amperage electromagnetic/electrostatic launchers?
Electromagnetic launchers (coilguns or railguns) use extremely high amperages and voltages, but I was wondering if are there very high voltage very low amperage electromagnetic/electrostatic launchers....
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Applying 1 gram-force for 1000 seconds to 1kg mass
I am looking into ion thrusters and the small amount of propulsion they provide.
I am really new to this, so I want to understand. If we have mass of 1 kg in space and we are able to apply to it a 1 ...
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Why is accelerating more air slower more efficient than less air faster?
According to this answer on Aviation Stack Exchange, when propelling an airplane it is more efficient to accelerate a bigger amount of air a little than to accelerate a small amount of air a lot. Why ...
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Where does Energy get lost in the Rocket Ship propulsion vs "direct acceleration" scenario? [closed]
The scenario is as follows. In a hypothetical future drive I spend energy E to accelerate a mass of propellant m to velocity v (e.g., plasma state propellant in the very powerful circular accelerator),...
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Frame of reference for work done against air resistance by ground vehicle
An online cycling calculator shows power required to overcome air resistance for given wind speed and groundspeed. To cycle at 30mph in still air requires twice the power of cycling at 15mph with a ...
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Propulsion of a spacecraft [closed]
If a craft is positioned at the strongest point of the earth's electromagnetic field being either positive or negative and the craft activates the same field it would repel each other would it create ...
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If photons can be used to accelerate solar sails, why can't they be ejected from a spacecraft and be used as an "engine?"
I'm not really sure why or how, but photons apparently have momentum. This goes against my very limited sense of physics, as they have no mass at all. How is this possible?
At any rate, I came to ...
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Can one build a nuclear jet engine based on alpha emitter for small space satellite?
Let assume a metal tube open on one side having alpha emitter material on the other blocked side. Since alpha particles are blocked by the metal they will be emitted only through the open side and ...
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Are all conservation of momentum scenarios simply particles bouncing on walls? [duplicate]
All explanations of jet propulsion that I've seen are formulated as "due to conservation of momentum, air with momentum coming out of one end means the rocket must gain momentum in the opposing ...
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Rocket propulsion energy efficiency
What ratio of final to initial mass of a rocket to achieves the highest energy efficiency - the highest ratio of final mass kinetic energy to chemical energy expended? And more generally the relation ...
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What are the light emissions from an ion engine?
Consider an ion thruster like a DS4G (Dual-Stage 4 Grid) thruster. Gas is released, ionized, and accelerated. Assume it's in a vacuum, be it a chamber or space. Also assume the propellant is Xenon.
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Can an ion thruster work without applied voltage?
In this image, power is used to apply voltage to the charged grids.
But if no voltage is applied, would ions still be accelerated by Coulomb forces to create thrust? If not, why?
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Why is hydrogen considered the most efficient rocket fuel and how it relates to the concept of specific impulse (ISP)?
Why is hydrogen considered the most efficient fuel? I mean I know it is very light and can be accelerated very fast, but can’t you use a denser fuel but throw it at a slower speed bunch, and it’ll ...
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Do EM waves carry momentum and if they do can it be used to generate thrust? [duplicate]
I read EM waves carry momentum and can exert pressure, if this is the case can ejecting them be used to generate thrust? Radiation pressure is cited as a real thing but I read about the EM drive and ...
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Propeller design comparison [closed]
Why does boat/airplane propellers are designed so differently then of a turbine/pump propellers? (blade spacing, pitch, blade shape and width, etc) although both just push fluids backwards
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Relationship between fuel consumption and kinetic energy increase
The spacecraft with the same physical properties is moving in space. Let's assume that there are no resistance in space.
A stationary observer observes a spacecraft whose speed varies from 100 m/s to ...
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Double the speed, four times the fuel, yet again [closed]
This question has been asked several times already but it usually involves pushing against the Earth or a rocket carrying the fuel within itself. Let's simplify the problem to a projectile pushed by ...
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The formula of the net external force and rocket propulsion [duplicate]
The mathematical representation of the net external force on a system is $\vec F_{net} = \frac {d\vec P}{dt}$, which is the rate of change of linear momentum of the system. If we substitute $\vec P = ...
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Unclear negative sign in rocket propulsion equation
The usual proof of Rocket propulsion goes something like this (University of Central Florida, Rocket propulsion)
$mv = (m-dm_g)(v+dv) + dm_g(v-v_{rel})$
where:
m - initial weight of rocket
v - ...
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Could Zapata’s Flying airboard be used on Space missions [closed]
The following Zapata’s flying air board (FAB) can fly on Earth for 10 minutes up to 3km ceiling, carrying 100kg person at a speed of 150km/hr. I was wondering if it could fly on Moon or Mars, or ...
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Does a box of Pendulum's weigh more if they are swinging?
The question is more specifically to explain why the box doesn't weigh more, because if it did then I could revolutionize space travel.
Consider a rigid box suspending two counter oscillating ...
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Regarding Speed of launched rocket inside the atmosphere
I am a 15 yr old, so please forgive my mistakes as I have not entirely read rocket mechanics.
I have been wondering why rockets accelerate to mind-boggling speeds, (mach7-8 or even more)when that must ...
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How would one go about writing the momentum equilibrium for a rocket whose thrust is equal to the force of gravity? (The rocket's "hanging" in the sky
My question specifically is where do we look for the "missing" momentum. If I understand the situation correctly we have some momentum from the exhaust of the rocket. Where do we get the &...
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The relationship of yaw and roll on a spacecraft using Trust Vector Control
I’ve previously asked the question how does applying rudder (yaw) on aircraft also cause roll. Turns out it’s caused by both the rudder usually being above or below the center of mass and the ...
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Optimization of using a speaker membrane as a propulsion unit - best frequency and shape of the excitation curve
with optimized frequency and excitation curve pattern, a speaker membrane vibrates with a higher speed away from the speaker (representing frequency 1) and with a lower speed back to the speaker (...
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The Orion Project --- do the predicted speeds violate the Tsiolkovsky Equation?
I understand that a conventional rocket may move faster than its thrust but IIRC the equation developed in the 19th century the speed is limited to 4/3 the thrust speed.
Now, I understand that the ...
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Why are the blades of a pedestal fan so different from the blades on an aircraft propeller?
Both fans and propellers move a quantity of air. In the former, that is the end goal. In the latter, this movement of air creates a force in the direction opposite to the airflow. So, why are the ...
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Propellant less propulsion when there is nothing to push against
Is there a way for a vehicle to move without losing mass when there is nothing for the vehicle to push against? For example, a helicopter flying around in a vacuum.
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Can relativistic mass increase be used to increase propulsion momentum?
If the propellant used in a rockets is accelerated to near relativistic speed before being ejected from a space craft (accelerating the propellant molecules in a loop before releasing them), can the ...
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Resources for Rocket propulsion
I am a Mechanical Engineering student who is very much interested in Rocket propulsion. Lately I have been searching for good resources to learn concepts about rocket propulsion. I'd be glad to get ...
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Why does a rocket engine that produces a constant thrust over a set period of time have less energy if it has more mass? (Zero-$g$) [closed]
A rocket engine with the thrust of 1N working for 10 seconds will add more kinetic energy to the rocket if it is attached to a 10kg rocket and less if it is attached to a 20kg rocket. The rocket ...
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How does the thrust achieved in my model differ from a rocket engine?
I am experimenting with a design that looks this,
using both straight and 90 degree curved pipes:
I am supplying compressed air marked by yellow arrows and the pipe is producing a very small force in ...
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tGiven a propulsion system with constant power, how long does it take to travel a given distance in space? (non-rel. and relativistic)
Suppose a space ship of mass $m$ is travelling away from our solar system, starting with "starting speed" $v_{start} > v_{escape\ \odot}$, meaning it will escape sun and have some ...
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Would metallic hydrogen be powerful enough to fuel a 1g rocket?
I have read that the issue with a 1g rocket is that no fuel in existence is powerful enough to provide a constant acceleration of 9.8 meters per second for years on end, and it would take hundreds of ...
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Why flapping rudder produce net thrust if one half-stroke produce thrust and second half-stroke drag?
In small sailing boat like optimist is well know technique when there is no wind, rudder pupming which push boat forward.You just need push-pull rudder stick left to right with fast movement.
Rudder ...
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