HaloMods "Classic" Read-only Archive

OK, now for the non-philosophical more scientific question.

In the aspect of rockets, they carry millions of pounds of fuel to generate enough thrust to carry a human into space. This fuel lasts only a few minutes.

Now, I doubt that many of us are physics majors, but how would one go about generating thrust to carry a person, but for quite a bit longer?
Like, lets say, half an hour.

Is there a type of fuel composition that burns slowly, but releases large amounts of energy, enough to carry a person?

I hate to back up on this, but the best example I can give is Iron Man. I know, I know, shutup
But he's got a suit that sorta molds around him, but he's still somehow got enough fuel to last him quite awhile during flight.

Again, is there a fuel last burns slow, but generates that thrust needed?
Or, really, do you need all that much fuel? Because in a rocket, the fuel is also carrying a ship. And I'd only be looking, hypothetically, to carry about 65 kilograms.
Again, thirty minutes, 65 kilograms.

Under the effect of Earth's gravity, I don't think there is fuel that burns slowly enough and releases a enough energy to last for 30 minutes and carry a relatively large weight.

Remember that all a rocket is, is a controlled explosion.

I can haz jetpack?

Ion thrusters.
I don't know much about thrusters, maybe these kinds of things(Ion thrusters) already exist or are being researched.. they're all about gas right?

Infern0 wrote:Ion thrusters.
I don't know much about thrusters, maybe these kinds of things(Ion thrusters) already exist or are being researched.. they're all about gas right?

Electric engines?
Impractical. (on Earth)

Many current designs use xenon gas due to its low ionisation, reasonably high atomic number, inert nature, and low erosion. However, xenon is globally in short supply and very expensive.

Jet man,
http://www.youtube.com/watch?v=j-66AcTo9TU
He's going to fly over the english channel tomorrow.

Also impractical.

Impractical.*

Also, ion thrusters work best in space, as there is nearly negligible friction. The force produced by them is then able to be used fully. On Earth, this type of propulsion would be pointless in its current state.

Aumaan: What do you mean by thrust to "carry a person?" If you mean directly opposing gravity, then you need more fuel than you need if you're going horizontally, because you don't need to resist it as much. Look at a car. Mine holds 12 gallons of fuel only, but can carry myself and my car for 400+ miles. It's a matter of how efficient the power source is, and what forces you need to resist. Of course a rocket needs large amounts of fuel, it's extremely massive. A smaller mass will need less...

EDIT: Ah, only saw your mass example only now.
So, let's say you want to launch the 65kg normal to the Earth. Gravity is going to give you an opposing force of (65kg*9.8m/sec) 637 Newtons throughout the launch.
Now, let's find the energy needed.
1 Joule is equal to 1 N being moved 1 meter.
91 RON Gasoline has about 131.73233 Megajoules per gallon.
That one gallon can move an object of 637 N up to a height of 206801 meters (neglecting air friction, by the way, which can be a pretty big opposing force).

And now I'm lost on figuring out the time with it. But this is a basic idea of how to work this. Of course, you'd probably want to use rocket motors or something. That way, you can then contact the manufacturer, get exact force numbers, calculate air resistance and other variables, and come up with how much fuel you need, then fix numbers to account for extra thrust for all the extra mass of the fuel you added.
tl;dr you don't need a tank the size of the Space Shuttle. The point is that fuel by itself doesn't have a set burn time. You're not going to throw a match in a tank of gasoline and say "lol thrust." It's the devices that use the fuel and how they use it that matters.

shadowkhas wrote:Aumaan: What do you mean by thrust to "carry a person?" If you mean directly opposing gravity, then you need more fuel than you need if you're going horizontally, because you don't need to resist it as much.

Assume flight. For instance, one would not go completely vertical during flight. You would get the distance from the earth a bit first, then you'd fly horizontal. But even then, you need enough force horizontally to effectively cancel out the effect of gravity.

shadowkhas wrote: Look at a car. Mine holds 12 gallons of fuel only, but can carry myself and my car for 400+ miles.

Yeah, but the only forces being resisted for a car is friction and drag.
So basically... friction. Gravity and Normal force cancel out for a car.
Assume that I'm trying to accomplish, "flight."

shadowkhas wrote:It's a matter of how efficient the power source is, and what forces you need to resist.

The power source isn't necessarily the issue for me. The problem is the relatively short lifespan it would have. Gravity is the force trying to be overcome.

shadowkhas wrote:Of course a rocket needs large amounts of fuel, it's extremely massive. A smaller mass will need less...

Indeed, but lets say the fuel amount is proportional to the mass of the object. Even if I had enough to lift a decent sized object, in proportion to the ship, it only has enough fuel for a few minutes.
And that's assuming there are no variations of different variables one needs to take into account.

Minature nuclear reactor.

Well, the problem is that fuel takes up space, which means more weight, which means more fuel to carry that weight, which requires more weight, thus needing more fuel :\.

But as you burn the fuel the load gets lighter.

First you would need to figure out how much force is needed to hold a 200lb object steady in the air, find a fuel that can meet that requirement, figure out how much fuel is burned per minute (or per second if you want to be really accurate), add that much weight to the 200lb total and repeat until you reach 30 minutes.

Cryticfarm wrote:Well, the problem is that fuel takes up space, which means more weight, which means more fuel to carry that weight, which requires more weight, thus needing more fuel :\.

But it's a solveable problem, unless he wants to go at the speed of light.

Launching from within Earth's atmosphere is stupid, dangerous, and unnecessary. Large spacecraft should be built in space, with smaller shuttlecraft ferrying crew and cargo in and out of the atmosphere.

Honestly, ion drives are only feasible if we develop a small (ish) fusion reactor to power it. In the mean time, nuclear pulse propulsion.

Rockets produce a large amount of heat. Iron man is completely unrealistic (ATM). Best bet for the time being is a propeller system. If you get too high you could pass out or you wont be able to breathe.

Who said anything about Iron Man? That movie was mostly terrible.

I did in my initial post. And it was a great movie.

The woman ruined it for me.

Yodel wrote:Honestly, ion drives are only feasible if we develop a small (ish) fusion reactor to power it.

?!

Ion engines are perfectly feasible, except in the atmosphere. Fusion reactors are a smaller concern than the fact that there's just not enough ions that can be accelerated at one time to create a reasonable force.

We're not talking about the same distance.

I'm talking about Alpha Centauri-ish distance.

I still prefer Nuclear Pulse Propulsion.