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Questions tagged [propulsion]

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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 ...
Xiaobao's user avatar
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2 votes
1 answer
54 views

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 ...
AllGames YT's user avatar
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18 views

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 ...
Marc Kerr's user avatar
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1 answer
57 views

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 ...
wonderwave's user avatar
1 vote
0 answers
49 views

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 ...
bonbon's user avatar
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2 answers
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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 ...
Justintimeforfun's user avatar
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1 answer
45 views

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....
Fulano's user avatar
  • 277
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1 answer
95 views

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 ...
The Physics Noob's user avatar
1 vote
2 answers
222 views

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 ...
Wyatt's user avatar
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1 answer
50 views

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),...
J Ho's user avatar
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2 answers
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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 ...
Argonaut's user avatar
-2 votes
1 answer
46 views

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 ...
Pravesh Maharaj's user avatar
1 vote
1 answer
75 views

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 ...
Sovereign Inquiry's user avatar
0 votes
2 answers
74 views

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 ...
Amos Fenigstein's user avatar
4 votes
7 answers
2k views

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 ...
one two's user avatar
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1 answer
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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 ...
ddddmmmm's user avatar
1 vote
0 answers
49 views

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. ...
cthon's user avatar
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2 answers
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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?
Beom's user avatar
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1 vote
1 answer
564 views

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 ...
acornator's user avatar
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1 answer
86 views

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 ...
FourierFlux's user avatar
1 vote
1 answer
28 views

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
ron vais's user avatar
3 votes
3 answers
538 views

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 ...
NOH WHIREA's user avatar
1 vote
0 answers
99 views

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 ...
Jay's user avatar
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1 vote
1 answer
329 views

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 = ...
Aditya Bansal's user avatar
3 votes
3 answers
276 views

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 - ...
Nem Denemam's user avatar
-1 votes
1 answer
41 views

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 ...
estinamir's user avatar
0 votes
1 answer
100 views

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 ...
A McKelvy's user avatar
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3 votes
2 answers
117 views

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 ...
Sai Anish Reddy's user avatar
1 vote
1 answer
57 views

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 &...
Kamil Jakubowski's user avatar
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1 answer
50 views

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 ...
CancelAnime's user avatar
1 vote
1 answer
50 views

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 (...
Zardo's user avatar
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1 vote
1 answer
68 views

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 ...
releseabe's user avatar
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0 votes
2 answers
64 views

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 ...
user85392's user avatar
0 votes
1 answer
54 views

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.
suyashsingh234's user avatar
-1 votes
1 answer
86 views

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 ...
Adrian Lutchman's user avatar
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0 answers
48 views

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 ...
2 votes
2 answers
84 views

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 ...
Xkeyscore's user avatar
0 votes
1 answer
116 views

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 ...
Escape75's user avatar
0 votes
1 answer
98 views

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 ...
JaPaGe's user avatar
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1 vote
1 answer
129 views

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 ...
Ben Warner's user avatar
2 votes
4 answers
244 views

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 ...
22flower's user avatar
  • 613
2 votes
3 answers
155 views

Are bacterial flagella the most efficient propulsion system at the microscopic scale?

Bacterial flagella can be regarded as microscopic propellers. The rotor is a long, helical protein filament powered by proton gradient. When protons pass through the gap between the rotor and stator, ...
哲煜黄's user avatar
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15 votes
9 answers
9k views

Can a balloon start from Earth and fly to the Moon, using Helium for lift to the top of the atmosphere and then as propellant?

The JP Aerospace's Tandem airship achieved a record-breaking 28,982 meters for the highest airship flight. After reaching this height, can the helium balloon be used as a propellant, the same way if ...
Ilya Gazman's user avatar
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-1 votes
2 answers
63 views

Do you have to leave something behind to go forward? (ie a contained system)

By "behind" I mean a particle outside of the box. ( assume a 1d system)Imagine a closed box. And at the very center of that box, is a device that fires particles 1,2 in opposite direction. ...
jensen paull's user avatar
  • 6,636
-1 votes
1 answer
74 views

Is photon drive reaction less propulsion? [duplicate]

If photon dont have mass how can produce thrust, it seems that violate Newton 3. law? If light dont have mass how can push solar sail?
22flower's user avatar
  • 613
0 votes
4 answers
95 views

Linear acceleration, gravity, and flipping 180° to slow down

In The Expanse ships use linear acceleration for gravity with the decks placed perpendicular to the thrust vector, this creating a "floor." When it comes time to decelerate a ship would need ...
DaynaT's user avatar
  • 3
4 votes
3 answers
2k views

How can satellites change direction without any medium in space? [duplicate]

How can satellites change direction without any medium in space? How do spaceships move in space if there is no medium? How does Newton's third law of motion work in space?
ABHAY SATPUTE's user avatar
2 votes
0 answers
96 views

Wouldn't a black-hole starship quickly lose its black hole?

There seem to be somewhat serious proposals to propel a starship using a black hole (after all it has its own Wikipedia page!). The idea is to use the Hawking radiation from a small black hole and a ...
user34722's user avatar
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0 votes
1 answer
146 views

Einstein propulsion system

Will an extended body(cylinder) with asymmetric energy distribution across its H axis experience free-fall(geodesic)acceleration in free space(outside of any influences) in vacuum because of the time ...
Alien's user avatar
  • 11
1 vote
1 answer
92 views

Would a relativistic rocket need more fuel if it were powered externally?

If a relativistic rocket is pushed by a laser sail, in the frame of reference from which the laser is being fired, the ship is gaining mass and needs more and more energy to accelerate it any further, ...
Ben Warner's user avatar

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