# 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 ...
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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 ...
1 vote
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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 ...
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....
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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 ...
1 vote
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 ...
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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 ...
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 ...
1 vote
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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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1 vote
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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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1 vote
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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 ...
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 ...
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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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1 vote
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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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1 vote
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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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### 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, ...
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### 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 ...
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### 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. ...
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### 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?
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### 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 ...
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?
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 ...
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### 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 ...
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