# Tag Info

27

As far as I understand you want the "windmill" to drive a dynamo. Have you ever tried turning a dynamo? It takes some force to do so, and that force is then (partially) turned into electricity. So the dynamo is braking your windmill and unless there is some power input to the windmill (wind), it will eventually come to stop. But there is no wind so your ...

24

To flyby or impact Venus varies from 3.45 to 3.6 km/s from LEO for the optimal time every 19 months. Mars varies from 3.55 to 3.9 km/s for the optimal time every 26 months. So on average, getting to Venus is a little less energy than getting Mars. But not by much. It could even be a tiny bit more in some years. If you also want to get barely into orbit ...

21

No, not really. The atmosphere of Mars is very thin. It has below 1% of the pressure on Earth. That means it has less than 1% of the force of wind on Earth with the same speed. Wind only occures at dawn or dusk. Wind happens when there is a pressure gradient between two areas of an atmosphere. Pressure gradients are caused by temparature- and humidity ...

21

The maximum percentage wasted to noise is approximately 1%. The acoustic efficiency, defined as the ratio of the sound power to the rocket exhaust's mechanical power, for the majority of these data range between 0.2 and 1 percent...with 0.5% as the most probable value. NASA SP-8072 ACOUSTIC LOADS GENERATED BY THE PROPULSION SYSTEM Using the equation for ...

18

This is actually pretty difficult to do, because it depends on where from due to uneven distribution of matter (local parameters), how far from the galactic center due to radial velocity, the direction in which you want to reach escape velocity (how much of the radial velocity can be used), and that it's hard to estimate mass of the Milky Way (global ...

16

If you're asking about interstellar travel, then the answer is pretty simple; For diffuse, unfocused sources of light like the one emitted by stars, photon flux density decreases with the inverse square of the distance to its source, and with it photon pressure (imparted momentum of absorbed or, better yet, reflected photons) on the sail. So you accelerate ...

16

To beam the power to the rocket, especially when needing high acceleration, is not what I will expect to show up in the near future. However, separating the energy source from the propellant is the idea behind the nuclear thermal rocket. Here, energy comes from a reactor, and you can choose more freely in higher performing propellants. Because a NTR is ...

15

You'll need a nuclear reactor for that because the process of dissociation of water into constituent hydrogen and oxygen consumes vast amounts of energy and for an ascent stage you'll also need a very high energy density to provide sufficient thrust. Direct anode/cathode system like you describe (i.e. electrolysis) is wasteful when you don't require ...

15

No, it wouldn't work. In order to drive the treadmill, momentum would have to be transferred from the satellites to the treadmill. The sats would slow down and eventually stop. The "highway" itself wouldn't be stable, either. Since it's moving at a different speed from the satellites, it cannot be moving at circular orbital speed for its altitude by ...

15

A conventional thruster with two liquid propellants requires energy too. But it is chemical energy stored in the propellants. Ion thrusters use no chemical energy at all, all the energy of the ion beam is from the electrical energy used by the thruster. In fact, a conventional rocket engine with a lot more thrust than a ion thruster uses a lot more of ...

14

It is what your velocity would be at a sufficient distance from Earth that its gravity doesn't matter, squared. That velocity is $v_\infty$, so $C_3=v_\infty^2$. It can be calculated at any distance from Earth as your specific energy (energy per unit mass), times two: $C_3 = v_\infty^2 = v^2-{2\mu\over r}$ So wherever you are, use the magnitude of your ...

14

Human powered vehicles used within domed or cavern cities would seem to be extremely plausible. One way to look at it is a simple bicycle is less complex than a powered vehicle. The power source (aka a Human) is extremely complex and maintenance intensive, but given that we already have a functioning human and want to get that human to some other place, a ...

14

The second table here essentially answers your question. Venus transfer from Low Earth Orbit is 3.5 km/s, Mars transfer is 3.6. This will allow you to impact either body (on Venus you will need to make sure your vehicle is tough enough to actually impact, rather than dissolving in the atmosphere, but that's not really the point). In either case, you can ...

13

The ISS has a number of thermal management systems. The most visible part are the radiators attached to the main truss (they are the two sets of 3 white panels just to the left and right of middle, and yes, there's a tear towards the end of the first one on the right side) Those panels are part of the External Thermal Control System (ETCS), if I'm not ...

13

NO As a rule of thumb: if you think you invented either a way to generate infinite energy or infinite propellant: you are wrong. But [...] No. Always. Your craft will gain a velocity vector of e. To retrieve the bullets you need to apply to them a velocity vector of -e. If you do this using a liquid, the liquid will accelerate by e. If you do ...

12

The answer is a clear no because Hubble Space Telescope (HST) uses a fixed focal length of 57.6 m. The only thing you'd achieve by re-purposing it as a solar concentrator would be to melt its focal plane assembly and likely everything around it. HST is a Cassegrain reflector and its mirror assembly is utterly unsuitable to applications where adjustable focal ...

12

No: The heat produced by atmospheric reentry isn't a happy side effect of returning to the earth, it's a byproduct of the fact that your satellite/orbiter has enough kinetic energy to be circling the earth every 90 minutes and you want it to stop doing that and come down. To have something you've made for the purpose of harvesting energy reenter the ...

12

Well, we don't really know how much energy a Mars base would need, but we can make some rough estimates. Bases like McMurdo and Mawson have power capacities of several hundred to several thousand kilowatts. Now, we're talking about a Mars base, presumably we're going to need a little more power than that. Let's estimate that Mars Base One will require 10,...

12

Considering fuel consumption or energy expenditure may be misleading, because of the huge change in mass over the flight as fuel is expended. 2/3 of the fuel is expended by the first stage, which only produces 1/3 of the total velocity, for example. Another way to look at the question is through delta-v expenditure; according to Bob Braeunig's simulation ...

12

Consider the windmill as a system. If there is no wind blowing on the windmill, there is no energy being input into the system. If you pull power out of the windmill, energy is being output from the system. With an output and no input, whatever energy is in the system will be drained and not renewed.

12

Here's a brief answer since some people are trying to close the question and prevent answers: As @ikrase points out answers to the Physics SE question Why is the Peltier / Seebeck Effect's efficiency so low in practical devices? are helpful here. Briefly, there are two main parts to an RTG's conversion efficiency Thermodynamics limit The fraction of the ...

11

It would be highly problematic for reaction wheels to serve dual purposes as reaction control devices and energy storage mechanisms. It might be possible, but the implementation would be extremely complicated. Starting with a simpler case of a three-wheel design, a desired spacecraft attitude and/or slew rate uniquely determines the wheel speed. That is, ...

11

Very simple answer: You would need some kind of heating panels through which to let the water flow while it gets heated. Solar panels are thin slices of silicon. You will not be able to build the water heating panels lighter than the solar panels, and even if you somehow did, you would still have to carry a steam turbine. As a commenter already pointed out, ...

11

The thing to notice about this type of drive is that the ions encounter the positively charged accelerating grid first. The ions that provide the thrust to the rocket are positively charged as well, so they will be repelled and contained within the plasma chamber. The ions' only means of reaching the interior of the accelerating grid is diffusion, meaning an ...

10

There are two issues I see with this idea: The overall mass of the system necessary to be able to store meaningful amounts of energy. The effect of such a device on the attitude control capabilities of a spacecraft. If those can be solved, or at least mitigated, this might be a viable idea.

10

You are correct that flywheels can be used for energy storage like batteries. As with all engineering trades, this comes down to many factors: mass, cost, efficiency, lifetime, reliability ... Being in 0g means you don't have to support the weight of the flywheel on the bearings. That is an advantage, but not a huge one, compared to 1g. Having ...

10

Very simple answer. You are looking at the wrong metric for efficiency. The most expensive thing on a space station is not area, you don't pay per foot of "land" (and its associated sunlight) in space. The most expensive thing is mass, and getting it up there. A steam engine is heavy per unit power compared to a solar panel (especially when compared to the ...

10

Don't convert it into heat in the first place, and then don't dissipate it fast. MSL used an electromagnetic brake to slow the descent of the rover from the skycrane. It dissipated the energy into a resistor. Here, instead store the energy in a superconducting magnet. It can remain there as long as you can keep the magnet cold, and you can then either use ...

10

Unless the lubrication system fails in the dynamo that is in vacuum, electrical generation will work. Magnetic fields are unaffected by air or the lack of, at least at the level under consideration. Earth's magnetic field is too weak to have an effect on the generation of electricity by a dynamo. You can see how weak is the magnetic field of our planet by ...

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