New answers tagged fuel
1
I think it comes down to this: you need both attitude control and thrust for a spacecraft to be able to do its job, and Cavea-B is only good at one of those jobs. Hydrazine, though less efficient, can power both your attitude control system and your primary thrusters, and so you only need one big pressurized tank. I do think it could be used for orbital ...
0
Other answers have focused on the fact that you wouldn't want to run a rocket engine on gases because the tanks would be too large. One thing that hasn't been mentioned yet is the turbopumps.
Turbopumps consist of a turbine which runs on burned fuel and oxidiser. This runs a pump which pumps the liquid fuel from a low pressure tank to the high pressure ...
0
Burning gases is an aim.
Carrying fuel of maximum density is another.
Propellant density and thus increased propellan payload was (and is) of such interest that in the 1990s the use of "Slush Hydrogen" was propoesed - ex mix of Solid (!) and liquid Hydrogen which increased Hydrogen payload by about 20%. The problems proved to be considerable.
A summary of ...
15
Yes, and it is currently being done on a few engines, notably SpaceX's Raptor engines. They run on liquid oxygen and liquid methane. These are run through turbopumps in two different mixture ratios, burning a small part of the fuel which spins the pumps and vaporizes the rest of the fuel. When they enter the combustion chamber they are both in gaseous form. ...
0
You need a liquid to cool a large and hot combustion chamber efficiently. Ablative cooling has been used for smaller engines only. Heat transfer from the solid chamber walls to a gas is too small for cooling.
6
To complement the answer:
1 L contains 1141 g of liquid oxygen
1 L contains 1 g of gaseous oxygen (at 1ATM)
Of course you can compress it but the container will add more weight (highly undesirable).
But that's not over!
Rockets consume not only a lot of propellant, but they consume it fast.
A Saturn V consumes 18000 kg every second.
That would be ...
25
Possible: yes.
Feasable: not really (at least not for power applications).
The main trick is energy density (per volume) - gases tend to be quite significantly less dense than liquids - and thus the tanks would need to be much larger and heavier - so they are commonly used in their condensed liquid form.
For small engines gases have been used - both as ...
2
One mission profile thought up for the VASIMR involves initially travelling closer to the sun to take advantage of the stronger solar flux to run the engine at high power, releasing a payload on a long coasting trajectory and slowing the launching vehicle back down to return to Earth.
The idea is still a little half-baked at present (the engine performance ...
0
Amount of fuel/propellant needed to get the ship up to 0.05C (and then back down to stationary) for a 4.7ly trip.
Russel Borogrove covered this nicely above. The answer is unambiguously "too much". When your required delta-V exceeds your exhaust velocity, your mass ratio shoots up exponentially. 0.05c is pretty gosh-darn fast... about the speed that fusion ...
3
Yes, ion engines are somewhat of a false economy in the sense that they rely on electrical power on top of their mass and their propellant (e.g. Xenon).
So, compared to a chemical rocket engine where engine mass, thrust, specific impulse, plus propellant (and the mass of the tanks to store it) is about everything you need to plan an hypothetical spaceship, ...
4
Are you burning the hydrogen in a fuel cell to get the power for an ion drive? I don't think that's wise. You'd get more delta/v using the hydrogen and oxygen in a conventional rocket.
A nuclear reactor fuel mass I don't think would be prohibitive. According to this site, generating 200 MW for a year would require about 5 tons of fuel. You're bringing ...
17
I do suspect there's an obvious way to work it out from the specific impulse, which I know is Ns/kg.. but I'm not quite sure how I use that information. Does it mean that an engine with a specific impulse of 12000Ns/kg, can put out 1N of force for 12000 seconds, using 1kg of propellant?
Exactly so. "Specific impulse" is short for "mass-specific impulse", ...
2
As such, what I'm looking for is the derived equation from the rocket equation, where I can enter the target deltaV and the specific impulse of the engine, and the equation will spit out the fuel mass required per kg of payload. This may actually be within my ability to solve... but I've never been confident in rearranging formulae.
Here’s the rocket ...
1
AU or any other space distance measure would not be good.
As an example, once you reach Sun escape velocity you would be able to travel many AU for free outside the solar system without expending any further mass.
It would be more meaningful Kg of fuel per Kg of payload per dV (delta velocity).
dV is the actual measure of "distance" between orbits so to ...
2
It’s completely impractical to get to even .05c with either chemical or ion rockets.
Here’s the rocket equation, rearranged to “mass fraction form”:
$$M_f = 1 - \frac{m_1}{m_0} = 1-e^{-\Delta V / v_\text{e}}$$
where $M_f$ is the propellant mass fraction (the part of the initial total mass that is turned into rocket exhaust).
The delta-v term is 15,000,...
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