Questions tagged [propulsion]
320 questions
58
votes
6 answers
Why are rockets so big?
I'm curious why rockets are so big in their size. Since both the gravitational potential one need to overcome in order to put thing into orbit, and the chemical energy burned from the fuel, are proportional to the mass, so if we shrink the rocket…
xslittlegrass
- 873
51
votes
2 answers
What is the possibility of a railgun assisted orbital launch?
Basic facts: The world's deepest mine is 2.4 miles deep. Railguns can acheive a muzzle velocity of a projectile on the order of 7.5 km/s. The Earth's escape velocity is 11.2 km/s.
It seems to me that a railgun style launch device built into a deep…
AdamRedwine
- 5,053
45
votes
5 answers
Where does the extra kinetic energy of the rocket come from?
Consider a rocket in deep space with no external forces. Using the formula for linear kinetic energy
$$\text{KE} = mv^2/2$$
we find that adding $100\ \text{m/s}$ while initially travelling at $1000\ \text{m/s}$ will add a great deal more energy to…
Nomoturtle
- 461
39
votes
10 answers
Why don't modern spacecraft use nuclear power?
The Voyager 1 & 2 spacecraft launched in 1977 with Plutonium as their source of electricity. 34 years later they claim these two spacecraft have enough power to last them until at least 2020. That means they'll have had enough power to last them at…
John Conde
25
votes
12 answers
Why do spacecrafts take off with rockets instead of just ascending like an aircraft until they reach space?
I guess it's not a very educated question, but I never quite understood why spacecrafts have to shoot up and can't just reach space by simply continuing an upwards ascent like an airplane.
clueless
- 251
24
votes
12 answers
Can rockets fly without burning any fuel with the help of gases under extreme pressure only?
Why is it necessary to burn the hydrogen fuel coming out of the engine for the lift of rockets?
If it is done to create a greater reaction force on the rocket then why can't we get the same lift with just adjusting the speed of the hydrogen gas…
Ankit
- 8,944
- 2
- 32
- 90
23
votes
1 answer
What are the proposed theoretical explanations for the EmDrive?
The EmDrive is a proposed propulsion mechanism for spacecraft in which some form of microwave device provides the propulsion. The consensus from the physics community, including many voices on this site, is that the proposed device would violate…
Emilio Pisanty
- 137,480
19
votes
1 answer
If an astronaut got stuck in the middle of a space station, can he propel himself towards a wall by blowing air out of his mouth?
Consider the astronaut as floating in the middle of the "Kibo" (ISS module) without him having any initial motion. The module has a diameter of 4.2 m (inner), and the goal is to reach any of the module's walls by only blowing air through his mouth.…
Adriel Mattheuz Estolano
- 323
- 2
- 8
16
votes
1 answer
Does positronium have a stable crystalline phase?
I wonder if there is a way to stabilize and store positronium in a way that the mass of storage device is negligible to the antimatter fuel
It is known that excited Ps atoms with high n (rydberg or rydberg-like) have estimated lifetimes of the order…
lurscher
- 14,933
15
votes
9 answers
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 you release a balloon without tying the end, it…
Ilya Gazman
- 2,177
15
votes
4 answers
NASA's "Impossible" Space Engine
Recently, there was some news that said that the researchers at NASA have come across some impossible kind of space engine which does not require any fuel. I have read at a few places like here, here and here. They all say that this engine seems to…
Yashbhatt
- 1,804
13
votes
2 answers
The interstellar medium reflects extremely low-frequency radio waves. Could we use this fact to build a more efficient photon rocket?
According to the equations of MHD, electromagnetic waves cannot propagate in a plasma if they are below the plasma frequency. (For more information, see this question about astronomical-wavelength radio waves and this question about the plasma…
Thorondor
- 4,110
- 2
- 23
- 46
12
votes
3 answers
Rockets in vacuum vs. Rocket on earth
Recently my physics teacher during a rant said something that piqued my interest. Heres what he said "There are more problems visiting other stars if you wanted a rocket to go 99% the speed of light you'd need an extreme amount of energy and the…
HyperDoge
- 259
10
votes
4 answers
What Problems for 50 year space probe to Alpha Centauri?
I'm thinking speculatively. NASA is doing experiment with ion thrust tech. Assuming, that inside the next 5 years, we could create a probe which would take on the order of 30 to 50 years to reach Alpha Centauri: What problems would it have?
ie: …
Charles Teague
- 367
10
votes
2 answers
Why is Xenon favored as the propellant in electric thrusters?
Most of the articles I've read on electric thrusters mention that Xenon is generally, with some exceptions, used as the propellant (or would it be termed reaction mass?). They never mention why though.
Whats so special about Xenon?
(I'd postulate…
jasper
- 501