27 votes
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How come we don’t put a huge windmill-like machine in space?

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 ...
DarkDust's user avatar
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24 votes
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Does it take more energy to get to Venus or to Mars?

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 ...
Mark Adler's user avatar
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23 votes
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How much of the energy of a rocket ends up as a noise?

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 ...
Organic Marble's user avatar
15 votes

Why are Ion Thrusters so energy hungry?

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 ...
Uwe's user avatar
  • 49k
15 votes

Icy Hot Astronauts

Common wisdom says that space is cold. I wouldn't go so far as to call that a misconception, but it's certainly a bit of a misunderstood fact. See, space is not cold in the way your fridge or a block ...
leftaroundabout's user avatar
14 votes

Does it take more energy to get to Venus or to Mars?

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 ...
Steve Linton's user avatar
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13 votes

Never reducing propellant for space propulsion

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 ...
Antzi's user avatar
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13 votes
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Why are RTGs so inefficient?

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 ...
uhoh's user avatar
  • 149k
12 votes

Could thermal energy be collected by dragging a thermoconductive device against the outer atmosphere

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 ...
1337joe's user avatar
  • 7,206
12 votes
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Solar panels on Mars?

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 ...
Phiteros's user avatar
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12 votes
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Why are Ion Thrusters so energy hungry?

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, ...
Mark H's user avatar
  • 286
12 votes
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What is the distribution of ∆V amongst different stages of rocket flight?

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 ...
Russell Borogove's user avatar
12 votes

How come we don’t put a huge windmill-like machine in space?

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 ...
Organic Marble's user avatar
12 votes

How much of the energy of a rocket ends up as a noise?

Of the the 0.2% to 1% of energy that is generated as sound, most of the sound is generated well after the exhaust gases have fulfilled their purpose of thrust: https://en.m.wikipedia.org/wiki/...
Keith Knauber's user avatar
10 votes

Dissipating large amounts of energy fast, in space

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 ...
Mark Adler's user avatar
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10 votes

In the absolute vacuum of Space, will an electric dynamo still work?

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. ...
fred_dot_u's user avatar
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9 votes

Why are Ion Thrusters so energy hungry?

There is a sense in which the wonderfully high ISP of ion thrusters is the cause of their energy hunger, independently of the detail of their operation. It works like this: we need a certain amount ...
dmckee --- ex-moderator kitten's user avatar
9 votes
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What is the relation between the rocket equation and work, energy and power?

If you're in vacuum, the power represented by the kinetic energy of the thrust is the thrust force times the exhaust velocity (g times Isp) over two: $$P={g I_{sp}T\over 2}$$ One SSME in vacuum ...
Mark Adler's user avatar
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9 votes
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"Free energy" moving the space elevator possible?

Yes, but E' > E is dubious, at least in case of Earth. The point of reversal lies exactly at the GEO altitude, where the elevator moves at speed proper for that ...
SF.'s user avatar
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9 votes

Rocket Turbopump Energy Balance

Where does that pressurization energy go? Into the flow and then into the vehicle, exactly as you would expect! I am assuming (like you) that the most immediate effect of a nuclear turbo-pump like ...
A McKelvy's user avatar
  • 2,482
8 votes

Is wind-power a viable backup power source for Mars One?

Yes, to an extent. A few key facts: While the atmosphere has 1% of the pressure of Earth's, it consists primarily of carbon dioxide (MW = 44) much more than nitrogen (MW = 28). Thus the effective ...
PearsonArtPhoto's user avatar
  • 121k
8 votes

Rocket explosion compared to kT of TNT; has one ever knocked something over at a distance?

National Geographic reports that the 2014 Antares explosion carrying a Cygnus v4 for the Cygnus CRS Orb-3 mission "knocked two spectators off the bed of their pickup truck and another off her dock. ...
Polygnome's user avatar
  • 6,936
7 votes

What are the energy-to-mass ratios of some fuels/oxidizers, when including the oxidizer?

First we have to go back to the chemical equations, and this time, include the standard enthalpy of combustion. Hydrogen: 2 H$_2$ + O$_2$ → 2 H$_2$O + 572 kJ/mol Methane: CH$_4$ + 2 O$_2$ → CO$_2$ + ...
DrZ214's user avatar
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6 votes

Dissipating large amounts of energy fast, in space

In a vacuum, there are only two ways to get rid of the heat, radiators and sublimators. You can not simply get the energy in the heat back to useful forms like electricity, due to the laws of ...
SE - stop firing the good guys's user avatar
6 votes
Accepted

Could thermal energy be collected by dragging a thermoconductive device against the outer atmosphere

Reentry heat is not some magically created energy - it's all dissipation of energy that was painstakingly pumped into the orbital vehicle on ascent, so you will never break even with what you spent on ...
SF.'s user avatar
  • 55k
6 votes

Solar panels on Mars?

I don't have the reputation to comment on Phiteros's answer, but I would like to add that a huge constraint of solar panels on Mars is the weather. Mars doesn't have much of an atmosphere, but what it ...
Arthur Dent's user avatar
  • 1,135
6 votes

In the absolute vacuum of Space, will an electric dynamo still work?

This isn't quite as trivial a question as it first seems, since a self-excited dynamo needs an initial external magnetic field to start working. In principle, the Earth's magnetic field, weak as it ...
Ilmari Karonen's user avatar
6 votes

Solar Flux on Mars Surface

Where you are on the surface of Mars as well as the opacity of the atmosphere and various other effects will effect the result, but the below memo seems to show anywhere between 95 to 308 W/m² (which ...
Phil_12d3's user avatar
  • 468

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